JPH049393B2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for manufacturing a semiconductor laser.

[Prior Art] Semiconductor lasers are desired to be able to operate with a low threshold current in various respects.

Therefore, as a first conventional example, a semiconductor active layer is formed in a stripe shape, and the stripe-shaped semiconductor active layer is formed into a semiconductor buried layer having a refractive index lower than that of the semiconductor active layer from its side surface. On the other hand, a PN junction is formed in the semiconductor buried layer which is reverse biased by the operating power source for supplying operating current to the semiconductor active layer, thus providing an operating current to the semiconductor active layer. A constricted operating current is passed from the power supply, and the light obtained by this is
It has been proposed to have a configuration in which it is confined within a semiconductor active layer.

However, in the case of such conventional semiconductor lasers, in order to obtain laser light with a large output,
If the operating current supplied from the operating power supply to the semiconductor active layer is increased, the voltage of the operating power supply must be increased accordingly, so the reverse bias applied to the PN junction formed in the semiconductor buried layer is The voltage increases, resulting in leakage currents in the semiconductor buried layer through the PN junction it forms, and in some cases, breakdown of the PN junction.

For this reason, in the case of the conventional semiconductor laser described above, there is a certain limit to the ability to obtain laser light with a large output and high luminous efficiency.
Due to the leakage current flowing through the PN junction in the semiconductor buried layer, Joule heat is generated internally, which has the disadvantage of accelerating the deterioration of the semiconductor laser.

Furthermore, as a second conventional example, in order to improve such drawbacks, for example, Japanese Patent Application Laid-Open No. 117295/1983 discloses that after forming a double heterostructure on a conductive semiconductor substrate, the same structure is mesa-processed. However, a technique for further embedding with a high resistivity semiconductor layer has been proposed.

[Problem to be solved by the invention]

However, this technology epitaxially grows a double heterostructure on a conductive substrate, then processes mesa stripes and grows buried crystals.
Requires multiple crystal growth steps. Therefore, it has disadvantages in terms of yield and mass productivity.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a novel method for manufacturing a semiconductor laser that does not have the above-mentioned drawbacks.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a method for manufacturing a semiconductor laser, in which a striped window is formed from the first main surface side on an insulating substrate having first and second main surfaces facing each other. forming striped grooves in the insulating substrate by etching using a mask layer having a
a step of sequentially laminating a lower semiconductor cladding layer having a first conductivity type, a semiconductor active layer having a higher refractive index than the insulating substrate, and an upper semiconductor cladding layer of a conductivity type opposite to that of the lower semiconductor cladding layer; ,
forming a recess to a depth reaching the lower semiconductor cladding layer by etching using a mask layer with a partially opened window from the second main surface of the insulating substrate; connecting respective electrodes to the upper cladding layer;
It is characterized by consisting of.

[Effect]

In the present invention, after crystal growth of a double heterostructure is formed on an insulating substrate, a recess is provided that reaches the lower cladding layer from the back surface of the substrate, resulting in a simple manufacturing process that requires only one crystal growth process. With this method, it is possible to fabricate a semiconductor laser in which the active layer has a lower refractive index and is embedded in an insulating substrate.

〔Example〕

1 and 2 show an example of a semiconductor laser manufactured according to the present invention, which has an insulating substrate 1 made of, for example, a single crystal InP substrate doped with Fe.

In this case, the insulating substrate 1 has first and second main surfaces 2 and 3 that are parallel and face each other, and first and second end faces 4 and 5 that are parallel and face each other.

Thus, grooves 6 are formed in the insulating substrate 1, extending from the main surface 2 side between the end surfaces 4 and 5 in a striped shape.

Further, in the trench 6, a first semiconductor cladding layer 7 of, for example, N type, and a first semiconductor cladding layer 7 of N type or P type, N in the figure.
A P-type semiconductor active layer 8 and a P-type second semiconductor cladding layer 9 are laminated in that order from the main surface 3 side to form a laminate 13, and are arranged with the trench 6 buried. ing.

In this case, the laminate 13 has Fabry-Perot reflective surfaces 14 facing parallel to each other on the end surfaces 4 and 5.
and 15. Note that the semiconductor cladding layers 7 and 9 can both be made of a semiconductor made of InP, and the semiconductor active layer 8 can be made of a semiconductor having the same lattice constant as the semiconductor cladding layers 7 and 9.
It may be made of a GaInAsP-based semiconductor.

Further, from the main surface 3 side of the insulating substrate 1,
A recess 10 is formed reaching the semiconductor cladding layer 7, so that the recess 10 is formed in the semiconductor cladding layer 7.
An electrode 11 extending from the side onto the inner surface of the recess 10 and onto the main surface 3 is electrically connected to the semiconductor cladding layer 9 , while an electrode 11 extending from the side onto the main surface 2 is connected to the semiconductor cladding layer 9 . An electrode 12 is connected to the ohmic.

The above is an exemplary configuration of a semiconductor laser manufactured according to the present invention.

Actually, a semiconductor laser having such a configuration can be manufactured in the following manner according to the present invention.

That is, as shown in FIG. 3A, main surfaces 2' and 3' become the above-mentioned insulating substrate 1, and therefore, parts thereof become the main surfaces 2 and 3 described above in FIGS. 1 and 2. An insulating substrate 1' having a structure is prepared in advance.

As shown in FIG. 3B, the main surface 2' has a striped window 21 having approximately the same width as the groove 6 described above in FIGS. 1 and 2, and is made of, for example, SiO ₂ , Si ₃ N ₄ is formed by a method known per se.

Next, the third etching process is performed on the insulating substrate 1' using the mask layer 22 as a mask.
As shown in FIG. C, a groove 6', a portion of which becomes the groove 6 described above in FIGS. 1 and 2, is formed in the insulating substrate 1'.

Next, in the groove 6', as shown in FIG. 3D, a semiconductor layer 7 is formed, a portion of which becomes the semiconductor clad layer 7, the semiconductor active layer 8, and the semiconductor clad layer 9 described above in FIGS. 1 and 2. ', 8' and 9' are formed by, for example, a liquid phase growth method.

Next, after or before dissolving the mask layer 22 from the main surface 2' of the insulating substrate 1', the main surface is coated on the insulating substrate 1' as shown in FIG. 3E. Starting from the 3' side, a plurality of recesses 10 as described above in FIGS. 1 and 2 are formed to a depth that reaches the semiconductor layer 7' by an etching process using a mask layer (not shown).

Next, as shown in FIG.
A conductive layer 11' is formed which extends continuously on the inner surface and main surface 3' of the semiconductor layer 9', and a part of which becomes the electrode described above in FIGS. 1 and 2. ,
and a conductive layer 1 which is connected and extended on the main surface 2' and a part of which becomes the electrode 12 described above in FIGS. 1 and 2.
2' is formed.

Next, the insulating substrate 1' is placed together with the semiconductor layers 7', 8' and 9' and the conductive layers 11' and 12'.
At a position between adjacent recesses 10, cleavage is performed along a plane perpendicular to the extending direction of the groove 6' to obtain Fabry-Perot reflective surfaces 14 and 15 facing each other in parallel.

In the manner described above, a plurality of semiconductor lasers as described above in FIGS. 1 and 2 are obtained.

The above has clarified the configuration of an example of the method for manufacturing a semiconductor laser according to the present invention.

According to the semiconductor laser manufactured according to the present invention,
If a bias power source with the electrode 12 side positive is connected between the electrodes 11 and 12, an operating current flows to the semiconductor active layer 8 through the semiconductor cladding layers 7 and 9.
In response, the semiconductor active layer 8 emits light,
That is, in the semiconductor active layer 8, the cladding layers 7 and 9
propagates while being confined by the reflecting surfaces 14 and 1.
5, the laser beam is thus oscillated, and the laser beam is emitted to the outside from one or both of the reflecting surfaces 14 and 15.

In this case, since the semiconductor active layer 8 is formed in the groove 6 and has a striped shape, the semiconductor active layer 8 corresponds to the semiconductor active layer in the conventional semiconductor laser described above.

Further, the semiconductor active layer 8 has a configuration in which an insulating substrate 1 is embedded from the side surface thereof, and the insulating substrate 1 constricts the operating current from the operating power source to the semiconductor active layer 8. It has the effect of flushing out water. Therefore, the insulating substrate 1 corresponds to the semiconductor buried layer in the conventional semiconductor laser described above.

Therefore, the semiconductor laser manufactured according to the present invention shown in FIGS. 1 and 2 has the characteristic of operating at a low threshold current, similar to the conventional semiconductor laser.

Further, in the case of the semiconductor laser manufactured according to the present invention shown in FIGS. 1 and 2, the insulating substrate 1 is the first
Although it corresponds to the semiconductor buried layer of the conventional semiconductor laser, it is not made of a semiconductor like the semiconductor buried layer, nor does it form a PN junction.

Therefore, even if the operating current supplied to the semiconductor active layer 8 from the operating power source is increased so that a large output laser beam can be obtained, leakage current will not occur as in the case of the semiconductor laser of the first conventional example. As a result, Joule heat is generated inside the semiconductor laser, which accelerates deterioration of the semiconductor laser and prevents breakdown from occurring.

Therefore, in the case of the semiconductor laser manufactured according to the present invention shown in FIGS. 1 and 2, the laser beam is
Compared to conventional semiconductor lasers, the present invention has the characteristics of being able to provide a larger output and a higher luminous efficiency over a long period of time.

On the other hand, whereas the second conventional example required two crystal growth steps, the present invention requires only one crystal growth process, making device fabrication very easy. Moreover, in the case of the semiconductor laser manufactured according to the present invention,
By forming the recess, the electrode is connected to the lower cladding layer without intervening the substrate, so that the influence of the resistance component of the substrate can be removed. Therefore, it is also advantageous in terms of thermal stability.

By the way, the insulating substrate 1 is doped with Fe,
The length between the end faces 4 and 5 is 200 μm, and the width is 400 μm. The groove 6 formed in the insulating substrate 1 is 50 μm wide.
Further, the semiconductor cladding layer 7 is made of Sn-doped N-type InP having a carrier concentration of 2×10 ¹⁸ cm ^-3 and a thickness of 3 μm. , the semiconductor active layer 8 is made of Ga _0.26 In _0.74 As _0.56 P _0.44 with a thickness of 0.2 μm, which is N _- type but not actively doped with N-type impurities; Layer 9, Zn
The laminated body 13 consisting of the semiconductor cladding layers 7 and 9 and the semiconductor active layer 8 is made of P-type InP doped with a carrier concentration of 1×10 ¹⁸ cm ^-3 and a thickness of 1.5 μm. is 50 μm, which is the same as the groove 6, and the thickness is 4.7 μm, which is the same as the depth of the groove 6, and the length between the reflective surfaces 14 and 15 of the Fabry-Perot, that is, the resonator length, is 200 μm, which is the same as the length of the insulating substrate 1. As a result, laser light oscillation with a wavelength of 1.28 μm was obtained with a low threshold current of 45 mA.

Also, from the operating power supply, a width with an amplitude of 4.6A
When a 100ns pulse current was supplied, a large laser light pulse output of 530mW was obtained.

In the above description, only one example of the present invention has been shown, and detailed description of the drawings will be omitted. It is also possible to have a configuration in which the electrodes 12 are connected via. Further, in order to obtain a semiconductor laser similar to that described above with reference to FIGS. 1 and 3, after going through the steps described above with reference to FIGS. , the groove 6 has a different etching selectivity than that of the semiconductor cladding layer 7 with respect to the etchant used in the step of forming the recess 10 in the insulating substrate 1, and has, for example,
A semiconductor layer made of a GaInAsP-based semiconductor is formed, and then a semiconductor cladding layer 7 is formed on the semiconductor layer.
and 9 and the semiconductor active layer 8, and then in the step of forming the recess 10 in the insulating substrate 1, the semiconductor layer under the semiconductor cladding layer 7 is removed, thereby forming the recess 10. Formation may be facilitated to manufacture a desired semiconductor laser, and various other modifications and changes may be made without departing from the spirit of the present invention.

〔Effect of the invention〕

As explained above, according to the present invention, after a double heterostructure is grown in a groove formed in an insulating substrate, a recess is provided that reaches the lower cladding layer from the back surface of the substrate, and thereby the crystal growth process is performed. With a simple manufacturing method that requires only one step, it is possible to realize a high-performance semiconductor laser that has no leakage current, has high output, and can be controlled in a single transverse mode.

[Brief explanation of drawings]

FIG. 1 is a schematic plan view showing an example of a semiconductor laser manufactured according to the present invention. FIG. 2 is a sectional view taken along the - line. Figures 3 A to F are
1A and 1B are schematic cross-sectional views showing sequential steps of an example of a method for manufacturing a semiconductor laser according to the present invention. 1... Insulating substrate, 2, 3... Main surface, 4, 5...
... end face, 6 ... groove, 7, 9 ... semiconductor cladding layer, 8 ... semiconductor active layer, 10 ... recess, 11,
12... Electrode, 13... Laminate, 14, 15...
reflective surface.

Claims (1)

[Claims] 1. An insulating substrate having first and second main surfaces facing each other is etched using a mask layer having striped windows from the first main surface side. forming a striped groove in the insulating substrate; a lower semiconductor cladding layer having a first conductivity type; and a semiconductor active layer having a refractive index higher than that of the insulating substrate; The lower semiconductor cladding layer is etched by sequentially stacking an upper semiconductor cladding layer of a conductivity type opposite to that of the lower semiconductor cladding layer, and by etching using a mask layer partially opened from the second main surface of the insulating substrate. A method for manufacturing a semiconductor laser, comprising the steps of: forming a recess deep enough to reach a semiconductor cladding layer; and connecting electrodes to the lower semiconductor cladding layer and the upper cladding layer, respectively.