JP5076964B2 - Semiconductor laser and method of manufacturing the semiconductor laser - Google Patents

Description

  The present invention relates to a semiconductor laser and a method for manufacturing the semiconductor laser.

Non-Patent Document 1 describes a method for manufacturing a multilayer quantum wire laser. This multilayer quantum wire laser is manufactured as follows. A resist pattern is drawn by an electron beam exposure method to form a resist mask, and an insulating film mask is formed by etching using this resist mask. A quantum wire is formed by CH ₄ / H ₂ reactive ion etching using this insulating film mask. An InP semiconductor is buried on the side surface of the quantum wire and regrown by metal organic vapor phase epitaxy to produce a multilayer quantum wire structure. In addition, a GaInAsP semiconductor is used for the optical confinement layer.

Non-Patent Document 2 describes a DFB laser. This DFB laser has a thin line active layer containing a GaInAsP semiconductor. An InP semiconductor is formed on the side surface of the thin line active layer by the metal organic vapor phase regrowth method to embed the thin line. An optical confinement layer made of a GaInAsP semiconductor is provided on the thin line active layer.
H. Yagi et al .: JJAP, 43 (2004) pp.3401-3409 N. Nunoya et al .: JSTQE, (2001) pp249

  Both the multiple quantum wire laser and the DFB laser described in Non-Patent Literature 1 and Non-Patent Literature 2 each have a buried region made of an InP semiconductor provided between quantum wires (or thin wires). Further, these lasers have an optical confinement layer made of GaInAsP on the quantum wires (or wires).

  In a semiconductor laser in which such a structure is provided on an n-type semiconductor substrate, the valence band side band offset of the InP semiconductor with respect to the optical confinement layer made of GaInAsP semiconductor is large. For this reason, in a semiconductor laser fabricated by depositing an InP semiconductor on the top surface of a quantum wire when the quantum wire is embedded, this InP semiconductor serves as a barrier against the movement of holes, thus preventing the injection of holes into the active region. It is done. Therefore, in order to obtain a semiconductor laser with good characteristics, it is necessary to precisely control the embedding of the quantum wire so that the InP semiconductor is not deposited on the upper surface of the quantum wire. However, this control is not easy. In the semiconductor lasers described in Non-Patent Documents 1 and 2, a p-type semiconductor substrate is used so that the InP semiconductor does not become a barrier against the movement of holes. In a semiconductor laser fabricated on a p-type semiconductor substrate, the valence band side band offset between the optical confinement layer and the InP semiconductor does not hinder hole injection into the active region.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a semiconductor laser having a structure capable of avoiding the formation of a barrier that prevents hole injection and controlling the embedding of quantum wires. Another object of the present invention is to provide a method for manufacturing this semiconductor laser.

  A semiconductor laser according to the present invention includes a first optical confinement layer provided on an n-type cladding region, a plurality of quantum wires provided on the first optical confinement layer and periodically arranged, and A buried semiconductor region having a first portion provided on the side surface and the first optical confinement layer and a second portion provided on the upper surface of each quantum wire; A buried optical region including aluminum and indium as a group III element and arsenic as a group V element. The band gap of the buried semiconductor region is the second optical confinement layer provided on the second optical confinement layer. It is characterized by being larger than the band gap of the confinement layer and larger than the largest band gap of the quantum wires.

  According to this semiconductor laser, the second portion of the buried semiconductor region is provided between the quantum wire and the second optical confinement layer. Since this buried semiconductor region contains aluminum and indium as group III elements and arsenic as group V elements, the valence band side band offset between the second portion and the second optical confinement layer can be reduced. Therefore, the buried semiconductor region does not serve as a barrier that prevents hole injection, and a semiconductor laser with good characteristics can be obtained. In addition, the side surface of the quantum wire is buried by the first portion of the buried semiconductor region. The buried semiconductor region having the first portion contains aluminum and indium as group III elements and arsenic as group V elements. Therefore, carriers can be confined in the lateral direction of the quantum wire.

  The semiconductor laser according to the present invention is characterized in that the buried semiconductor region is made of an AlInAs semiconductor. According to this semiconductor laser, since the second portion of the buried semiconductor region on the quantum wire is made of an AlInAs semiconductor made of the same material as the first portion, the second portion has a potential with respect to electrons from the quantum wire. It becomes a barrier. Accordingly, since carrier overflow can be suppressed, a semiconductor laser having good temperature characteristics can be obtained.

  The semiconductor laser according to the present invention is characterized in that the thickness of the second portion is 20 nm or more and 50 nm or less. According to this semiconductor laser, since the thickness of the second portion is 20 nanometers or more, the second portion can function as an electron blocking layer. Further, when the thickness of the second portion is greater than 50 nanometers, the element resistance is increased.

  The semiconductor laser according to the present invention further includes an n-type substrate, and the buried semiconductor region is undoped.

  A method of manufacturing a semiconductor laser according to the present invention includes a step of growing a first optical confinement layer on an n-type cladding layer, a step of growing a multiple quantum well layer on the optical confinement layer, and a plurality of quantum wires. Etching a multi-quantum well layer using a mask having a periodic pattern for forming a plurality of periodically arranged quantum wires, removing the mask, and embedding the quantum wires, A step of integrally growing an embedded semiconductor layer on a side surface and an upper surface of each quantum wire and the first optical confinement layer; a step of growing a second optical confinement layer on the embedded semiconductor layer; In addition, the group III element contains aluminum and indium, and the group V element contains arsenic. The band gap of the buried semiconductor layer is larger than the band gap of the semiconductor constituting the second optical confinement layer, and the quantum It is characterized by being larger than the maximum band gap of the thin wire.

  In this method of fabricating a semiconductor laser, an embedded semiconductor layer is integrally grown on the side surface and upper surface of the quantum wire and on the first optical confinement layer to embed the quantum wire. Therefore, the buried semiconductor layer is also formed on the upper surface of the quantum wire. On the other hand, since this buried semiconductor layer contains aluminum and indium as group III elements and arsenic as group V elements, the buried semiconductor layer is a substantial barrier to holes moving toward the quantum wires. It will not be. Therefore, it is necessary to grow the buried semiconductor layer by strictly controlling the thickness of the buried semiconductor layer grown on the side surface of each quantum wire and the first optical confinement layer so as to be equal to the height of the upper surface of the quantum wire. There is no. Therefore, the buried semiconductor layer can be grown not only on the side surface of each quantum wire and the first optical confinement layer, but also on the upper surface of each quantum wire, and the above precise control is performed. And the quantum wire 57 can be embedded. Such growth of the buried semiconductor layer facilitates control of the process of embedding the quantum wires.

  According to the present invention, there is provided a semiconductor laser having a structure capable of controlling the embedding of a quantum wire capable of avoiding the formation of a barrier that prevents hole injection, and a method for manufacturing the semiconductor laser.

  The knowledge of the present invention can be easily understood by considering the following detailed description with reference to the accompanying drawings shown as examples. Subsequently, embodiments of the semiconductor laser and the method for manufacturing the semiconductor laser of the present invention will be described with reference to the accompanying drawings. Where possible, the same parts are denoted by the same reference numerals.

  FIG. 1 is a perspective view showing the structure of the semiconductor laser according to the present embodiment. The semiconductor laser 10 includes a first cladding layer 13, a first optical confinement layer 15, a plurality of quantum wires 17, a buried semiconductor layer 19, a second optical confinement layer 21, and a second cladding layer 25. The first cladding layer 13 is provided on the main surface 11 a of the semiconductor substrate 11. The semiconductor substrate 11 and the first cladding layer 13 are made of an n-type semiconductor. This n-type semiconductor can be, for example, an n-type InP semiconductor.

  FIG. 2 is a schematic diagram showing an enlarged cross section of a portion A shown in FIG. The first optical confinement layer 15 is provided on the first cladding layer 13. The first optical confinement layer 15 can be, for example, an n-type GaInAsP semiconductor. The thickness of the first optical confinement layer 15 is, for example, 150 nm. Preferably, the thickness of the first optical confinement layer 15 may be 100 nm or more. The thickness of the first light confinement layer 15 may be 170 nm or less.

A plurality of quantum wires 17 are periodically arranged on the first optical confinement layer 15. Quantum wires 17 has a width W which is defined in the direction of the predetermined axis A _X, are arranged at a period Λ of the predetermined axis A _X direction. The width W of the quantum wire 17 is preferably 90 nm or less in order to operate as a DFB laser at a low current. In order to obtain a high differential gain based on the lateral quantum confinement effect of the quantum wire 17, the width W of the quantum wire 17 is preferably 30 nm or less. The width W of the quantum wire 17 needs to be 15 nm or more. The period Λ of the quantum wire 17 is a Bragg period corresponding to the wavelength of laser oscillation. For example, in order to obtain an oscillation wavelength of 1550 nm, the period Λ is 240 nm. For example, in order to obtain an oscillation wavelength of 1300 nm, the period Λ is 200 nm. The quantum wire 17 has a quantum well structure. The quantum well structure can include alternately arranged barrier layers 17a and well layers 17b. The uppermost layer of the quantum well structure can be the third optical confinement layer 17c. The barrier layer 17a is made of, for example, an undoped GaInAsP semiconductor. The well layer 17b is made of, for example, an undoped GaInAsP semiconductor. The third optical confinement layer 17c is made of, for example, an undoped GaInAsP semiconductor.

  Each quantum wire 17 is located on the first area 15 b of the surface 15 a of the first optical confinement layer 15. On the side surface of each quantum wire 17, the second area 15 c on the first optical confinement layer 15, and the upper surface of each quantum wire, an embedded semiconductor layer 19 grown integrally is provided. The buried semiconductor layer 19 is made of a semiconductor containing aluminum and indium as a group III element and arsenic as a group V element, and this semiconductor is preferably undoped. This semiconductor can be, for example, an AlInAs semiconductor. Since the side surface of the quantum wire 17 is embedded with the buried semiconductor layer 19, carriers can be confined in the side surface direction of the quantum wire 17.

  A second optical confinement layer 21 is provided on the buried semiconductor layer 19. The second optical confinement layer 21 is made of, for example, a p-type GaInAsP semiconductor. The thickness of the second optical confinement layer 21 is, for example, 110 nm. Preferably, the thickness of the second optical confinement layer 21 can be 60 nm or more. In addition, the thickness of the second optical confinement layer 21 can be 130 nm or less.

FIG. 3 is a diagram showing a band structure in the semiconductor laser 10 shown in FIGS. 1 and 2. In FIG. 3, reference numerals BG0 and BG1 indicate the band gap of the portion composed of the well layer 17b and the barrier layer 17a, reference numeral BG2 indicates the band gap of the embedded semiconductor layer 19 on the upper surface of the quantum wire 17, and reference numerals BG3 indicates the band gap of the second optical confinement layer 21, reference numeral BG4 indicates the band gap of the third optical confinement layer 17c of the quantum wire 17, and reference numeral BG5 indicates the band gap of the first optical confinement layer 15. As shown in FIG. 3, when the embedded semiconductor layer 19 is made of an AlInAs semiconductor and the second optical confinement layer 21 and the third optical confinement layer 17c are made of a GaInAsP semiconductor, the embedded semiconductor layer 19 and the second optical confinement layer are formed. 21 and the third optical confinement layer 17c have band offsets ΔE _V1 and ΔE _{V2 in} the valence band of about 10 meV, and band offsets ΔE _C1 and ΔE _C2 of the conduction band are about 200 meV. Accordingly, the band offsets ΔE _V1 and ΔE _V2 of the valence band between the embedded semiconductor layer 19 and the second optical confinement layer 21 and the third optical confinement layer 17c are one digit greater than the band offsets ΔE _C1 and ΔE _C2 of the conduction band. Thus, the buried semiconductor layer 19 is unlikely to be a barrier for the hole HL moving from the p-type cladding toward the quantum wire 17. Further, the band offsets ΔE _C1 and ΔE _C2 of the conduction band between the buried semiconductor layer 19 and the second optical confinement layer 21 and the third optical confinement layer 17c are one digit or more larger than the band offsets ΔE _V1 and ΔE _V2 of the valence band. Therefore, the embedded semiconductor layer 19 functions as an electron blocking layer for the electron EL from the quantum wire 17. Therefore, the overflow of electrons can be reduced, and a semiconductor laser having good temperature characteristics can be obtained. The thickness H of the buried semiconductor layer 19 on the upper surface of the quantum wire 17 is preferably 20 nm or more so that the buried semiconductor layer 19 functions well as an electron block layer. In order to reduce the increase in device resistance due to the embedded semiconductor layer 19 on the upper surface of the quantum wire 17, the thickness H is preferably 50 nm or less.

Reference is again made to FIG. The first cladding layer 13, the first light confinement layer 15, a plurality of quantum wires 17, embedded semiconductor layer 19 and the second light confinement layer 21 constitute a semiconductor mesa extending along a predetermined axis A _X. Further, the semiconductor mesa has a stripe shape and its side surface is embedded by the embedded region 23.

  The buried region 23 includes, for example, a first p-type current confinement layer 23a, an n-type current confinement layer 23b, and a second p-type current confinement layer 23c. The first p-type current confinement layer 23a is provided on the side surface of the semiconductor mesa and the surface of the first cladding layer 13, and covers the surface of the first cladding layer 13 and the side surface of the semiconductor mesa. The n-type current confinement layer 23b is provided on the first p-type current confinement layer 23a. The second p-type current confinement layer 23 c is provided between the n-type current confinement layer 23 b and the second cladding layer 25. These current confinement layers 23a to 23c are made of, for example, n-type or p-type InP. A p-n-p-n structure is formed in this stack.

  A second clad layer 25 is provided on the semiconductor mesa and the buried region 23. The second cladding layer 25 is made of a p-type semiconductor, for example, a p-type InP semiconductor. A contact layer 27 is provided on the second cladding layer 25. The contact layer 27 can be a p-type GaInAs semiconductor, for example. An insulating film 29 is formed on the contact layer 27. The insulating film 29 has an opening corresponding to the upper surface of the semiconductor mesa. Next, the first electrode film 31 is formed. The contact layer 27 is in ohmic contact with the electrode film 31 through the opening. A second electrode film 33 is provided on the back surface 11 b opposite to the main surface 11 a of the semiconductor substrate 11, and the second electrode film 33 and the semiconductor substrate 11 are in ohmic contact.

An example of the material, dopant element, dopant concentration, and thickness of each layer of the semiconductor laser described above is shown below.
First cladding layer 13: n-type InP, Si, 1 × 10 ¹⁸ cm ⁻³ , thickness 500 nm
First optical confinement layer 15: n-type GaInAsP, Si, 5 × 10 ¹⁷ cm ⁻³ , thickness 150 nm
Barrier layer 17a: undoped GaInAsP, thickness 11 nm
Well layer 17b: undoped GaInAsP, thickness 7 nm
Third optical confinement layer 17c: undoped GaInAsP, thickness 40 nm
Embedded semiconductor layer 19: undoped AlInAs
Second optical confinement layer 21: p-type GaInAsP, Zn, 5 × 10 ¹⁷ cm ⁻³ , thickness 110 nm
Second cladding layer 25: p-type InP, Zn, 1 × 10 ¹⁸ cm ⁻³ , thickness 2000 nm
Contact layer 27: p-type GaInAs, Zn, 1 × 10 ¹⁹ cm ⁻³ , thickness 500 nm

  As described above, in this embodiment, the AlInAs buried semiconductor layer 19 is provided between the upper surface of the quantum wire 17 and the second optical confinement layer 21. According to the AlInAs buried semiconductor layer 19, the valence band offset with respect to the second optical confinement layer 21 made of the p-type GaInAsP semiconductor is smaller than the conduction band offset. Therefore, the buried semiconductor layer 19 does not serve as a barrier that prevents hole injection. For this reason, a semiconductor laser with good characteristics can be obtained. Further, the side surface of the quantum wire 17 is embedded with an embedded semiconductor layer 19. The buried semiconductor layer 19 makes it possible to confine carriers in the lateral direction of the quantum wire 17. Further, since the embedded semiconductor layer 19 is integrally provided on the upper surface of the quantum wire 17 together with the side surface of the quantum wire 17, the embedded semiconductor layer 19 positioned on the upper surface of the quantum wire 17 serves as an electron block layer. It has a function. Accordingly, since the electron overflow moving from the first cladding layer 13 toward the quantum wire 17 can be reduced, a semiconductor laser having good temperature characteristics can be obtained.

  Next, steps of a method for manufacturing a semiconductor laser according to an embodiment of the present invention will be described with reference to FIGS.

  As shown in FIG. 4A, a first cladding layer 43 made of an n-type InP semiconductor and a first optical confinement layer 45 made of an n-type GaInAsP semiconductor are grown in order on a semiconductor substrate 41 made of an n-type semiconductor. . The semiconductor substrate 41 can be, for example, InP. A plurality of undoped GaInAsP semiconductor layers are grown on the first optical confinement layer 45 to form a multiple quantum well layer 47. The multiple quantum well layer 47 includes a barrier layer 47a, a well layer 47b, and a third optical confinement layer 47c. These growths are performed, for example, by metal organic vapor phase epitaxy.

As shown in FIG. 4B, an insulating film 59 is formed on the multiple quantum well layer 47. This formation is performed by a plasma CVD method using, for example, a silane-based gas and an oxygen-based gas as process gases. As an example of the silane-based gas, monosilane is used. As an example of the oxygen-based gas, oxygen gas is used. The insulating film 59 is made of silicon oxide such as SiO ₂ . The thickness of the insulating film 59 is preferably about 20 nm in order to ensure an etching selectivity with the resist mask 63.

  Next, a resist film 61 is formed on the insulating film 59. This formation is performed by applying a resist for electron beam exposure.

  As shown in FIG. 4C, a resist mask 63 is formed on the insulating film 59. This formation is performed by exposing and developing the resist film 61 by an electron beam exposure method. The resist mask 63 has a plurality of fine line patterns arranged periodically in order to form a plurality of fine lines arranged periodically in the insulating film 59. The period Λ of the fine line pattern for manufacturing the DFB laser element is a Bragg period. For example, the period Λ for setting the oscillation wavelength 1550 nm is 240 nm, and the period Λ for setting the oscillation wavelength 1300 nm is 200 nm, for example.

As shown in FIG. 4D, the insulating film 59 is etched using the resist mask 63 to form the insulator mask 65 on the multiple quantum well layer 47. For this etching, for example, reactive ion etching (RIE) using CF ₄ gas can be used. The shape of the resist mask 63 is transferred to the insulator mask 65. After the etching, the resist mask 63 is removed, and an insulator mask 65 for forming a plurality of periodically arranged quantum wires 57 is formed. The removal of the resist mask 63 is performed by, for example, O ₂ ashing.

As shown in FIG. 5A, the multiple quantum well layer 47 is etched using the insulator mask 65 to form a plurality of quantum wires 57. In an example of this etching, reactive ion etching (RIE) using CH ₄ / H ₂ is used. In the step of etching the multi-quantum well layer 47, it is preferable to repeatedly perform, for example, RIE using CH ₄ / H ₂ and O ₂ ashing to remove the carbon polymer deposited on the semiconductor surface during the etching. . By repeating in this way, an arrangement of quantum wires excellent in perpendicularity can be obtained.

  As shown in FIG. 5B, wet etching is performed after dry etching is completed in order to remove a damaged layer by dry etching. For this etching, for example, a sulfuric acid-based solution is used. After the wet etching, the insulator mask 65 is removed. For example, the mask made of silicon oxide is removed by etching with buffered hydrofluoric acid.

As shown in FIG. 5C, an embedded semiconductor layer 49 is integrally grown on the side surface and upper surface of each quantum wire 57 and on the first optical confinement layer 45 to embed the quantum wire 57. Therefore, the buried semiconductor layer 49 is also formed on the upper surface of the quantum wire 57. On the other hand, the buried semiconductor layer 49 contains aluminum and indium as group III elements and arsenic as group V elements. For example, the buried semiconductor layer 49 is made of an AlInAs semiconductor. Therefore, the buried semiconductor layer 49 does not become a substantial barrier to holes moving toward the quantum wire 57.
Therefore, the buried semiconductor layer is controlled by strictly controlling the side surface of each quantum wire 57 and the thickness of the buried semiconductor layer 49 grown on the first optical confinement layer 45 to the height of the upper surface of the quantum wire 57. There is no need to grow 49. Therefore, the embedded semiconductor layer 49 can be grown not only on the side surface of each quantum wire 57 and the first optical confinement layer 45 but also on the upper surface of each quantum wire 57, so that the quantum wire 57 is embedded. Can do. Without such precise control as described above, the growth of such a buried semiconductor layer 49 facilitates control of the process of embedding the quantum wire 57. The growth rate of the embedded semiconductor layer 49 is preferably a low speed of 500 nm / h or less. With this growth rate, a flat growth interface can be obtained.

  As shown in FIG. 5D, a second optical confinement layer 51 made of a p-type GaInAsP semiconductor is grown on the buried semiconductor layer 49. Due to the large electron barrier by the embedded semiconductor layer 49, electrons from the quantum wire 57 do not reach the second optical confinement layer 51. On the other hand, holes from the p-type cladding reach the quantum wire 57 through the buried semiconductor layer 49.

  Next, a second cladding layer 55 made of a p-type InP semiconductor is grown on the second optical confinement layer 51.

  Thereafter, a contact layer 67 is grown on the second cladding layer 55. Further, in order to obtain a single transverse mode, a refractive index waveguide structure such as a BH type stripe structure with a stripe width of about 1 μm is formed.

FIG. 1 is a perspective view showing the structure of a semiconductor laser device according to an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view showing a part of FIG. FIG. 3 is a diagram showing a band structure of the semiconductor laser element shown in FIG. FIG. 4A, FIG. 4B, FIG. 4C, and FIG. 4D are diagrams showing a manufacturing process of a semiconductor laser in a method of manufacturing a semiconductor laser. FIG. 5A, FIG. 5B, FIG. 5C, and FIG. 5D are diagrams showing a semiconductor laser manufacturing process in a method of manufacturing a semiconductor laser.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Semiconductor laser, 11, 41 ... Semiconductor substrate, 13, 43 ... 1st clad layer, 15, 45 ... 1st optical confinement layer, 17, 57 ... Quantum wire, 17a, 47a ... Barrier layer, 17b, 47b ... Well Layers 17c, 47c ... third optical confinement layer 19, 49 ... buried semiconductor layer 21, 51 ... second optical confinement layer 23 ... buried region 25, 55 ... second cladding layer 27 ... contact layer 29 ... Insulating films 31, 33 ... Electrode films, 47 ... Multiple quantum well layers.

Claims (5)

a first optical confinement layer provided on the n-type cladding region;
A plurality of quantum wires provided on the first optical confinement layer and arranged periodically;
A buried semiconductor region having a side surface of each quantum wire and a first portion provided on the first optical confinement layer and a second portion provided on an upper surface of each quantum wire, and embedding the quantum wire When,
A second optical confinement layer provided on the buried semiconductor region,
The buried semiconductor region contains aluminum and indium as group III elements and arsenic as group V elements,
A semiconductor laser characterized in that a band gap of the buried semiconductor region is larger than a band gap of the second optical confinement layer and larger than a maximum band gap of the quantum wires. The semiconductor laser according to claim 1, wherein the buried semiconductor region is made of an AlInAs semiconductor. 3. The semiconductor laser according to claim 1, wherein a thickness of the second portion is not less than 20 nanometers and not more than 50 nanometers. an n-type substrate;
The semiconductor laser according to claim 1, wherein the buried semiconductor region is undoped. A method for fabricating a semiconductor laser, comprising:
Growing a first optical confinement layer on the n-type cladding layer;
Growing a multiple quantum well layer on the optical confinement layer;
Etching the multiple quantum well layer using a mask having a periodic pattern for a plurality of quantum wires to form a plurality of periodically arranged quantum wires;
Removing the mask;
In order to embed the quantum wires, a step of integrally growing an embedded semiconductor layer on a side surface and an upper surface of each quantum wire and on the first optical confinement layer;
Growing a second optical confinement layer on the buried semiconductor layer;
The buried semiconductor layer contains aluminum and indium as group III elements and arsenic as group V elements,
The band gap of the buried semiconductor layer is larger than the band gap of the semiconductor constituting the second optical confinement layer and larger than the maximum band gap of the quantum wire.

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