Optical semiconductor equipment

Abstract

To obtain an optoelectronic device that can prevent a decrease in frequency bandwidth. [Solution] The optical modulator 2 has a semiconductor layer 22 including a first conductivity type layer 13, an absorption layer 23, and a second conductivity type layer 15 formed in 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. A first pad 8 is connected to the first electrode 6. A second pad 9 is connected to the second electrode 7. The semiconductor layer 22 has a waveguide 10 and a first terrace 11 and a second terrace 12 arranged on opposite sides of the waveguide 10. The first pad 8 and the second pad 9 are placed on the first terrace 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 9.

Description

Technical Field

[0005]

[0001] The present disclosure relates to an optical semiconductor device.

Background Art

[0002] An optical semiconductor device in which a laser section and an optical modulator are monolithically integrated has been proposed (see, for example, Patent Document 1). The optical modulator operates differentially by a differential voltage applied between an anode pad and a cathode pad. By arranging the anode pad and the cathode pad of the optical modulator on terraces on the same side with respect to the waveguide, the lengths of the wires connected to both pads can be made the same.

Prior Art Documents

Patent Documents

[0007] In this disclosure, a groove is formed in the semiconductor layer between the first pad and the second pad. This groove interrupts the leakage current path between the two, reducing the leakage current and improving the response, especially in the high-frequency range. As a result, a decrease in frequency bandwidth can be prevented. [Brief explanation of the drawing]

[0008] [Figure 1] This is a top view showing an optical semiconductor device according to Embodiment 1. [Figure 2] This is a cross-sectional view of the laser section along AA' in Figure 1. [Figure 3] This is a cross-sectional view of the optical modulator along BB' in Figure 1. [Figure 4] This is a cross-sectional view of the optical modulator along CC' in Figure 1. [Figure 5] This is a cross-sectional view along DD' in Figure 1. [Figure 6] This is a cross-sectional view along EE' in Figure 1. [Figure 7] This is a top view showing an optical semiconductor device related to a comparative example. [Figure 8] This is a cross-sectional view along AA' in Figure 7. [Figure 9] This figure shows the frequency response characteristics of Embodiment 1 and the comparative example. [Figure 10] It is a top view showing the optical semiconductor device according to Embodiment 2. [Figure 11] It is a cross-sectional view taken along the line A-A' of FIG. 10. [Figure 12] It is a diagram showing the frequency response characteristics of Embodiment 2 and the comparative example. [Figure 13] It is a top view showing the optical semiconductor device according to Embodiment 3. [Figure 14] It is a top view showing the optical semiconductor device according to Embodiment 4. [Figure 15] It is a top view showing Modification 1 of the optical semiconductor device according to Embodiment 4. [Figure 16] It is a top view showing Modification 2 of the optical semiconductor device according to Embodiment 4. [Figure 17] It is a top view showing the optical semiconductor device according to Embodiment 5. [Figure 18] It is a cross-sectional view of the first optical modulator taken along the line A-A' of FIG. 17. [Figure 19] It is a cross-sectional view of the second optical modulator taken along the line B-B' of FIG. 17. [Figure 20] It is a top view showing the optical semiconductor device according to Embodiment 6. [Figure 21] It is a top view showing the optical semiconductor device according to Embodiment 7. [Figure 22] It is a cross-sectional view showing the optical semiconductor device according to Embodiment 8. [Figure 23] It is a top view showing the optical semiconductor device according to Embodiment 9. [Figure 24] It is a cross-sectional view taken along the line A-A' of FIG. 23.

Embodiments for Carrying Out the Invention

[0009] The optical semiconductor device according to the embodiment will be described with reference to the drawings. The same or corresponding components may be denoted by the same reference numerals, and the repeated description may be omitted.

[0010] Embodiment 1 Figure 1 is a top view showing an optoelectronic device according to Embodiment 1. This optoelectronic 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 electro-absorption modulator.

[0011] 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 due to the differential voltage applied between the cathode pad 8 and the anode pad 9.

[0012] The first terrace 11 and the second terrace 12 are positioned on opposite sides of the waveguide 10. The cathode pad 8 and the anode pad 9 are positioned on the first terrace 11. This allows the wires connected to the anode pad 9 and the wires connected to the cathode pad 8 to be the same length.

[0013] Figure 2 is a cross-sectional view of the laser section along AA' in Figure 1. 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 has a multi-quantum well (MQW) structure of InGaAsP.

[0014] The active layer 14 is patterned in a stripe shape in plan view, and both sides are filled with a filling layer (not shown). The filling layer has a two-layer structure of Fe-InP and n-InP layers, or an InP PNP structure. A diffraction grating 17 is formed within the p-InP cladding layer 15.

[0015] Grooves 18 and 19 are formed in the p-InGaAs contact layer 16, p-InP cladding layer 15, and n-InP cladding layer 13 on both sides of the active layer 14. The upper surface of the p-InGaAs contact layer 16 and the inner surfaces of the grooves 18 and 19 are covered with an insulating film 20. An opening is formed in the insulating film 20 above the mesa structure between the grooves 18 and 19, and the anode electrode 5 is connected to the p-InGaAs contact layer 16 through this opening. An opening is formed in the insulating film 20 at the bottom surface of the groove 18, and the cathode electrode 4 is connected to the n-InP cladding layer 13 through this opening. An n-electrode 21 is formed on the lower surface of the semi-insulating InP substrate 3.

[0016] Figure 3 is a cross-sectional view of the optical modulator along BB' in Figure 1. 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 a semiconductor layer 22. Within the mesa structure between grooves 18 and 19, an absorption layer 23 is stacked on top of the n-InP cladding layer 13. The absorption layer 23 is a multiple quantum well structure of InGaAsP.

[0017] Grooves 18 and 19 are formed spaced apart from each other in the p-InGaAs contact layer 16, the p-InP cladding layer 15, and the n-InP cladding layer 13. The grooves 18 and 19 limit the width of the absorption layer 23, allowing it to function as a waveguide 10. The semiconductor layer 22 has the waveguide 10 and a first terrace 11 and a second terrace 12 positioned opposite each other from the waveguide 10. An opening is formed in the insulating film 20 at the bottom of the groove 18, and the cathode electrode 6 is connected to the n-InP cladding layer 13 through this opening. The cathode pad 8 is positioned on the first terrace 11 via the insulating film 20 and is connected to the cathode electrode 6.

[0018] Figure 4 is a cross-sectional view of the optical modulator along CC' in Figure 1. An opening is formed in the insulating film 20 on the waveguide 10, and the anode electrode 7 is connected to the p-InGaAs contact layer 16 through this opening. The anode pad 9, like the cathode pad 8, is placed on the first terrace 11 via the insulating film 20 and is connected to the anode electrode 7.

[0019] Figure 5 is a cross-sectional view along DD' in Figure 1. The active layer 14 and the absorption layer 23 are connected by a transparent waveguide layer 24. A transparent waveguide layer 24 is also formed between the absorption layer 23 and the exit end face. The transparent waveguide layer 24 consists of a single layer of InGaAsP.

[0020] Figure 6 is a cross-sectional view along EE' in Figure 1. The cathode electrode 6 and anode electrode 7 of the optical modulator 2 are each connected to a differential power supply 25. The differential power supply 25 operates in a push-pull configuration by alternately applying voltage to one end as positive and the other as negative. However, the voltage on the anode side may be varied, and the potential on the cathode side may be set to zero. A load resistor R is connected in parallel to the pn junction 26 of the optical modulator 2. The load resistor R is provided outside the device for impedance matching.

[0021] A groove 27 is formed in the semiconductor layer 22 between the cathode pad 8 and the anode pad 9. Specifically, the groove 27 penetrates the p-InP cladding layer 15 and the n-InP cladding layer 13 and reaches the semi-insulating InP substrate 3. The groove 27 may be formed simultaneously with grooves 18 and 19.

[0022] The n-InP cladding layer 13 is typically very low in resistance to reduce the series resistance of the optical modulator 2. Therefore, the groove 27 needs to remove at least a portion of the n-InP cladding layer 13, and it is preferable that the groove 27 penetrates the n-InP cladding layer 13. If a high-density n-type layer is provided over the entire surface of the n-InP cladding layer 13 to connect the n-InP cladding layer 13 and the cathode electrode 6, the groove 27 also needs to divide this n-type layer.

[0023] Next, the effects of this embodiment will be explained in comparison with a comparative example. Figure 7 is a top view showing an optoelectronic device according to the comparative example. Figure 8 is a cross-sectional view along AA' in Figure 7. The groove 27 is not formed in the comparative example. The cathode pad 8 and the 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 resistor R1, which is a leakage current path, exists in the semiconductor layer 22 between the cathode pad 8 and the anode pad 9.

[0024] Furthermore, the cathode pad 8 of the optical modulator 2 and the cathode electrode 4 of the laser unit 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, which is a leakage current path, exists in the semiconductor layer 22 between the anode pad 9 and the cathode electrode 4. Note that the positions of the cathode pad 8 and anode pad 9 of the optical modulator 2 may be reversed. In this case, a potential difference will occur between the anode electrode 7 of the optical modulator 2 and the cathode electrode 4 of the laser unit 1, resulting in leakage current.

[0025] The current due to the anode voltage of the differential power supply 25 flows through two paths: one through the load resistor R and resistor R2, and the other through the capacitance C of the insulating film 20 and resistors R1 and R2. The current due to the cathode voltage flows through resistor R2 to the cathode electrode 4 of the laser unit 1.

[0026] As the frequency increases, the impedance of capacitance C decreases, and the leakage current flowing through resistor R1 increases. This increase in leakage current reduces the current flowing through the load resistor R, thus decreasing the voltage applied to the optical modulator 2. Consequently, as the frequency increases, the leakage current increases and the extinction ratio decreases, resulting in a reduced frequency bandwidth.

[0027] In contrast, in this embodiment, a groove 27 is formed in the semiconductor layer 22 between the cathode pad 8 and the anode pad 9. This groove 27 divides the leakage current path between the two, reducing the leakage current and improving the response, especially in the high-frequency range. As a result, a decrease in frequency bandwidth can be prevented. Note that a similar effect can be obtained even in a semiconductor device consisting only of an optical modulator without the laser unit 1 by forming a groove 27 between the cathode pad 8 and the anode pad 9.

[0028] Figure 9 shows the frequency response characteristics of Embodiment 1 and the comparative example. The vertical axis of the figure shows the relative frequency dependence of the optical intensity amplitude when the voltage amplitude of the pulse applied to the optical modulator is kept constant and the frequency is changed. In this embodiment, it can be seen that both the frequency dependence of the optical response to anode voltage modulation and the frequency dependence of the optical response to cathode voltage modulation are improved compared to the comparative example.

[0029] Embodiment 2 Figure 10 is a top view showing an optoelectronic device according to Embodiment 2. Figure 11 is a cross-sectional view along AA' in Figure 10. In addition to the groove 27 of Embodiment 1, a groove 28 is also formed between the cathode pad 8 of the optical modulator 2 and the cathode electrode 4 of the laser unit 1. The groove 28 electrically isolates the low-resistance layers such as the p-InP cladding layer 15 and the n-InP cladding layer 13. As a result, the leakage current flowing to the cathode electrode 4 of the laser unit 1 due to the cathode voltage is reduced, and the amplitude of cathode modulation is increased.

[0030] Furthermore, if the positions of the cathode pad 8 and anode pad 9 of the optical modulator 2 are reversed, a groove 28 will be formed between the anode pad 9 of the optical modulator 2 and the cathode electrode 4 of the laser unit 1. In other words, a groove 28 will be 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 unit 1 and the cathode electrode 4.

[0031] Figure 12 shows the frequency response characteristics of Embodiment 2 and the comparative example. In this embodiment, it can be seen that both the frequency response for anode modulation and the frequency response for cathode modulation are improved compared to the comparative example. The two grooves 27 and 28 make the frequency response characteristics for anode modulation and cathode modulation almost the same, enabling ideal differential operation.

[0032] Furthermore, in the comparative example, the presence of resistors R1 and R2 means that the current paths due to the cathode voltage and the current paths due to the anode voltage are different, and their impedances are also different. In contrast, in this embodiment, grooves 27 and 28 divide the current paths through resistors R1 and R2, so that the current due to both voltages flows only through the load resistor R. As a result, the impedances of the anode and cathode sides become equal. Consequently, the amplitude and phase of the noise on the anode and cathode sides can be matched, maximizing the noise reduction effect of differential operation.

[0033] Embodiment 3 Figure 13 is a top view showing an optoelectronic device according to Embodiment 3. A groove 27 is formed along the outer circumference 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. It is desirable that the groove 27 be formed in the entire area of ​​the outer circumference of the cathode pad 8, but it may be formed in only a part of it. In addition, the groove 27 may be formed along the outer circumference of the anode pad 9. Other configurations and effects are the same as in Embodiment 1.

[0034] Embodiment 4 Figure 14 is a top view showing an optoelectronic device according to Embodiment 4. Grooves 27 are formed along the outer circumferences of the cathode pad 8 and the anode pad 9, respectively. It is desirable that the grooves 27 be formed in the entire area of ​​the outer circumference of the cathode pad 8 and the anode pad 9, but they may be formed in only a part of it. The other configurations and effects are the same as in Embodiment 1.

[0035] It is preferable that the area of ​​the anode pad 9 and the area of ​​the cathode pad 8 are the same. By making the parasitic capacitance of both pads the same, the frequency response characteristics of anode modulation and cathode modulation become almost the same, enabling ideal differential operation. Furthermore, by making the impedance of the anode and cathode sides the same, the amplitude and phase of the noise on the anode and cathode sides can be matched, thereby maximizing the noise reduction effect of differential operation.

[0036] Figure 15 is a top view showing a modified example 1 of the optical semiconductor device according to Embodiment 4. The groove 27 is formed not only around the outer periphery of the pads but also across the entire region between the cathode pad 8 and the anode pad 9. Figure 16 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 in a rectangular shape that includes the outer periphery of the pads and the space between the pads. However, the insulating film 20 and semiconductor layer 22 remain directly beneath the cathode pad 8 and the anode pad 9. There are no particular restrictions on the length and width of the groove 27 as long as it can electrically isolate the pads.

[0037] Embodiment 5 Figure 17 is a top view showing an optical semiconductor device according to Embodiment 5. The optical modulator 2 has a first optical modulator 2a and a second optical modulator 2b arranged in the direction of light propagation. Figure 18 is a cross-sectional view of the first optical modulator along AA' in Figure 17. A common electrode 29 is connected to the p-InGaAs contact layer 16 of the first optical modulator 2a. A cathode electrode 6 is connected to the n-InP cladding layer 13 of the first optical modulator 2a at the bottom of the groove 18.

[0038] Figure 19 is a cross-sectional view of the second optical modulator along BB' in Figure 17. 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 at the bottom of the groove 19. Thus, 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.

[0039] Similar to Embodiment 4, grooves 27 are formed along the outer circumference of the cathode pad 8 and the anode pad 9. The grooves 27 interrupt the leakage current path between the cathode pad 8 and the anode pad 9, reducing the leakage current and thus preventing a decrease in frequency bandwidth. The other configurations are the same as in Embodiment 4.

[0040] Embodiment 6 Figure 20 is a top view showing an optical semiconductor device according to Embodiment 6. Multiple modulator-integrated laser diodes are integrated on a single chip. The waveguides 10 of the multiple laser diodes are arranged parallel to each other. One laser unit 1 and multiple optical modulators 2 connected to it may be integrated on a single chip. The wavelengths of the emitted light from the multiple laser diodes may be different or the same, and are set appropriately depending on the application. Grooves 27 are formed along the outer circumference of the cathode pad 8 and anode pad 9 of each optical modulator 2. That is, grooves 27 are formed between the cathode pad 8 and anode pad 9 in each of the multiple optical modulators 2. This makes it possible to suppress leakage current flowing from one optical modulator 2 to another optical modulator 2 or laser unit 1.

[0041] Embodiment 7 Figure 21 is a top view showing an optoelectronic device according to Embodiment 7. When grooves 27 are formed in the semiconductor layer 22, the chip becomes prone to cracking due to external stress. In particular, when stress is applied to a narrow area of ​​the chip by the chip pickup collet during assembly, the chip becomes prone to cracking. Therefore, a dummy pad 30 of the same height as the cathode pad 8 and anode pad 9 is placed on the second terrace 12, which is opposite to the first terrace 11 where the cathode pad 8 and anode pad 9 are located. The dummy pad 30 is a floating electrode that is not connected to the semiconductor layer 22 or any other electrodes. The dummy pad 30 distributes the pressure from the collet, thereby reducing chip cracking.

[0042] Embodiment 8 Figure 22 is a cross-sectional view showing an optoelectronic device according to Embodiment 8. Figure 22 corresponds to a cross-sectional view along EE' in Figure 1. The groove 27 is entirely filled with an insulating film 20. This reduces surface irregularities on the device, allowing for uniform application of the resist when forming the cathode electrode 6 and anode electrode 7 near the groove 27. Consequently, it becomes possible to narrow the line width of the cathode electrode 6 and anode electrode 7.

[0043] Embodiment 9 Figure 23 is a top view showing an optoelectronic device according to Embodiment 9. Figure 24 is a cross-sectional view along AA' in Figure 23. Instead of the groove 27 of Embodiment 1, a high-resistivity layer 31 is formed between the cathode pad 8 and the anode pad 9 by implanting proton, silicon, helium, or argon ions into the p-InP cladding layer 15 and the n-InP cladding layer 13 to increase their resistance. This high-resistivity layer 31 divides the leakage current path between the cathode pad 8 and the anode pad 9, reducing the leakage current and thus preventing a decrease in frequency bandwidth. The other configurations are the same as in Embodiment 1. Note that the grooves 27 and 28 of Embodiments 2 to 7 may also be replaced with the high-resistivity layer 31.

[0044] Although preferred embodiments have been described in detail above, the invention is not limited to the embodiments described above, and various modifications and substitutions can be made to the embodiments described above without departing from the scope of the claims. Various aspects of this disclosure are described below as appendices. (Note 1) circuit board and A semiconductor layer comprising a first conductivity type layer, an absorption layer, and a second conductivity type layer formed sequentially on the substrate, and an optical modulator having a first electrode connected to the first conductivity type layer and a second electrode connected to the second conductivity type layer, A first pad connected to the first electrode, The device comprises a second pad connected to the second electrode, The semiconductor layer has a waveguide and a first terrace and a second terrace arranged on opposite sides of the waveguide. The first pad and the second pad are arranged on the first terrace with an insulating film in between. An optoelectronic semiconductor device characterized in that a groove is formed in the semiconductor layer between the first pad and the second pad. (Note 2) The optical semiconductor device according to Appendix 1, characterized in that the groove penetrates the first conductivity type layer and the second conductivity type layer. (Note 3) The aforementioned substrate further comprises the optical modulator and a monolithically integrated laser unit, The laser unit has electrodes positioned on the first terrace, The optical semiconductor device according to Appendix 1 or 2, characterized in that the groove is also formed between the first pad and the second pad that is closer to the electrode and the electrode. (Note 4) The optical semiconductor device according to any one of appendices 1 to 3, characterized in that the groove is formed along the outer circumference of at least one of the first pad and the second pad. (Note 5) The optical semiconductor device according to any one of appendices 1 to 4, characterized in that the groove is formed over the entire region between the first pad and the second pad. (Note 6) The optical modulator is characterized by having a first optical modulator and a second optical modulator arranged in the direction of light propagation and electrically connected in series with respect to each other, as described in any of the appendices 1 to 5. (Note 7) The optical modulator has a plurality of optical modulators, The optical semiconductor device according to any one of appendices 1 to 5, characterized in that the groove is formed between the first pad and the second pad in each of the plurality of optical modulators. (Note 8) The optical semiconductor device according to any one of appendices 1 to 7, further comprising a dummy pad disposed on the second terrace and having the same height as the first pad and the second pad. (Note 9) The optical semiconductor device according to any one of the appendices 1 to 8, characterized in that the groove is entirely filled with the insulating film. (Note 10) circuit board and A semiconductor layer comprising a first conductivity type layer, an absorption layer, and a second conductivity type layer formed sequentially on the substrate, and an optical modulator having a first electrode connected to the first conductivity type layer and a second electrode connected to the second conductivity type layer, A first pad connected to the first electrode, The device comprises a second pad connected to the second electrode, The semiconductor layer has a waveguide and a first terrace and a second terrace arranged on opposite sides of the waveguide. The first pad and the second pad are arranged on the first terrace with an insulating film in between. An optoelectronic semiconductor device characterized in that a high-resistivity layer is formed between the first pad and the second pad by implanting proton, silicon, helium, or argon ions into the semiconductor layer to increase its resistance. [Explanation of symbols]

[0045] 1 Laser section, 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 terrace, 12 Second terrace, 13 n-InP cladding layer (first conductivity layer), 15 p-InP cladding layer (second conductivity layer), 20 Insulating film, 22 Semiconductor layer, 23 Absorption layer, 27, 28 Grooves, 30 Dummy pad, 31 High-resistivity layer

Claims

1. circuit board and A semiconductor layer comprising a first conductivity layer, an absorption layer, and a second conductivity layer formed sequentially on the substrate, and an optical modulator having 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, The device comprises a second pad connected to the second electrode, The semiconductor layer has a waveguide and a first terrace and a second terrace arranged on opposite sides of the waveguide. The first pad and the second pad are arranged on the first terrace with an insulating film in between. An optical semiconductor device characterized in that a groove is formed in the semiconductor layer between the first pad and the second pad.

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

3. The aforementioned substrate further comprises the optical modulator and a monolithically integrated laser unit, The laser unit has electrodes positioned on the first terrace, The optical semiconductor device according to claim 1 or 2, characterized in that the groove is also formed between the first pad and the second pad that is closer to the electrode and the electrode.

4. The optical semiconductor device according to claim 1 or 2, characterized in that the groove is formed along the outer circumference 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 over the entire region between the first pad and the second pad.

6. The optical modulator is characterized by having a first optical modulator and a second optical modulator arranged in the direction of light propagation and electrically connected in series with respect to each other, as described in claim 1 or 2.

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

8. The optical semiconductor device according to claim 1 or 2, further comprising a dummy pad disposed on the second terrace 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 groove is entirely filled with the insulating film.

10. circuit board and A semiconductor layer comprising a first conductivity layer, an absorption layer, and a second conductivity layer formed sequentially on the substrate, and an optical modulator having 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, The device comprises a second pad connected to the second electrode, The semiconductor layer has a waveguide and a first terrace and a second terrace arranged on opposite sides of the waveguide. The first pad and the second pad are arranged on the first terrace with an insulating film in between. An optoelectronic semiconductor device characterized in that a high-resistivity layer is formed between the first pad and the second pad by implanting proton, silicon, helium, or argon ions into the semiconductor layer to increase its resistance.

Images