Optical semiconductor device

Abstract

The present disclosure can obtain an optical semiconductor device capable of preventing degradation of a frequency band. An optical modulator (2) is provided with: a semiconductor layer (22) including a first conductivity-type layer (13), an absorption layer (23), and a second conductivity-type layer (15) formed in this order on a substrate (3); a first electrode (6) connected to the first conductivity-type layer (13); and a second electrode (7) connected to the second conductivity-type layer (15). The first pad (8) is connected to the first electrode (6). The second pad (9) is connected to the second electrode (7). The semiconductor layer (22) has a waveguide (10), and a first platform and a second platform (12) which are disposed on opposite sides with respect to the waveguide. The first pad (8) and the second pad are disposed on the first stage (11) via an insulating film (20). A groove (27) is formed in the semiconductor layer (22) between the first pad (8) and the second pad.

Description

Technical Field

[0001] This disclosure relates to optical semiconductor devices. Background Technology

[0002] An optical semiconductor device that monolithically integrates a laser unit and an optical modulator is proposed (see, for example, Patent Document 1). The optical modulator operates differentially by applying a differential voltage between the anode pad and the cathode pad. By arranging the anode pad and the cathode pad of the optical modulator on the same side of the waveguide terrace, the length of the wires connecting the two pads can be made to be the same.

[0003] Patent Document 1: Japanese Patent No. 5891920

[0004] Because leakage current flows between the two pads of the optical modulator during differential operation, the voltage applied to the absorber layer of the optical modulator decreases. Since the leakage current flows through the capacitance beneath the electrodes of the optical modulator, the leakage current increases with higher frequencies, resulting in a lower extinction ratio. Consequently, there is a problem of reduced frequency bands where the optical modulator can operate normally. Summary of the Invention

[0005] This disclosure is made to solve the aforementioned problems, and its purpose is to obtain an optical semiconductor device that can prevent bandwidth reduction.

[0006] The optical semiconductor device disclosed herein is characterized by comprising: a substrate; an optical modulator having a semiconductor layer comprising a first conductivity layer, an absorption layer, and a second conductivity layer sequentially formed on the substrate, a first electrode connected to the first conductivity layer, and a second electrode connected to the second conductivity layer; a first pad connected to the first electrode; and a second pad connected to the second electrode, wherein the semiconductor layer has a waveguide and a first platform and a second platform disposed opposite to each other relative to the waveguide, the first pad and the second pad being disposed on the first platform via an insulating film, and a groove being formed between the first pad and the second pad in the semiconductor layer.

[0007] In this disclosure, a trench is formed in the semiconductor layer between the first pad and the second pad. This trench disconnects the leakage current path between them, thereby reducing leakage current and thus particularly improving the response in the high-frequency region. As a result, bandwidth degradation can be prevented. Attached Figure Description

[0008] Figure 1 This is a top view of the optical semiconductor device according to Embodiment 1.

[0009] Figure 2 It is along Figure 1 A cross-sectional view of the laser section cut by A-A'.

[0010] Figure 3 It is along Figure 1 A cross-sectional view of an optical modulator cut by B-B'.

[0011] Figure 4 It is along Figure 1 A cross-sectional view of a C-C' cut optical modulator.

[0012] Figure 5 It is along Figure 1 A cross-sectional view cut by D-D'.

[0013] Figure 6 It is along Figure 1 A sectional view cut by E-E'.

[0014] Figure 7 This is a top view of the optical semiconductor device involved in the comparative example.

[0015] Figure 8 It is along Figure 7 A sectional view cut by A-A'.

[0016] Figure 9 This is a graph showing the frequency response characteristics of Embodiment 1 and the comparative example.

[0017] Figure 10 This is a top view of the optical semiconductor device involved in Embodiment 2.

[0018] Figure 11 It is along Figure 10 A sectional view cut by A-A'.

[0019] Figure 12 This is a graph showing the frequency response characteristics of Embodiment 2 and the comparative example.

[0020] Figure 13 This is a top view of the optical semiconductor device involved in Embodiment 3.

[0021] Figure 14 This is a top view of the optical semiconductor device involved in Embodiment 4.

[0022] Figure 15 This is a top view showing a modified example 1 of the optical semiconductor device according to embodiment 4.

[0023] Figure 16 This is a top view showing a modified example 2 of the optical semiconductor device according to embodiment 4.

[0024] Figure 17This is a top view of the optical semiconductor device according to Embodiment 5.

[0025] Figure 18 It is along Figure 17 A cross-sectional view of the first optical modulator cut by A-A'.

[0026] Figure 19 It is along Figure 17 A cross-sectional view of the second optical modulator cut by B-B'.

[0027] Figure 20 This is a top view of the optical semiconductor device according to Embodiment 6.

[0028] Figure 21 This is a top view of the optical semiconductor device according to Embodiment 7.

[0029] Figure 22 This is a cross-sectional view of the optical semiconductor device according to Embodiment 8.

[0030] Figure 23 This is a top view of the optical semiconductor device according to Embodiment 9.

[0031] Figure 24 It is along Figure 23 A sectional view cut by A-A'.

[0032] Explanation of reference numerals in the attached figures

[0033] 1...Laser unit; 2...Optical modulator; 2a...First optical modulator; 2b...Second optical modulator; 3...Semi-insulating InP substrate (substrate); 4...Cathode electrode (electrode); 6...Cathode electrode (first electrode); 7...Anode electrode (second electrode); 8...Cathode pad (first pad); 9...Anode pad (second pad); 10...Waveguide; 11...First platform; 12...Second platform; 13...n-InP cladding (first conductivity layer); 15...p-InP cladding (second conductivity layer); 20...Insulating film; 22...Semiconductor layer; 23...Absorbing layer; 27, 28...Groove; 30...Dummy pad; 31...High resistivity layer. Detailed Implementation

[0034] The optical semiconductor device according to the embodiments will be described with reference to the accompanying drawings. The same or corresponding components are labeled with the same reference numerals, and repeated descriptions are sometimes omitted.

[0035] Implementation Method 1

[0036] Figure 1This is a top view showing the optical semiconductor device according to Embodiment 1. This optical semiconductor device is a modulator-integrated laser diode in which a laser unit 1 and an optical modulator 2 are monolithically integrated on a semi-insulating InP substrate 3. The laser unit 1 is a distributed-feedback laser diode (DFB-LD). The optical modulator 2 is an electroabsorption modulator.

[0037] The laser unit 1 has a cathode electrode 4 and an anode electrode 5. The optical modulator 2 has a cathode electrode 6 and an anode electrode 7. A cathode pad 8 is connected to the cathode electrode 6. An anode pad 9 is connected to the anode electrode 7. The optical modulator 2 operates differentially by applying a differential voltage between the cathode pad 8 and the anode pad 9.

[0038] A first platform 11 and a second platform 12 are arranged on opposite sides of the waveguide 10. A cathode pad 8 and an anode pad 9 are disposed on the first platform 11. As a result, the wires connected to the anode pad 9 can be the same length as the wires connected to the cathode pad 8.

[0039] Figure 2 It is along Figure 1 A cross-sectional view of the laser section taken along line A-A'. An n-InP cladding layer 13, an active layer 14, a p-InP cladding layer 15, and a p-InGaAs contact layer 16 are sequentially stacked on a semi-insulating InP substrate 3. The active layer 14 is an InGaAsP multi-quantum well (MQW) structure.

[0040] The active layer 14 is patterned as stripes when viewed from above, and is embedded on both sides by embedded layers (not shown). The embedded layers are a double-layer structure of Fe-InP and n-InP layers, or a PNP structure of InP. A diffraction grating 17 is formed in the p-InP cladding 15.

[0041] Grooves 18 and 19 are formed on both sides of the active layer 14, and on the p-InGaAs contact layer 16, p-InP cladding layer 15, and n-InP cladding layer 13. The upper surface of the p-InGaAs contact layer 16 and the inner surfaces of the grooves 18 and 19 are covered by an insulating film 20. An opening is formed in the insulating film 20 above the mesa structure between the grooves 18 and 19, through which the anode electrode 5 is connected to the p-InGaAs contact layer 16. An opening is formed in the insulating film 20 on the bottom surface of the groove 18, through which the cathode electrode 4 is connected to the n-InP cladding layer 13. An n-electrode 21 is formed on the lower surface of the semi-insulating InP substrate 3.

[0042] Figure 3 It is along Figure 1 A cross-sectional view of a B-B' cut optical modulator. On a semi-insulating InP substrate 3, an n-InP cladding layer 13, a p-InP cladding layer 15, and a p-InGaAs contact layer 16 are sequentially stacked as semiconductor layer 22. An absorption layer 23 is stacked within the mesa structure between trenches 18 and 19, and on top of the n-InP cladding layer 13. The absorption layer 23 is an InGaAsP multi-quantum-well structure.

[0043] Grooves 18 and 19 are formed in a mutually separated manner in the p-InGaAs contact layer 16, p-InP cladding layer 15, and n-InP cladding layer 13. Grooves 18 and 19 limit the lateral width of the absorption layer 23 to function as waveguide 10. Semiconductor layer 22 has waveguide 10 and first platform 11 and second platform 12 disposed opposite to each other relative to waveguide 10. An opening is formed on the bottom surface of groove 18 and in insulating film 20, through which cathode electrode 6 is connected to n-InP cladding layer 13. Cathode pad 8 is disposed on first platform 11 via insulating film 20 and connected to cathode electrode 6.

[0044] Figure 4 It is along Figure 1 A cross-sectional view of a C-C' cut optical modulator. An opening is formed on the waveguide 10 and on the insulating film 20, through which the anode electrode 7 is connected to the p-InGaAs contact layer 16. The anode pad 9 is disposed on the first platform 11 via the insulating film 20, similar to the cathode pad 8, and is connected to the anode electrode 7.

[0045] Figure 5 It is along Figure 1 A cross-sectional view taken at D-D'. The active layer 14 and the absorber layer 23 are connected by a transparent waveguide layer 24. A transparent waveguide layer 24 is also formed between the absorber layer 23 and the emission end face. The transparent waveguide layer 24 is composed of a single layer of InGaAsP.

[0046] Figure 6 It is along Figure 1 A cross-sectional view taken along the E-E' axis. The cathode electrode 6 and anode electrode 7 of the optical modulator 2 are respectively connected to the differential power supply 25. The differential power supply 25 performs a push-pull operation by alternately applying voltage with one end positive and the other negative. It is not limited to this; voltage fluctuations can also be caused on the anode side to make the potential on the cathode side 0. A load resistor R is connected in parallel with respect to the pn junction 26 of the optical modulator 2. The load resistor R is located externally to the device for impedance matching.

[0047] A trench 27 is formed between the cathode pad 8 and the anode pad 9, and on the semiconductor layer 22. Specifically, the trench 27 penetrates the p-InP cladding layer 15 and the n-InP cladding layer 13 and reaches the semi-insulating InP substrate 3. The trench 27 may also be formed simultaneously with trenches 18 and 19.

[0048] To reduce the series resistance of the optical modulator 2, the n-InP cladding 13 typically has a very low resistance. Therefore, the trench 27 needs to remove at least a portion of the n-InP cladding 13, preferably through it. If a high-concentration n-type layer is provided on the entire surface of the n-InP cladding 13 to connect it to the cathode electrode 6, the trench 27 also needs to disconnect this n-type layer.

[0049] Next, the effects of this embodiment will be explained by comparing it with a comparative example. Figure 7 This is a top view of the optical semiconductor device involved in the comparative example. Figure 8 It is along Figure 7 A cross-sectional view taken along line A-A'. In the comparative example, groove 27 is not formed. The cathode pad 8 and anode pad 9 are connected at high frequency via the insulating film 20, the p-InP cladding layer 15, and the n-InP cladding layer 13. Therefore, a resistance R1 exists in the semiconductor layer 22 between the cathode pad 8 and the anode pad 9 as a leakage current path.

[0050] Furthermore, the cathode pad 8 of the optical modulator 2 and the cathode electrode 4 of the laser section 1 are also connected at high frequency via the insulating film 20, the p-InP cladding layer 15, and the n-InP cladding layer 13. Therefore, a resistor R2 exists in the semiconductor layer 22 between the anode pad 9 and the cathode electrode 4, serving as a leakage current path. Moreover, the positions of the cathode pad 8 and the anode pad 9 of the optical modulator 2 can also be reversed. In this case, a potential difference is generated between the anode electrode 7 of the optical modulator 2 and the cathode electrode 4 of the laser section 1, resulting in leakage current.

[0051] The differential power supply 25, based on the anode voltage, flows through the paths of the load resistors R and R2, and through the paths of the capacitor C, resistor R1, and resistor R2 in the insulating film 20. The current based on the cathode voltage flows through resistor R2 to the cathode electrode 4 of the laser section 1.

[0052] The higher the frequency, the lower the impedance of capacitor C, and the higher the leakage current flowing through resistor R1. This increased leakage current reduces the current flowing through the load resistor R, thus decreasing the voltage applied to the optical modulator 2. Therefore, the higher the frequency, the greater the leakage current, the lower the extinction ratio, and consequently, the lower the bandwidth.

[0053] In contrast, in this embodiment, a trench 27 is formed in the semiconductor layer 22 between the cathode pad 8 and the anode pad 9. The leakage current path between them is interrupted by the trench 27, thereby reducing leakage current and thus improving the response, particularly in the high-frequency region. As a result, bandwidth reduction can be prevented. Furthermore, even in semiconductor devices without the optical modulator unit of the laser section 1, the same effect can be achieved by forming the trench 27 between the cathode pad 8 and the anode pad 9.

[0054] Figure 9 This is a graph showing the frequency response characteristics of Embodiment 1 and the comparative example. The vertical axis in the graph represents the frequency dependence of the light intensity amplitude when the voltage amplitude of the pulse applied to the light modulator is kept constant and the frequency is changed. It can be seen that in this embodiment, the frequency dependence of the light response modulated by the anode voltage and the frequency dependence of the light response modulated by the cathode voltage are both improved compared to the comparative example.

[0055] Implementation Method 2

[0056] Figure 10 This is a top view of the optical semiconductor device involved in Embodiment 2. Figure 11 It is along Figure 10 A cross-sectional view taken along line A-A'. Not only is the groove 27 of Embodiment 1 formed, but a groove 28 is also formed between the cathode pad 8 of the optical modulator 2 and the cathode electrode 4 of the laser section 1. The groove 28 electrically separates the low-resistivity layers such as the p-InP cladding layer 15 and the n-InP cladding layer 13. As a result, the leakage current flowing in the cathode electrode 4 of the laser section 1 due to the cathode voltage is reduced, thus increasing the amplitude of the cathode modulation.

[0057] Furthermore, when the positions of the cathode pad 8 and anode pad 9 of the optical modulator 2 are reversed, a groove 28 is formed between the anode pad 9 of the optical modulator 2 and the cathode electrode 4 of the laser section 1. That is, a groove 28 is formed between the cathode pad 8 and anode pad 9 of the optical modulator 2 that is closer to the cathode electrode 4 of the laser section 1 and the cathode electrode 4.

[0058] Figure 12 This is a graph showing the frequency response characteristics of Embodiment 2 and the comparative example. It can be seen that in this embodiment, both the frequency response to anode modulation and the frequency response to cathode modulation are improved compared to the comparative example. The frequency response characteristics of anode modulation and cathode modulation are made almost identical by using two slots 27 and 28, thus enabling ideal differential operation.

[0059] Furthermore, since resistors R1 and R2 are present in the comparative example, the paths of the current based on the cathode voltage and the current based on the anode voltage are different, resulting in different impedances. In contrast, in this embodiment, the current paths flowing through resistors R1 and R2 are interrupted by slots 27 and 28, so the current based on both voltages flows only in the load resistor R. Consequently, the impedances on the anode and cathode sides become equal. As a result, the amplitude and phase of the noise on the anode and cathode sides can be made consistent, maximizing the noise reduction effect based on differential operation.

[0060] Implementation Method 3

[0061] Figure 13 This is a top view showing the optical semiconductor device according to Embodiment 3. A groove 27 is formed along the outer periphery of the cathode pad 8. The closer the groove 27 is to the pad, the smaller the capacitance between the pad and the back metal, thus improving the frequency characteristics. Although it is preferable that the groove 27 is formed in all areas of the outer periphery of the cathode pad 8, it may also be formed in a portion. Alternatively, the groove 27 may be formed along the outer periphery of the anode pad 9. Other structures and effects are the same as in Embodiment 1.

[0062] Implementation Method 4

[0063] Figure 14 This is a top view showing the optical semiconductor device according to Embodiment 4. Grooves 27 are formed along the outer periphery of the cathode pad 8 and the anode pad 9, respectively. While it is preferable that the grooves 27 are formed over all areas of the outer periphery of the cathode pad 8 and the anode pad 9, they may also be formed over only a portion. Other structures and effects are the same as in Embodiment 1.

[0064] Preferably, the areas of the anode pad 9 and the cathode pad 8 are the same. By making the parasitic capacitances of the two pads the same, the frequency response characteristics of the anode modulation and the cathode modulation become almost identical, thus enabling ideal differential operation. Furthermore, by making the impedances of the anode and cathode sides the same, the amplitude and phase of the noise on the anode and cathode sides can be made consistent, thereby maximizing the noise reduction effect based on differential operation.

[0065] Figure 15 This is a top view showing a modified example 1 of the optical semiconductor device according to embodiment 4. A groove 27 is formed not only around the outer periphery of the pads, but also integrally in the area between the cathode pad 8 and the anode pad 9. Figure 16This is a top view showing a modified example 2 of the optical semiconductor device according to embodiment 4. In comparative example 2, the groove 27 is formed as a quadrilateral shape including the outer periphery of the pads and the portion between the pads. However, an insulating film 20 and a semiconductor layer 22 remain directly below the cathode pad 8 and the anode pad 9. The length and width of the groove 27 are not particularly limited as long as it can electrically separate the pads.

[0066] Implementation Method 5

[0067] Figure 17 This is a top view showing the optical semiconductor device according to Embodiment 5. The optical modulator 2 has a first optical modulator 2a and a second optical modulator 2b arranged along the direction of light travel. Figure 18 It is along Figure 17 A cross-sectional view of the first optical modulator cut along line A-A'. The common electrode 29 is connected to the p-InGaAs contact layer 16 of the first optical modulator 2a. The cathode electrode 6 is connected to the n-InP cladding layer 13 of the first optical modulator 2a at the bottom surface of the groove 18.

[0068] Figure 19 It is along Figure 17 A cross-sectional view of the second optical modulator, cut along a B-B' axis. The anode electrode 7 is connected to the p-InGaAs contact layer 16 of the second optical modulator 2b. The common electrode 29 is connected to the n-InP cladding layer 13 of the second optical modulator 2b on the bottom surface of the trench 19. Therefore, the first optical modulator 2a and the second optical modulator 2b are electrically connected in series. The first optical modulator 2a and the second optical modulator 2b operate differentially between the cathode pad 8 and the anode pad 9.

[0069] Similar to Embodiment 4, grooves 27 are formed along the outer periphery of the cathode pad 8 and the anode pad 9, respectively. The grooves 27 disconnect the leakage current path between the cathode pad 8 and the anode pad 9, thereby reducing leakage current and preventing bandwidth degradation. Other structures are the same as in Embodiment 4.

[0070] Implementation Method 6

[0071] Figure 20This is a top view showing the optical semiconductor device according to Embodiment 6. Multiple modulator-integrated laser diodes are integrated onto a single chip. The waveguides 10 of the multiple laser diodes are arranged parallel to each other. A laser unit 1 and multiple optical modulators 2 connected thereto are integrated onto a single chip. The wavelengths of the emitted light from the multiple laser diodes can be different or the same, depending on the application. A groove 27 is formed along the outer periphery of the cathode pad 8 and anode pad 9 of each optical modulator 2. That is, in each of the multiple optical modulators 2, a groove 27 is formed between the cathode pad 8 and the anode pad 9. This suppresses leakage current flowing from one optical modulator 2 to other optical modulators 2 or the laser unit 1.

[0072] Implementation Method 7

[0073] Figure 21 This is a top view showing the optical semiconductor device according to Embodiment 7. When a trench 27 is formed in the semiconductor layer 2, the chip is prone to breakage due to external stress. In particular, the chip is prone to breakage when stress is applied to a narrow area of ​​the chip by the chip pick-up chuck during assembly. To address this, a dummy pad 30, at the same height as the first platform 11 on the opposite side from the first platform 11 where the cathode pad 8 and anode pad 9 are disposed, is disposed. The dummy pad 30 is a floating electrode that is neither connected to the semiconductor layer 22 nor to other electrodes. With the dummy pad 30, the pressure of the chuck is dispersed, thereby reducing the risk of chip breakage.

[0074] Implementation Method 8

[0075] Figure 22 This is a cross-sectional view of the optical semiconductor device according to Embodiment 8. Figure 22 Corresponding to along Figure 1 A cross-sectional view taken at E-E'. The groove 27 is entirely embedded in the insulating film 20. This reduces the surface roughness of the device, allowing for uniform application of the resist used when forming the cathode electrode 6 and anode electrode 7 near the groove 27. Consequently, the linewidth of the cathode electrode 6 and anode electrode 7 can be narrowed.

[0076] Implementation Method 9

[0077] Figure 23 This is a top view of the optical semiconductor device according to Embodiment 9. Figure 24 It is along Figure 23A cross-sectional view taken along line A-A'. Instead of the groove 27 in Embodiment 1, a high-resistivity layer 31 is formed between the cathode pad 8 and the anode pad 9, which has been made highly resistive by injecting protons, silicon, helium, or argon ions into the p-InP cladding layer 15 and the n-InP cladding layer 13. This high-resistivity layer 31 disconnects the leakage current path between the cathode pad 8 and the anode pad 9, thereby reducing the leakage current and preventing bandwidth degradation. Other structures are the same as in Embodiment 1. Alternatively, the grooves 27 and 28 in Embodiments 2-7 can be replaced with the high-resistivity layer 31.

[0078] While the preferred embodiments have been described in detail above, the invention is not limited to these embodiments. Various modifications and substitutions can be made to the embodiments described above without departing from the scope of the claims. Hereinafter, various embodiments of this disclosure will be described as appendices.

[0079] (Appendix 1) An optical semiconductor device, characterized in that,

[0080] The aforementioned optical semiconductor device includes:

[0081] substrate;

[0082] An optical modulator has a semiconductor layer comprising a first conductivity layer, an absorption layer and a second conductivity layer sequentially formed on the substrate, a first electrode connected to the first conductivity layer, and a second electrode connected to the second conductivity layer.

[0083] The first pad is connected to the first electrode mentioned above; and

[0084] The second pad is connected to the second electrode mentioned above.

[0085] The aforementioned semiconductor layer has a waveguide and a first platform and a second platform disposed opposite to each other relative to the waveguide.

[0086] The first pad and the second pad are disposed on the first platform via an insulating film.

[0087] A groove is formed between the first pad and the second pad, and in the semiconductor layer.

[0088] (Appendix 2) The optical semiconductor device according to Appendix 1 is characterized in that,

[0089] The aforementioned groove extends through the aforementioned first conductive layer and the aforementioned second conductive layer.

[0090] (Note 3) The optical semiconductor device according to Note 1 or 2 is characterized in that,

[0091] It also includes a laser unit, which is monolithically integrated with the aforementioned optical modulator on the aforementioned substrate.

[0092] The aforementioned laser unit has electrodes disposed on the aforementioned first platform.

[0093] The aforementioned groove is also formed between the electrode and the electrode on the side of the first pad and the second pad.

[0094] (Appendix 4) The optical semiconductor device according to any one of Appendices 1 to 3, characterized in that,

[0095] The groove is formed along the outer periphery of at least one of the first pad and the second pad.

[0096] (Appendix 5) The optical semiconductor device according to any one of Appendices 1 to 4, characterized in that,

[0097] The aforementioned groove is formed in the entire area between the first pad and the second pad.

[0098] (Appendix 6) The optical semiconductor device according to any one of Appendices 1 to 5, characterized in that,

[0099] The aforementioned optical modulator has a first optical modulator and a second optical modulator that are arranged along the direction of light travel and electrically connected in series with each other.

[0100] (Appendix 7) The optical semiconductor device according to any one of Appendices 1 to 5, characterized in that,

[0101] The aforementioned optical modulator has multiple optical modulators.

[0102] In each of the plurality of optical modulators, the groove is formed between the first pad and the second pad.

[0103] (Appendix 8) The optical semiconductor device according to any one of Appendices 1 to 7, characterized in that,

[0104] It also has a dummy pad configured on the second platform and having the same height as the first and second pads.

[0105] (Appendix 9) The optical semiconductor device according to any one of Appendices 1 to 8, characterized in that,

[0106] The entire groove is embedded in the insulating film.

[0107] (Appendix 10) An optical semiconductor device, characterized in that,

[0108] The aforementioned optical semiconductor device includes:

[0109] substrate;

[0110] An optical modulator has a semiconductor layer comprising a first conductivity layer, an absorption layer and a second conductivity layer sequentially formed on the substrate, a first electrode connected to the first conductivity layer, and a second electrode connected to the second conductivity layer.

[0111] The first pad is connected to the first electrode mentioned above; and

[0112] The second pad is connected to the second electrode mentioned above.

[0113] The aforementioned semiconductor layer has a waveguide and a first platform and a second platform disposed opposite to each other relative to the waveguide.

[0114] The first pad and the second pad are disposed on the first platform via an insulating film.

[0115] Between the first pad and the second pad, a high-resistivity layer is formed by injecting protons, silicon, helium or argon ions into the semiconductor layer to achieve high resistance.

Claims

1. An optical semiconductor device, characterized in that, The optical semiconductor device includes: substrate; An optical modulator has a semiconductor layer comprising a first conductivity layer, an absorption layer, and a second conductivity layer sequentially formed on the substrate, a first electrode connected to the first conductivity layer, and a second electrode connected to the second conductivity layer; The first pad is connected to the first electrode; and The second pad is connected to the second electrode. The semiconductor layer has a waveguide and a first platform and a second platform disposed opposite to each other relative to the waveguide. The first pad and the second pad are disposed on the first platform via an insulating film. A groove is formed between the first pad and the second pad, and in the semiconductor layer.

2. The optical semiconductor device according to claim 1, characterized in that, The groove extends through the first conductive layer and the second conductive layer.

3. The optical semiconductor device according to claim 1 or 2, characterized in that, It also includes a laser unit, which is monolithically integrated with the optical modulator on the substrate. The laser unit has electrodes disposed on the first platform. The groove is also formed between the electrode and the electrode on the side of the first pad and the second pad that is closer to the electrode.

4. The optical semiconductor device according to claim 1 or 2, characterized in that, The groove is formed along the outer periphery of at least one of the first pad and the second pad.

5. The optical semiconductor device according to claim 1 or 2, characterized in that, The groove is formed in the entire area between the first pad and the second pad.

6. The optical semiconductor device according to claim 1 or 2, characterized in that, The optical modulator has a first optical modulator and a second optical modulator arranged along the direction of light travel and electrically connected in series with each other.

7. The optical semiconductor device according to claim 1 or 2, characterized in that, The optical modulator has multiple optical modulators. In each of the plurality of optical modulators, the groove is formed between the first pad and the second pad.

8. The optical semiconductor device according to claim 1 or 2, characterized in that, It also has a dummy pad configured on the second platform and having the same height as the first pad and the second pad.

9. The optical semiconductor device according to claim 1 or 2, characterized in that, The entire groove is embedded in the insulating film.

10. An optical semiconductor device, characterized in that, The optical semiconductor device includes: substrate; An optical modulator has a semiconductor layer comprising a first conductivity layer, an absorption layer, and a second conductivity layer sequentially formed on the substrate, a first electrode connected to the first conductivity layer, and a second electrode connected to the second conductivity layer; The first pad is connected to the first electrode; and The second pad is connected to the second electrode. The semiconductor layer has a waveguide and a first platform and a second platform disposed opposite to each other relative to the waveguide. The first pad and the second pad are disposed on the first platform via an insulating film. Between the first pad and the second pad, a high-resistivity layer is formed, which is made high-resistivity by injecting protons, silicon, helium or argon ions into the semiconductor layer.

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