CN116131094A - Optical semiconductor device - Google Patents

Abstract

An optical semiconductor device includes a substrate, a semiconductor multilayer formed over the substrate and including an optical functional layer, an insulating film formed over the semiconductor multilayer, and an electrode formed over 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 to each other. At least a portion of the insulating film in a region overlapping with the electrode is thinner than a region of the insulating film not overlapping with the electrode.

Description

Optical semiconductor device

Cross Reference to Related Applications

The present application claims priority from Japanese patent applications JP2022-020198, filed on 14 months 2, 2022, and JP2021-185154 filed on 12 months 11, 2021, the contents of which are incorporated herein by reference.

Technical Field

The present disclosure relates generally to optical semiconductor devices.

Background

An optical semiconductor device for optical communication may include an optical functional layer that converts electricity into light or converts light into electricity. For example, the laser and external modulator may include optical functional layers using multiple quantum well layers. Further, in the light receiving element, the optical functional layer may be formed of a semiconductor absorption layer. In many cases, the optical semiconductor device may include an electrode made of metal so as to apply a voltage to the optical functional layer, wherein a portion of the electrode is electrically and physically connected to the semiconductor layer. Further, the optical semiconductor device may include an insulating film disposed on a surface of the semiconductor layer on which no metal is disposed for protection purposes.

Disclosure of Invention

When the optical semiconductor device is driven, the optical functional layer and other semiconductor layers, electrodes, and the like of the optical semiconductor device generate heat. The generated heat degrades the characteristics of the optical semiconductor device. For example, a continuous wave laser (CW laser) that outputs continuous light has a light output characteristic as its main characteristic. The light output is expected to be large, and at the same driving current, the light output increases as the temperature of the optical semiconductor device decreases. In an environment where the external temperature is constant, when a large amount of heat generated by the optical semiconductor device is released to the outside, the effective temperature of the optical semiconductor device decreases and the light output increases. In other optical semiconductor devices and CW lasers, it is important to release a large amount of heat generated by the optical semiconductor devices to the outside.

As described above, the optical semiconductor device may include the metal electrode and the insulating film (protective film). The electrode may be made of metal, and thus may have high thermal conductivity, and may provide excellent heat dissipation. The insulating film may be an oxide film or a silicon nitride film. These materials have lower thermal conductivity than semiconductors and metals, which may inhibit the generated heat from being released to the outside.

Further, the connection region between the electrode and the semiconductor layer may be limited to a narrow region. For example, in an optical semiconductor device having a stripe structure (stripe structure), a contact point between an electrode and a semiconductor layer is limited to only an upper surface of the stripe structure. However, from the standpoint of heat dissipation, the electrodes extend to a region wider than the width of the bar-shaped structure. In this case, the insulating film is provided in order to realize insulation between the electrode and the semiconductor layer provided on the region other than the region on the stripe structure.

Therefore, an insulating film is widely arranged on the surface of the semiconductor layer except for a small partial region, and an electrode is arranged on the insulating film. Therefore, the wide insulating film is located in a path for releasing heat generated in the semiconductor layer to the outside. As a result, the heat dissipation amount is limited, which becomes a factor that degrades the characteristics of the optical semiconductor device.

Some embodiments disclosed herein address the above stated problems and provide an optical semiconductor device that provides improved heat dissipation.

In some embodiments, an optical semiconductor device includes a substrate; a semiconductor multilayer formed on a substrate and including an optical functional layer; an insulating film formed over 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 to each other, and wherein at least a portion of a region of the insulating film overlapping the electrode is thinner than a region of the insulating film not overlapping the electrode.

In some embodiments, the optical semiconductor device provides excellent heat dissipation.

Drawings

Fig. 1 is a top view of an example of an optical semiconductor device according to a first exemplary embodiment of the present invention.

Fig. 2 is a schematic cross-sectional view taken along line A-A' of the optical semiconductor device shown in fig. 1.

Fig. 3 is a schematic cross-sectional view taken along line A-A' of fig. 1 of a modified example 1 of an optical semiconductor device according to a first exemplary embodiment of the present invention.

Fig. 4 is a schematic cross-sectional view taken along line A-A' of fig. 1 of an optical semiconductor device according to a second exemplary embodiment of the present invention.

Fig. 5 is a schematic cross-sectional view taken along line A-A' of fig. 1 of a modified example 1 of an optical semiconductor device according to a second exemplary embodiment of the present invention.

Fig. 6 is a schematic cross-sectional view taken along line A-A' of fig. 1 of an optical semiconductor device according to a third exemplary embodiment of the present invention.

Fig. 7 is a schematic cross-sectional view taken along line A-A' of fig. 1 of a modified example 1 of an optical semiconductor device according to a third exemplary embodiment of the present invention.

Fig. 8 is a schematic cross-sectional view taken along line A-A' of fig. 1 of an optical semiconductor device according to a fourth exemplary embodiment of the present invention.

Fig. 9 is a schematic cross-sectional view taken along line A-A' of fig. 1 of a modified example 1 of an optical semiconductor device according to a fourth exemplary embodiment of the present invention.

Fig. 10 is a schematic cross-sectional view taken along line A-A' of fig. 1 of a modified example 2 of an optical semiconductor device according to a fourth exemplary embodiment of the present invention.

Fig. 11 is a schematic cross-sectional view taken along line A-A' of fig. 1 of an optical semiconductor device according to a fifth exemplary embodiment of the present invention.

Fig. 12 is a schematic cross-sectional view taken along line A-A' of fig. 1 of a modified example 1 of an optical semiconductor device according to a fifth exemplary embodiment of the present invention.

Detailed Description

Some embodiments are described in detail below with reference to the accompanying drawings. In the drawings, the same members are denoted by the same reference numerals and have the same or equivalent functions, and repeated description thereof may be omitted for simplicity. Note that the figures referred to below are for illustration of exemplary embodiments only and are not necessarily drawn to scale.

Fig. 1 is a top view of an optical semiconductor device 1 according to a first exemplary embodiment of the present invention. Fig. 2 is a schematic cross-sectional view taken along line A-A' of fig. 1. Here, the optical semiconductor device 1 is an edge-emitting CW laser. The optical semiconductor device 1 may comprise a stripe structure 3. The top electrode 20 may be disposed on the surface of the optical semiconductor device 1. The top electrode 20 may be an electrode formed on a part of the insulating film 26, and is a metal film containing Au, for example. The metal film may be formed of a variety of materials. In addition, on the upper surface of the optical semiconductor device 1, an insulating film 26 may be disposed in a region other than the top electrode 20. As shown in fig. 2, an insulating film 26 may also be disposed under the top 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. The low reflection end face coating film 11 may be disposed on the end face on the left side of fig. 1, and the high reflection end face coating film 12 may be disposed on the end face on the right side of fig. 1. The coating film may be merely an example, and the low reflection end surface coating film may be disposed on both end surfaces.

As shown in fig. 2, in the optical semiconductor device 1, the stripe-shaped structure 3 may be formed on the first conductive type substrate 21. The buried layer 30 may be arranged on each side of the bar-shaped structure 3. The buried layer 30 may be a semi-insulating semiconductor layer or a semiconductor layer in which a plurality of p-type and n-type semiconductor layers may be combined. The insulating film 26 may be disposed on an upper surface of the buried layer 30. The stripe-shaped structure 3 may be formed on a portion of the substrate 21 so as to include a plurality of semiconductor layers. The plurality of semiconductor layers may be formed to include, from the bottom, the first conductivity-type optical confinement layer 22, the active layer 23 (optical function layer) formed of the multiple quantum well layer, the second conductivity-type optical confinement layer 24, the second conductivity-type cladding layer 25, and the contact layer 35. The diffraction grating layer 33 may be formed in the middle of the second conductive type cladding layer 25. The bar structure 3 may or may not comprise a portion of the substrate 21. The layer from the first conductivity type optical confinement layer 22 to the contact layer 35 may be hereinafter referred to as "semiconductor multilayer". Further, in the first example embodiment, the semiconductor multilayer may include the stripe-shaped structure 3 and the buried layer 30 formed on each side of the stripe-shaped structure 3. The rear electrode 31 may be disposed at the rear side of the substrate 21. In the first exemplary embodiment, the semiconductor multilayer may be a CW laser corresponding to a 1.3 μm wavelength band. However, the embodiments described herein may not be limited thereto, and the wavelength band of the laser light output by the semiconductor multilayer may be another wavelength band. Further, an insulating substrate may be used as the substrate 21. In this case, it may be necessary to dispose a first conductive type semiconductor layer between the substrate 21 and the stripe-shaped structure 3, and the substrate 21 may be an insulating substrate.

In some embodiments, the insulating film 26 may cover the semiconductor multilayer except for a region where the semiconductor multilayer and the top electrode 20 may be electrically connected to each other, and at least a portion of a region of the insulating film 26 overlapping the top electrode 20 may be thinner than a region of the insulating film 26 not overlapping the top electrode 20. In the first example embodiment, as shown in fig. 2, the thickness of the insulating film 26 may be different between a region where the top electrode 20 and the buried layer 30 overlap each other and a region where the top electrode 20 and the buried layer 30 do not overlap each other. The region of the insulating film 26 overlapping the top electrode 20 may be thinner than the region of the insulating film 26 not overlapping the top electrode 20.

In the optical semiconductor device 1, when a voltage (injection current) is applied between the top electrode 20 and the rear electrode 31, the active layer 23 can emit light. In addition to light emission, the active layer 23 may generate heat. In addition, other semiconductor layers may also generate heat due to the flow of current. The heat generated in the semiconductor multilayer can be released to the outside through the substrate 21 and the buried layer 30. In the optical semiconductor device 1 of the first exemplary embodiment, the stripe-shaped structure 3 may be formed on the top surface side of the substrate 21. For example, the distance from the top electrode 20 to the active layer 23 may be several micrometers, while the distance from the active layer 23 to the rear electrode 31 may be as thick as several tens of micrometers to 100 micrometers. Therefore, the generated heat can be released to the external environment more largely on the top electrode 20 side than on the rear electrode 31 side. Further, the amount of heat generation becomes larger at a position closer to the active layer 23, and thus most of the generated heat can be released from the top electrode 20 side. A portion of the heat may pass through the strip-shaped structures 3 and may be directly released from the top electrode 20. However, as a heat dissipation path, there may be a path leading to the top electrode 20 through the buried layer 30, in addition to the foregoing.

An insulating film 26 may be disposed between the top electrode 20 and the buried layer 30. The insulating film 26 may be a silicon oxide film, a silicon nitride film, an aluminum oxide film, or the like, in which the thermal conductivity may be smaller than that of the semiconductor multilayer as described above. Therefore, the insulating film 26 disposed between the top electrode 20 and the buried layer 30 may hinder heat dissipation. However, in the first example embodiment, the insulating film 26 in the region overlapping with the top electrode 20 may be formed thin. The insulating film 26 in this region may be, for example, 100 nm or less. Therefore, heat can be released to the outside without significantly reducing heat dissipation.

Meanwhile, the insulating film 26 in the region not overlapping with the top electrode 20 may be provided in several hundred nanometers. When the thickness of the insulating film 26 in the region not overlapping the top electrode 20 is set to be the same as the thickness of the region overlapping the top electrode 20, there may be a risk that the function of the insulating film 26 as a protective film in the region not overlapping the top electrode 20 may not be sufficiently obtained, and there may be a risk that the reliability of the optical semiconductor device 1 may be affected. Further, in the region where the top electrode 20 is arranged, the top electrode 20 serves as a protective film, and thus the reliability is not significantly affected even if the insulating film 26 is thinned.

With this configuration, an optical semiconductor device having excellent optical characteristics due to excellent heat dissipation can be provided while ensuring reliability.

Fig. 3 is a schematic cross-sectional view taken along the line A-A' of fig. 1 of modified example 1 of the optical semiconductor device 1. The difference from the foregoing is in the shape of the insulating film 26. In modification 1, the thickness of the insulating film 26 near each end of the top electrode 20 is larger than that near the bar-shaped structure 3. That is, a part of the thick region of the insulating film 26 overlaps a part of the end of the top electrode 20. Such a structure may be excellent from the viewpoint of manufacturability. In the manufacturing process of the optical semiconductor device 1, after forming the buried layer 30 and the semiconductor multilayer and disposing the insulating film 26, the top electrode 20 may be disposed on the insulating film 26. In the above, the end portion of the top electrode 20 and the boundary of the thickness variation of the insulating film 26 are matched with each other, but such matching may not be obtained due to manufacturing variations. In this case, for example, the top electrode 20 may not overlap with the thin region of the insulating film 26. As described above, when the insulating film 26 is thin, there may be a concern that the reliability may be lowered. In order to avoid a structure in which a thin region of the insulating film 26 is not covered by the top electrode 20 due to manufacturing variations, in modification 1, the thickness of the insulating film 26 near the end of the top electrode 20 may be intentionally set to be the same as the thickness of a region that does not overlap with the top electrode 20. With this configuration, the risk that the thin region of the insulating film 26 may not overlap with the top electrode 20 can be reduced. Although modification 1 may provide less heat dissipation than the first exemplary embodiment, the influence may be small because the boundary of the thickness change is a region away from the bar-shaped structure 3. The position of the boundary of the thickness variation of the insulating film 26 can be determined in consideration of the manufacturing variation. Specifically, it may be desirable to set the area where the thin insulating film 26 and the top electrode 20 overlap each other to at least 50% or more of the area of the top electrode 20. Further, it may be desirable that the length in the A-A' section of the region where the thin insulating film 26 and the top electrode 20 overlap each other is ensured to be 10 μm or more on one side of the stripe structure. The length of the A-A' section of the region where the top electrode 20 and the thick insulating film 26 overlap each other may be, for example, 3 micrometers.

Fig. 4 is a schematic cross-sectional view of an optical semiconductor device 201 according to a second exemplary embodiment of the present invention, taken along line A-A' of fig. 1. The difference from the first exemplary embodiment is that the insulating film in the first exemplary embodiment is integrally formed of a single material, whereas in the second exemplary embodiment, the insulating film 26 may include 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, the second insulating layer having a material different from that of the first insulating layer. As shown in fig. 4, the optical semiconductor device 201 according to the second exemplary embodiment may include a first insulating layer 27 that may overlap the top electrode 20 and a second insulating layer 28 disposed in a region that does not overlap the top electrode 20. Here, the first insulating layer 27 and the second insulating layer 28 may be made of materials different from each other. For example, the first insulating layer 27 may be a silicon nitride film, and the second insulating layer 28 may be a silicon oxide film. Alternatively, the first insulating layer 27 may be a silicon oxide film, and the second insulating layer 28 may be a silicon nitride film. Still alternatively, any one of the first insulating layer 27 and the second insulating layer 28 may be made of aluminum oxide.

In the first exemplary embodiment, it may be desirable to form two regions having different thicknesses in the insulating film 26 made of one material. There are several production methods available to form two regions with different thicknesses. For example, there may be a method including thinning only a region of the insulating film 26 formed thick by etching, which may overlap with the top electrode 20. In the case of such a production method, the etching amount depends on the etching time, and thus there may be a concern that stable film thickness control cannot be performed. Meanwhile, in the second exemplary embodiment, the region of the insulating film 26 overlapping the top electrode 20 and the region of the insulating film 26 not overlapping it may be made of different materials. Accordingly, the first insulating layer 27 and the second insulating layer 28 can be formed separately, and thus each insulating layer can be formed to a desired thickness. As a result, stable film thickness control can be performed. Needless to say, the effects described in the first exemplary embodiment can also be obtained in the second exemplary embodiment. In particular, the silicon nitride film can provide a larger thermal conductivity than the silicon oxide film, and thus an optical semiconductor device that can provide a larger heat dissipation can be provided by using the silicon nitride film as the first insulating layer 27 and the silicon oxide film as the second insulating layer 28. Similarly, the aluminum oxide film may provide greater thermal conductivity than the silicon oxide film, and thus the first insulating layer 27 may be made of aluminum oxide.

Fig. 5 is a schematic cross-sectional view taken along line A-A' of fig. 1 of modified example 1 of the optical semiconductor device 201. A difference from the foregoing is that a portion of the second insulating layer 28 may overlap with an end portion of the top electrode 20. As described with reference to fig. 3, it may be undesirable from a reliability standpoint that the thin first insulating layer 27 that does not overlap the top electrode 20 is exposed. According to modification example 1, an optical semiconductor device 201 excellent in manufacturability can be provided.

Fig. 6 is a schematic cross-sectional view of an optical semiconductor device 301 according to a third exemplary embodiment of the present invention, taken along line A-A' of fig. 1. The difference from the second exemplary embodiment is that the first insulating layer 27 may be disposed to a region not overlapping with the top electrode 20. As shown in fig. 6, a first insulating layer 27 disposed in a region not overlapping with the top electrode 20 may be disposed under the second insulating layer 28. The second insulating layer 28 may be disposed in a region that does not overlap the top electrode 20. In the second exemplary embodiment, the boundary position between the first insulating layer 27 and the second insulating layer 28 may be affected by manufacturing variations. In the manufacturing process of the structure shown in fig. 5, for example, after the first insulating layer 27 is formed in a desired region, a region in which the first insulating layer 27 may be formed may be masked. Then, the second insulating layer 28 may be formed in a region that may not be masked. However, due to alignment accuracy of the mask, the boundary of the region to be masked and the position of the end portion of the first insulating layer 27 may be displaced from each other. In the event of displacement, there may be a risk that the second insulating layer 28 cannot form, and the semiconductor layer (in this case the buried layer 30) may remain exposed. However, in this structure, the surface of the optical semiconductor device 301 may be covered with the first insulating layer 27, and thus the semiconductor layer is not exposed even when the formation position of the second insulating layer 28 is displaced. Therefore, an optical semiconductor device excellent in reliability can be provided. Further, as a method involving removing only the second insulating layer 28 after continuously forming the first insulating layer 27 and the second insulating layer 28, a difference in wet etching rate may be utilized. When an etchant having a high etching rate with respect to only the second insulating layer 28 is used, only the second insulating layer 28 under the top electrode 20 can be removed by using a mask having an opening portion corresponding to the top electrode 20. That is, as a mask for determining each shape of the second insulating layer 28 and the top electrode 20, the same mask may be used, which may be desirable in terms of manufacturability.

Fig. 7 is a schematic cross-sectional view taken along line A-A' of fig. 1 of modified example 1 of the optical semiconductor device 301 of the third exemplary embodiment. A difference from the foregoing is that a portion of the second insulating layer 28 may overlap with an end portion of the top electrode 20. Further, in the above-described structure, there may be a fear that a region where the thin first insulating layer 27 may not overlap with any one of the top electrode 20 and the second insulating layer 28 may occur due to manufacturing variations. In modification example 1, in the same manner as the above-described effect, the thick second insulating layer 28 can be arranged in the region not covered by the top electrode 20, and as a result, an optical semiconductor device with excellent reliability can be provided.

Fig. 8 is a schematic cross-sectional view of an optical semiconductor device 401 according to a fourth exemplary embodiment of the present invention, taken along the line A-A' of fig. 1. The difference from the third exemplary embodiment is that the first insulating layer 27 may be formed on the second insulating layer 28 in a region where the insulating film 26 does not overlap with the top electrode 20. Specifically, as shown in fig. 8, a first insulating layer 27 disposed in a region not overlapping with the top electrode 20 may be disposed on the second insulating layer 28. According to this structure, it is possible to prevent the formation of the region where the semiconductor layer (the buried layer 30 in the fourth exemplary embodiment) is not covered with the insulating film 26 in the same manner as the third exemplary embodiment.

Fig. 9 is a schematic cross-sectional view of a modified example 1 of an optical semiconductor device 401 of the fourth exemplary embodiment, taken along the line A-A' of fig. 1. A difference from fig. 8 is that a portion of the second insulating layer 28 may overlap with an end portion of the top electrode 20. Further, in the structure of the fourth exemplary embodiment, there may be a fear that a region where the thin first insulating layer 27 does not overlap with any one of the top electrode 20 and the second insulating layer 28 may occur due to manufacturing variations. In modification example 1, in the same manner as the above-described effect, the thick second insulating layer 28 can be arranged in the region where the thin first insulating layer 27 is not covered by the top electrode 20, and as a result, an optical semiconductor device with excellent reliability can be provided.

Fig. 10 is a schematic cross-sectional view taken along line A-A' of fig. 1 of a modified example 2 of an optical semiconductor device 401 according to a fourth exemplary embodiment. The difference from fig. 9 is that only the second insulating layer 28 may be formed in a region where the insulating film 26 and the top electrode 20 do not overlap each other. That is, only the first insulating layer 27 may be formed under the top electrode 20 except near the end portion. Meanwhile, at an end portion of the top electrode 20, a first insulating layer 27 and a second insulating layer 28 may be formed, and the first insulating layer 27 may be disposed on the second insulating layer 28. Only the second insulating layer 28 may be formed in a region not overlapping with the top electrode 20. This configuration may have two advantages. One of the advantages is advantageous from a stress point of view. The insulating film 26 may serve as a stress factor with respect to the semiconductor layer. In general, when the thickness of the film is large, the stress may be large. In modification 2, the thickness of the insulating film 26 in the region not overlapping with the top electrode 20 may be thinner than that in fig. 6 to 9. Therefore, the generation of stress can be suppressed as much as possible, while the advantage of providing a structure in which the surface of the semiconductor layer is firmly covered with the insulating film 26 can be maintained.

A second advantage is the stability of the shape formation of the top electrode 20. As one of the production methods of the top electrode 20, there may be a method including forming an electrode on the entire surface and then removing unnecessary regions so as to have a desired shape. The manufacturing process of modification example 2 is as follows. First, each layer up to the semiconductor layer (i.e., each layer up to the buried layer 30 and the contact layer 35) may be formed. Next, a second insulating layer 28 may be formed in a desired region. Then, the first insulating layer 27 may be formed on the entire surface. At this point, the first insulating layer 27 may also be formed in a region on the second insulating layer 28 that does not overlap with the top electrode 20 later (the same state as shown in fig. 9 without the top electrode 20). Next, an electrode may be formed on the entire surface of the first insulating layer 27. The method of forming the electrode may be, for example, a deposition method. Next, the region that will become the top electrode 20 may be masked, and the electrode in the unmasked region may be removed. Milling methods and the like may be used to remove the electrodes. In this case, only the electrode may be removed to leave the first insulating layer 27, but there may be a risk that an area where the electrode cannot be sufficiently removed may occur due to a change in the wafer surface. As a result, there may be a risk of the shape of the top electrode 20 being unstable when viewed as a whole wafer. In view of the foregoing, by removing a larger amount of the electrode to such an extent that the first insulating layer 27 is removed at the same time as the electrode is removed, the risk that the electrode may remain can be reliably eliminated. In this case, a part of the second insulating layer 28 may also be removed, but as long as the second insulating layer 28 is also formed thicker so that the thickness that is ultimately used as the protective film is maintained, there is no problem. Then, the second insulating layer 28 may be a region distant from the bar-shaped structure 3, and thus heat dissipation is less affected even when the second insulating layer 28 is somewhat thick. Therefore, according to the structure of modification example 2, the following advantages can be obtained. First, when the insulating film 26 is formed such that a large part thereof in a region overlapping with the top electrode 20 includes only the thin first insulating layer 27, heat dissipation can be improved, and characteristics of the optical semiconductor device 401 can be improved. Further, when the insulating film 26 is formed such that the insulating film 26 in a region not overlapping with the top electrode 20 includes only the second insulating layer 28 thicker than the first insulating layer 27, reliability can be improved. Further, the first insulating layer 27 and the second insulating layer 28 can overlap each other at the end portion of the second insulating layer 28, and thus formation of a region where the semiconductor layer (here, the buried layer 30) is not covered with the insulating film 26 due to influence of manufacturing variations can be prevented. In addition, the formation of the shape of the top electrode 20 can be stabilized.

Fig. 11 is a schematic cross-sectional view of an optical semiconductor device 501 according to a fifth exemplary embodiment of the present invention, taken along the line A-A' of fig. 1. The fifth exemplary embodiment is different in that the first insulating layer 27 may be disposed on each side surface of the bar-shaped structure 3. The optical semiconductor device 501 may be a ridge optical semiconductor device. The stripe structure 3 may be formed of the second conductive type cladding layer 25 including the diffraction grating layer 33 and the contact layer 35. Further, similar semiconductor layers may be arranged on each side of the bar-shaped structure 3. The first conductive type optical confinement layer 22, the active layer 23, and the second conductive type optical confinement layer 24 may be widely disposed on the substrate 21. In the same manner as in the other embodiments, the insulating film 26 overlapping the top electrode 20 may include only the first insulating layer 27 in the vicinity of the stripe-shaped structure 3. In addition, the side surfaces of the bar-shaped structures 3 may also be covered with the first insulating layer 27. In the region not overlapping with the top electrode 20, the insulating film 26 may include only the second insulating layer 28. Near the end of the top electrode 20, the insulating film 26 may include a first insulating layer 27 and a second insulating layer 28. In the region close to the stripe-shaped structure 3, the insulating film 26 may include only the thin first insulating layer 27, and thus the optical semiconductor device 501 may provide excellent heat dissipation. Further, the structures of the other embodiments and modified examples described above may be applied to the configuration of the end portion of the top electrode 20 and the insulating film 26 in the region not covered by the top electrode 20.

Fig. 12 is a schematic cross-sectional view taken along the line A-A' of fig. 1 of a modified example 1 of an optical semiconductor device 501 according to a fifth exemplary embodiment. The difference from fig. 11 is that the second insulating layer 28 may also be arranged in a part of the side surface of the bar-shaped structure 3. The modification example 1 is characterized in that the second insulating layer 28 may be disposed between the side surface of the bar-shaped structure 3 and the first insulating layer 27 in the lower portion of the side surface of the bar-shaped structure 3. In the case of the ridge optical semiconductor device of the related art, the insulating film 26 covering each side surface of the stripe structure 3 may have the same thickness between a region overlapping with the top electrode 20 and a region not overlapping therewith. Accordingly, the insulating film 26 on the side surface of the bar-shaped structure 3 may have a thickness sufficient to serve as a protective layer. Therefore, when considering the loss of the waveguide mode, the boundary portion between the insulating film 26 and the top electrode 20 in the insulating film 26, which is permeated by the waveguide mode, may be sufficiently small. However, in the fifth exemplary embodiment, the insulating film 26 may be formed as a thinner layer than the protective layer in order to improve heat dissipation. As a result, the portion of the waveguide mode penetrating into the top electrode 20 becomes large, and there may be a risk that the loss of the waveguide mode may increase. In view of the above, in modification 1, the insulating film 26 covering the stripe-shaped structure 3 may be formed to be thick only on the active layer 23 side, and the active layer 23 side may be the center of light. Specifically, the side surface of the bar-shaped structure 3 may have a structure in which the lower portion is covered with the first insulating layer 27 and the second insulating layer 28, and the upper portion may be covered with only the first insulating layer 27. The second insulating layer 28 may have a thickness that serves as a protective layer, and thus the waveguide mode may be suppressed from penetrating into the top electrode 20 portion. Although the structure shown in fig. 11 is better from the standpoint of heat dissipation, modification example 1 may be better when the optical characteristics are also considered. It may only be necessary to select any one of these structures depending on the operating temperature and the desired characteristics. The width covered by the second insulating layer 28 on the side surfaces of the bar-shaped structures 3 may be determined according to desired characteristics. For example, when half or more of the height of the stripe structure 3 is covered, loss of the waveguide mode can be reduced. Further, the entire side surface of the bar-like structure 3 may be covered with the second insulating layer 28. Even with this structure, the region slightly distant from the bar-shaped structure 3 can be covered with only the first insulating layer 27, and thus an effect of improving heat dissipation can be obtained.

The present invention is not limited to the above-described embodiments, and various modifications may be made thereto. For example, the optical semiconductor device is not limited to the above example, and may be an electro-absorption modulator, an MZ modulator, an amplifier, or a light receiving element. In the case of these optical semiconductor devices, the optical functional layer serves as an absorption layer.

The foregoing disclosure provides illustration and description, but is not intended to be exhaustive or to limit the embodiments to the precise form disclosed. Modifications and variations are possible in light of the above disclosure or may be acquired from practice of the embodiments. Moreover, any of the embodiments described herein can be combined unless the foregoing disclosure explicitly provides a reason for one or more implementations not being combinable.

Even though particular combinations of features are recited in the claims and/or disclosed in the specification, these combinations are not intended to limit the disclosure of the various embodiments. Indeed, many of these features may be combined in ways not specifically set forth in the claims and/or disclosed in the specification. Although each of the dependent claims listed below may depend directly on only one claim, the disclosure of various embodiments includes a combination of each dependent claim with each other claim in the claim set. As used herein, a phrase referring to "at least one" of a series of items refers to any combination of those items, including single components. As an example, "at least one of a, b, or c" is intended to encompass a, b, c, a-b, a-c, b-c, and a-b-c, as well as any combination of a plurality of like items.

No element, act, or instruction used herein should be construed as critical or essential unless explicitly described as such. Furthermore, as used herein, the articles "a" and "an" are intended to include one or more items, and may be used interchangeably with "one or more". Furthermore, as used herein, the article "the" is intended to include, and be used interchangeably with, one or more items associated with the article "the. Furthermore, as used herein, the term "collection" is intended to include one or more items (e.g., related items, unrelated items, or a combination of related and unrelated items), and can be used interchangeably with "one or more". If only one item is referred to, the phrase "only one" or similar language is used. Further, as used herein, the terms "having", and the like are intended to be open terms. Furthermore, the phrase "based on" is intended to mean "based, at least in part, on" unless explicitly stated otherwise. Furthermore, as used herein, the term "or" is inclusive in a series of uses and may be used interchangeably with "and/or" unless otherwise specifically indicated (e.g., if used in conjunction with "either" or "only one"). Further, spatially relative terms, such as "below," "lower," "above," "upper," and the like, may be used herein for ease of description to describe one element or feature's relationship to another element or feature as illustrated in the figures. Spatially relative terms are intended to encompass different orientations of the device, apparatus and/or element in use or operation in addition to the orientation depicted in the figures. The device may be otherwise oriented (rotated 90 degrees or other orientations) and the spatially relative descriptors used herein interpreted accordingly.

Claims (13)

1. An optical semiconductor device comprising:

a substrate;

a semiconductor multilayer formed on a substrate and including an optical functional layer;

an insulating film formed over 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 to each other, and

wherein at least a portion of the insulating film in a region overlapping the electrode is thinner than a region of the insulating film not overlapping the electrode.

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

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

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

5. The optical semiconductor device according to claim 4, wherein the first insulating layer is provided in a region not overlapping with the electrode.

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

7. The optical semiconductor device according to claim 5, wherein a first insulating layer provided in a region not overlapping with the electrode is provided over the second insulating layer.

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

9. The optical semiconductor device according to claim 1, wherein the semiconductor multilayer comprises a stripe structure and buried layers formed on each side of the stripe structure.

10. The optical semiconductor device according to claim 4,

wherein the semiconductor multilayer includes a stripe-shaped structure, and

wherein a first insulating layer is provided on each side surface of the bar-shaped structure.

11. The optical semiconductor device according to claim 10, wherein the second insulating layer is provided between a side surface of the stripe-shaped structure and the first insulating layer in a lower portion of the side surface of the stripe-shaped structure.

12. The optical semiconductor device according to claim 1, wherein the thin region of the insulating film comprises one of a silicon nitride film or an aluminum oxide film.

13. The optical semiconductor device according to claim 1, wherein the thick region of the insulating film comprises a silicon oxide film.

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