JP5534826B2 - Semiconductor optical device, optical transmission module, optical transmission / reception module, optical transmission device, and manufacturing method thereof - Google Patents

Description

  The present invention relates to a semiconductor optical device, an optical transmission module, an optical transmission / reception module, an optical transmission device, and a manufacturing method thereof, and more particularly, to an improvement in characteristics of a semiconductor optical device including a modulator having a buried heterostructure.

  In recent years, in long-distance optical communications at high transmission speeds, for example, a modulator unit such as an electroabsorption modulator (hereinafter referred to as an EA (Electro-Absorption) modulator) is integrated on the same semiconductor substrate as the light emitter unit. The modulator integrated type semiconductor optical device is used.

  The EA modulator is a modulation that modulates light by selectively applying an electric field to the active region of the EA modulator using the quantum confinement Stark effect (hereinafter referred to as QCSE). It is a vessel. Here, the active region is a so-called single-quantum well (hereinafter referred to as SQW) layer or a multiple-quantum well (hereinafter referred to as MQW) layer. Hereinafter, in this specification, MQW includes SQW in addition to normal MQW. Note that QCSE refers to an effect that when an electric field is applied to the MQW layer, the absorption edge of light in the MQW layer shifts to the long wavelength side.

  In the MQW layer, semiconductor thin film layers having different band gaps are alternately stacked. Here, the semiconductor thin film layer having a large band gap is a barrier layer, and the semiconductor thin film layer having a small band gap is a well layer. The extinction characteristics and transmission characteristics of the modulator are controlled by designing the thicknesses of the well layers and barrier layers of the MQW layer and the number of well layers of the MQW layer. However, the limit value of the transmission speed greatly depends on the parasitic capacitance of the modulator. That is, the band of the modulator and the parasitic capacitance have an inverse correlation, and it is necessary to further reduce the parasitic capacitance in order to realize a higher transmission rate.

  Semiconductor optical elements mainly have a ridge waveguide structure and a buried heterostructure (hereinafter referred to as a BH structure).

  FIG. 15 is a cross-sectional view showing a structure of an EA modulator according to the prior art having a ridge waveguide structure. The ridge waveguide structure is a structure in which a semiconductor layer serving as a ridge is provided above the MQW layer 13 serving as an active region. As shown in FIG. 15, an n-type InP buffer layer 11, an n-type InGaAsP lower guide layer 12, an MQW layer 13, and a p-type InGaAsP upper guide layer 14 are sequentially formed on an n-type InP substrate 10. Here, the well layer and the barrier layer of the MQW layer 13 are both made of InGaAsP to which no impurity is added. In the MQW layer 13, a p-type InP cap layer 201, a p-type InP cladding layer 16, and a p-type InGaAs contact layer 17 are formed as semiconductor layers to be ridge portions above the region to be the waveguide region. . As described above, this structure is called a low mesa structure 203 because it has an MQW that becomes an active region under the ridge portion. On the other hand, the BH structure described later is called a high mesa structure because MQW serving as an active region exists in the ridge portion.

  Both sides of the ridge portion of the low mesa structure 203 are covered with the passivation film 21, and both sides thereof are embedded with an organic insulator such as a polyimide resin 202. Further, a p-type electrode 22 is provided on the upper side of the lomesa structure 203, and an n-type electrode 23 is provided on the lower side of the n-type InP substrate 10.

  By applying an electric field to the lower side of the semiconductor layer to be the ridge portion through the semiconductor layer to be the ridge portion, the ridge portion of the region spreading laterally in the figure of the MQW layer 13 to be the active region is formed. The substantial refractive index of the region below the semiconductor layer is substantially increased as compared with the other regions, so that the region below the semiconductor layer serving as the ridge portion becomes the waveguide region. Therefore, such a structure is called a ridge waveguide structure.

  FIG. 16 is a diagram illustrating a structure of an EA modulator according to the related art having a BH structure. FIG. 16A is a cross-sectional view of the EA modulator. The cross section shown in FIG. 16A corresponds to the cross section passing through the 1D-1D broken line of FIG. 1A showing the semiconductor optical device according to the embodiment of the present invention. The BH structure is a multilayer structure including the MQW layer 13 serving as an active region, and both sides of the mesa stripe structure 101 formed by removing a region outside the waveguide region are embedded with semiconductor layers. Refers to the structure. Patent Document 1 discloses an EA modulator integrated semiconductor optical device in which an EA modulator having a BH structure is integrated.

  In the EA modulator shown in FIG. 16A, on an n-type InP substrate 10, an n-type InP buffer layer 11, an n-type InGaAsP lower guide layer 12, an MQW layer 13 serving as an active region, and a p-type InGaAsP upper guide layer. 14, a p-type InP cap layer 15, a p-type InP clad layer 16, and a p-type InGaAs contact layer 17 are stacked. Of these multilayer structures, the outside of the waveguide region is removed up to the upper surface of the n-type InP buffer layer 11 to form a mesa stripe structure 101.

  Both sides of the mesa stripe structure 101 are buried with a buried layer 18 made of semi-insulating InP. When the buried layer 18 is further crystal-grown from the upper surface of the mesa stripe structure 101, there is a phenomenon in which the buried layer 18 is laminated in a sloped manner along the (111) B plane due to the crystal structure of the buried layer 18. Therefore, the upper surface of the buried layer 18 has a shape as shown in FIG. Here, of the upper surface of the embedded layer 18 that spreads on both sides of the upper surface of the mesa stripe structure 101, the sloped portion is the upper slope portion, and the flat portion that extends further outward is the upper flat portion.

  A passivation film 21, which is an insulating film, is formed on the top surfaces of the mesa stripe structure 101 and the buried layer 18. The passivation film 21 is formed on a part of the top surface of the mesa stripe structure 101 and a part of the top surface of the buried layer 18. Is not formed and is a through hole 121a.

  A p-type electrode 22 is formed above the mesa stripe structure 101 and the buried layer 18, and the p-type electrode 22 is connected to the p-type InGaAs contact layer 17 at the uppermost layer of the mesa stripe structure 101 through the through hole 121 a. Has been. An n-type electrode 23 is provided on the lower side of the n-type InP substrate 10.

  FIG. 16B is a diagram showing the shape of the passivation film 21 of the EA modulator shown in FIG. That is, the through hole 121a, which is a region where the passivation film 21 is not formed, is located at the center of FIG. Note that FIG. 16A corresponds to a cross section that penetrates the vicinity of the center of FIG.

  The through hole 121a shown in FIG. 16B has a rectangular shape. That is, the inner edge of the passivation film 21 has a rectangular shape. Of the inner edge of the passivation film 21, left and right portions extending in the vertical direction in the figure are referred to as extending portions. FIG. 16B shows a case in which the left and right extending portions of the inner edge of the passivation film 21 are positioned at the boundary between the upper surface slope portion and the upper surface flat portion of the buried layer 18 shown in FIG. It is shown. That is, the through hole 121a shown in FIG. 16B is formed in the lateral direction of FIG. 16B from the left end of the upper surface slope portion of the buried layer 18 via the upper surface of the mesa stripe structure 101 and the buried layer 18 on the other side. It is provided over the right end of the upper surface slope portion.

  Of the inner edge of the passivation film 21, the left and right extending portions are positioned on the inner side of the boundary between the upper surface slope portion and the upper surface flat portion of the embedded layer 18. 18 upper surface slope portions. In this case, when the p-type electrode 22 is formed on the upper side of the passivation film 21 so as to cover the through-hole 121 a, the p-type electrode 22 is formed in the vicinity of the extension portion of the passivation film 21 due to the layer thickness of the passivation film 21. There is a possibility of causing cuts. If the disconnection occurs, the electrical connection between the p-type electrode 22 and the p-type InGaAs contact layer 17 on the uppermost layer of the mesa stripe structure 101 becomes insufficient, which may affect the characteristics of the modulator. is there.

  Therefore, conventionally, the right end and the left end of the through hole 121a in the figure are formed so as to be located at the boundary between the upper slope portion and the upper flat portion of the buried layer 18 or outside the boundary (upper flat portion), respectively. It is common. That is, the extending portions on the left and right sides of the passivation film 21 are formed so as to be positioned on the boundary between the upper slope portion and the upper flat portion of the buried layer 18 or on the outer side (upper flat portion) of the boundary. Is common. In other words, conventionally, the extending portions on the left and right sides of the passivation film 21 generally do not reach the upper surface slope portion of the buried layer 18.

  FIG. 17 is a top view of an EA modulator according to the prior art having a BH structure. FIG. 16A corresponds to a cross section that penetrates the vicinity of the center of FIG. A p-type electrode 22 is formed on the upper side of the passivation film 21 shown in FIG. In FIG. 17, the through-hole 121 a is indicated by a broken line, and the passivation film 21 is disposed below the p-type electrode 22 in a region of the p-type electrode 22 that is outside the through-hole 121 a. .

  As shown in FIG. 17, the p-type electrode 22 is connected to a wire in a region extending in the vertical direction in the drawing covering the through hole 121a and a flat portion on the upper surface of the buried layer 18 located on the left side in the drawing. A region to be an electrode pad to be formed. Of the p-type electrode 22, the region extending in the vertical direction in the drawing covering the through-hole 121 a has a mesa stripe upper surface portion 22 c and buried slope portions 22 b located on both sides thereof, and serves as an electrode pad region. Has an electrode pad portion 22a. As shown in FIG. 17, in order to prevent the upper surface slope portion of the buried layer 18 from being exposed, actually, not only the through hole 121a but also the portion located further inside from the inner edge of the passivation film 21 is a p-type electrode. 22 is spread, and the embedded inclined surface portion 22b and the mesa stripe upper surface portion 22c of the p-type electrode 22 each include a portion of the passivation film 21 located on the inner side of the inner edge.

JP 2004-273993 A

  In general, in the ridge waveguide structure, the MQW layer serving as the active region is formed wider outside both sides of the semiconductor layer serving as the ridge portion, so that when the electric field is applied to the modulator, the active region In contrast, the electric field is not applied efficiently. Therefore, the carriers generated in the modulator part are not sufficiently emitted from the active region, and some carriers are accumulated in the active region, and even when light is emitted from the semiconductor optical device, In the modulator section, light is absorbed. Therefore, the ridge waveguide structure is a disadvantageous structure when high output emission is desired for the semiconductor optical device.

  On the other hand, in the BH structure, the multilayer structure including the MQW layer serving as the active region has a mesa stripe structure, and both sides of the mesa stripe structure are buried with the buried layers, and therefore, compared with the ridge waveguide structure. An electric field is applied to the active region more efficiently. Therefore, the BH structure is an advantageous structure when high output emission is desired for the semiconductor optical device.

  Conventionally, in the BH structure, a structure in which the buried layer is a pn bond has been used. However, in recent years, the buried layer has become a semi-insulating semiconductor as a structure for reducing the parasitic capacitance to enable higher transmission speed. A layered structure is used. Here, as the semi-insulating semiconductor layer, a semiconductor layer to which a metal such as iron (Fe) or ruthenium (Ru) is added as an impurity is used.

FIG. 18 is a diagram illustrating a parasitic capacitance of an EA modulator according to the related art having a BH structure. FIG. 18A shows the parasitic capacitance of the EA modulator shown in FIG. In the EA modulator, parasitic capacitance mainly exists between the p-type electrode 22 and the n-type electrode 23. First, in the p-type electrode 22, a pad part capacitance C ₁ exists between the electrode pad part 22 a and the n-type electrode 23. Further, in the p-type electrode 22, the mesa stripe structure 101 is located below the mesa stripe upper surface portion 22 c, and in the mesa stripe structure, there exists a junction capacitance C ₃ across the MQW layer 13 serving as an active region. doing. On both sides of the mesa stripe structure 101, of the p-type electrode 22, slope capacitances C _2a and C _2b exist between the buried slope portion 22 b and the n-type electrode 23, respectively. Since the parasitic capacitance C _all of the modulator can be approximated by the sum of these capacitances, the parasitic capacitance C _all is expressed as C _all ≈C ₁ + C _2a + C _2b + C ₃ .

  For example, when an InP layer doped with Fe as an impurity is used as the buried layer 18, the EA modulator length is 100 μm, the buried layer 18 is 5 μm thick, the MQW layer 13 is 0.18 μm thick, and mesa stripes. The structure 101 has a layer thickness of 3.5 μm, the mesa stripe structure 101 has a width of 1.5 μm, the through hole 121 a has a width of 9.5 μm, and the p-type electrode 22 has a width of 11.5 μm. The bandwidth of the EA modulator calculated from the existing parasitic capacitance is 15.3 GHz. This calculated value is also consistent with the experimentally obtained bandwidth. Here, the value of the band of the modulator obtained by the calculation includes the effect of increasing the parasitic capacitance due to the mutual diffusion of Fe contained in the buried layer 18 and zinc (Zn) contained in the multilayer of the mesa stripe structure 101. Yes.

As described above, in order to realize an EA modulator capable of a higher transmission rate than the transmission rate corresponding to this band, it is necessary to further reduce the parasitic capacitance C _all of the EA modulator. In order to reduce the parasitic capacitance C _all , it is conceivable to further increase the thickness of the buried layer 18. This is because the capacitance is generally inversely proportional to the distance between the electrodes. However, in the EA modulator according to the prior art shown in FIG. 16A, if the layer thickness of the buried layer 18 is further increased, a new problem arises for capacity reduction.

  FIG. 18B is a cross-sectional view showing another example of the main part of the EA modulator according to the prior art. The EA modulator shown in FIG. 18B is obtained by further increasing the thickness of the buried layer 18 of the EA modulator shown in FIGS. 16A and 18A. As described above, when the buried layer 18 is further crystal-grown from the upper surface of the mesa stripe structure 101, the buried layer 18 is laminated so as to be inclined along the (111) B plane. In the EA modulator shown in (1), the slope of the upper surface of the buried layer 18 is further increased as the thickness of the buried layer 18 is increased.

Compared to the EA modulator shown in FIG. 18 (a), the EA modulator shown in FIG. 18 (b), since the thickness of the buried layer 18 is larger, the distance between the electrode pad portion capacitance C ₁ is It is larger, which is a factor to reduce the pad portion capacitance C _1. However, as the layer thickness of the buried layer 18 increases, the area of the upper slope portion of the buried layer 18 also increases, and the area of the buried slope portion 22b of the p-type electrode 22 increases. Therefore, the area of the electrodes of the slope portion capacitances C _2a and C _2b is increased, which is a factor for increasing the respective capacitances.

That is, of the parasitic capacitance _{C all} the EA modulator according to prior art, the slope portion capacitance _{C 2a,} in _{C 2b,} and the layer thickness of the buried layer 18, the inclined surface portion capacitance _{C 2a,} the area of the _{C 2b} are tradeoffs This is a relationship and becomes a problem for capacity reduction. Therefore, simply increasing the thickness of the buried layer 18 does not reduce the parasitic capacitance C _all in the EA modulator.

In contrast, if the EA modulator having a ridge waveguide structure, both sides of the low mesa structure 203 may be filled with polyimide resin 202 is small material dielectric constant epsilon _r. Since the dielectric constant ε _r of the polyimide resin 202 is small, the parasitic capacitance is reduced as compared with an EA modulator having a general BH structure. Further, since the dielectric constant epsilon _r of the polyimide resin 202 is small, of the p-type electrode 22, increasing the area of the electrode pad portion 22a, an increase in the pad portion capacitance C ₁ is suppressed, the design constraints Is small.

  Therefore, for example, the structure mainly used in the EA modulator operating at a high transmission rate of 40 Gbit / s has a reduced parasitic capacitance despite having a disadvantageous structure in the optical output. The structure is a ridge waveguide structure. Therefore, in an EA modulator integrated DFB laser element in which an EA modulator as a modulator section and a distributed feedback laser (hereinafter referred to as a DFB laser) as a light emitter section are integrated on the same semiconductor substrate. In order to operate at a high transmission speed of 40 Gbit / s, a ridge waveguide structure is used.

  However, in order to realize a higher-power semiconductor optical device that operates at a higher transmission speed, further reduction in parasitic capacitance is required in the BH structure that is advantageous in optical output.

  In view of the above problems, an object of the present invention is to provide a semiconductor optical device, an optical transmission module, and an optical transmission / reception module in which characteristics are further improved by adopting a structure in which parasitic capacitance is reduced in a semiconductor optical device having a BH structure. An optical transmission device and a manufacturing method thereof are provided.

  (1) In order to solve the above-described problem, a semiconductor optical device according to the present invention is a semiconductor optical device including a modulator unit that modulates and emits light input along an emission direction, and the modulation The vessel portion includes an active layer and is arranged adjacent to both sides of the mesa stripe structure extending in the emission direction and on both sides of the top surface of the mesa stripe structure with respect to the stacking direction. Except for a buried layer having a top slope portion that spreads as a slope and a top flat portion that spreads further outward, and a through-hole region that extends on both sides of the top surface of the mesa stripe structure and extends along the emission direction. A passivation film formed on an upper surface of the mesa stripe structure and an upper surface of the buried layer, and the emission covering the through-hole region And an electrode formed to include a wire connection pad region located above a portion of the upper flat portion on one side of the buried layer, and on the inner edge of the passivation film Each of the extending portions on both sides of the upper surface of the mesa stripe structure along the emitting direction, and at least a part of the extending portions on the other side is the one of the buried layers on the other side. It extends to the upper surface slope part.

  (2) In the semiconductor optical device according to the above (1), all the extending portions on the other side may extend to the upper surface slope portion of the buried layer on the other side.

  (3) In the semiconductor optical device according to (1), at least a part of the outer edge of the electrode on the other side and extending in the emission direction is formed on the other side of the buried layer. It may be inside the upper flat portion.

  (4) In the semiconductor optical device according to (2), all of the outer edge of the electrode on the other side and extending in the emission direction are flat top portions of the buried layer on the other side. It may be inside.

  (5) In the semiconductor optical device according to any one of (1) to (4), a joint portion of the electrode with the wire connection region is formed on the extending portion on the one side of the passivation film. And all of the extending portion on the one side of the passivation film other than the portion serving as the bonding portion may extend to the upper surface slope portion of the buried layer on the one side.

  (6) In the semiconductor optical device according to (5), a part of the outer edge of the electrode on the one side and extending in the emission direction is flat on the upper surface of the buried layer on the one side. It may be inside the part.

  (7) In the semiconductor optical device according to any one of (1) to (6), the embedded layer may include a semiconductor to which iron, ruthenium, or a combination thereof is added as an impurity. Good.

  (8) In the semiconductor optical device according to any one of (1) to (7), the modulator unit may be an electroabsorption modulator or a Mach-Zehnder modulator.

  (9) The semiconductor optical device module according to the present invention may be a semiconductor optical device module on which the semiconductor optical device according to any one of (1) to (8) is mounted.

  (10) A method of manufacturing a semiconductor optical device according to the present invention is a method of manufacturing a semiconductor optical device including a modulator unit that modulates and outputs light input along an emission direction, and includes an active layer. And a step of forming a mesa stripe structure extending in the emission direction, an upper surface slope portion extending as a slope with respect to the stacking direction on both sides of the upper surface of the mesa stripe structure, and an upper surface flat portion extending further outward And a step of forming a buried layer adjacent to both sides of the mesa stripe structure, and on the top surface of the mesa stripe structure and the top surface of the buried layer, spreading on both sides of the top surface of the mesa stripe structure and emitting direction Forming a passivation film excluding a through-hole region extending along the direction, and covering the through-hole region with the emission method And forming an electrode including a wire connection pad region located above a part of the upper flat portion of the buried layer on one side, and an inner edge of the passivation film And at least part of the extending portions on the other side in the step of forming the passivation film, each of which includes extending portions extending along the emission direction on both sides of the upper surface of the mesa stripe structure. May be characterized in that the passivation film is formed so as to reach the upper surface slope of the buried layer on the other side.

  (11) In the method of manufacturing a semiconductor optical device according to (10), in the step of forming the passivation film, all the extending portions on the other side are inclined on the upper surface of the buried layer on the other side. The passivation film may be formed so as to cover the part.

  (12) In the method for manufacturing a semiconductor optical device according to (10), in the step of forming the electrode, at least one of the outer edges of the electrode on the other side and extending in the emission direction. The electrode may be formed so that the portion is inside the flat portion on the upper surface of the buried layer on the other side.

  (13) In the method of manufacturing a semiconductor optical device according to (11), in the step of forming the electrode, all of the outer edge of the electrode on the other side and extending in the emission direction are The electrode may be formed so as to be inside an upper flat portion of the buried layer on the other side.

  (14) In the method of manufacturing a semiconductor optical device according to any one of (10) to (13), in the step of forming the passivation film, the extending portion on the one side of the passivation film includes: The electrode has a bonding portion with the wire connection region, and all of the extending portions on the one side of the passivation film other than the portion serving as the bonding portion are inclined surfaces on the upper surface of the buried layer on the one side. The passivation film may be formed so as to extend to.

  (15) In the method of manufacturing a semiconductor optical device according to (14), in the step of forming the electrode, a part of the outer edge of the electrode on the one side and extending in the emission direction is The electrode may be formed so as to be inside an upper flat portion of the buried layer on the one side.

  (16) The method for manufacturing a semiconductor optical device according to any one of (10) to (15), wherein in the step of forming the buried layer, the buried layer is made of iron, ruthenium, or a combination thereof. May be formed including a semiconductor added as an impurity.

  (17) In the method of manufacturing a semiconductor optical device according to any one of (10) to (16), the modulator unit may be an electroabsorption modulator or a Mach-Zehnder modulator. Good.

  (18) The semiconductor optical module according to the present invention may be a semiconductor optical element module on which the semiconductor optical element manufactured by the method according to any one of (10) to (17) is mounted.

  (19) The optical transmission module or the optical transmission / reception module according to the present invention may be an optical transmission module or an optical transmission / reception module on which the semiconductor optical element module according to (9) or (18) is mounted. Good.

  (20) The optical transmission device according to the present invention may be an optical transmission device including the optical transmission module or the optical transmission / reception module according to (19).

  According to the present invention, in a semiconductor optical device having a BH structure, a semiconductor optical device, an optical transmission module, an optical transmission / reception module, an optical transmission device, and the like, whose characteristics are further improved by reducing the parasitic capacitance A manufacturing method is provided.

1 is a top view of an EA modulator integrated DFB laser device according to an embodiment of the present invention. FIG. 1 is a cross-sectional view of an EA modulator integrated DFB laser device according to an embodiment of the present invention. 1 is a cross-sectional view of an EA modulator integrated DFB laser device according to a first embodiment of the present invention. It is a figure which shows the structure of the modulator part of the EA modulator integrated DFB laser element which concerns on the 1st Embodiment of this invention. It is sectional drawing of the oscillator part of the EA modulator integrated DFB laser element which concerns on embodiment of this invention. It is a top view of the modulator part of the EA modulator integrated DFB laser device according to the first embodiment of the present invention. It is a top view which shows the process of the manufacturing method of the EA modulator integrated type DFB laser device concerning the embodiment of the present invention. It is sectional drawing which shows the process of the manufacturing method of the EA modulator integrated DFB laser element which concerns on embodiment of this invention. It is a top view which shows the process of the manufacturing method of the EA modulator integrated type DFB laser device concerning the embodiment of the present invention. It is sectional drawing which shows the process of the manufacturing method of the EA modulator integrated DFB laser element which concerns on embodiment of this invention. It is a top view which shows the process of the manufacturing method of the EA modulator integrated type DFB laser device concerning the embodiment of the present invention. It is sectional drawing which shows the process of the manufacturing method of the EA modulator integrated DFB laser element which concerns on embodiment of this invention. It is a top view which shows the process of the manufacturing method of the EA modulator integrated type DFB laser device concerning the embodiment of the present invention. It is sectional drawing which shows the process of the manufacturing method of the EA modulator integrated DFB laser element which concerns on embodiment of this invention. It is a top view which shows the process of the manufacturing method of the EA modulator integrated type DFB laser device concerning the embodiment of the present invention. It is sectional drawing which shows the process of the manufacturing method of the EA modulator integrated DFB laser element which concerns on embodiment of this invention. It is a top view which shows the process of the manufacturing method of the EA modulator integrated type DFB laser device concerning the embodiment of the present invention. It is sectional drawing which shows the process of the manufacturing method of the EA modulator integrated DFB laser element which concerns on embodiment of this invention. It is sectional drawing which shows the process of the manufacturing method of the EA modulator integrated DFB laser element which concerns on embodiment of this invention. It is a top view which shows the process of the manufacturing method of the EA modulator integrated type DFB laser device concerning the embodiment of the present invention. It is sectional drawing which shows the process of the manufacturing method of the EA modulator integrated DFB laser element which concerns on embodiment of this invention. It is sectional drawing which shows the process of the manufacturing method of the EA modulator integrated DFB laser element which concerns on embodiment of this invention. It is a top view which shows the process of the manufacturing method of the EA modulator integrated type DFB laser device concerning the embodiment of the present invention. It is sectional drawing which shows the process of the manufacturing method of the EA modulator integrated DFB laser element which concerns on embodiment of this invention. It is sectional drawing which shows the process of the manufacturing method of the EA modulator integrated DFB laser element which concerns on embodiment of this invention. It is a top view which shows the process of the manufacturing method of the EA modulator integrated type DFB laser device concerning the embodiment of the present invention. It is sectional drawing which shows the process of the manufacturing method of the EA modulator integrated DFB laser element which concerns on embodiment of this invention. 1 is a schematic top view of an EA modulator integrated DFB laser device according to a first embodiment of the present invention. FIG. FIG. 5 is a schematic top view of an EA modulator integrated DFB laser device according to a second embodiment of the present invention. It is an upper surface schematic diagram of the EA modulator integrated type DFB laser device according to the prior art. It is sectional drawing of the modulator part of the EA modulator integrated DFB laser element which concerns on the 2nd Embodiment of this invention. It is a figure showing the structure of the optical transmission module which concerns on the 3rd Embodiment of this invention. It is sectional drawing which shows the structure of the EA modulator based on a prior art which has a ridge waveguide structure. It is a figure which shows the structure of the EA modulator based on a prior art which has BH structure. 1 is a top view of an EA modulator according to the prior art having a BH structure. FIG. It is a figure showing the parasitic capacitance of the EA modulator based on a prior art which has a BH structure.

  Embodiments according to the present invention will be described in detail below. However, the drawings shown below are merely examples of each embodiment, and the size of the drawings and the scales described in the present examples do not necessarily match.

[First Embodiment]
The semiconductor optical device according to the first embodiment of the present invention is an EA modulator integrated DFB laser device 1 having a transmission speed of 40 Gbit / s and having a BH structure.

  FIG. 1A is a top view of the EA modulator integrated DFB laser device 1 according to this embodiment. As described above, the EA modulator integrated DFB laser device 1 includes a modulator unit 2 made of an EA modulator and an oscillator unit 3 made of a DFB laser integrated on the same n-type InP substrate 10 (not shown). ing. The multilayer structure of the EA modulator integrated DFB laser device 1 has a waveguide region extending in the lateral direction in the figure near the center. Light is oscillated from the waveguide region of the oscillator unit 3 to the waveguide region of the modulator unit 2. The light is modulated by the modulator unit 2 and light is emitted from the left end in the figure accordingly.

  As shown in FIG. 1A, a passivation film 21 is formed on the upper surface of the EA modulator integrated DFB laser element 1. As described above, the passivation film 21 is not formed on a part of the upper surface of the EA modulator integrated DFB laser element 1, and there is a through hole 21a (not shown). A p-type electrode 22 is formed on each of the modulator section 2 and the oscillator section 3 so as to cover the through hole 21a. Further, the left end face in the figure from which light is emitted is covered with an antireflection film 35, and the right end face in the figure on the opposite side is covered with a high reflection film 36.

A semiconductor optical device length _{L 1} is the length of the EA modulator integrated DFB laser element 1 in the horizontal direction of the figure (emission direction) is 650 .mu.m. The semiconductor optical element length L ₁ is a distance from the antireflection film 35 to the high reflection film 36. Of the semiconductor optical element length L ₁ , the modulator portion length L _3, which is the length of the modulator portion 2 in the horizontal direction in the figure, is 100 μm. The semiconductor optical element width _{L 2} is a view in vertical length of the EA modulator integrated DFB laser element 1 is 400 [mu] m.

  FIG. 1B is a cross-sectional view of the EA modulator integrated DFB laser device 1 according to this embodiment. FIG. 1B shows a cross section through the 1B-1B broken line of the EA modulator integrated DFB laser device 1 shown in FIG. 1A. As shown in FIG. 1B, the EA modulator integrated DFB laser element 1 has a multilayer structure, and the modulator unit 2 and the oscillator unit 3 have different structures. Each structure will be described later.

  FIG. 1C is a cross-sectional view of the modulator section 2 of the EA modulator integrated DFB laser device 1 according to this embodiment. FIG. 1C shows a cross section through the 1C-1C broken line of the EA modulator integrated DFB laser device 1 shown in FIG. 1A.

  FIG. 1D is a diagram showing the structure of the modulator unit 2 of the EA modulator integrated DFB laser device 1 according to this embodiment. FIG. 1D (a) shows a cross section of the EA modulator integrated DFB laser device 1 shown in FIG. 1A through a 1D-1D broken line.

  Similar to the EA modulator according to the prior art shown in FIG. 16, the modulator section 2 of the EA modulator integrated DFB laser device 1 according to this embodiment has a multilayer structure including an MQW layer 13 serving as an active region. The stripe structure 101 has a BH structure in which both sides of the mesa stripe structure 101 are buried with the buried layer 18.

  The modulator unit 2 of the EA modulator integrated DFB laser device 1 according to this embodiment is mainly composed of the EA modulator according to the prior art shown in FIG. 16, the shape of the passivation film 21, and the shape of the p-type electrode 22. Different. That is, it has a feature in the shape of the through hole 21a, which is a region where the passivation film 21 is not formed.

  As shown in FIG. 1C and FIG. 1D (a), the modulator section 2 of the EA modulator integrated DFB laser device 1 according to this embodiment includes an n-type InP buffer layer 11 and an n-type InP substrate 10. An InGaAsP lower guide layer 12, an MQW layer 13 serving as an active region, a p-type InGaAsP upper guide layer 14, a p-type InP cap layer 15, a p-type InP cladding layer 16, and a p-type InGaAs contact layer 17 are laminated. Here, the well layer and the barrier layer of the MQW layer 13 are both made of InGaAsP to which no impurity is added, and the thickness of the MQW layer 13 is about 0.25 μm. In addition, the well layer and the barrier layer of the MQW layer 13 may use InGaAlAs or the like instead of InGaAsP. Zn is used as an impurity added to the p-type layers such as the p-type InGaAsP upper guide layer 14, the p-type InP cap layer 15, the p-type InP cladding layer 16, and the p-type InGaAs contact layer 17.

  Of these multilayer structures, the outside of the waveguide region is removed up to the upper surface of the n-type InP buffer layer 11, and the mesa stripe structure 101 is formed. The total layer thickness from the n-type InGaAsP lower guide layer 12 to the p-type InGaAs contact layer 17 is the height of the mesa stripe structure 101, and the height of the mesa stripe structure 101 is about 3.5 μm. The width of the mesa stripe structure 101 shown in the cross-sectional views of FIGS. 1C and 1D (a) is about 1.5 μm.

  Both sides of the mesa stripe structure 101 are buried by the buried layer 18. Here, the buried layer 18 is made of InP to which Ru is added as an impurity. As described above, when the buried layer 18 is further crystal-grown from the upper surface of the mesa stripe structure 101, the buried layer 18 is laminated so as to be inclined along the (111) B plane due to the crystal structure of the buried layer 18. . The upper surface of the buried layer 18 is composed of an upper surface slope portion extending on both sides of the upper surface of the mesa stripe structure, and an upper surface flat portion extending in parallel with the n-type InP substrate 10 on both sides thereof.

  Here, the distance from the lower surface of the buried layer 18 to the upper flat portion of the buried layer 18 is the layer thickness of the buried layer 18. The buried layer 18 according to this embodiment has a thickness of 7 μm. This layer thickness is about 2 μm larger than the typical thickness of the buried layer 18 of the conventional EA modulator integrated DFB laser device 1, which is 5 μm. As described above, increasing the layer thickness of the buried layer 18 is a factor that reduces the parasitic capacitance of the modulator section 2.

  As described above, since both sides of the upper surface of the mesa stripe structure 101 spread along the (111) B surface when being stacked above the upper surface of the mesa stripe structure 101, the layer thickness of the buried layer 18 is increased. Along with this, the upper surface slope portion of the buried layer 18 further expands, and the area of the upper surface slope portion increases.

As shown in FIG. 1C, the buried layer 18 to the opening width L ₄ of, while the boundary of the top surface slope portion and the upper surface flat portion of the side, and the distance to the boundary of the top surface slope portion and the upper surface flat portion of the other side. In this case, the opening width _{L 4} of the buried layer 18 is 11 [mu] m.

  A passivation film 21, which is an insulating film, is formed on the top surfaces of the mesa stripe structure 101 and the buried layer 18. The passivation film 21 is formed on a part of the top surface of the mesa stripe structure 101 and a part of the top surface of the buried layer 18. Is not formed, and is a through hole 21a.

  A p-type electrode 22 is formed above the mesa stripe structure 101 and the buried layer 18, and the p-type electrode 22 is connected to the p-type InGaAs contact layer 17 at the uppermost layer of the mesa stripe structure 101 through the through hole 21 a. doing. An n-type electrode 23 is provided on the lower side of the n-type InP substrate 10.

  FIG. 1D (b) is a diagram showing the shape of the passivation film 21 of the EA modulator shown in FIG. 1D (a). That is, there is a region where the passivation film 21 is not formed in the center of FIG. 1D (b), and this region is the through hole 21a. Note that FIG. 1D (a) corresponds to a cross section that penetrates the vicinity of the center of FIG. 1D (b) in the horizontal direction in the drawing.

  The inner edge of the passivation film 21 shown in FIG. 1D (b) has a front part 43 spreading in the lateral direction in the figure in the front (lower side in the figure) and the emission direction (vertical direction in the figure) from both ends of the front part. ) And a rear portion 44 that extends rearward (upper side in the drawing) in the horizontal direction in the drawing.

  Since the electrode pad portion 22a of the p-type electrode 22 is provided on the upper side of the left passivation film 21 in the drawing, the left extending portion in the drawing is extended to the electrode pad side among the extending portions extending along the emission direction. The portion 41 and the extending portion on the right side in the figure are referred to as the other-side extending portion 42.

  Unlike the passivation film 21 of the EA modulator according to the prior art shown in FIG. 16B, the other side extending portion 42 of the passivation film 21 extends to the upper surface slope portion on the right side of the buried layer 18. That is, the other side extending portion 42 is further on the right side than the right end of the upper surface of the mesa stripe structure 101 in the drawing, and is on the left side of the boundary between the upper surface slope portion and the upper surface flat portion on the right side of the buried layer 18.

  The electrode pad side extending portion 41 of the passivation film 21 has a concave joint portion 41b in the vicinity of the center in the figure, and the electrode pad side extending front portion 41a and the electrode pad side extending portion are respectively provided before and after the joint portion 41b. There is a rear part 41c. The electrode pad side extending front part 41a and the electrode pad side extending rear part 41c, which are parts other than the joint part 41b, of the electrode pad side extending part 41 are the left side of the buried layer 18 as in the other side extending part 42. It extends to the top slope part. That is, the electrode pad side extending front part 41a and the electrode pad side extending rear part 41c are further to the left than the left end in the figure of the upper surface of the mesa stripe structure 101, and the upper surface slope part and the upper surface flat on the left side of the buried layer 18 It is on the right side of the division boundary.

  Of the inner edge of the passivation film 21, the through hole 21 a, which is a region where the passivation film 21 is not formed, is formed in a convex shape by the joint portion 41 b having a concave shape. As described above, the p-type electrode 22 is connected to the p-type InGaAs contact layer 17 in the uppermost layer of the mesa stripe structure 101 through the through hole 21a. The through-hole 21a has an inner edge of the passivation film 21. The convex region corresponding to the joint portion 41b makes electrical connection more reliable.

  Among the inner edges of the passivation film 21, the electrode pad side extending front part 41 a and the electrode pad side extending rear part 41 c and the other side extending part 42 extend to the upper surface slope part of the buried layer 18. The through hole 21a according to this embodiment shown in (b) has a smaller area than the through hole 121a according to the prior art shown in FIG. 16 (b).

Here, the electrode pad side stretched front portion 41a or the electrode pad side stretched rear portion 41c, the distance to the other side extending portion 42, as shown in FIG. 1C, defined as a through-hole width L _5. In the prior art, the through-hole width L ₅ is about 11 μm, which is the same as the opening width L ₄ of the buried layer 18. However, the through-hole width L _{5 according} to this embodiment is smaller than the opening width L ₄ of the buried layer 18. It is possible to be about 5 μm.

  FIG. 2 is a top view of the modulator unit 2 of the EA modulator integrated DFB laser device 1 according to this embodiment. That is, the portion corresponding to the modulator unit 2 in the EA modulator integrated DFB laser device 1 according to the embodiment shown in FIG. 1A is schematically shown. Similarly to FIG. 17, the p-type electrode 22 is formed on the upper side of the passivation film 21 shown in FIG. 1D. In FIG. 2, the through-hole 21 a is indicated by a broken line, and the passivation film 21 is disposed below the p-type electrode 22 in a region outside the through-hole 21 a in the p-type electrode 22. .

  As shown in FIG. 2, the p-type electrode 22 includes a region extending in the vertical direction in the figure so as to cover the through hole 21a, and a region to be an electrode pad on the left side in the figure. In the region of the p-type electrode 22 that becomes an electrode pad, there is an electrode pad portion 22a. As shown in FIG. 2, the p-type electrode 22 extends not only to the through hole 21 a but also to a portion located further inside from the inner edge of the passivation film 21 in order to prevent the upper surface slope portion of the buried layer 18 from being exposed. ing.

  Therefore, as described above, the through hole 21a has a smaller area than the through hole 121a according to the prior art shown in FIG. 17, and the p-type electrode 22 provided so as to cover the through hole 21a is also the same. In addition, the area is smaller than that of the p-type electrode 22 according to the prior art.

Of FIG lateral side of the width of the p-type electrode 22, the width in the portion where the electrode pad portion 22a is not provided, is defined as a p-type electrode width L _6. In the prior art, the p-type electrode width is required to be about 13 μm larger than the through-hole width of 11 μm. However, the p-type electrode width L _{6 according} to this embodiment is greater than the through-hole width L _{5 of} about 5 μm. Can be set to about 7 μm.

  As a result, in the modulator section 2 of the EA modulator integrated DFB laser device 1 according to this embodiment, it is possible to increase the layer thickness of the buried layer 18 while suppressing an increase in the area of the p-type electrode 22. . As a result, it is possible to reduce the parasitic capacitance in the BH structure capable of emitting a high output as compared with the ridge waveguide structure.

  In the prior art, the inner edge of the passivation film 21 is formed so as not to reach the slope of the upper surface of the buried layer 18 with emphasis on the electrical connection of the electrodes. On the other hand, in the modulator section 2 of the EA modulator integrated DFB laser device 1 according to the present embodiment, the junction portion 41b is provided on the inner edge of the passivation film 21, so that the p-type electrode 22 and the mesa stripe structure 101 are provided. The electrical connection with the upper surface of is secured. The electrode pad-side stretched front part 41a and the electrode pad-side stretched rear part 41c, and the other-side stretched part 42, which are parts other than the joint part 41b among the stretched parts of the passivation film 21, are the upper surface slopes of the buried layer 18. By being formed so as to cover the part, the area of the electrode is reduced.

  FIG. 1E is a cross-sectional view of the oscillator unit 3 of the EA modulator integrated DFB laser device 1 according to this embodiment. FIG. 1E shows a section through the 1E-1E broken line of the EA modulator integrated DFB laser device 1 shown in FIG. 1A. Similar to the modulator unit 2 of the EA modulator integrated DFB laser device 1 according to the embodiment, the oscillator unit 3 of the EA modulator integrated DFB laser device 1 according to the embodiment also has a BH structure. .

  The oscillator unit 3 of the EA modulator integrated DFB laser device 1 according to this embodiment includes an n-type InP buffer layer 11, an n-type InGaAsP lower guide layer 30, and an MQW layer serving as an active region on an n-type InP substrate 10. 31, a p-type InGaAsP upper guide layer 32, an InP spacer layer 33, a diffraction grating layer 34, a p-type InP cladding layer 16, and a p-type InGaAs contact layer 17 are laminated. Then, like the modulator section 2 of the EA modulator integrated DFB laser device 1 according to the present embodiment, these multilayer structures are mesa stripe structures 101, and both sides of the mesa stripe structures 101 are embedded with the embedded layers 18. It is. Here, in the MQW layer 31, like the MQW layer 13, the well layer and the barrier layer of the MQW layer 13 are both made of InGaAsP to which no impurity is added. Similarly, the MQW layer 13 may use InGaAlAs or the like instead of InGaAsP.

In the modulator section 2 of the EA modulator integrated DFB laser device 1 according to this embodiment, as described above, the buried layer 18 has a thickness of 7 μm, the MQW layer 13 has a thickness of 0.25 μm, and the mesa stripe width is 1. The height of the mesa stripe structure 101 is 3.5 μm, the through hole width L ₅ is 5 μm, and the p-type electrode width L ₆ is 7 μm. The band of the modulator unit 2 of the EA modulator integrated DFB laser device 1 according to this embodiment is about 40.4 GHz.

  When the buried layer 18 uses an InP layer to which Fe is added as an impurity, the band of about 25 GHz is improved compared to the band of the EA modulator according to the prior art described above which is 15.3 GHz. Yes.

  Next, a manufacturing method of the EA modulator integrated DFB laser device 1 according to this embodiment will be described with reference to FIGS. 3A to 11B.

  First, a multilayer that is a part of the multilayer structure of the modulator unit 2 is formed. That is, an n-type InP buffer layer 11, an n-type InGaAsP lower guide layer 12, an MQW layer 13 serving as an active region, a p-type InGaAsP upper guide layer 14, and a p-type InP cap layer 15 are formed on an n-type InP substrate 10. It is formed by metal organic chemical vapor deposition (hereinafter referred to as MO-CVD). FIG. 3A is a top view showing this step and FIG. 3B is a cross-sectional view. FIG. 3B shows a cross section through the 3B-3B broken line shown in FIG. 3A.

  A protective mask 51 is formed in a region above the waveguide region of the modulator section 2 in the p-type InP cap layer 15 that is the uppermost layer of the multilayer structure. Thereafter, the multilayer structure other than the region to be the modulator portion 2, that is, the multilayer structure in the region to be the oscillator portion 3 is removed by etching until reaching the upper surface of the n-type InP buffer layer 11. FIG. 4A is a top view showing this step and FIG. 4B is a cross-sectional view. FIG. 4B shows a cross section through the broken line 4B-4B shown in FIG. 4A.

  Next, a multilayer that is part of the multilayer structure of the oscillator unit 3 is formed. That is, an n-type InGaAsP lower guide layer 30, an MQW layer 31 serving as an active region, a p-type InGaAsP upper guide layer 32, an InP spacer layer 33, a diffraction pattern on the n-type InP buffer layer 11 in the region serving as the oscillator unit 3. A p-type InGaAsP layer 52 to be the lattice layer 34 is formed using MO-CVD. At this time, the modulator unit 2 and the oscillator unit 3 are optically connected by a known bad joint technique. FIG. 5A is a top view showing this step and FIG. 5B is a cross-sectional view. FIG. 5B shows a cross section through the 5B-5B broken line shown in FIG. 5A.

  Further, the diffraction grating layer 34 is formed by forming a diffraction grating in the p-type InGaAsP layer 52 by interference exposure. The diffraction grating may be formed not by the interference exposure method but by the electron beam drawing method (EB method). Further, as described above, since the protective mask 51 is formed in the upper surface of the modulator unit 2 in the region above the waveguide region, no diffraction grating is formed in this region. FIG. 6A is a top view showing this step and FIG. 6B is a cross-sectional view. FIG. 6B shows a cross section through the 6B-6B broken line shown in FIG. 6A.

  After forming the diffraction grating layer 34, the protective mask 51 formed on the upper surface of the modulator unit 2 is removed. Further, a p-type InP cladding layer 16 and a p-type InGaAs contact layer 17 are formed on the upper surface of the multilayer structure of the modulator unit 2 and the oscillator unit 3. Here, the total thickness of the p-type InP cladding layer 16 and the p-type InGaAs contact layer 17 is preferably about 2 μm. FIG. 7A is a top view showing this step and FIG. 7B is a cross-sectional view. FIG. 7B shows a cross section through the 7B-7B broken line shown in FIG. 7A.

  After the multilayer structure is formed, a protective film 53 is formed on the upper surface of the p-type InGaAs contact layer 17 in a region above the waveguide region. Thereafter, the mesa stripe structure 101 is removed by removing the region other than the region where the protective film 53 is formed on the upper surface of the multilayer structure up to the upper surface of the n-type InP buffer layer 11 by dry etching or wet etching. Form. Of the multilayer structure, etching is performed to a height sufficiently lower than the MQW layer 13 of the modulator unit 2 and the MQW layer 31 of the oscillator unit 3, and the etching depth is about 3.5 μm. FIG. 8A is a top view showing this step, and FIGS. 8B and 8C are cross-sectional views. 8B shows a cross section through the 8B-8B broken line shown in FIG. 8A, and FIG. 8C shows a cross section through the 8C-8C broken line shown in FIG. 8A.

  After forming the mesa stripe structure 101, an embedded layer 18 is formed by growing an InP layer doped with Ru as an impurity on both sides of the mesa stripe structure 101 at a growth temperature of about 550 ° C. to 570 ° C. . Thereby, a BH structure is formed. Further, the region near the boundary between the modulator unit 2 and the oscillator unit 3 is removed from the p-type InGaAs contact layer 17 which is the uppermost layer of the mesa stripe structure 101. As a result, the p-type InGaAs contact layer 17 of the modulator section 2 and the p-type InGaAs contact layer 17 of the oscillator section 3 are electrically insulated. Therefore, the groove formed by being removed is called an isolation groove. FIG. 9A is a top view showing this step, and FIGS. 9B and 9C are cross-sectional views. 9B shows a cross section through the 9B-9B broken line shown in FIG. 9A, and FIG. 9C shows a cross section through the 9C-9C broken line shown in FIG. 9A.

  After forming the isolation groove, a passivation film 21 is formed on the entire wafer surface, and then a part of each of the regions to be the modulator unit 2 and the oscillator unit 3 is removed from the formed passivation film 21. Through holes 21a. FIG. 10A is a top view showing this step, and FIGS. 10B and 10C are cross-sectional views. 10B shows a cross section passing through the 10B-10B broken line shown in FIG. 10A, and FIG. 10C shows a cross section passing through the 10C-10C broken line shown in FIG. 10A.

  FIG. 10A shows through holes 21 a provided in the modulator unit 2 and the oscillator unit 3. Here, the through hole 21a is a region in the upper surface of the multilayer where the passivation film 21 is not formed. Details of the shape of the through hole 21a of the modulator section 2 are shown in FIG. 1D (b). As described above, the through hole width is 5 μm. On the other hand, since the DFB laser of the oscillator unit 3 is not significantly affected by the parasitic capacitance, the through hole 21a is, as in the past, from the boundary between the upper surface slope portion and the upper surface flat portion on one side of the buried layer 18 to the other side. It is provided across the boundary between the upper surface slope portion and the upper surface flat portion of the buried layer 18 on the side.

After forming the through hole 21a, the p-type electrode 22 is formed so as to cover the through hole 21a of the modulator unit 2 and the oscillator unit 3, respectively. Thereafter, the lower surface of the wafer is polished until the wafer becomes about 100 μm, the n-type electrode 23 is formed, and the wafer process is completed. FIG. 11A is a top view after the wafer process is completed, and FIG. 11B is a cross-sectional view. FIG. 11B shows a cross section passing through the 11B-11B broken line shown in FIG. 11A. FIG. 11A shows the p-type electrode 22 provided in each of the modulator unit 2 and the oscillator unit 3. Details of the shape of the p-type electrode 22 of the modulator section 2 are shown in FIG. As described above, the p-type electrode width L ₆ is 7 μm. On the other hand, since the DFB laser of the oscillator unit 3 is not significantly affected by the parasitic capacitance, the p-type electrode 22 has a shape spreading on both sides of the waveguide region as shown in FIG. 11A.

  After the wafer process is completed, the wafer is further cleaved into a bar shape, an antireflection film 35 is formed on the end face on the modulator section 2 side, and a high reflection film 36 is formed on the end face on the oscillator section 3 side. By cleaving, the EA modulator integrated DFB laser device 1 according to the embodiment shown in FIGS. 1A to 1E is completed.

[Second Embodiment]
The semiconductor optical device according to the second embodiment of the present invention is an EA modulator integrated DFB laser device 1 having a BH structure, as in the first embodiment. The EA modulator integrated DFB laser device 1 according to this embodiment has the same basic configuration as the EA modulator integrated DFB laser device 1 according to the first embodiment, but the passivation of the modulator unit 2 is performed. The shapes of the film 21 and the p-type electrode 22 are mainly different.

  12A is a schematic top view of the EA modulator integrated DFB laser device 1 according to the first embodiment, and FIG. 12C is a schematic top view of the EA modulator integrated DFB laser device 1 according to the related art. . The inner edge of the passivation film 21 of the modulator unit 2 of the EA modulator integrated DFB laser device 1 according to the first embodiment is formed as shown in FIG. 1D (b). Since the extended rear portion 41c and the other-side extended portion 42 reach the upper surface slope portion of the buried layer 18, the area of the through hole 21a according to the first embodiment is the same as that of the through hole 121a according to the related art. It can be made smaller than the area.

  As shown in FIG. 12A, the p-type electrode 22 according to the first embodiment is formed so as to cover the through-hole 21a and extend in the vertical direction in the drawing and includes the electrode pad portion 22a. By reducing the area of the through hole 21a according to the first embodiment, the area of the p-type electrode 22 formed so as to cover the through hole can be made smaller than the area of the p-type electrode 22 according to the prior art. It is done.

  Of the outer edge of the p-type electrode 22, the portion on the opposite side (right side) of the electrode pad portion 22 a and extending in the vertical direction in the drawing is inside the upper flat portion of the right buried layer 18. Furthermore, a part of the outer edge of the p-type electrode 22 on the electrode pad portion 22a side (left side) and extending in the vertical direction in the figure is inside the upper flat portion of the left buried layer 18.

  FIG. 12B is a schematic top view of the EA modulator integrated DFB laser device 1 according to this embodiment. The other side extended portion 42 of the passivation film 21 according to the embodiment extends to the upper surface slope portion of the right buried layer 18, similarly to the other side extended portion 42 of the passivation film 21 according to the first embodiment.

  The electrode pad side extending portion 41 of the passivation film 21 according to this embodiment is different from the electrode pad side extending portion 41 of the passivation film 21 according to the first embodiment, and is similar to the conventional technique shown in FIG. Further, it is located at the boundary between the upper surface slope portion and the upper surface flat portion of the left buried layer 18. That is, the electrode pad side extending portion 41 of the passivation film 21 according to the embodiment does not reach the upper surface slope portion of the left buried layer 18. Therefore, the area of the through hole 21a according to the second embodiment can be made smaller than the area of the through hole 121a according to the conventional technique.

  As shown in FIG. 12B, the p-type electrode 22 according to this embodiment is formed so as to cover the through-hole 21a and extend in the vertical direction in the drawing and include the electrode pad portion 22a. By reducing the area of the through hole 21a, the area of the p-type electrode 22 formed so as to cover the through hole 21a can be made smaller than the area of the p-type electrode 22 according to the prior art.

  In the modulator section 2 of the EA modulator integrated DFB laser device 1 according to the present embodiment, the area of the p-type electrode 22 according to the present embodiment is smaller than the area of the p-type electrode 22 according to the related art. It is possible to increase the thickness of the buried layer 18 while suppressing an increase in the area of the p-type electrode 22. As a result, it is possible to reduce the parasitic capacitance in the BH structure capable of emitting a high output as compared with the ridge waveguide structure.

  The electrode pad side extending portion 41 of the passivation film 21 according to the embodiment is located at the boundary between the upper surface slope portion and the upper surface flat portion of the left buried layer 18, as in the prior art shown in FIG. The shape of the passivation film 21 according to the embodiment does not contribute to the area reduction of the through hole 21a on the electrode pad side. Therefore, the modulator unit 2 of the EA modulator integrated DFB laser device 1 according to this embodiment is compared with the modulator unit 2 of the EA modulator integrated DFB laser device 1 according to the first embodiment. The structure is such that securing the electrical connection between the p-type electrode 22 and the upper surface of the mesa stripe structure 101 is prioritized over the effect of reducing the parasitic capacitance.

  FIG. 13 is a cross-sectional view of the modulator section 2 of the EA modulator integrated DFB laser device 1 according to this embodiment. The cross section of the modulator section 2 according to this embodiment shown in FIG. 13 corresponds to the cross section of the EA modulator integrated DFB laser element 1 shown in FIG. As described above, unlike the modulator unit 2 according to the first embodiment shown in FIG. 1C, the electrode pad side extending portion 41 of the passivation film 21 of the modulator unit 2 of the present embodiment has the embedded layer 18 on the left side in the drawing. Is located at the boundary between the upper surface slope portion and the upper surface flat portion. That is, the electrode pad extending portion 41 does not reach the upper surface slope portion of the buried layer 18. However, as described above, the electrode pad portion 22 a side and the other side extending portion 42 on the other side extend to the upper surface slope portion of the buried layer 18.

As a result, the through hole width L _{5 according to} the present embodiment is larger than 5 μm, which is the value of the through hole width L _{5 according} to the first embodiment, and is 7.5 μm. Accordingly, the p-type electrode width L _{6 according} to this embodiment is larger than 7 μm, which is the value of the p-type electrode width L _{6 according} to the first embodiment, and is 9.5 μm.

The EA modulator integrated DFB laser device 1 according to this embodiment has the same dimensions as the EA modulator integrated DFB laser device 1 according to the first embodiment. That is, the buried layer 18 has a layer thickness of 7 μm, the MQW layer 13 has a layer thickness of 0.25 μm, the mesa stripe width is 1.5 μm, the mesa stripe structure 101 has a height of 3.5 μm, and the through-hole width L ₅ is 7. 5 μm, and the p-type electrode width L ₆ is 9.5 μm. The band of the modulator unit 2 of the EA modulator integrated DFB laser device 1 according to this embodiment is about 39.1 GHz.

  In the case where the buried layer 18 is an InP layer to which Fe is added as an impurity, the band of about 24 GHz is improved compared to the band of the EA modulator according to the prior art described above which is 15.3 GHz. Yes.

  The manufacturing method of the EA modulator integrated DFB laser device 1 according to this embodiment has the same basic configuration as the manufacturing method of the EA modulator integrated DFB laser device 1 according to the first embodiment. The manufacturing method of the EA modulator integrated DFB laser device 1 according to this embodiment is formed in the process of forming the passivation film 21 and the manufacturing method of the EA modulator integrated DFB laser device 1 according to the first embodiment. The shape of the passivation film 21 and the shape of the p-type electrode 22 formed in the step of forming the p-type electrode 22 are mainly different.

  The present invention is characterized in that, of the inner edge of the passivation film 21, at least a part of the extending portion extending in the emission direction reaches the upper surface slope portion of the buried layer 18. Since at least a part of the extending portion reaches the upper surface slope portion of the buried layer 18, the area of the through hole 21a can be made smaller than the area of the through hole 121a according to the related art. Accordingly, the area of the p-type electrode 22 formed so as to cover the through hole 21a can be made smaller than the area of the p-type electrode 22 according to the prior art, so that the parasitic capacitance of the semiconductor optical device can be reduced. I can do it.

  Since the p-type electrode 22 and the upper surface of the mesa stripe structure 101 are electrically connected by the through hole 21a, the other side extending portion on the other side on the electrode pad portion 22a side of the inner edge of the passivation film 21 It is desirable that at least a part of 42 extends to the upper surface slope portion of the buried layer 18. As a result, the area of the p-type electrode 22 can be reduced. It is further preferable that at least a part of the outer edge of the p-type electrode 22 on the other side on the electrode pad portion 22a side and extending in the emission direction is inside the upper flat portion of the other buried layer. .

  It is further preferable that the other extended portion 42 extends to the upper surface slope portion of the buried layer 18. Thereby, the area of the p-type electrode 22 can be further reduced. It is further desirable that all of the outer edge of the p-type electrode 22 on the other side on the electrode pad portion 22a side and extending in the emission direction is inside the flat portion on the upper surface of the buried layer on the other side.

  It is further desirable that a part of the electrode pad side extending portion 41 on the electrode pad portion 22 a side of the inner edge of the passivation film 21 reaches the upper surface slope portion of the buried layer 18. Thereby, the area of the p-type electrode 22 can be further reduced. It is further preferable that a part of the outer edge of the p-type electrode 22 on the electrode pad portion 22a side and extending in the emission direction is inside the flat portion of the upper surface of the other buried layer.

  When a part of the electrode pad side extending portion 41 of the inner edge of the passivation film 21 reaches the upper surface slope portion of the buried layer 18, electrical connection between the p-type electrode 22 and the upper surface of the mesa stripe structure 101 is established. In order to ensure, it is desirable that the inner edge of the passivation film 21 has the joint portion 41 b shown in FIG. 2, and the portion other than the joint portion 41 b extends to the upper surface slope portion of the buried layer 18.

  For example, as shown in FIG. 1D (b), the inner edge of the passivation film 21 includes a front part 43 and a rear part 44 that extend on both sides of the upper surface of the mesa stripe structure 101, and an electrode pad side extension part 41 and the other side that extend in the emission direction. It consists of the extending | stretching part 42, and the shape of the passivation film 21 becomes a shape extended | stretched elongate in an output direction. In the vicinity of the front portion 43 and the front portion 44, unlike FIG. 1D (b), the inner edge of the passivation film 21 may be greatly curved. However, the extended portion is curved at both ends thereof. It does not include the curved curve.

  Although the shape of the joint portion 41b can be considered variously, as shown in FIG. 2, the inner edge of the passivation film 21 has a concave bent shape, and the joint portion 41b is outside the upper surface of the mesa stripe structure 101. It is desirable that the portion located at the boundary between the upper surface slope portion and the upper surface flat portion of the buried layer 18 is located further outside the boundary.

  The shape of the passivation film 21 and the shape of the p-type electrode 22 should be designed taking into consideration the balance between the required band and the electrical connection, the positional accuracy for forming the p-type electrode 22, and the like. .

  Although the case where an InP layer to which Ru is added as an impurity is used as the buried layer 18 of the EA modulator integrated DFB laser device 1 according to the first and second embodiments has been described above. The impurities are not limited to Ru, and may be other metals such as Fe or a combination of Fe and Ru.

  However, Fe and Zn have a feature that they easily diffuse each other. Therefore, when Fe is contained as an impurity in the buried layer 18, Fe and Zn are contained in the p-type multilayer of the mesa stripe structure 101 and Fe contained in the buried layer 18. Zn tends to interdiffusion. Therefore, when Fe is contained in the buried layer 18 as an impurity, Zn diffuses into the buried layer 18 and the parasitic capacitance of the buried layer 18 increases.

  On the other hand, interdiffusion of Ru and Zn is greatly suppressed compared to the case of Fe and Zn. Therefore, the buried layer 18 is preferably a semiconductor layer such as an InP layer to which Ru is added as an impurity.

[Third Embodiment]
The optical transmission module according to the third embodiment of the present invention is an optical transmission module 4 on which the EA modulator integrated DFB laser device 1 according to the first embodiment or the second embodiment is mounted. The optical transmission module 4 can perform optical transmission in a band of about 35 GHz.

  FIG. 14 is a diagram illustrating the configuration of the optical transmission module 4 according to this embodiment. In the EA modulator integrated DFB laser device 1 according to the first embodiment or the second embodiment, an AuSn solder is used for a chip carrier 70 made of aluminum nitride (AlN) with a 50Ω termination resistor. It is installed. The chip carrier 70 is mounted on the upper side of a Peltier 71 that is a temperature adjusting means, and these are mounted on a package 72. A thermistor 73, a monitor photodiode 74, an optical isolator 75, and a condenser lens 76 are further mounted on the package 72. Here, the condensing lens 76 is a lens for condensing light onto the fiber 77 connected to the light emission destination.

  Control means (not shown) is provided outside the optical transmission module 4 according to this embodiment, and APC (Auto Power Control) control is performed on the optical transmission module 4 by the control means. That is, the monitor photodiode 74 receives the rear output light output from the rear end face of the EA modulator integrated DFB laser element 1 and outputs it as a monitor current 81 to the control means. Corresponding to the monitor current 81, a laser drive current 82 is supplied to the oscillator unit 3 of the EA modulator integrated DFB laser element 1. By APC control, the output power of the output light 84 of the optical transmission module 4 can be kept constant. A modulator drive signal 83 is supplied to the modulator section 2 of the EA modulator integrated DFB laser element 1.

  Further, ATC (Auto Temperature Control) control is performed on the optical transmission module 4 by the control means. That is, the thermistor 73 detects the temperature of the EA modulator integrated DFB laser element 1 and outputs the detected temperature as a monitor temperature 85 to the control means. A Peltier drive current 86 is supplied to the Peltier 71 corresponding to the monitor temperature 85. By the ATC control, the temperature of the EA modulator integrated DFB laser device 1 can be kept constant.

  Similarly, the optical transceiver module according to this embodiment includes an optical transmission unit on which the EA modulator integrated DFB laser device 1 according to the first embodiment or the second embodiment is mounted, and a known optical reception unit. The optical transceiver module 5 is provided. The configuration of the optical transmission unit of the optical transmission / reception module 5 is the same as the configuration of the optical transmission module 4.

  Furthermore, the optical transmission apparatus according to this embodiment is the optical transmission apparatus 6 on which the optical transmission module 4 or the optical transmission / reception module 5 is mounted. Other configurations of the optical transmission device 6 are the same as those known.

  The package 72 is a metal material processed into a box shape. The package 72 includes a bottom plate made of CuW alloy having high thermal conductivity, a frame made of FeNi alloy, a ceramic feedthrough in which a wiring pattern is formed to transmit an electric signal to the inside of the package 72, a lead terminal, and a cap for seam welding. It consists of parts such as seam rings, sapphire glass for hermetically sealing light extraction windows, lens holders and pipe members for welding and fixing optical fibers, etc., using brazing materials such as brazing materials and AuSn solder Assembled.

  The semiconductor optical device, the optical transmission module, the optical transmission / reception module, the optical transmission apparatus, and the manufacturing methods thereof according to the present invention have been described above. The present invention realizes reduction of parasitic capacitance caused by electrodes provided in a semiconductor optical device. Although the EA modulator integrated DFB laser device 1 is shown as an example of the semiconductor optical device according to the embodiment, the structure of the modulator unit 2 is not limited to the EA modulator. For example, another modulator such as a Mach-Zehnder type modulator may be used. Further, unlike the EA modulator integrated DFB laser element 1, the modulator unit 2 is not limited to the modulator integrated semiconductor optical device integrated on the same semiconductor substrate as the oscillator unit 3. The semiconductor optical device according to the present invention may be an external modulator provided outside the output side of the laser device. Here, the external modulator is, for example, an EA modulator or a Mach-Zehnder type modulator. The semiconductor optical device according to the present invention is not limited to a modulator, and the present invention can be applied as a structure that reduces the parasitic capacitance of other semiconductor optical devices having a BH structure.

DESCRIPTION OF SYMBOLS 1 EA modulator integrated DFB laser element, 2 modulator part, 3 oscillator part, 4 optical transmission module, 5 optical transmission / reception module, 6 optical transmission apparatus, 10 n-type InP substrate, 11 n-type InP buffer layer, 12 n-type InGaAsP lower guide layer, 13 MQW layer, 14 p-type InGaAsP upper guide layer, 15 p-type InP cap layer, 16 p-type InP clad layer, 17 p-type InGaAs contact layer, 18 buried layer, 21 passivation film, 21a through hole , 22 p-type electrode, 22a electrode pad part, 22b buried slope part, 22c mesa stripe upper surface part, 23 n-type electrode, 30 n-type InGaAsP lower guide layer, 31 MQW layer, 32 p-type InGaAsP upper guide layer, 33 InP Spacer layer, 34 diffraction grating layer, 35 antireflection film, 36 high reflection film, DESCRIPTION OF SYMBOLS 1 Electrode pad side extending | stretching part, 41a Electrode pad side extending | stretching front part, 41b Joint part, 41c Electrode pad side extending | stretching rear part, 42 Other side extending | stretching part, 43 Front part, 44 Back part, 51 Protection mask, 52 p-type InGaAsP layer , 53 Protective film, 70 Chip carrier, 71 Peltier, 72 Package, 73 Thermistor, 74 Monitor photodiode, 75 Optical isolator, 76 Condensing lens, 77 Fiber, 81 Monitor current, 82 Laser drive current, 83 Modulator drive signal, 84 output light, 85 monitor temperature, 86 Peltier drive current, 101 mesa stripe structure, 121a through hole, 201 p-type InP cap layer, 202 polyimide resin, 203 low mesa structure, C ₁ pad part capacitance, C _2a , C _2b slope part capacity, _{C 3} junction _{capacitance, C all} parasitic Amount.

Claims (18)

A semiconductor optical device comprising a modulator unit that modulates and emits light input along an emission direction,
The modulator section is
A mesa stripe structure including an active layer and extending in the emission direction;
An upper surface slope portion that is disposed adjacent to both sides of the mesa stripe structure and that extends from both sides of the upper surface of the mesa stripe structure as it proceeds in the stacking direction ; An embedded layer having
A passivation film formed on the upper surface of the mesa stripe structure and the upper surface of the buried layer, except for a through-hole region extending on both sides of the upper surface of the mesa stripe structure and extending in the emission direction;
An electrode extending over the through-hole region and extending in the emission direction, and further including a wire connection pad region located above a part of the upper flat portion on one side of the buried layer; Prepared,
The inner edge of the passivation film is provided with extending portions extending along the emission direction on both sides of the upper surface of the mesa stripe structure,
The one side and out of the extending portion on the other side, at least in part, which extends to the upper surface inclined surface portion of the buried layer of the other side,
Of the outer edge of the electrode, at least a part of the portion extending in the emission direction on the other side is inside the outer edge of the upper surface slope portion of the buried layer on the other side,
A semiconductor optical device. The semiconductor optical device according to claim 1,
All of the extending portions on the other side extend to the upper surface slope portion of the buried layer on the other side,
A semiconductor optical device. The semiconductor optical device according to claim 2,
Of the outer edge of the electrode, all the portions on the other side and extending in the emission direction are inside the outer edge of the upper surface slope portion of the buried layer on the other side,
A semiconductor optical device. A semiconductor optical device according to any one of claims 1 to 3 ,
The extension portion on the one side of the passivation film includes a joint portion with the wire connection region of the electrode,
Of the extended portion on the one side of the passivation film, all but the portion that becomes the bonding portion extends to the upper surface slope portion of the buried layer on the one side.
A semiconductor optical device. The semiconductor optical device according to claim 4 ,
Of the outer edge of the electrode, a part of the portion extending in the emission direction on the one side is inside the outer edge of the upper surface slope portion of the buried layer on the one side,
A semiconductor optical device. A semiconductor optical device according to any one of claims 1 to 5 ,
The buried layer includes a semiconductor to which iron or ruthenium or a combination thereof is added as an impurity.
A semiconductor optical device. A semiconductor optical device according to any one of claims 1 to 6 ,
The modulator section is an electroabsorption modulator or a Mach-Zehnder modulator.
A semiconductor optical device. Mounting a semiconductor optical device according to any one of claims 1 to 7, the semiconductor optical device module. A method for manufacturing a semiconductor optical device comprising a modulator unit that modulates and emits light input along an emission direction,
Forming a mesa stripe structure including an active layer and extending in the emission direction;
As proceeding in the laminating direction, an embedded layer having a top slope portion that becomes a slope that spreads from both sides of the top surface of the mesa stripe structure and a flat top portion that spreads outward from each other is adjacent to both sides of the mesa stripe structure. And forming the process,
Forming a passivation film on the top surface of the mesa stripe structure and the top surface of the buried layer, excluding through-hole regions extending on both sides of the top surface of the mesa stripe structure and extending along the emission direction;
Covering the through-hole region and extending in the emission direction, and further including a wire connection pad region located above a part of the upper surface flat portion of the buried layer on one side, and forming an electrode; , Including,
The inner edge of the passivation film is provided with extending portions extending along the emission direction on both sides of the upper surface of the mesa stripe structure,
In the step of forming the passivation film,
The one side and out of the extending portion on the other side, at least in part, to span the upper surface inclined surface portion of the buried layer of the other side, to form the passivation film,
In the step of forming the electrode,
The electrode is formed such that at least a part of the outer edge of the electrode on the other side and extending in the emission direction is on the inner side of the outer edge of the upper surface slope portion of the buried layer on the other side. ,
A method of manufacturing a semiconductor optical device. A method of manufacturing a semiconductor optical device according to claim 9 ,
In the step of forming the passivation film,
Forming the passivation film so that all of the extending portions on the other side reach the upper surface slope portion of the buried layer on the other side,
A method of manufacturing a semiconductor optical device. It is a manufacturing method of the semiconductor optical element according to claim 10 ,
In the step of forming the electrode,
Of the outer edge of the electrode, the electrode is formed so that all the portions on the other side and extending in the emission direction are inside the outer edge of the upper surface slope portion of the buried layer on the other side.
A method of manufacturing a semiconductor optical device. A method of manufacturing a semiconductor optical device according to any one of claims 9 to 11 ,
In the step of forming the passivation film,
The extension portion on the one side of the passivation film includes a joint portion with the wire connection region of the electrode,
Forming the passivation film so that all of the extension part on the one side of the passivation film, except for the part serving as the bonding part, reaches the upper-surface slope part of the buried layer on the one side;
A method of manufacturing a semiconductor optical device. A method of manufacturing a semiconductor optical device according to claim 12 ,
In the step of forming the electrode,
Of the outer edge of the electrode, forming the electrode so that a part of the portion extending in the emission direction on the one side is inside the outer edge of the upper surface slope portion of the buried layer on the one side,
A method of manufacturing a semiconductor optical device. A method for manufacturing a semiconductor optical device according to any one of claims 9 to 13 ,
In the step of forming the buried layer,
Forming the buried layer including a semiconductor to which iron or ruthenium or a combination thereof is added as an impurity;
A method of manufacturing a semiconductor optical device. A method for manufacturing a semiconductor optical device according to any one of claims 9 to 14 ,
The modulator section is an electroabsorption modulator or a Mach-Zehnder modulator.
A method of manufacturing a semiconductor optical device. Mounting a semiconductor optical device manufactured by the method according to any of claims 9 to 15, the semiconductor optical device module. An optical transmission module or an optical transmission / reception module on which the semiconductor optical element module according to claim 8 or 16 is mounted. 18. An optical transmission device on which the optical transmission module or optical transmission / reception module according to claim 17 is mounted.

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