JP2020004754A - Semiconductor optical element and optical transmission module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a stress received from an electrode layer on a side surface of an upper part of a mesa structure protruding from an embedded layer in an embedded heterostructure type semiconductor laser in which the upper part of the mesa structure protrudes from the embedded layer. A semiconductor optical device has a substrate 118 having a first conductive type, an active layer 119 provided on the substrate 118, and a second conductive type provided on the active layer 119 and different from the first conductive type. A mesa structure including a clad layer 120 and a contact layer 121 having a second conductive type provided on the clad layer 120, an embedded layer 122 provided on the substrate 118 and embedding the mesa structure, and a contact layer 121. It has an electrode layer 116, which includes at least two layers provided on the embedded layer 122. In semiconductor optical elements, the upper part of the mesa structure is exposed from the embedded layer 122, and is deposited on one layer and / or one layer of the electrode layers 116 deposited on the mesa structure and the embedded layer 122. Layers are separated by the upper sidewall of the mesa structure. [Selection diagram] FIG. 4

Description

  The present invention relates to a semiconductor optical device, a method for manufacturing the same, and an optical transmission module.

    Semiconductor lasers, one of the semiconductor optical devices, are used in various applications such as optical communication, information processing, and light sources, and are required to have low cost, low power consumption, small size, high optical output, and high reliability. . Generally, a semiconductor optical device has a semiconductor crystal forming a pn junction and a metal forming an electrode.

  Among the semiconductor optical devices, a buried heterostructure (BH) has a semiconductor crystal forming a pn junction in a mesa structure, and a side portion of the mesa structure is buried with a buried layer of a semi-insulating semiconductor. Therefore, the electrodes are arranged over the upper surface of the mesa structure (the exposed surface above the contact layer) and the upper surface of the embedded layer.

  Generally, a metal constituting an electrode of a semiconductor optical device is formed on a semiconductor crystal layer by a high-temperature process such as electron beam evaporation. When the temperature of the formed metal drops from a high temperature to room temperature, stress is generated in the semiconductor crystal due to a difference in thermal expansion coefficient between the semiconductor and the metal. It is known that such stress adversely affects the performance of the semiconductor optical device. Therefore, various proposals have been made so far to alleviate such stress.

  In Patent Document 1, in a double-channel planar buried heterostructure (DC-PBH) type semiconductor laser, a relationship between stress generated in a semiconductor crystal due to Pt constituting an electrode and reliability is reported. . For example, Patent Literature 1 proposes cutting a TiPtAu ohmic electrode along the mesa portion near both outer sides of the mesa structure.

  Patent Document 2 reports the relationship between stress of a semiconductor crystal due to metal and variation in characteristics of a laser active layer or a light absorption layer in a ridge type semiconductor laser. For example, Patent Document 2 proposes to add a slit for reducing stress to an electrode on a mesa structure.

  Patent Literature 3 proposes that in a ridge-type semiconductor laser, stress in an active layer immediately below the ridge due to an electrode is relaxed. For example, Patent Document 3 proposes a structure in which a cavity is provided in a sidewall portion of a contact layer above a ridge and a sidewall portion of a semiconductor ridge structure immediately below a contact.

  Patent Literature 4 reports a relationship between stress and reliability of a nitride semiconductor layer and a ridge in an ridge structure of a nitride semiconductor laser. For example, Patent Document 4 proposes a structure in which a gap is provided between a protective film on a semiconductor layer and an electrode on the protective film at a ridge base.

JP-A-64-28884 JP 2012-256712 A JP 2012-94564 A JP 2012-59890 A

  In the above-described BH structure, the upper surface of the mesa structure and the upper surface of the buried layer are generally substantially the same. However, in the manufacturing process of the BH structure, a process of projecting the upper part of the mesa structure from the buried layer is included. There is. In a semiconductor optical device in which a part of the mesa structure protrudes from the buried layer, an electrode is also formed on a part of the side surface of the protruding mesa structure. Therefore, in the mesa structure, the stress of the electrode is felt not only from the upper surface but also from the side surfaces. As a result, the protruding mesa structure is more affected by the electrodes than the non-protruding mesa structure. Therefore, we have found that stress relaxation is particularly important in a BH structure type semiconductor laser in which the upper part of the mesa structure protrudes.

  However, the stress relaxation disclosed in Patent Document 1 relieves the stress of the BH structure in which the contact layer is not exposed from the buried layer. Further, the stress relaxation disclosed in Patent Documents 2 to 4 is a stress relaxation of a ridge type semiconductor laser, not a BH structure type semiconductor laser. Therefore, with the stress relaxation disclosed in Patent Documents 1 to 4, there is a possibility that the stress relaxation of the BH structure type semiconductor laser cannot be sufficiently realized.

  Based on the above understanding, the present inventors have studied the stress relaxation disclosed in Patent Documents 1 to 4. As a result, the present inventors have found that the stress relaxation disclosed in Patent Literatures 1 to 4 can improve the SSR (Side Mode Suppression Ratio) characteristics of a BH semiconductor laser in which a contact layer is partially or entirely exposed from a buried layer. It was discovered that the adverse effects were not sufficiently mitigated.

  Therefore, an object of the present invention is to reduce the stress applied to the side surface of the mesa structure projecting from the buried layer from the electrode layer in the BH structure type semiconductor laser having the mesa structure projecting from the buried layer.

(1) The semiconductor optical device of the present application has a substrate having a first conductivity type, an active layer provided on the substrate, and a second conductivity type provided on the active layer and different from the first conductivity type. A mesa structure including a clad layer, and a contact layer having a second conductivity type provided on the clad layer; a buried layer provided on the substrate and embedding the mesa structure; An electrode layer including at least two layers provided on the layer. In the semiconductor optical device, an upper portion of the mesa structure is exposed from the buried layer, and one of the electrode layers and / or one of the electrode layers deposited on the mesa structure and the buried layer is formed on the mesa structure. Other layers to be deposited separate at the upper sidewall of the mesa structure.

(2) In the semiconductor optical device according to (1), the thickness of the other layer is greater than the thickness of a portion where the upper part of the mesa structure is exposed from the buried layer, and the other layer is on the contact layer. To the buried layer, and the one layer is separated by an upper sidewall of the mesa structure.

(3) In the semiconductor optical device according to (1), a thickness of the one layer is larger than a thickness of a portion where an upper part of the mesa structure is exposed from the buried layer, and the one layer is on the contact layer. And the buried layer is continuously connected, and the other layer is separated by an upper sidewall of the mesa structure.

(4) In the semiconductor optical device according to (1), a region of the mesa structure exposed from the buried layer is a part of the contact layer.

(5) In the semiconductor optical device according to (1), a total thickness of the one layer and the other layer is smaller than a thickness of an upper portion of the mesa structure exposed from the buried layer.

(6) In the semiconductor optical device according to any one of (1) to (4), the total thickness of the one layer and the other layer is a thickness at which an upper part of the mesa structure is exposed from the buried layer. Thicker than

(7) In the semiconductor optical device according to any one of (1) to (3), a region exposed from the buried layer in the mesa structure is the entire contact layer.

(8) In the semiconductor optical device according to any one of (1) to (7), one of the electrode layers is Ti, and the other of the electrode layers is Pt.

(9) The optical transmission module of the present application includes the semiconductor optical device according to any one of (1) to (8).

(10) The optical transceiver module of the present application includes the semiconductor optical device according to any one of (1) to (8).

  According to the present invention, in a BH structure type semiconductor laser in which an upper portion of a mesa structure protrudes from a buried layer, a stress received from an electrode layer on a side surface of the upper portion of the mesa structure protruding from the buried layer is reduced.

1 shows an optical transceiver module including an optical transmitter module according to an embodiment of the present invention. 1 shows an optical transmission module equipped with a semiconductor optical device according to an embodiment of the present invention. 1 shows a top view of a semiconductor optical device according to an embodiment of the present invention. 1 shows a sectional view of a semiconductor optical device according to an embodiment of the present invention. 1 shows an enlarged cross-sectional view of a mesa structure of a semiconductor optical device according to an embodiment of the present invention. 1 shows an enlarged cross-sectional view of a mesa structure of a semiconductor optical device according to an embodiment of the present invention. 1 shows an enlarged cross-sectional view of a mesa structure of a semiconductor optical device according to an embodiment of the present invention. 1 shows an enlarged cross-sectional view of a mesa structure of a semiconductor optical device according to an embodiment of the present invention. 1 shows an enlarged cross-sectional view of a mesa structure of a semiconductor optical device according to an embodiment of the present invention. 1 illustrates a method for manufacturing a semiconductor optical device according to an embodiment of the present invention. 1 illustrates a method for manufacturing a semiconductor optical device according to an embodiment of the present invention. 1 illustrates a method for manufacturing a semiconductor optical device according to an embodiment of the present invention. 1 illustrates a method for manufacturing a semiconductor optical device according to an embodiment of the present invention.

[First Embodiment]
FIG. 1 shows an optical transmitting and receiving module including the optical transmitting module according to the embodiment of the present application. The optical transmission / reception module 100 includes a housing 101, a printed circuit board 103 provided in the housing 101 and having an edge connector 102, a light transmission module 106 (TOSA: Transmitter Optical Sub Assembly), and a light reception module 107 (ROSA: Receiver). Optical Sub Assemblies) and optical fiber connectors 108 a and 108 b attached to the housing 101. The printed board 103 has an integrated circuit 104 on the printed board 103.

  The printed circuit board 103 is connected to the optical transmitting module 106 and the optical receiving module 107 by a flexible substrate 105, respectively. The optical fiber connectors 108a and 108b are optically aligned with the optical transmitting module 106 and the optical receiving module 107, respectively.

  The integrated circuit 104 has a signal reproducing function and an amplifying function. The optical transmission module 106 has a function of converting an electric signal into an optical signal. The optical receiving module 107 has a function of converting an optical signal into an electric signal.

  The edge connector 102 outputs an electric signal from the optical receiving module 107 to a host device (not shown), and outputs an electric signal from the host device (not shown) to the optical transmitting module 106. The optical fiber connectors 108a and 108b function as input / output means of the optical transceiver module 100. That is, the input light is input to the optical receiving module 107 via an optical fiber (not shown) connected to the optical fiber connector 108b, and the output light is an optical fiber (not shown) connected to the optical fiber connector 108a. ) Is output from the optical transmission module 106.

  FIG. 2 shows an optical transmission module according to the present embodiment. The optical transmission module 106 includes a chip carrier 109, a semiconductor optical device 110 mounted on the chip carrier 109, and a convex lens 111.

  The semiconductor optical device 110 emits light. The convex lens 111 converts the light emitted from the semiconductor optical device 110 into parallel light or converged light.

  FIG. 3 is a top view of the semiconductor optical device according to the present embodiment. The illustrated semiconductor optical device 110 is an electro-absorption modulator-distributed feedback laser (EA-DFB). The semiconductor optical device 110 has a laser unit 112, a waveguide unit 113, a modulator unit 114, and a mesa structure (mesa stripe) 115.

  An electrode 116 is provided above the laser unit 112. The electrode 116 may include at least two metal layers. The laser section 112 is preferably a DFB laser element, but may be another type of laser element. An electrode 116 and an electrode pad 117 are provided above the modulator section 114. The modulator section 114 is preferably an EA light modulator, but may be another type of light modulator.

  FIG. 4 is a cross-sectional view of the semiconductor optical device 110 according to the embodiment of the present invention, taken along line A-A '. The illustrated semiconductor optical device 110 is a BH structure type semiconductor laser embedded with a semi-insulating semiconductor. Note that the cross-sectional view shown in FIG. 4 is not limited to the cross-section taken along the line AA # in FIG. 3, and any cross-section of the laser unit 112 has the structure shown in FIG.

  The semiconductor optical device 110 includes a substrate 118 having the first conductivity type, a mesa structure 115 provided on the surface of the substrate 118, a buried layer 122 burying the mesa structure 115, and a passivation provided on a part of the buried layer 122. A film 123, a mesa structure 115, a buried layer 122, a Ti layer 124 covering the passivation film 123, a Pt layer 125 provided on the Ti layer 124, an Au layer 126 provided on the Pt layer 125, An electrode 127 having the first conductivity type is formed on the back surface.

  The mesa structure 115 has an active layer 119, a cladding layer 120 provided on the active layer 119 and having a second conductivity type different from the first conductivity type, and a second conductivity type provided on the cladding layer 120. It has a contact layer 121. The Ti layer 124, the Pt layer 125, and the Au layer 126 form an electrode layer 116 having the second conductivity type. In the present embodiment, the mesa structure 115 has a vertically striped resonator structure in FIG. Although omitted in this description, the mesa structure 115 may include other layers such as an SCH layer and a diffraction grating layer. However, the uppermost layer of the mesa structure 115 is a contact layer. In the present embodiment, the substrate 118 is an n-type InP substrate, the active layer 119 is a multiple quantum well containing InGaAsP, the cladding layer 120 is a p-type InP layer, and the contact layer 121 is a p-type InGaAs layer. Further, the mesa structure 115 resonator structure was a λ / 4 shift diffraction grating structure.

  The semiconductor optical device 110 is made of an InGaAsP material, but may be made of another material. The buried layer 122 is made of a semi-insulating semiconductor. Here, an InP layer to which Fe was added was used. On the upper surface of the contact layer 121, the electrode layer 116 composed of the Ti layer 124, the Pt layer 125, and the Au layer 126 forms an ohmic electrode, so that low-resistance electrical connection is sufficiently maintained. In the present embodiment, the first conductivity type is n-type and the second conductivity type is p-type. However, in some embodiments, the first conductivity type may be p-type and the second conductivity type may be n-type.

  In consideration of energization and heat radiation of the semiconductor optical device and post-processes (wire bonding, soldering), it is preferable to use Au as an electrode. However, since Au in the electrode layer diffuses into the semiconductor layer in the mesa structure, the reliability and characteristics of the semiconductor optical device may be deteriorated. In order to prevent such diffusion of Au into the semiconductor layer, a Pt electrode layer is provided below the Au electrode layer as a barrier layer. The contact layer 121 and the Au layer 126 do not directly contact each other, and the diffusion of Au into the semiconductor crystal is suppressed by the barrier metal effect of the Pt layer 125. However, since the bonding strength of Pt to the semiconductor is weak, a Ti layer 124 is provided between the Pt layer 125 and the buried layer 122 and the upper portion of the mesa structure 115 to form an adhesive layer and an ohmic electrode.

  As described above, Au needs to spread to a region other than the mesa structure for conduction and heat dissipation. Therefore, even if the stress applied to the mesa structure by the Au electrode layer is large, the stress applied to the semiconductor layer by the Au layer is inevitable. However, the Pt layer and the Ti layer are provided mainly for purposes other than the energization, which is the original function of the electrode. Therefore, it is preferable that the Pt layer and the Ti layer do not exert a stress on the mesa structure.

  As a result of intensive studies from the above viewpoints, the present inventors have found that in order to alleviate the stress exerted by the Pt layer and the Ti layer on the mesa structure, the Pt electrode layer in contact with the side surface of the mesa structure and / or the Pt electrode layer in contact with the Ti electrode layer and the upper surface thereof The inventors have conceived of weakening the connection between the electrode layer and / or the Ti electrode layer. Specifically, the present inventors have proposed a semiconductor optical device in which a Pt electrode layer and / or a Ti electrode layer are separated at the upper part and the side part of the mesa structure. The Pt layer and / or the Ti layer are preferably formed only on the upper portion of the mesa structure, but are actually formed to some extent on the side portions of the mesa structure.

  Since the electrode layer of the semiconductor optical device described above is separated at the side of the mesa structure, the stress by the electrode layer on the side of the contact layer, which is the upper part of the mesa structure, is reduced, and the stress of the entire mesa structure is reduced. As a result, the present inventors have found that the SMSR yield of the semiconductor optical device according to the present embodiment is improved by 3%.

  FIG. 5 is an enlarged cross-sectional view of the mesa structure of the semiconductor optical device according to the present embodiment in FIG. 4B. In the present embodiment, the entire contact layer 121 is exposed from the buried layer 122. That is, in the present embodiment, the upper part of the mesa structure 115 exposed from the buried layer 122 is the contact layer 121. In the present embodiment, both the Ti layer 124 and the Pt layer 125 are separated from each other on the side of the contact layer 121 and are discontinuous. Further, the thickness of the region formed above each contact layer 121 is substantially equal to the thickness of the region formed above each buried layer 122. In some embodiments, a layer located below the contact layer 121 (for example, the cladding layer 120) may be exposed from the buried layer 122. In the present embodiment, the thickness of the Ti layer 124 is smaller than the thickness of the portion of the contact layer 121 exposed from the buried layer 122 (hereinafter referred to as H) (Ti layer <H), and the thickness of the Pt layer 125 is also smaller. It is thinner than the thickness of the exposed portion (Pt thickness <H). Further, the sum of the thicknesses of the Ti layer 124 and the Pt layer 125 is larger than H. Therefore, the Au layer 126 disposed on the Pt layer 125 does not contact the side of the exposed portion (the contact layer 121 which is a semiconductor layer), and there is no concern about Au diffusion. In this embodiment, the thickness of the portion of the contact layer 121 exposed from the buried layer 122 is 200 nm, the thickness of the Ti layer 124 is 100 nm, the Pt layer 125 is 150 nm, and the Au layer 126 is 1000 nm. .

  In the mesa structure shown in FIG. 5, the Ti layer 124 is separated and discontinuous at the side of the contact layer 121. Therefore, in the semiconductor optical device according to the present embodiment, the stress exerted on the mesa structure 115 by the Ti layer 124 is reduced as compared with the case where the semiconductor layers are continuous. Further, the Pt layer 125 is similarly discontinuous, and the stress exerted on the mesa structure 115 by the Pt layer 125 is reduced.

[Second embodiment]
FIG. 6 is an enlarged sectional view of the mesa structure of the semiconductor optical device according to the present embodiment. This embodiment is the same as the first embodiment except that the Pt layer 125 is continuous on the side wall of the mesa structure 115. In this embodiment, the thickness of the Pt layer is 250 nm. Since the Ti layer 124 is separated at the side wall of the mesa structure 115, the stress exerted on the contact layer 121 by the Ti layer 124 is reduced. Therefore, a similar effect can be obtained in the present embodiment.

[Third embodiment]
FIG. 7 is an enlarged sectional view of the mesa structure of the semiconductor optical device according to the present embodiment. This embodiment is the same as the first embodiment except that the Ti layer 124 is continuous on the side wall of the mesa structure 115. In this embodiment, the thickness of the Ti layer is 250 nm. Since the Pt layer 125 is separated by the side wall of the mesa structure 115, the stress applied to the contact layer 121 is reduced. Therefore, a similar effect can be obtained in the present embodiment.

[Fourth embodiment]
FIG. 8 is an enlarged sectional view of the mesa structure of the semiconductor optical device according to the present embodiment. This embodiment is the same as the first embodiment except that a part of the contact layer 121 is exposed from the buried layer 122 and the thickness of the Pt layer is different. In this embodiment, the thickness H of the exposed portion is 150 nm, and the thickness of the Pt layer is 100 nm. Also in the present embodiment, even if only a part of the contact layer 121 is exposed, the Ti layer 124 and the Pt layer 125 are separated by the side wall of the mesa structure 115, so that the contact layer 121 is exposed to the exposed part. Stress is relieved. Therefore, a similar effect can be obtained in the present embodiment. Conversely, even if a part of the cladding layer 120 is exposed in the mesa structure, the same effect as in the present embodiment can be obtained if the Ti layer 124 and / or the Pt layer 125 are discontinuous.

[Fifth Embodiment]
FIG. 9 is an enlarged sectional view of the mesa structure of the semiconductor optical device according to the present embodiment. This embodiment is the same as the first embodiment except that the thicknesses of the Ti layer 124 and the Pt layer 125 are different. Here, the thickness of the Ti layer was 50 nm, and the thickness of the Pt layer was 100 nm. The thickness H of the portion of the contact layer 121 exposed from the buried layer 122 is 200 nm. In the present embodiment, since the Ti layer 124 and the Pt layer 125 are separated from each other at the side wall of the mesa structure 115, the stress applied to the exposed portion of the contact layer 121 is reduced. However, since the total thickness of the Ti layer 124 and the Pt layer 125 is smaller than H, the Au layer 126 is in contact with the side wall of the mesa structure. When the Au layer 126 is in contact with the semiconductor layer (contact layer 121), there is a possibility that Au diffuses into the semiconductor. However, if the region is small, the influence on reliability and the like is small. Therefore, the effect of the present invention can be obtained also in this structure.

  The first to third embodiments and the fourth and fifth embodiments may be appropriately combined. The present invention is characterized in that, in a state where a part of the mesa structure is exposed from the buried layer, the Ti layer and / or the Pt layer are discontinuously arranged from the upper part of the mesa to the upper part of the buried layer.

[Method of Manufacturing Semiconductor Optical Device According to Embodiment]
FIGS. 10, 11, 12, and 13 show a method of manufacturing a semiconductor optical device according to the present embodiment. First, as shown in FIG. 10, an active layer 119 suitable for light emission including a plurality of layers is deposited on a substrate 118, a cladding layer 120 is deposited on the active layer 119, and a p-type InP cladding layer 120 is deposited. A contact layer 121 is deposited thereon. Substrate 118 may be, for example, an n-type InP substrate. Active layer 119 may be, for example, a multiple quantum well. The active layer 119 may also include a diffraction grating layer for controlling a laser oscillation state. The contact layer 121 may be, for example, p-type InGaAs.

  Next, a mesa structure 115 is formed by an etching process, and then a BH structure is formed by selectively depositing a buried layer 122. For example, the buried layer 122 may be semi-insulating InP. Preferably, the width of the mesa structure 115 is determined so as to satisfy the single mode oscillation condition. The width of the mesa structure 115 may be, for example, about 2 micrometers or less. At the time of crystal growth of the buried layer 122, a mask having a width slightly larger than the mesa width is arranged above the mesa, so that the buried layer 122 has a slightly flat region above the mesa as shown in FIG. And then extend obliquely upward along the crystal plane, followed by a flat portion. Subsequently, after a passivation film 123 is formed on the upper surface of the buried layer 122, the passivation film 123 is etched with a width larger than the width of the mesa structure 115, and a structure for electrical connection with the mesa structure 115 is created. (FIG. 11).

  Thereafter, as shown in FIG. 12, etching is performed so that the side portions of contact layer 121 are exposed from buried layer 122. The contact layer 121 is entirely or partially exposed from the buried layer 122.

  Next, as shown in FIG. 13, a Ti layer 124, a Pt layer 125, and an Au layer 126 are deposited in this order. As a result, a p-type electrode is formed. Finally, an n-type electrode 127 is formed on the back surface of the substrate 118.

  With the above structure, the present invention has an electrical connection with a small resistance value by an ohmic electrode made of Ti, Pt and Au on the upper surface of the contact layer, and the Ti layer 124 and / or the Pt layer 125 are separated at the contact layer side. By doing so, the stress on the contact layer side due to the Ti layer 124 and / or the Pt layer 125 is reduced. Thereby, the stress applied to the mesa structure 115 is reduced. As a result, the change in the refractive index and the change in the pitch of the diffraction grating due to the stress are reduced, thereby improving the SMSR yield.

  Although the present embodiment has described the InGaAsP-based EA-DFB laser, a similar effect can be expected for a semiconductor laser using another material having a BH structure and a semiconductor laser integrated device. Further, it goes without saying that the same effect can be obtained in the optical transmitting module 106 and the optical transmitting / receiving module 100 using the semiconductor optical element 110.

  REFERENCE SIGNS LIST 100 optical transmitting / receiving module, 101 housing, 102 edge connector, 103 printed circuit board, 104 integrated circuit, 105 flexible substrate, 106 optical transmitting module, 107 optical receiving module, 108 a, b optical fiber connector, 109 chip carrier, 110 semiconductor optical element , 111 convex lens, 112 laser unit, 113 waveguide unit, 114 modulator unit, 115 mesa structure, 116 electrode, 117 electrode pad, 118 substrate, 119 active layer, 120 clad layer, 121 contact layer, 122 buried layer, 123 passivation Film, 124 Ti layer, 125 Pt layer, 126 Au layer, 127 electrodes.

Claims (10)

A substrate having a first conductivity type;
An active layer provided on the substrate, a cladding layer provided on the active layer and having a second conductivity type different from the first conductivity type, and a contact layer having a second conductivity type provided on the cladding layer And a mesa structure including
A buried layer provided on the substrate, and burying the mesa structure;
An electrode layer including at least two layers provided on the contact layer and the buried layer;
Has,
An upper portion of the mesa structure is exposed from the buried layer,
One of the electrode layers deposited on the mesa structure and the buried layer and / or another layer deposited on the one layer is separated by a top sidewall of the mesa structure;
A semiconductor optical device, comprising: The semiconductor optical device according to claim 1, wherein
The thickness of the other layer is greater than the thickness of the portion where the top of the mesa structure is exposed from the buried layer,
The other layer is continuously connected from the contact layer to the buried layer,
The one layer is separated by an upper sidewall of the mesa structure;
A semiconductor optical device, comprising: The semiconductor optical device according to claim 1, wherein
The thickness of the one layer is greater than the thickness of a portion where the upper part of the mesa structure is exposed from the buried layer,
The one layer is continuously connected on the buried layer from the contact layer,
The other layer is separated by an upper sidewall of the mesa structure;
A semiconductor optical device, comprising: The semiconductor optical device according to claim 1, wherein
In the mesa structure, a region exposed from the buried layer is a part of the contact layer.
A semiconductor optical device, comprising: The semiconductor optical device according to claim 1, wherein
The sum of the thicknesses of the one layer and the other layer is smaller than the thickness of the top of the mesa structure exposed from the buried layer.
A semiconductor optical device, comprising: The semiconductor optical device according to claim 1, wherein:
The sum of the thicknesses of the one layer and the other layer is greater than the thickness of the top of the mesa structure exposed from the buried layer,
A semiconductor optical device, comprising: The semiconductor optical device according to claim 1, wherein:
In the mesa structure, a region exposed from the buried layer is the entire contact layer.
A semiconductor optical device, comprising: The semiconductor optical device according to claim 1, wherein:
One of the electrode layers is Ti;
The other of the electrode layers is Pt;
A semiconductor optical device, comprising:   An optical transmission module comprising the semiconductor optical device according to claim 1.   An optical transceiver module comprising the semiconductor optical device according to claim 1.

Images