semiconductor optical device

Abstract

To provide a semiconductor optical element excellent in heat dissipation and reliability.SOLUTION: A semiconductor optical element includes a substrate, a semiconductor multilayer formed on the substrate and including a light emitting active layer, an insulating film formed on the semiconductor multilayer, and an electrode formed on a portion of the insulating film, and the insulating film covers the semiconductor multilayer except for a region where the semiconductor multilayer and the electrode are electrically connected, and at least a portion of a region overlapping with the electrode is thinner than a region not overlapping with the electrode.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a semiconductor optical device. [Background technology]

[0002] Semiconductor optical elements used in optical communications have an optical functional layer that converts electricity to light or light to electricity. For example, lasers and external modulators are known to use multiple quantum well layers as their optical functional layers. In photodetectors, the optical functional layer is composed of a semiconductor absorption layer. Semiconductor optical elements generally have electrodes made of metal to apply voltage to the optical functional layer. Part of the electrode is electrically and physically connected to the semiconductor layer. Some semiconductor optical elements are also known to have an insulating film placed on the surface of the semiconductor layer where no metal is placed for protection. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-118345 Summary of the Invention [Problem to be solved by the invention]

[0004] When a semiconductor optical device is operating, the optical functional layer, other semiconductor layers, electrodes, etc. generate heat. The generated heat is one of the factors that degrade the characteristics of the semiconductor optical device. For example, the optical output characteristic is a major characteristic of a CW laser (Continuous Wave laser), which outputs continuous light. A larger optical output is preferable, but under the same driving current, a lower temperature of the semiconductor optical device will result in a higher optical output. In an environment with the same external temperature, if more heat is released from the semiconductor optical device to the outside, the effective temperature of the semiconductor optical device will decrease and the optical output will improve. It is important to release as much heat generated by the semiconductor optical device to the outside as possible, not only for CW lasers but also for other semiconductor optical devices.

[0005] As mentioned above, semiconductor optical devices have metal electrodes and an insulating film (protective film). Because the electrodes are made of metal, they have high thermal conductivity and excellent heat dissipation properties. On the other hand, oxide films or silicon nitride films are often used for the insulating film. These materials have lower thermal conductivity than semiconductors and metals, which hinders the release of generated heat to the outside.

[0006] Furthermore, the connection area between the electrode and the semiconductor layer may be limited to a narrow area. For example, in a semiconductor optical device with a striped structure, the contact point between the electrode and the semiconductor layer is limited to only the top surface of the stripe. However, from the viewpoint of heat dissipation, the electrode extends to an area wider than the width of the stripe. In this case, the insulating film described above is disposed to insulate the electrode from the semiconductor layer except on the stripe. This structure is disclosed in Patent Document 1.

[0007] Therefore, the surface of the semiconductor layer is covered with an insulating film, with the electrodes placed on top of it, except for a small area. This means that the insulating film is positioned in the path through which heat generated in the semiconductor layer is released to the outside. As a result, the amount of heat dissipation is limited, which is a factor that deteriorates the characteristics of the semiconductor optical device.

[0008] The present invention addresses the above-mentioned problems by providing a semiconductor optical device with excellent heat dissipation properties. [Means for solving the problem]

[0009] The semiconductor optical element of the present invention comprises a substrate, a semiconductor multilayer formed on the substrate and including an optical functional layer, an insulating film formed on the semiconductor multilayer, and an electrode formed on a portion of the insulating film, wherein the insulating film covers the semiconductor multilayer except for a region where the semiconductor multilayer and the electrode are electrically connected, and at least a portion of the region overlapping with the electrode is thinner than a region not overlapping with the electrode. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a semiconductor optical device with excellent heat dissipation properties. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is an example of a top view of a semiconductor optical device according to the first embodiment. [Figure 2] FIG. 2 is a schematic cross-sectional view of the semiconductor optical device shown in FIG. 1 taken along line AA'. [Figure 3] FIG. 3 is a schematic cross-sectional view taken along line AA′ of the first modification of the semiconductor optical device according to the first embodiment of the present invention. [Figure 4] FIG. 4 is a schematic cross-sectional view of the semiconductor optical device according to the second embodiment taken along line AA'. [Figure 5] FIG. 5 is a schematic cross-sectional view taken along line AA′ of the first modification of the semiconductor optical device according to the second embodiment of the present invention. [Figure 6] FIG. 6 is a schematic cross-sectional view of the semiconductor optical device according to the third embodiment taken along line AA'. [Figure 7] FIG. 7 is a schematic cross-sectional view taken along line AA′ of Modification 1 of the semiconductor optical device according to the third embodiment of the present invention. [Figure 8] FIG. 8 is a schematic cross-sectional view of the semiconductor optical device according to the fourth embodiment taken along the line AA'. [Figure 9] FIG. 9 is a schematic cross-sectional view taken along the line AA′ of the first modification of the semiconductor optical device according to the fourth embodiment of the present invention. [Figure 10] FIG. 10 is a schematic cross-sectional view taken along the line AA′ of the second modification of the semiconductor optical device according to the fourth embodiment of the present invention. [Figure 11] FIG. 11 is a schematic cross-sectional view of the semiconductor optical device according to the fifth embodiment taken along the line AA'. [Figure 12] FIG. 12 is a schematic cross-sectional view taken along the line AA′ of the first modification of the semiconductor optical device according to the fifth embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In all drawings for explaining the embodiments, components having the same functions are designated by the same reference numerals, and repeated explanations thereof will be omitted. The drawings shown below are merely for explaining examples of the embodiments, and the size of the drawings does not necessarily correspond to the scale described in the examples.

[0013] [First embodiment] FIG. 1 is a top view of a semiconductor optical device 1 according to a first embodiment. FIG. 2 is a schematic cross-sectional view taken along line A-A' in FIG. 1. The semiconductor optical device 1 is an edge-emitting CW laser. The semiconductor optical device 1 has a stripe structure 3. A surface electrode 20 is disposed on the surface of the semiconductor optical device 1. The surface electrode 20 is an electrode formed on a portion of an insulating film 26, and is, for example, a metal film containing Au. The metal film may be composed of multiple materials. An insulating film 26 is disposed on the top surface of the semiconductor optical device 1 in an area other than the surface electrode 20. As shown in FIG. 2, the insulating film 26 is also disposed under the surface electrode 20. The insulating film 26 is, for example, a silicon oxide film, a silicon nitride film, or an aluminum oxide film. Details of the insulating film 26 will be described later. A low-reflection end face coating film 11 is disposed on the left facet of FIG. 1, and a high-reflection end face coating film 12 is disposed on the right facet. Note that the coating film is merely an example; both end faces may be low-reflection end face coating films.

[0014] As shown in FIG. 2, the semiconductor optical device 1 has a striped structure 3 formed on a first-conductivity substrate 21. Buried layers 30 are disposed on both sides of the striped structure 3. The buried layer 30 is a semi-insulating semiconductor layer or a semiconductor layer formed by combining multiple p-type and n-type semiconductor layers. An insulating film 26 is disposed on the upper surface of the buried layer 30. The striped structure 3 is configured to include multiple semiconductor layers on a portion of the substrate 21. The multiple semiconductor layers include, from bottom to top, a first-conductivity optical confinement layer 22, an active layer 23 (optical functional layer) formed of a multiple quantum well layer, a second-conductivity optical confinement layer 24, a second-conductivity cladding layer 25, and a contact layer 35. A diffraction grating layer 33 is provided in the second-conductivity cladding layer 25. Note that the striped structure 3 may or may not include a portion of the substrate 21. Hereinafter, the layers from the first-conductivity optical confinement layer 22 to the contact layer 35 will be referred to as a semiconductor multilayer. In this embodiment, the semiconductor multilayer includes a striped structure 3 and buried layers 30 formed on both sides of the striped structure 3. A back electrode 31 is disposed on the back side of the substrate 21. In this embodiment, the semiconductor multilayer is a CW laser compatible with 1.3 μm. However, the wavelength band of the laser light output from the semiconductor multilayer is not limited to this, and may be other wavelength bands. The substrate 21 may also be an insulating substrate. In this case, a first conductivity type semiconductor layer needs to be disposed between the insulating substrate 21 and the striped structure 3.

[0015] A feature of the present disclosure is that the insulating film 26 covers the semiconductor multilayer except for the region where the semiconductor multilayer and the surface electrode 20 are electrically connected, and at least a portion of the region overlapping with the surface electrode 20 is thinner than the region not overlapping with the surface electrode 20. In this embodiment, as shown in Fig. 2, the thickness of the insulating film 26 is different between the region where the surface electrode 20 and the buried layer 30 overlap and the region where they do not overlap. The insulating film 26 is thinner in the region overlapping with the surface electrode 20 than in the region where they do not overlap.

[0016] In the semiconductor optical device 1, the active layer 23 emits light when a voltage is applied (current is injected) between the front electrode 20 and the back electrode 31. The active layer 23 generates heat in addition to emitting light. The other semiconductor layers also generate heat due to the flow of current. The heat generated in the semiconductor multilayer is dissipated to the outside via the substrate 21 and the buried layer 30. In the semiconductor optical device 1 of this embodiment, the striped structure 3 is formed on the very front surface side of the substrate 21. For example, the distance from the front electrode 20 to the active layer 23 is several μm, while the distance from the active layer 23 to the back electrode 31 is as large as several tens of μm to 100 μm. Therefore, more of the generated heat is dissipated to the external environment from the front electrode 20 side than from the back electrode 31 side. Furthermore, the amount of heat generated is greater closer to the active layer 23. Therefore, most of the generated heat is dissipated from the front electrode 20 side. Some of the heat passes through the striped structure 3 and is dissipated directly from the front electrode 20. However, there is another heat dissipation path that leads to the front electrode 20 via the buried layer 30.

[0017] An insulating film 26 is disposed between the surface electrode 20 and the buried layer 30. As described above, the insulating film 26 is a silicon oxide film, a silicon nitride film, an aluminum oxide film, or the like, which has a lower thermal conductivity than the semiconductor multilayer. Therefore, the insulating film 26 disposed between the surface electrode 20 and the buried layer 30 hinders heat dissipation. However, in this embodiment, the insulating film 26 in the region overlapping with the surface electrode 20 is formed thin. The insulating film 26 in this region has a thickness of, for example, 100 nm or less. Therefore, it is possible to dissipate heat to the outside without significantly reducing heat dissipation performance.

[0018] On the other hand, the insulating film 26 in the region not overlapping with the surface electrode 20 is several hundred nanometers thick. If the thickness of the insulating film 26 in the region not overlapping with the surface electrode 20 were the same as the thickness of the region overlapping with the surface electrode 20, the insulating film 26 in the region not overlapping with the surface electrode 20 might not be able to fully function as a protective film, which might affect the reliability of the semiconductor optical device 1. Furthermore, in the region where the surface electrode 20 is disposed, the surface electrode 20 functions as a protective film, so even if the insulating film 26 is made thinner, there is substantially no effect on reliability.

[0019] This configuration makes it possible to provide a semiconductor optical device that is excellent in optical characteristics due to its excellent heat dissipation properties while ensuring reliability.

[0020] [Variation 1] FIG. 3 is a schematic cross-sectional view of a modified semiconductor optical device 1 taken along line A-A'. The difference from the above is the shape of the insulating film 26. In this modified example, the thickness of the insulating film 26 near the edge of the surface electrode 20 is greater than the thickness near the striped structure 3. That is, a portion of the thick region of the insulating film 26 overlaps a portion of the edge of the surface electrode 20. This structure is advantageous from the viewpoint of manufacturability. The manufacturing procedure for the semiconductor optical device 1 involves forming the buried layer 30 and the semiconductor multilayer, disposing the insulating film 26, and then disposing the surface electrode 20 on the insulating film 26. In the above example, the edge of the surface electrode 20 and the boundary where the thickness of the insulating film 26 changes coincide. However, this may not occur due to manufacturing variations. In such cases, for example, the surface electrode 20 may not overlap the thin region of the insulating film 26. As mentioned above, a thin insulating film 26 may result in reduced reliability. To avoid a structure in which the thin region of the insulating film 26 is not covered by the surface electrode 20 due to manufacturing variations, in this modification, the thickness of the insulating film 26 near the edge of the surface electrode 20 is intentionally set to the same thickness as the region not overlapping with the surface electrode 20. This configuration reduces the possibility that the thin region of the insulating film 26 does not overlap with the surface electrode 20. Although this embodiment is inferior to the first embodiment in terms of heat dissipation, the boundary where the thickness changes is located away from the striped structure 3, so the impact is small. The position of the boundary where the thickness of the insulating film 26 changes may be determined taking manufacturing variations into consideration. Specifically, it is preferable that the region where the thin insulating film 26 and the surface electrode 20 overlap occupy at least 50% of the area of ​​the surface electrode 20. Furthermore, it is preferable that the length of the AA' cross section of the region where the thin insulating film 26 and the surface electrode 20 overlap is 10 μm or more on one side of the striped structure 3. The length of the AA' cross section of the region where the surface electrode 20 and the thick insulating film 26 overlap may be, for example, 3 μm. [Second embodiment]

[0021] FIG. 4 is a schematic cross-sectional view of a semiconductor optical device 201 according to the second embodiment taken along line A-A' in FIG. 1. The second embodiment differs from the first embodiment in that the insulating film in the first embodiment is integrally formed from a single material, whereas the second embodiment includes a first insulating layer formed in a thin region of the insulating film 26 and a second insulating layer formed in a thick region of the insulating film 26 from a material different from that of the first insulating layer. As shown in FIG. 4, the semiconductor optical device 201 according to the second embodiment includes a first insulating layer 27 overlapping the front electrode 20 and a second insulating layer 28 disposed in a region not overlapping the front electrode 20. The first insulating layer 27 and the second insulating layer 28 are made of different materials. For example, the first insulating layer 27 is a silicon nitride film, and the second insulating layer 28 is a silicon oxide film. The two may be reversed, or one of the insulating layers may be aluminum oxide.

[0022] In the first embodiment, two regions of different thicknesses must be formed in the insulating film 26 made of a single material. There are several manufacturing methods for forming these two regions of different thicknesses, including a method in which a thick insulating film 26 is formed and then thinned by etching only the region overlapping the surface electrode 20. This manufacturing method involves a concern that stable film thickness control may be impossible because the amount of etching depends on the etching time. On the other hand, in the second embodiment, the region of the insulating film 26 overlapping the surface electrode 20 and the region not overlapping the surface electrode 20 are made of different materials. Therefore, the first insulating layer 27 and the second insulating layer 28 can be formed separately, allowing them to be formed to the desired thickness. This enables stable film thickness control. It goes without saying that the second embodiment also achieves the same effects as the first embodiment. In particular, since silicon nitride has better thermal conductivity than silicon oxide, using silicon nitride for the first insulating layer 27 and silicon oxide for the second insulating layer 28 can provide a semiconductor optical device with superior heat dissipation. Similarly, since aluminum oxide has better thermal conductivity than silicon oxide, the first insulating layer 27 may be made of aluminum oxide.

[0023] [Variation 1] 5 is a schematic cross-sectional view taken along line A-A' of a modified semiconductor optical device 201. The difference from the above is that a portion of the second insulating layer 28 overlaps with the end of the front surface electrode 20. As explained in FIG. 3, it is undesirable from the viewpoint of reliability if the thin first insulating layer 27 that does not overlap with the front surface electrode 20 is exposed. This modified semiconductor optical device 201 can be provided with excellent manufacturability.

[0024] [Third embodiment] FIG. 6 is a schematic cross-sectional view of a semiconductor optical device 301 according to the third embodiment taken along line A-A' in FIG. 1. This embodiment differs from the second embodiment in that the first insulating layer 27 is disposed in an area that does not overlap with the surface electrode 20. As shown in FIG. 6, the first insulating layer 27 disposed in an area that does not overlap with the surface electrode 20 is disposed below the second insulating layer 28. The second insulating layer 28 is disposed in an area that does not overlap with the surface electrode 20. In the second embodiment, the position of the boundary between the first insulating layer 27 and the second insulating layer 28 is affected by manufacturing variations. For example, the manufacturing procedure for the structure shown in FIG. 5 may involve forming the first insulating layer 27 in a desired area, then masking the area where the first insulating layer 27 was formed. Then, the second insulating layer 28 is formed in the unmasked area. However, depending on the accuracy of mask alignment, the boundary of the masked area may not be aligned with the edge of the first insulating layer 27. If this misalignment occurs, the second insulating layer 28 may not be formed, leaving the semiconductor layer (in this case, the buried layer 30) exposed. However, in this structure, because the surface of the semiconductor optical device 301 is covered with the first insulating layer 27, the semiconductor layer will not be exposed even if the formation position of the second insulating layer 28 is misaligned. This allows for a highly reliable semiconductor optical device. Furthermore, after the first insulating layer 27 and the second insulating layer 28 are successively formed, the difference in wet etching rate can be utilized to remove only the second insulating layer 28. By using an etchant with a fast etching rate only for the second insulating layer 28, it is possible to remove only the second insulating layer 28 below the surface electrode 20 using a mask with an opening in the area of ​​the surface electrode 20. In other words, the same mask can be used to determine the shape of the second insulating layer 28 and the surface electrode 20, resulting in excellent manufacturability.

[0025] [Variation 1] 7 is a schematic cross-sectional view taken along line A-A' of a modified semiconductor optical device 301 of the third embodiment. The difference from the above is that a portion of the second insulating layer 28 overlaps with an end portion of the surface electrode 20. Even in the above structure, there is a concern that, due to manufacturing variations, there may be an area where the thin first insulating layer 27 does not overlap with either the surface electrode 20 or the second insulating layer 28. In this modified example, as with the effects described above, the thick second insulating layer 28 is disposed in the area not covered by the surface electrode 20, making it possible to provide a semiconductor optical device with excellent reliability.

[0026] [Fourth embodiment] 8 is a schematic cross-sectional view of a semiconductor optical device 401 according to the fourth embodiment taken along line A-A' in FIG. 1. The difference from the third embodiment is that a first insulating layer 27 is formed on a second insulating layer 28 in a region where the insulating film 26 does not overlap with the surface electrode 20. Specifically, as shown in FIG. 8, the first insulating layer 27 disposed in a region where the insulating film 26 does not overlap with the surface electrode 20 is disposed on the second insulating layer 28. This structure can prevent the formation of a region where the semiconductor layer (the buried layer 30 in this embodiment) is not covered with the insulating film 26, as in the third embodiment.

[0027] [Variation 1] 9 is a schematic cross-sectional view taken along line A-A' according to Modification 1 of the semiconductor optical device 401 of the fourth embodiment. The difference from FIG. 8 is that a portion of the second insulating layer 28 overlaps with an end of the front surface electrode 20. Even in the structure of the fourth embodiment, there is a concern that, due to manufacturing variations, there may be an area where the thin first insulating layer 27 does not overlap with either the front surface electrode 20 or the second insulating layer 28. As with the effects described above, this modification provides a semiconductor optical device with excellent reliability by disposing the thick second insulating layer 28 in the area where the thin first insulating layer 27 is not covered with the front surface electrode 20.

[0028] [Variation 2] FIG. 10 is a schematic cross-sectional view of a semiconductor optical device 401 according to a second modification of the fourth embodiment, taken along line A-A'. This modification differs from FIG. 9 in that only the second insulating layer 28 is formed in the region where the insulating layer 26 and the surface electrode 20 do not overlap. That is, only the first insulating layer 27 is formed below the surface electrode 20, except near the edge. On the other hand, both the first insulating layer 27 and the second insulating layer 28 are formed at the edge of the surface electrode 20, with the first insulating layer 207 disposed on the second insulating layer. Furthermore, only the second insulating layer 28 is formed in the region where the surface electrode 20 does not overlap. This configuration has two advantages. The first advantage is that it is advantageous in terms of stress. The insulating film 26 can be a stress factor for the semiconductor layer. Generally, the stress is greater when the film is thicker. In this second modification, the thickness of the insulating film 26 in the region where the surface electrode 20 does not overlap is thinner than in FIGS. 6 to 9. This configuration minimizes stress while still providing the advantage of ensuring that the surface of the semiconductor layer is covered with the insulating film 26.

[0029] The second advantage is the stabilization of the shape of the surface electrode 20. One method for manufacturing the surface electrode 20 is to form an electrode over the entire surface and then remove excess areas to achieve the desired shape. The manufacturing procedure for this modification is as follows: First, the semiconductor layer (i.e., each layer up to the buried layer 30 and the contact layer 35) is formed. Next, the second insulating layer 28 is formed in the desired area. Next, the first insulating layer 27 is formed over the entire surface. At this point, the first insulating layer 27 is formed on the second insulating layer 28, even in areas that will not overlap with the future surface electrode 26 (similar to the state without the surface electrode 20 in Figure 9). Next, an electrode is formed over the entire surface of the first insulating layer 27. The electrode is formed by, for example, evaporation. Next, the area that will eventually become the surface electrode 20 is masked, and the electrode in the unmasked area is removed. The electrode is removed by milling or other methods. At this time, it is possible to remove only the electrode and leave the first insulating layer 27, but due to variations within the wafer surface, there is a risk that areas where the electrode is not completely removed may occur. As a result, the shape of the surface electrode 20 may become unstable across the entire wafer. Therefore, by removing the first insulating layer 27 at the same time as removing the electrode, it is possible to reliably eliminate the possibility of the electrode remaining. While part of the second insulating layer 28 may also be removed, this is not a problem as long as the second insulating layer 28 is formed thick enough to ultimately function as a protective film. Furthermore, because the second insulating layer 28 is located away from the striped structure 3, even if it is slightly thick, its impact on heat dissipation is minimal. Therefore, the structure of this modified example offers the following advantages. First, by configuring the insulating film 26 in the region overlapping the surface electrode 20 to include only the thin first insulating layer 27, heat dissipation is improved, thereby improving the characteristics of the semiconductor optical device 401. Furthermore, by configuring the insulating film 26 in the region not overlapping the surface electrode 20 to include only the second insulating layer 28, which is thicker than the first insulating layer 27, reliability is improved. Moreover, since the first insulating layer 27 and the second insulating layer 28 overlap at the end of the second insulating layer 28, it is possible to prevent the formation of a region in the semiconductor layer (here, the buried layer 30) that is not covered by the insulating film 26 due to the influence of manufacturing variations. Furthermore, it is possible to stabilize the shape formation of the surface electrode 20.

[0030] [Fifth embodiment] FIG. 11 is a schematic cross-sectional view of a semiconductor optical device 501 according to the fifth embodiment, taken along line A-A' in FIG. 1. A feature of this embodiment is that the first insulating layer 27 is disposed on the side of the striped structure 3. The semiconductor optical device 501 is a ridge-type semiconductor optical device. The mesa striped structure 3 is formed of a second-conductivity cladding layer 25 including a diffraction grating layer 33 and a contact layer 35. Similar semiconductor multilayers are disposed on both sides of the striped structure 3. The first-conductivity optical confinement layer 22, the active layer 23, and the second-conductivity optical confinement layer 24 are disposed broadly on the substrate 21. As in the other embodiments, the insulating film 26 overlapping the front electrode 20 near the striped structure 3 includes only the first insulating layer 27. The side of the striped structure 3 is also covered with the first insulating layer 27. In the region not overlapping the front electrode 20, the insulating film 26 includes only the second insulating layer 28. Near the end of the surface electrode 20, the insulating film 26 includes a first insulating layer 27 and a second insulating layer 28. In the region close to the striped structure 3, the insulating film 26 includes only the thin first insulating layer 27, making it possible to provide a semiconductor optical device 501 with excellent heat dissipation properties. Furthermore, the configuration of the insulating film 26 at the end of the surface electrode 20 and in the region not covered by the surface electrode 20 may be the same as that of the other embodiments and modifications described above.

[0031] [Variation 1] FIG. 12 is a schematic cross-sectional view of a modified semiconductor optical device 501 of the fifth embodiment taken along line A-A'. The difference from FIG. 11 is that a second insulating layer 28 is also disposed on a portion of the side surface of the striped structure 3. A feature of this modified example is that the second insulating layer 28 is disposed below the side surface of the striped structure 3, between the side surface of the striped structure 3 and the first insulating layer 27. In a conventional ridge-type semiconductor optical device, the insulating film 26 covering the side surface of the striped structure 3 has the same thickness in the region overlapping with the surface electrode 20 and the region not overlapping with it. Therefore, the insulating film 26 on the side surface of the striped structure 3 is thick enough to function as a protective layer. Therefore, when considering the loss of the guided mode, the leakage of the guided mode into the insulating film 26 is sufficiently small at the boundary between the insulating film 26 and the surface electrode 20. However, in the fifth embodiment, the insulating film 26 is thinner than the protective layer to improve heat dissipation. This increases the leakage of the guided mode into the surface electrode 20, which may increase the loss of the guided mode. Therefore, in this modification, the insulating film 26 covering the striped structure 3 is thicker only on the side of the active layer 23, which is the center of light. Specifically, the lower part of the side of the striped structure 3 is covered with both the first insulating layer 27 and the second insulating layer 28, and the upper part is covered only with the first insulating layer 27. The second insulating layer 28 is thick enough to function as a protective layer, thereby suppressing the leakage of the waveguide mode to the surface electrode 20. While the structure shown in FIG. 11 is superior in terms of heat dissipation, this modification may be superior when optical properties are also taken into account. The choice of either structure should be determined based on the operating temperature and required characteristics. Note that the width of the second insulating layer 28 covering the side of the striped structure 3 can be determined based on the required characteristics. However, covering more than half the height of the striped structure 3 can reduce waveguide mode loss. Alternatively, the entire side of the striped structure 3 may be covered with the second insulating layer 28. Even with this structure, the area slightly away from the striped structure 3 is covered only with the first insulating layer 27, thereby improving heat dissipation.

[0032] The present invention is not limited to the above-described embodiments and various modifications are possible. For example, the semiconductor optical element is not limited to the above-described examples and may be an electroabsorption modulator, an MZ modulator, an amplifier, or a light receiving element. In the case of these semiconductor optical elements, the optical functional layer functions as an absorption layer. [Explanation of symbols]

[0033] 1 semiconductor optical element, 3 stripe structure, 11 low-reflection end face coating film, 12 high-reflection end face coating film, 20 front surface electrode, 21 substrate, 22 first conductivity type optical confinement layer, 23 active layer, 24 second conductivity type optical confinement layer, 25 second conductivity type cladding layer, 26 insulating film, 27 first insulating layer, 28 second insulating layer, 30 buried layer, 31 back electrode, 33 diffraction grating layer, 35 contact layer, 201 semiconductor optical element, 301 semiconductor optical element, 401 semiconductor optical element, 501 semiconductor optical element.

Claims

1. A substrate; a semiconductor multilayer formed on the substrate and including an optical functional layer; an insulating film formed on the semiconductor multilayer; an electrode formed on a portion of the insulating film, the insulating film covers the semiconductor multilayer except for a region where the semiconductor multilayer and the electrode are electrically connected, and at least a part of the region overlapping with the electrode is thinner than a region not overlapping with the electrode; The semiconductor multilayer includes a stripe structure and buried layers formed on both sides of the stripe structure. Semiconductor optical element.

2. 2. The semiconductor optical device according to claim 1, The thick region of the insulating film overlaps a part of an end of the electrode.

3. 3. The semiconductor optical device according to claim 1, The insulating film is integrally formed of a single material.

4. 3. The semiconductor optical device according to claim 1, The insulating film includes a first insulating layer formed in the thin region and a second insulating layer formed in the thick region from a material different from that of the first insulating layer.

5. 5. The semiconductor optical device according to claim 4, The semiconductor optical device, wherein the first insulating layer is formed in a region that does not overlap with the electrode.

6. 6. The semiconductor optical device according to claim 5, The first insulating layer, which is disposed in a region not overlapping with the electrode, is disposed below the second insulating layer.

7. 6. The semiconductor optical device according to claim 5, The first insulating layer, which is disposed in a region not overlapping with the electrode, is disposed on the second insulating layer.

8. 8. The semiconductor optical device according to claim 7, The semiconductor optical device, wherein the first insulating layer is disposed on the second insulating layer at the end of the electrode.

9. A substrate; a semiconductor multilayer formed on the substrate and including an optical functional layer; an insulating film formed on the semiconductor multilayer; an electrode formed on a portion of the insulating film, the insulating film covers the semiconductor multilayer except for a region where the semiconductor multilayer and the electrode are electrically connected, and at least a part of the region overlapping with the electrode is thinner than a region not overlapping with the electrode; the insulating film includes a first insulating layer formed in the thin region and a second insulating layer formed in the thick region from a material different from that of the first insulating layer, the semiconductor multilayer includes a stripe structure; the first insulating layer is disposed on a side surface of the stripe structure; The semiconductor optical device, wherein the second insulating layer is disposed below the side surface of the striped structure, between the side surface of the striped structure and the first insulating layer.

10. 10. The semiconductor optical device according to claim 1, The thin region of the insulating film includes a silicon nitride film or an aluminum oxide film.

11. 11. The semiconductor optical device according to claim 1, The thick region of the insulating film includes a silicon oxide film.

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