Optical semiconductor device and method for manufacturing the same

Abstract

An optical semiconductor device and a method for manufacturing the same, the method comprising: forming a first semiconductor layer; forming a first mask pattern on the first semiconductor layer in a first region where an electro-absorption modulator is formed; forming a flat portion along a first direction on the first semiconductor layer; forming a second semiconductor layer on the concave-convex portion; and forming an optical waveguide layer on the second semiconductor layer. The first mask pattern comprises a first pattern in the first region and a second pattern in a second region where a DFB laser is formed, the first pattern comprises a first opening pattern and a first covering pattern, and the second pattern comprises a second opening pattern and a second covering pattern, and a ratio of the first opening pattern to the first covering pattern is different from a ratio of the second opening pattern to the second covering pattern.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority from Japanese Patent Application No. JP2018-195767 filed on October 17, 2018, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to an optical semiconductor device and a method for manufacturing the same. Background Art

[0004] For example, Japanese Unexamined Patent Publication No. H10-163568 discloses a modulator-integrated semiconductor laser having a semiconductor laser section and a modulator section integrated with each other. Summary of the invention

[0005] A method for manufacturing an optical semiconductor device according to an aspect of the present disclosure is a method for manufacturing an optical semiconductor device, the optical semiconductor device including an electro-absorption modulator, a DFB laser, and a connection region connected between the electro-absorption modulator and the DFB laser in an integrated structure in a first direction on a semiconductor substrate, the manufacturing method including: forming a first semiconductor layer on a semiconductor substrate; forming a first mask pattern on the first semiconductor layer in the connection region and the first region forming the electro-absorption modulator; forming a flat portion along a first direction on the first semiconductor layer in the connection region using the first mask pattern; forming a second semiconductor layer on a concave-convex portion provided on the first semiconductor layer; and forming an optical waveguide layer on the second semiconductor layer. The first mask pattern includes a first pattern in the first region and a second pattern in the second region forming the DFB laser, the first pattern includes a first opening pattern and a first covering pattern adjacent to each other, and the second pattern includes a second opening pattern and a second covering pattern adjacent to each other. The ratio of the first opening pattern to the first covering pattern is different from the ratio of the second opening pattern to the second covering pattern.

[0006] According to another aspect of the present disclosure, an optical semiconductor device includes a laser, which includes: an electro-absorption modulator; a DFB laser; and a connection region connected between the electro-absorption modulator and the DFB laser in an integrated structure in a first direction on a semiconductor substrate; a first semiconductor layer having a concave-convex portion extending in a first direction on the semiconductor substrate; a second semiconductor layer disposed on the concave-convex portion of the first semiconductor layer; an active layer disposed on the second semiconductor layer; and an optical waveguide disposed on the second semiconductor layer, the optical waveguide being arranged with the electro-absorption modulator and the connection region. The duty ratio of the concave-convex portion in the connection region is greater on the DFB laser side than on the electro-absorption modulator side. The duty ratio of the concave-convex portion corresponds to the ratio of the length of the concave to the total length of the concave and convex adjacent to each other.

[0007] A method for manufacturing an optical semiconductor device according to another aspect of the present disclosure is a method for manufacturing an optical semiconductor device, the optical semiconductor device including a laser region, a connection region, and an optical modulation region sequentially arranged along an optical waveguide direction, the method including: forming a first semiconductor layer on a semiconductor substrate; forming a first mask pattern on the first semiconductor layer in the connection region; forming a concave-convex portion along the optical waveguide direction on the first semiconductor layer in the connection region using the first mask pattern; forming a second semiconductor layer on the first semiconductor layer on which the concave-convex portion is formed; and forming an optical waveguide layer on the second semiconductor layer. In forming the first mask pattern, a first mask pattern is formed in which a ratio of a length of a covering pattern along the optical waveguide direction to a total length of an opening pattern and a covering pattern located in the connection region and adjacent to each other along the optical waveguide direction is greater on the laser region side than on the optical modulation region side, and in forming the concave-convex portion, the concave-convex portion is formed in which a ratio of a length of a protrusion along the optical waveguide direction to a total length of a recess and a protrusion located in the connection region and adjacent to each other along the optical waveguide direction is greater on the laser region side than on the optical modulation region side. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The foregoing and other objects, aspects and advantages will be better understood through the following detailed description of preferred embodiments of the present disclosure with reference to the accompanying drawings, in which:

[0009] Figure 1A is a schematic plan view showing a semiconductor laser device according to an embodiment;

[0010] Figure 1B is along Figure 1A A cross-sectional view taken along line Ib-Ib in FIG.

[0011] Figures 2A to 2C is a diagram showing a method for manufacturing a semiconductor laser device according to an embodiment;

[0012] Figure 3 A to C are diagrams illustrating a method for manufacturing a semiconductor laser device according to an embodiment;

[0013] Figures 4A to 4C is a diagram showing a method for manufacturing a semiconductor laser device according to an embodiment;

[0014] Figure 5A and 5B is a diagram showing a method for manufacturing a semiconductor laser device according to an embodiment;

[0015] Figure 6 is an enlarged cross-sectional view showing main parts of the connection area and the optical modulation area after the sixth step;

[0016] Figure 7 is a schematic plan view showing the shape of a mask pattern; and

[0017] Figure 8 is a schematic cross-sectional view showing a concavo-convex portion according to a modification. DETAILED DESCRIPTION

[0018] [Problems to be Solved by the Present Disclosure]

[0019] Semiconductor lasers with integrated modulators are shown in Japanese Unexamined Patent Publication No. H10-163568. From the viewpoint of reducing internal loss, generally, the optical waveguide (active layer) of the semiconductor laser section (laser region) is ideally thin. From the viewpoint of high extinction ratio and low capacity, the optical waveguide (optical waveguide layer) of the modulator section (optical modulation region) is ideally thick. However, the thickness of the optical waveguide layer is more likely to cause light reflection than a simple increase in the thickness of the active layer, because the step at the end face connection portion (butt joint) between the semiconductor laser section and the modulator section is large. Therefore, in the case where the thickness of the active layer and the thickness of the optical waveguide layer are set differently, this may lead to deterioration of the coupling efficiency of the semiconductor laser section to the modulator section.

[0020] [Description of Embodiments of the Present Disclosure]

[0021] An embodiment of the present disclosure is a method for manufacturing a semiconductor laser device, the semiconductor laser device including a laser region, a connection region, and an optical modulation region sequentially arranged along an optical waveguide direction, the manufacturing method including: forming a first semiconductor layer on a semiconductor substrate; forming a first mask pattern on the first semiconductor layer in the connection region; forming a concave-convex portion along the optical waveguide direction on the first semiconductor layer in the connection region using the first mask pattern; forming a second semiconductor layer on the first semiconductor layer on which the concave-convex portion is formed; and forming an optical waveguide layer on the second semiconductor layer. In forming the first mask pattern, the first mask pattern is formed in which the ratio of the length of the covering pattern along the optical waveguide direction to the total length of the opening pattern and the covering pattern located in the connection region and adjacent to each other along the optical waveguide direction is greater on the laser region side than on the optical modulation region side, and in forming the concave-convex portion, the concave-convex portion is formed in which the ratio of the length of the protrusion along the optical waveguide direction to the total length of the recess and the protrusion located in the connection region and adjacent to each other along the optical waveguide direction is greater on the laser region side than on the optical modulation region side.

[0022] In the manufacturing method, a concavoconvex portion along the optical waveguide direction is formed on the first semiconductor layer in the connection area using a first mask pattern. In the formed concavoconvex portion, the ratio of the length of the protrusion along the optical waveguide direction to the total length of the depression and protrusion adjacent to each other along the optical waveguide direction in the connection area is greater on the laser area side than on the optical modulation area side. Here, in the second semiconductor layer grown on the first semiconductor layer on which the concavoconvex portion is formed, the capacity of the depression is larger in the area with a smaller ratio, so the thickness of the second semiconductor layer becomes thinner. Therefore, in the optical waveguide direction, the thickness of the second semiconductor layer located in the connection area is thinner on the optical modulation area side than on the laser area side. Therefore, even in the case of forming an optical waveguide layer thicker than the active layer, the formation of a large step on the end face connection portion between the active layer and the optical waveguide layer can be suppressed. Therefore, according to the manufacturing method, a semiconductor laser device can be manufactured, in which the thickness of the optical waveguide layer in the optical modulation area can be set to be greater than the thickness of the active layer in the laser area, while suppressing the degradation of the coupling efficiency from the laser area to the optical modulation area.

[0023] The manufacturing method may further include: forming a diffraction grating layer on the first semiconductor layer; and removing a portion of the diffraction grating layer located in the connection area and the optical modulation area to expose the first semiconductor layer. In the manufacturing method, when forming the first mask pattern, the first mask pattern may also be formed on the diffraction grating layer, and when forming the concavo-convex portion on the first semiconductor layer, the diffraction grating may be formed using the first mask pattern. In this case, for example, when the concavo-convex portion is formed on the first semiconductor layer, the diffraction grating may be formed in the laser area. Therefore, a semiconductor laser device that can achieve stable single-mode oscillation may be manufactured.

[0024] The ratio of the length of the protrusion to the total length of the recess and the protrusion may vary continuously or may vary stepwise along the optical waveguide direction. In this case, the thickness of the second semiconductor layer located in the connection region becomes thinner continuously or stepwise from the laser region side toward the optical modulation region side along the optical waveguide direction. Therefore, the thickness of the optical waveguide layer located in the connection region may become thicker continuously or stepwise from the laser region side toward the optical modulation region side along the optical waveguide direction. Therefore, no step is provided on the optical waveguide layer located in the connection region, or the formation of a large step on the optical waveguide layer may be suppressed, thereby preferably suppressing the degradation of the coupling efficiency from the laser region to the optical modulation region.

[0025] When forming the optical waveguide layer, the optical waveguide layer can be formed in the opening using a second mask pattern having an opening overlapping a portion of the second semiconductor layer, and the pattern width of the region of the opening located in the connection region can become narrower as it is closer to the optical modulation region in the optical waveguide direction. In this case, the growth rate of the optical waveguide layer around the laser region having a wide pattern width becomes smaller. Therefore, the formation of a large step on the end face connection portion between the active layer and the optical waveguide layer can be well suppressed, so that the degradation of the coupling efficiency from the laser region to the optical modulation region can be preferably suppressed.

[0026] The second mask pattern may have a pair of openings different from the opening, the pair of openings different from the opening may overlap with the second semiconductor layer, and the opening may be located between the pair of openings different from the opening in a direction intersecting with the optical waveguide direction in a plan view. In this case, on the second semiconductor layer, the semiconductor layer constituting the optical waveguide layer grows not only in the opening but also in the pair of openings different from the opening. Therefore, the growth rate of the optical waveguide layer in the opening further becomes smaller. Therefore, the film quality of the optical waveguide layer can be further improved, and the thickness of the optical waveguide layer can be preferably controlled. Therefore, the active layer can be connected to the optical waveguide layer without a sudden change in the refractive index.

[0027] Another embodiment of the present disclosure is a semiconductor laser device, which includes a laser region, a connection region, and an optical modulation region sequentially disposed on a semiconductor substrate along an optical waveguide direction, the semiconductor laser device including: a first semiconductor layer disposed on the semiconductor substrate, the first semiconductor layer having a concavo-convex portion on a first portion along the optical waveguide direction; a second semiconductor layer disposed on the concavo-convex portion of the first semiconductor layer; an active layer disposed on the second semiconductor layer located in the laser region; and an optical waveguide layer disposed on the second semiconductor layer located in the connection region and in the optical modulation region. In the semiconductor laser device, the duty ratio of the concavo-convex portion located in the connection region is greater on the laser region side than on the optical modulation region side, the duty ratio of the concavo-convex portion located in the optical modulation region is constant and equal to or less than the minimum value of the duty ratio of the concavo-convex portion located in the connection region, and the duty ratio is a ratio of the length of the protrusion along the optical waveguide direction to the total length of the depression and the protrusion adjacent to each other along the optical waveguide direction.

[0028] In the semiconductor laser device, in the concavo-convex portion provided on the first semiconductor layer, the ratio of the length of the protrusion along the optical waveguide direction to the total length of the concave and convex portions adjacent to each other in the connection region along the optical waveguide direction is greater on the laser region side than on the optical modulation region side. Here, in the thickness of the second semiconductor layer grown on the first semiconductor layer on which the concavo-convex portion is formed, the capacity of the concave is larger in the region with a smaller duty cycle, so the thickness of the second semiconductor layer becomes thinner. Therefore, in the optical waveguide direction, the thickness of the second semiconductor layer located in the connection region is thinner on the optical modulation region side than on the laser region side. Therefore, the semiconductor laser device can include an optical waveguide layer thicker than the active layer, while suppressing the formation of a large step on the end face connection portion between the active layer and the optical waveguide layer. Therefore, a semiconductor laser device can be obtained in which the thickness of the optical waveguide layer in the optical modulation region can be set to be greater than the thickness of the active layer in the laser region, while suppressing the degradation of the coupling efficiency from the laser region to the optical modulation region.

[0029] The duty ratio of the concave-convex portion located in the connection area may change continuously or gradually along the optical waveguide direction. In this case, the thickness of the second semiconductor layer located in the connection area becomes thinner continuously or gradually along the optical waveguide direction from the laser area side toward the optical modulation area side. Therefore, the thickness of the optical waveguide layer located in the connection area may become thicker continuously or gradually along the optical waveguide direction from the laser area side toward the optical modulation area side. Therefore, no step is provided on the optical waveguide layer located in the connection area, or the formation of a large step on the optical waveguide layer can be suppressed, so that the degradation of the coupling efficiency from the laser area to the optical modulation area can be preferably suppressed.

[0030] The height of the top surface of the active layer and the top surface of the optical waveguide layer may be equal. In this case, no step is provided on the top surfaces of the active layer and the optical waveguide layer, thereby preferably suppressing the degradation of the coupling efficiency of the laser region to the optical modulation region.

[0031] [Effects of the Embodiments of the Present Disclosure]

[0032] According to an embodiment of the present disclosure, a semiconductor laser device and a method for manufacturing the same can be provided, in which the thickness of the optical waveguide layer in the optical modulation region can be set to be greater than the thickness of the active layer in the laser region while suppressing the degradation of the coupling efficiency from the laser region to the optical modulation region.

[0033] [Description of Embodiments of the Present Disclosure]

[0034] Specific examples of semiconductor laser devices and methods for manufacturing the same according to embodiments of the present disclosure will be described below with reference to the accompanying drawings. In addition, it should be understood that the present disclosure is not limited to these examples, but is defined by the scope of the claims, and includes all modifications within the meaning and scope equivalent to the claims. In the following description, in the description of the drawings, the same elements are represented by the same reference numerals, and redundant explanations are omitted.

[0035] Figure 1A is a schematic plan view showing a semiconductor laser device according to an embodiment, and Figure 1B It is along Figure 1A A cross-sectional view taken along line Ib-Ib in FIG. Figure 1A and 1B The semiconductor laser device 1 (optical semiconductor device) shown is a laser device formed on a semiconductor substrate 11, and includes a laser region 2, a connection region 3, and an optical modulation region 4. The laser region 2, the connection region 3, and the optical modulation region 4 are sequentially arranged along one direction on the main surface 11a on the semiconductor substrate 11. In this embodiment, the laser region 2, the connection region 3, and the optical modulation region 4 are integrally formed on the semiconductor substrate 11. The one direction is the propagation direction (optical waveguide direction) of the light oscillated by the semiconductor laser device 1. In the following, the one direction is the direction X (optical waveguide direction). In the following, the direction perpendicular to the direction X in the horizontal direction is the direction Y (width direction), and the vertical direction perpendicular to the horizontal direction is the direction Z (thickness direction). The semiconductor laser device 1 in the plan view corresponds to the semiconductor laser device 1 observed from the direction Z.

[0036] The semiconductor substrate 11 is a seed substrate of a semiconductor layer included in the laser region 2 etc., and is an n-type semiconductor substrate including, for example, InP. On the back surface of the semiconductor substrate 11, a backside electrode having a conductive material such as metal may be provided.

[0037] The laser region 2 is a portion that oscillates laser light in the semiconductor laser device 1, and has a lower cladding layer 21, an active layer 22, an upper cladding layer 23, a contact layer 24, and an electrode 25. The lower cladding layer 21, the active layer 22, the upper cladding layer 23, the contact layer 24, and the electrode 25 are sequentially stacked on the main surface 11a of the semiconductor substrate 11. The lower cladding layer 21 and the upper cladding layer 23 are also included in the connection region 3 and the optical modulation region 4.

[0038] The lower cladding layer 21 is a layer that confines light between the inside of the active layer 22 and the inside of the optical waveguide layer 31, which will be described later. The lower cladding layer 21 is a compound semiconductor layer, and exhibits an n-type including, for example, InP. The thickness of the lower cladding layer 21 located in the laser region 2 (that is, the portion 21a of the lower cladding layer 21 located in the laser region 2) is, for example, 700 nm or more and 1,200 nm or less. The thickness of the portion 21a of the lower cladding layer 21 is constant. It should be noted that in this embodiment, the term "constant", the term "same", and any other term may include an error range. The error range is, for example, ±5%.

[0039] The portion 21a of the lower cladding layer 21 is provided with a diffraction grating 26, which is configured to feed back light of a specific wavelength to the active layer 22 in a distributed manner. These diffraction gratings 26 are formed in the laser region 2, so that stable single-mode oscillation can be achieved. Therefore, the semiconductor laser device 1 is used as a distributed feedback semiconductor laser (DFB laser). The diffraction grating 26 includes a refractive index different from the refractive index of the lower cladding layer 21. In the case where the lower cladding layer 21 is, for example, an InP semiconductor layer, the material constituting the diffraction grating 26 is, for example, InGaAsP.

[0040] The active layer 22 is an optical waveguide layer that can obtain gain by current injection, and is the core of the semiconductor laser device 1. The active layer 22 is a compound semiconductor layer having a quantum well structure including, for example, InGaAsP. As an example of a quantum well structure, a structure is adapted in which a well layer made of InGaAsP and a barrier layer made of InGaAsP whose composition is different from that of the InGaAsP of the well layer are alternately stacked. For example, the thickness of the active layer 22 is 180 nm or more and 220 nm or less.

[0041] The upper cladding layer 23 is a layer that confines light between the inside of the active layer 22 and the inside of the optical waveguide layer 31 together with the lower cladding layer 21, which will be described later. The upper cladding layer 23 is a compound semiconductor layer, and exhibits a p-type including, for example, InP. The thickness of the upper cladding layer 23 is constant, and is, for example, 1,500 nm or more and 2,000 nm or less.

[0042] The contact layer 24 is a compound semiconductor layer in ohmic contact with the electrode 25 and is, for example, a p-type InGaAsP layer. The electrode 25 is a conductive layer, and is provided on the contact layer 24 to which a direct current for oscillating laser light is supplied.

[0043] The connection region 3 is a portion that connects the laser region 2 to the optical modulation region 4 in the direction X, and has a lower cladding layer 21, an optical waveguide layer 31, and an upper cladding layer 23. The lower cladding layer 21, the optical waveguide layer 31, and the upper cladding layer 23 are sequentially stacked on the main surface 11a of the semiconductor substrate 11. The optical waveguide layer 31 is also included in the optical modulation region 4.

[0044] The thickness of the lower cladding 21 located in the connection area 3 (i.e., the portion 21b of the lower cladding 21 located in the connection area 3) is thinner on the optical modulation area 4 side than on the laser area 2 side in the direction X. The thickness of the portion 21b is, for example, 600nm or more and 1,100nm or less. In this embodiment, in the portion 21b of the lower cladding 21, the thickness of the end portion on the laser area 2 side is the thickest, and the thickness of the end portion on the optical modulation area 4 side is the thinnest. The portion 21b becomes thinner continuously from the laser area 2 side to the optical modulation area 4 side in the direction X. That is, the thickness of the portion 21b decreases from the laser area 2 side to the optical modulation area 4 side in the direction X at a constant ratio.

[0045] Similar to the active layer 22, the optical waveguide layer 31 is the core of the semiconductor laser device 1 and is a compound semiconductor layer extending along the direction X. The optical waveguide layer 31 has a quantum well structure including, for example, InGaAsP. In the direction X, the optical waveguide layer 31 and the active layer 22 are optically coupled to each other. Specifically, the end face of the optical waveguide layer 31 on the laser region 2 side is coupled with the end face of the active layer 22 on the connection region 3 side. Therefore, the semiconductor laser device 1 is provided with an end face connection portion between the active layer 22 and the optical waveguide layer 31. The thickness of the optical waveguide layer 31 located in the connection region 3 (that is, the portion 31a of the optical waveguide layer 31 located in the connection region 3) is thicker on the optical modulation region 4 side than on the laser region 2 side in the direction X. The thickness of the portion 31a is, for example, 180nm or more and 300nm or less. In this embodiment, in the portion 31a of the optical waveguide layer 31, the thickness of the end portion on the laser region 2 side is the thinnest, and the thickness of the end portion on the optical modulation region 4 side is the thickest. The portion 31a becomes thicker continuously from the laser region 2 side to the optical modulation region 4 side in the direction X. In addition, the height of the top surface F2 of the portion 31a is the same as the height of the top surface F1 of the active layer 22. Therefore, the thickness of the upper cladding layer 23 located in the connection region 3 is the same as the thickness of the upper cladding layer 23 located in the laser region 2.

[0046] The optical modulation region 4 is a portion in which oscillated laser light is modulated, and has a lower cladding layer 21, an optical waveguide layer 31, an upper cladding layer 23, a contact layer 41, and an electrode 42. The lower cladding layer 21, the optical waveguide layer 31, the upper cladding layer 23, the contact layer 41, and the electrode 42 are stacked in this order on the main surface 11a of the semiconductor substrate 11.

[0047] The thickness of the lower cladding layer 21 located in the optical modulation region 4 (i.e., the portion 21c of the lower cladding layer 21 located in the optical modulation region 4) is equal to or smaller than the thickness of the portion 21b in the connection region 3. In this embodiment, the thickness of the portion 21c of the lower cladding layer 21 corresponds to the thickness of the end portion on the optical modulation region 4 side in the portion 21b of the lower cladding layer 21. The thickness of the portion 21c is constant.

[0048] The optical waveguide layer 31 located in the optical modulation area 4 (i.e., the portion 31b of the optical waveguide layer 31 located in the optical modulation area 4) can absorb light oscillating in the laser area 2, and can also be specified as a light absorption layer. The thickness of the portion 31b of the optical waveguide layer 31 is equal to or greater than the thickness of the portion 31a of the connection area 3. In this embodiment, the thickness of the portion 31b corresponds to the thickness of the end portion on the optical modulation area 4 side in the portion 31a of the connection area 3. Similar to the portion 31a, the height of the top surface F3 of the portion 31b is the same as the height of the top surface F1 of the active layer 22. Therefore, the thickness of the upper cladding layer 23 located in the optical modulation area 4 is the same as the thickness of the upper cladding layer 23 located in the laser area 2 and the connection area 3.

[0049] The contact layer 41 is a compound semiconductor layer that is in ohmic contact with the electrode 42, and is, for example, a p-type InGaAsP layer. The contact layer 41 is separated from the contact layer 24. An insulating film may be provided between the contact layers 24 and 41. In this case, the contact layers 24 and 41 can be insulated from each other extremely well.

[0050] The electrode 42 is a conductive layer to which a signal for modulating laser light is supplied, and is provided on the contact layer 41. The electrode 42 is connected to the pad 43, for example, through a wiring portion 42a. The wiring portion 42a is a portion extending from a portion of the electrode 42 along the direction Y. The pad 43 is a conductive layer to which a line to which a signal is supplied is bonded, for example.

[0051] An insulating film may be formed on both end faces of the semiconductor laser device 1 in the direction X. Specifically, a configuration may be provided in which a high reflection film is formed on the end face of the semiconductor laser device 1 on the laser region 2 side, and an antireflection film may be formed on the end face of the semiconductor laser device 1 on the optical modulation region 4 side. In this semiconductor laser device 1, supplying a direct current to the electrode 25 causes laser oscillation in the active layer 22. The laser light oscillated and amplified in the active layer 22 is modulated in the optical waveguide layer 31 in the optical modulation region 4. The modulated laser light is output from the optical modulation region 4 to the outside.

[0052] Next, we will refer to Figures 2A to 5B A method of manufacturing the semiconductor laser device according to this embodiment is described. Figures 2A to 2C , Figure 3 A to C, Figures 4A to 4C as well as Figure 5A and 5B 1 is a diagram showing a method for manufacturing a semiconductor laser device 1 according to an embodiment. For illustration, Figure 2C , Figure 3 A to C, Figures 4A to 4C as well as Figure 5A and 5B The region that will eventually become the laser region 2, the region that will eventually become the connection region 3 and the region that will eventually become the optical modulation region 4 are shown.

[0053] First, if Figure 2A As shown, a first semiconductor layer 51 is formed on the main surface 11a of the semiconductor substrate 11 (first step). In the first step, the first semiconductor layer 51 is epitaxially grown on the main surface 11a by, for example, metal organic chemical vapor deposition. The first semiconductor layer 51 is, for example, an n-type InP layer. The thickness of the first semiconductor layer 51 is, for example, 500nm or more and 1,000nm or less.

[0054] Then, if Figure 2B As shown, a diffraction grating layer 52 is formed on the first semiconductor layer 51 (second step). In the second step, the diffraction grating layer 52 is epitaxially grown on the first semiconductor layer 51 by, for example, metal organic chemical vapor deposition. The diffraction grating layer 52 is, for example, an InGaAsP layer. The thickness of the diffraction grating layer 52 is, for example, 50 nm or more and 100 nm or less.

[0055] Then, if Figure 2C As shown, a portion of the diffraction grating layer 52 is removed (third step). In the third step, a portion of the diffraction grating layer 52 located in the connection area 3 and the optical modulation area 4 is removed to expose the first semiconductor layer 51. Specifically, first, a mask 53 is formed on a portion of the diffraction grating layer 52 located in the laser area 2. Subsequently, a portion of the diffraction grating layer 52 is removed using the mask 53. As a result, a first portion 51a of the first semiconductor layer 51 located in the connection area 3 and the optical modulation area 4 is exposed from the diffraction grating layer 52. A portion of the diffraction grating layer 52 corresponds to a portion of the diffraction grating layer 52 exposed from the mask 53, and is removed, for example, by dry etching. The mask 53 covering a portion of the diffraction grating layer 52 is, for example, a photoresist in a film shape.

[0056] Then, if Figure 3As shown in A, a mask pattern 54 is formed on the first portion 51a of the first semiconductor layer 51, and a mask pattern 55 is formed on the remaining diffraction grating layer 52 (fourth step). In the fourth step, for example, the mask pattern 54 and the mask pattern 55 are formed by photolithography. The mask pattern 54 and the mask pattern 55 are, for example, patterned photoresists. In this embodiment, a mask pattern 54 is formed on the first semiconductor layer 51 at least in the connection region 3. It should be noted that the mask patterns 54 and 55 are formed at the same time. Therefore, the mask patterns 54 and 55 can also be interpreted as, for example, the same first mask pattern.

[0057] The mask pattern 54 has a covering pattern 54a covering the first portion 51a of the first semiconductor layer 51 and a plurality of opening patterns 54b. The plurality of opening patterns 54b are periodically arranged along the direction X. Therefore, on the first portion 51a, the covering pattern 54a and the opening pattern 54b are alternately positioned in the direction X. Among the plurality of opening patterns 54b, the length of a portion of the opening pattern 54b along the direction X is different from that of other portions. Specifically, the length of the opening pattern 54b located in the connection area 3 along the direction X is longer on the optical modulation area 4 side than on the laser area 2 side. In this embodiment, the length of the opening pattern 54b located in the connection area 3 along the direction X is longer on the optical modulation area 4 side in the direction X, and is, for example, 40nm or more and 110nm or less. On the other hand, the length of the opening pattern 54b located in the optical modulation area 4 along the direction X is the same, and is, for example, 90nm or more and 110nm or less. At the portion of the mask pattern 54 located in the optical modulation area 4 , the length of the cover pattern 54 a sandwiched between adjacent opening patterns 54 b along the direction X is the same as the length of the opening pattern 54 b along the direction X.

[0058] The mask pattern 55 has a covering pattern 55a covering the diffraction grating layer 52 and a plurality of opening patterns 55b. The plurality of opening patterns 55b are periodically arranged along the direction X. Therefore, on the diffraction grating layer 52, the covering pattern 55a and the opening pattern 55b are alternately positioned in the direction X. The lengths of the opening patterns 55b along the direction X are the same, and are, for example, 99 nm or more and 101 nm or less. The lengths of the covering patterns 55a sandwiched between adjacent opening patterns 55b along the direction X are the same as the lengths of the opening patterns 55b along the direction X.

[0059] Then, if Figure 3As shown in FIG. 1B, a concavoconvex portion 61 along the direction X is formed on the first portion 51a using the mask pattern 54, and a diffraction grating 26 is formed using the mask pattern 55 (fifth step). In the fifth step, the position where the mask pattern 54 is exposed in the first portion 51a and the position where the mask pattern 55 is exposed in the diffraction grating layer 52 are etched. Thus, the concavoconvex portion 61 and the diffraction grating 26 each having a periodic structure along the direction X are formed. In this embodiment, the concavoconvex portion 61 is formed on the first semiconductor layer 51 at least in the connection region 3.

[0060] The concavoconvex portion 61 is a group of depressions and protrusions alternately formed on the surface of the first portion 51a along the direction X. Hereinafter, in the concavoconvex portion 61, the depression located in the connection area 3 is the depression 62, the protrusion located in the connection area 3 is the protrusion 63, and a group of depressions 62 and protrusions 63 adjacent to each other is the concavoconvex portion 64. The depression located in the optical modulation area 4 is the depression 65, the protrusion located in the optical modulation area 4 is the protrusion 66, and a group of depressions 65 and protrusions 66 adjacent to each other is the concavoconvex portion 67. The lengths of the depressions 62 and 65 and the protrusions 63 and 66 along the direction X are, for example, 40nm or more and 160nm or less. The depths of the depressions 62 and 65 (or the protrusion amounts of the protrusions 63 and 66) are the same, and are, for example, 250nm or more and 300nm or less.

[0061] In the following, a group of depressions and protrusions adjacent to each other is a concave-convex portion. The ratio of the length b of the protrusion along the direction X to the sum of the length a and the length b of the depression along the direction X (b / (a+b)) is defined as the duty ratio of the concave-convex portion. Therefore, the duty ratio of the concave-convex portion is smaller because the length of the depression along the direction X is longer. As described above, in the mask pattern 54, the length of the opening pattern 54b located in the connection area 3 along the direction X is longer on the optical modulation area 4 side than on the laser area 2 side. Therefore, in the concave-convex portion 61, the duty ratio of the concave-convex portion 64 located in the connection area 3 is larger on the laser area 2 side than on the optical modulation area 4 side. Similarly, the ratio of the length of the covering pattern 54a along the direction X to the total length of the covering pattern 54a and the opening pattern 54b located in the connection area 3 and adjacent to each other along the direction X is larger on the laser area 2 side than on the optical modulation area 4 side. In this embodiment, the duty ratio of the concave-convex portion 64 changes continuously along the direction X. The duty ratio of the concavo-convex portion 64 is 0.5 or more and 1 or less.

[0062] As described above, at the portion of the mask pattern 54 located in the optical modulation area 4, the length of the covering pattern 54a sandwiched between the adjacent opening patterns 54b along the direction X is the same as the length of the opening pattern 54b along the direction X. Therefore, in the concavo-convex portion 61, the duty ratio of the concavo-convex portion 67 located in the optical modulation area 4 is constant, that is, 0.5. That is, the duty ratio of the concavo-convex portion 67 is equal to or less than the minimum value of the duty ratio of the concavo-convex portion 64. It should be noted that in the case where the duty ratio of the concavo-convex portion 64 is 1, the concavo-convex portion 64 has no depression 62. Therefore, in this embodiment, the concavo-convex portion may not be formed on a part of the concavo-convex portion 61.

[0063] In the fifth step, in the first semiconductor layer 51, a part of the portion located in the laser region 2 is also etched. Therefore, in the laser region 2, a depression 71 and a protrusion 72 including an InGaAsP layer are provided, and the InGaAsP layer forming the diffraction grating 26 is removed from the depression 71. As described above, in the mask pattern 55, the length of the cover pattern 55a sandwiched between adjacent opening patterns 55b along the direction X is the same as the length of the opening pattern 55b along the direction X. Therefore, the length of the depression 71 along the direction X and the length of the protrusion 72 along the direction X are also the same. Therefore, the duty ratio of the concave-convex portion 73 configured by the depression 71 and the protrusion 72 adjacent to each other is 0.5. The length of the concave-convex portion 73 along the direction X is, for example, 198nm or more and 202nm or less.

[0064] Then, if Figure 3 As shown in C, on the first semiconductor layer 51 forming the first portion 51a, the second semiconductor layer 56 is formed (the sixth step). In the sixth step, first, the mask pattern 55 and the mask pattern 54 are removed. Subsequently, by, for example, metal organic chemical vapor deposition, the second semiconductor layer 56 as, for example, an n-type InP layer is epitaxially grown on the diffraction grating 26 and the first portion 51a. The thickness of the second semiconductor layer 56 is, for example, 100nm or more and 200nm or less. After the sixth step, the first semiconductor layer 51 and the second semiconductor layer 56 are integrated with each other to form the lower cladding layer 21 in which the diffraction grating 26 is buried. The concavo-convex portion 61 is buried by the second semiconductor layer 56 and disappears.

[0065] Figure 6 FIG. 2 is an enlarged cross-sectional view showing the main parts of the connection area 3 and the optical modulation area 4 after the sixth step. Figure 6 In the figure, for the sake of explanation, the concavoconvex part 61, the depressions 62 and 65, the protrusions 63 and 66, and the concavoconvex parts 64 and 67 are depicted with solid lines. Figure 6As shown, the thickness of the second semiconductor layer 56 grown in the connection area 3 becomes thinner as it is closer to the optical modulation area 4 side in the direction X. The thickness of the second semiconductor layer 56 grown in the optical modulation area 4 is constant and is equal to or less than the minimum value of the thickness of the second semiconductor layer 56 located in the connection area 3. The volumes of the second semiconductor layer 56 disposed on the concave-convex portions 64 located in the connection area 3 may all be the same. For example, in the connection area 3, the volumes V1 and V2 of the second semiconductor layer 56 disposed on different concave-convex portions 64 may be the same. The volume V1 and volume V3 of the second semiconductor layer 56 disposed on the concave-convex portion 67 located in the optical modulation area 4 may be the same.

[0066] Then, if Figure 4A As shown, an active layer 22 is formed on the second semiconductor layer 56 (the seventh step). In the seventh step, the active layer 22 having a quantum well structure is epitaxially grown by, for example, metal organic chemical vapor deposition. At the time point of the seventh step, the active layer 22 is arranged in the laser region 2 as well as the connection region 3 and the optical modulation region 4.

[0067] Then, if Figure 4B As shown, the portion of the active layer 22 located in the connection area 3 and the optical modulation area 4 is removed (eighth step). In the eighth step, first, a mask pattern 58 (second mask pattern) is formed on the active layer 22. Subsequently, the portion of the active layer 22 located in the connection area 3 and the optical modulation area 4 is removed using the mask pattern 58. Therefore, the active layer 22 remains in the laser area 2. In the connection area 3 and the optical modulation area 4, the second portion 56a of the second semiconductor layer 56 included in the lower cladding layer 21 is exposed.

[0068] Here, reference Figure 7 , the shape of the mask pattern 58 will be described in detail. Figure 7 is a schematic plan view showing the shape of the mask pattern 58. Figure 7 As shown, the mask pattern 58 has a mask portion 81 disposed on the active layer 22 located in the laser region 2 and a mask portion 82 disposed on the active layer 22 located in the connection region 3 and the optical modulation region 4. The mask portion 81 completely covers the active layer 22. The length L1 of the mask portion 81 along the direction Y is, for example, 100 μm or more and 150 μm or less.

[0069] The mask portion 82 covers a portion of the active layer 22 located in the connection region 3 and the optical modulation region 4, and has openings 83 to 85 sequentially arranged along the direction Y. The openings 83 and 85 are a pair of openings different from the opening 84, provided for adjusting the growth rate of the optical waveguide layer 31 formed in the opening 84, and overlap with the second semiconductor layer 56. The opening 83 is located on one end side in the direction Y, and the opening 85 is located on the other end side in the direction Y. On the other hand, the opening 84 is a portion where the optical waveguide layer 31 is formed, and overlaps with a portion of the second semiconductor layer 56. The opening 84 is located between the openings 83 and 85 in the direction Y. In the opening 84, a region 84a located in the connection region 3 presents a trapezoidal shape in a plan view. The width (pattern width) of the region 84a along the direction Y becomes narrower as it is closer to the optical modulation region 4 in the direction X. The maximum width W1 of the region 84a along the direction Y is, for example, 50 μm or more and 70 μm or less. The length L2 of the region 84a along the direction X is, for example, 40 μm or more and 80 μm or less. On the other hand, in the opening 84, the region 84b located in the optical modulation zone 4 has a rectangular shape in a plan view. The width W2 of the region 84b along the direction Y is, for example, 15 μm or more and 25 μm or less. The width W2 of the region 84b is the same as the width of the end portion of the region 84a on the side of the optical modulation zone 4. In the mask portion 82, the maximum width W3 of the portion that clamps the opening 84 along the direction Y is, for example, 20 μm or more and 30 μm or less. It should be noted that Figure 4B Corresponding to along Figure 7 84 is a cross-sectional view taken along a straight line passing through the opening 84 in the direction X.

[0070] Then, if Figure 4C As shown in FIG. 1 , on the second portion 56a of the second semiconductor layer 56 exposed from the active layer 22, the optical waveguide layer 31 is formed (ninth step). In the ninth step, the optical waveguide layer 31 is epitaxially grown in the opening 84 by metal organic chemical vapor deposition, for example, using the mask pattern 58. Subsequently, after the optical waveguide layer 31 is formed, the mask pattern 58 is removed. As described above, the width of the region 84a of the opening 84 formed on the mask pattern 58 along the direction Y becomes narrower as it is closer to the optical modulation region 4 in the direction X. Therefore, the growth rate of the optical waveguide layer 31 located in the connection region 3 becomes smaller as it is closer to the laser region 2. Therefore, the top surface F1 of the active layer 22 is aligned with the top surface F2 of the optical waveguide layer 31 located in the connection region 3.

[0071] Then, if Figure 5A As shown, the upper cladding layer 23 is formed on the active layer 22 and the optical waveguide layer 31 (the tenth step). In the tenth step, the upper cladding layer 23 is epitaxially grown on the active layer 22 and the optical waveguide layer 31 by, for example, metal organic chemical vapor deposition.

[0072] Then, if Figure 5B As shown, on the upper cladding layer 23, contact layers 24 and 41 and electrodes 25 and 42 are formed (eleventh step). In the eleventh step, a pad 43 can be formed when the electrodes 25 and 42 are formed (see Figure 1A ). Through the above steps, the semiconductor laser device 1 according to this embodiment is manufactured.

[0073] In the method for manufacturing the semiconductor laser device 1 according to the above-described embodiment, the concavoconvex portion 61 is formed along the direction X on the first portion 51a of the first semiconductor layer 51 using the mask pattern 54. In the concavoconvex portion 61 formed on the first portion 51a, the duty ratio of the concavoconvex portion 64 is larger on the laser region 2 side than on the optical modulation region 4 side. In addition, the duty ratio of the concavoconvex portion 67 is constant and is equal to or less than the minimum value of the duty ratio of the concavoconvex portion 64. Here, in the growth of the second semiconductor layer 56 on the first portion 51a, in the region where the duty ratio of the concavoconvex portion is small, the capacity of the depression is large, and thus the thickness of the second semiconductor layer 56 is thinner. Therefore, the thickness of the second semiconductor layer 56 located in the connection region 3 is thinner on the optical modulation region 4 side than on the laser region 2 side in the direction X. In addition to this, the thickness of the second semiconductor layer 56 located in the optical modulation region 4 is equal to or less than the thickness of the second semiconductor layer 56 located in the connection region 3. Therefore, even in the case of forming the optical waveguide layer 31 thicker than the active layer 22, it is possible to suppress the formation of a large step on the end face connection portion between the active layer 22 and the optical waveguide layer 31. Therefore, according to the method for manufacturing the semiconductor laser device 1 of this embodiment, it is possible to manufacture a semiconductor laser device 1 in which the thickness of the optical waveguide layer 31 in the optical modulation region 4 can be set larger than the thickness of the active layer 22 in the laser region 2 while suppressing the degradation of the coupling efficiency of the laser region 2 to the optical modulation region 4.

[0074] In addition to this, in the semiconductor laser device 1 according to the embodiment, the thickness of the second semiconductor layer 56 located in the connection region 3 is thinner on the optical modulation region 4 side than on the laser region 2 side in the direction X. Furthermore, the thickness of the second semiconductor layer 56 located in the optical modulation region 4 is equal to or smaller than the thickness of the second semiconductor layer 56 located in the connection region 3. Therefore, the semiconductor laser device 1 can include the optical waveguide layer 31 thicker than the active layer 22 while suppressing the formation of a large step on the end face connection portion between the active layer 22 and the optical waveguide layer 31. Therefore, the semiconductor laser device 1 can exert the above-mentioned operation and effects.

[0075] A large step is formed on the end face connection portion between the active layer 22 and the optical waveguide layer 31 because the difference between the thickness of the end face of the active layer 22 on the optical waveguide layer 31 side and the thickness of the end face of the optical waveguide layer 31 on the active layer 22 side is, for example, 40 nm or more.

[0076] The method for manufacturing the semiconductor laser device 1 according to the embodiment includes the steps of forming the diffraction grating layer 52 on the first semiconductor layer 51 and removing the portion of the diffraction grating layer 52 located in the connection region 3 and the optical modulation region 4 to expose the first portion 51a of the first semiconductor layer 51. In the fourth step, the mask pattern 55 is formed on the diffraction grating layer 52, and in the fifth step, the diffraction grating 26 is formed using the mask pattern 55. In this case, when the concavo-convex portion 61 is formed on the first portion 51a, the diffraction grating 26 can be formed in the laser region 2. Therefore, the semiconductor laser device 1 that can realize stable single-mode oscillation can be manufactured.

[0077] In this embodiment, the duty ratio of the concavo-convex portion 64 located in the connection region 3 changes continuously along the direction X. Therefore, the thickness of the second semiconductor layer 56 located in the connection region 3 becomes thinner continuously from the laser region 2 side to the optical modulation region 4 side along the direction X. Therefore, the thickness of the optical waveguide layer 31 located in the connection region 3 can become thicker continuously from the laser region 2 side to the optical modulation region 4 side along the direction X. Therefore, no step is provided on the optical waveguide layer 31 located in the connection region 3, so that the degradation of the coupling efficiency from the laser region 2 to the optical modulation region 4 can be preferably suppressed.

[0078] In this embodiment, in the ninth step, the optical waveguide layer 31 is formed in the opening 84 using the mask pattern 58 having the opening 84 overlapping the second portion 56a of the second semiconductor layer 56, and the pattern width of the region 84a in the connection region 3 located in the opening 84 becomes narrower as it is closer to the optical modulation region 4 in the direction X. In this case, the growth rate of the optical waveguide layer 31 around the laser region 2 having a wide opening width becomes smaller. Therefore, the formation of a large step on the end face connection region between the active layer 22 and the optical waveguide layer 31 can be well suppressed, so that the degradation of the coupling efficiency of the laser region 2 to the optical modulation region 4 can be preferably suppressed.

[0079] In this embodiment, the mask pattern 58 has openings 83 and 85 separated from the opening 84. The openings 83 and 85 overlap with the second portion 56a of the second semiconductor layer 56. In a plan view, the opening 84 is located between the openings 83 and 85 in a direction intersecting the direction X. In this case, on the second portion 56a, the semiconductor layer constituting the optical waveguide layer 31 grows not only in the opening 84 but also in the openings 83 and 85. Therefore, the growth rate of the optical waveguide layer 31 in the opening 84 becomes smaller. Therefore, the film quality of the optical waveguide layer 31 can be improved, and the thickness of the optical waveguide layer 31 can be controlled. Therefore, the active layer 22 can be connected to the optical waveguide layer 31 without a sudden change in the refractive index.

[0080] In this embodiment, the height of the top surface F1 of the active layer 22 is the same as the heights of the top surfaces F2 and F3 of the optical waveguide layer 31. In this case, no step is provided between the top surfaces of the active layer 22 and the optical waveguide layer 31, so that the degradation of the coupling efficiency of the laser region 2 to the optical modulation region 4 can be preferably suppressed.

[0081] Next, refer to Figure 8 , modifications of the embodiment will be described. Figure 8 : is a schematic cross-sectional view showing a concavo-convex portion according to a modification. Figure 8 In the figure, for the sake of explanation, the concavoconvex part 61, the depressions 62, 65 and 71, the protrusions 63, 66 and 72, and the concavoconvex parts 64 and 73 are depicted with solid lines. Figure 8 As shown, in the modification, the thickness of the second semiconductor layer 56 located in the connection region 3A changes stepwise along the direction X. Therefore, in the connection region 3A, the thickness of the optical waveguide layer 31 also changes stepwise along the direction X. In the connection region 3A, transition regions R1 to R3 arranged in sequence along the direction X from the laser region 2 side are defined. The length of the transition regions R1 to R3 along the direction X is, for example, 10 μm or more and 20 μm or less.

[0082] The duty ratio of all the concavo-convex portions included in the transition region R1 is 1, and no depression is formed in the transition region R1. Therefore, the thickness of the second semiconductor layer 56 located in the transition region R1 is constant. The duty ratio of all the concavo-convex portions included in the transition region R2 is, for example, 0.8. Therefore, the thickness of the second semiconductor layer 56 located in the transition region R2 is constant and thinner than the thickness of the second semiconductor layer 56 located in the transition region R1. In addition, the duty ratio of all the concavo-convex portions included in the transition region R3 is, for example, 0.65. Therefore, the thickness of the second semiconductor layer 56 located in the transition region R3 is constant and thinner than the thickness of the second semiconductor layer 56 located in the transition region R2. It should be noted that the thickness of the second semiconductor layer 56 located in the transition region R3 is thicker than the thickness of the second semiconductor layer 56 located in the optical modulation zone 4.

[0083] In this modification, the thickness T1 of the second semiconductor layer 56 located on the diffraction grating 26 is, for example, 130 nm, and the thickness T2 of the active layer 22 located in the laser region 2 is, for example, 200 nm. In the laser region 2, the lengths L11 and L12 of the recess 71 and the protrusion 72 along the direction X are, for example, 50 nm, respectively. The thickness T3 of the second semiconductor layer 56 located in the transition region R1 is, for example, 180 nm, and the thickness T4 of the optical waveguide layer 31 located in the transition region R1 is, for example, 220 nm. In the transition region R2, the thickness T5 of the second semiconductor layer 56 is, for example, 160 nm, the thickness T6 of the optical waveguide layer 31 is, for example, 240 nm, the length L13 of the recess 62 along the direction X is, for example, 40 nm, and the length L14 of the protrusion 63 along the direction X is, for example, 160 nm. In the transition region R3, the thickness T7 of the second semiconductor layer 56 is, for example, 140 nm, the thickness T8 of the optical waveguide layer 31 is, for example, 260 nm, the length L15 of the recess 62 along the direction X is, for example, 70 nm, and the length L16 of the protrusion 63 along the direction X is, for example, 130 nm. The lengths L17 and L18 of the recess 65 and the protrusion 66 along the direction X in the optical modulation area 4 are, for example, 100 nm, respectively. The thickness T9 of the second semiconductor layer 56 located on the protrusion 66 is, for example, 130 nm, and the thickness T10 of the optical waveguide layer 31 located in the optical modulation area 4 is, for example, 280 nm.

[0084] In this modification as well, operations and effects similar to those of the embodiment are exerted. In addition to this, the concavo-convex portion 64 in the connection region 3A can be easily formed, and thus the yield of the semiconductor laser device 1 can be improved.

[0085] It should be noted that in this modification, in the connection region 3A, the volumes V11 to V13 of the second semiconductor layer 56 disposed on different concavo-convex portions 64 are the same. The volumes V11 to V13 are also the same as the volume V21 of the second semiconductor layer 56 disposed on the concavo-convex portion 67 located in the optical modulation region 4. In addition to this, the volumes V11 to V13 are also the same as the volume V31 of the second semiconductor layer 56 located on the concavo-convex portion 73 in the laser region 2.

[0086] The semiconductor laser device and the manufacturing method thereof according to the present disclosure are not limited to the aforementioned embodiments and modifications, and various modifications may be made. For example, any one of the first to eleventh steps may be omitted. For example, in the case where a diffraction grating is not included in the semiconductor laser device, the second and third steps may be omitted. In addition, a part of the fourth step may also be omitted.

[0087] In this embodiment, the boundary of the concavo-convex portion formed on the first part of the first semiconductor layer disappears, but is not limited to this. For example, the boundary of the concavo-convex portion can be detected using, for example, a cross-sectional scanning electron microscope image. In the lower cladding, the boundary between the first semiconductor layer and the second semiconductor layer can be detected. In this case, the duty cycle of the concavo-convex portion is the same as the duty cycle before the concavo-convex portion is covered by the second semiconductor layer. For example, the duty cycle of the concavo-convex portion located in the connection area is greater on the laser area than on the optical modulation area side, and the duty cycle of the concavo-convex portion located in the optical modulation area is constant and equal to or less than the minimum value of the duty cycle of the concavo-convex portion located in the connection area.

[0088] In this modification, the opening of the mask pattern formed on the second semiconductor layer may not have a trapezoidal shape in a plan view. For example, the width of the opening along the direction Y may be gradually changed along the direction X. In this case, the width of the opening along the direction Y becomes narrower as it approaches the optical modulation region along the direction X. In the modification, an opening for forming the optical waveguide layer may be provided separately.

Claims

1. A method for manufacturing an optical semiconductor device, the optical semiconductor device comprising an electro-absorption modulator, a DFB laser, and a connection region connected between the electro-absorption modulator and the DFB laser in an integrated structure in a first direction on a semiconductor substrate, the manufacturing method comprising: forming a first semiconductor layer on a semiconductor substrate; forming a diffraction grating layer on a portion of the first semiconductor layer; forming a first mask pattern on the first semiconductor layer in the connection region, a first region forming the electro-absorption modulator, and a second region forming the diffraction grating layer included in the DFB laser; Using the first mask pattern, forming concavo-convex portions along the first direction on the first semiconductor layer, the first region, and the second region in the connection region; forming a second semiconductor layer on the concavo-convex portion provided on the first semiconductor layer; forming an active layer on the second semiconductor layer in the second region; as well as forming an optical waveguide layer on the second semiconductor layer in the first region and the connection region, wherein the first mask pattern includes a first pattern in the first region and a second pattern in the second region, the first pattern includes a first opening pattern and a first covering pattern adjacent to each other, and the second pattern includes a second opening pattern and a second covering pattern adjacent to each other, and The ratio of the first opening pattern to the first covering pattern is different from the ratio of the second opening pattern to the second covering pattern.

2. The manufacturing method according to claim 1, in, The first mask pattern includes a third pattern in the connection region, and Among them, in the third pattern, a ratio of the length of the cover pattern to the total length of the opening pattern and the cover pattern adjacent to each other is larger on the DFB laser side than on the electro-absorption modulator side.

3. The manufacturing method according to claim 1 or 2, in, In the forming of the concavoconvex portion, the concavoconvex portion is formed in which a ratio of a length of a protrusion to a total length of a recess and the protrusion adjacent to each other is larger on the DFB laser side than on the electro-absorption modulator side.

4. The manufacturing method according to claim 3, in, The duty ratio of the concavo-convex portion corresponds to a ratio of the length of the concave portion to the total length of the concave portion and the protrusion portion adjacent to each other, and Wherein, the duty cycle in the connection area changes continuously or gradually.

5. The manufacturing method according to claim 1 or 2, in, In the forming of the optical waveguide layer, a second mask pattern including an opening region above the second semiconductor layer is used, wherein the optical waveguide layer is formed in the opening region of the second mask pattern, and The width of the opening region of the second mask pattern is narrower as it is closer to the electro-absorption modulator in the first direction.

6. The manufacturing method according to claim 5, in, The second mask pattern includes a pair of opening regions over the second semiconductor layer that are different from the opening region, and Wherein, in the second mask pattern, the opening region is located between the pair of opening regions in a second direction intersecting with the first direction in a plan view.

7. An optical semiconductor device, comprising: A laser, comprising: Electroabsorption modulator; DFB laser; and a connection region, the connection region being connected between the electro-absorption modulator and the DFB laser in an integrated structure in a first direction on the semiconductor substrate; a first semiconductor layer, the first semiconductor layer having a concave-convex portion extending in the first direction on the semiconductor substrate; a second semiconductor layer, the second semiconductor layer being disposed on the concave-convex portion of the first semiconductor layer; an active layer, the active layer being disposed on the second semiconductor layer in the DFB laser; and an optical waveguide disposed on the second semiconductor layer, the optical waveguide being provided with the electro-absorption modulator and the connection region, wherein the duty ratio of the concavo-convex portion in the connection region is greater on the DFB laser side than on the electro-absorption modulator side, and The duty ratio of the concave-convex portion corresponds to a ratio of a length of a concave portion to a total length of the concave portion and the protrusion portion adjacent to each other.

8. The optical semiconductor device according to claim 7, in, The duty ratio of the concave and convex portions in the electro-absorption modulator is constant.

9. The optical semiconductor device according to claim 8, in, The duty ratio in the electro-absorption modulator is equal to or smaller than a minimum value of the duty ratio of the concavo-convex portion in the connection region.

10. The optical semiconductor device according to any one of claims 7 to 9, in, The duty ratio of the concavo-convex portion in the connection region changes continuously or gradually.

11. The optical semiconductor device according to any one of claims 7 to 9, in, The height of the top of the active layer is equal to the height of the top of the optical waveguide.

12. A method for manufacturing an optical semiconductor device, the optical semiconductor device comprising a laser region, a connection portion, and an optical modulation region sequentially arranged along an optical waveguide direction, the manufacturing method comprising: forming a first semiconductor layer on a semiconductor substrate; forming a diffraction grating layer on a portion of the first semiconductor layer; forming a first mask pattern on the first semiconductor layer in the connecting portion and on the diffraction grating layer; forming a concavo-convex portion on the first semiconductor layer in the connecting portion along the optical waveguide direction using the first mask pattern; forming a second semiconductor layer on the first semiconductor layer on which the concavo-convex portion is formed; forming an active layer on the second semiconductor layer in the laser region; as well as forming an optical waveguide layer on the second semiconductor layer in the optical modulation region and the connecting portion, wherein, in the forming of the first mask pattern, the first mask pattern is formed in which a ratio of a length of a covering pattern along the optical waveguide direction to a total length of an opening pattern and the covering pattern located in the connecting portion and adjacent to each other along the optical waveguide direction is greater on the laser region side than on the optical modulation region side, and Wherein, in forming the concavo-convex portion, the concavo-convex portion is formed so that a ratio of a length of a protrusion along the optical waveguide direction to a total length of a recess and the protrusion located in the connecting portion and adjacent to each other along the optical waveguide direction is greater on the laser zone side than on the optical modulation zone side.

13. The manufacturing method according to claim 12, in, In the forming of the concavo-convex portion, a diffraction grating is formed on the first semiconductor layer using the first mask pattern.

14. The manufacturing method according to claim 12 or 13, in, In the connection portion, the ratio of the length of the protrusion to the total length of the recess and the protrusion adjacent to each other changes continuously or stepwise along the optical waveguide direction.

15. The manufacturing method according to claim 12 or 13, in, In the forming of the optical waveguide layer, a second mask pattern including an opening overlapping a portion of the second semiconductor layer is used, wherein the optical waveguide layer is formed in the opening of the second mask pattern, and The pattern width of the region located in the connection portion and the opening is narrower as it approaches the optical modulation region in the optical waveguide direction.

16. The manufacturing method according to claim 15, in, the second mask pattern having a pair of openings different from the opening, wherein the pair of openings overlaps with the second semiconductor layer, and The opening is located between the pair of openings in a direction intersecting with the optical waveguide direction in a plan view.

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