US-20260126679-A1 - OPTICAL SEMICONDUCTOR DEVICE

US20260126679A1US 20260126679 A1US20260126679 A1US 20260126679A1US-20260126679-A1

Abstract

An optical semiconductor device includes: a substrate; an optical modulator including a semiconductor layer having a first conductive type layer, an absorbing layer and a second conductive type layer which are formed in this order on the substrate, a first electrode connected to the first conductive type layer, and a second electrode connected to the second conductive type layer; a first pad connected to the first electrode; and a second pad connected to the second electrode, wherein the semiconductor layer includes a waveguide, a first terrace and a second terrace positioned on the opposite sides with respect to the waveguide, the first pad and the second pad are placed on the first terrace via an insulating film, and a groove is formed in the semiconductor layer between the first pad and the second pad.

Inventors

Kyosuke Kuramoto
Asami Uchiyama
Eitaro Ishimura
Masaaki Shimada

Assignees

MITSUBISHI ELECTRIC CORPORATION

Dates

Publication Date: 20260507
Application Date: 20250723
Priority Date: 20241105

Claims (10)

1 . An optical semiconductor device comprising: a substrate; an optical modulator including a semiconductor layer having a first conductive type layer, an absorbing layer and a second conductive type layer which are formed in this order on the substrate, a first electrode connected to the first conductive type layer, and a second electrode connected to the second conductive type layer; a first pad connected to the first electrode; and a second pad connected to the second electrode, wherein the semiconductor layer includes a waveguide, a first terrace and a second terrace positioned on the opposite sides with respect to the waveguide, the first pad and the second pad are placed on the first terrace via an insulating film, and 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 , wherein the groove penetrates the first conductive type layer and the second conductive type layer.
3 . The optical semiconductor device according to claim 1 , further comprising a laser unit monolithically integrated with the optical modulator on the substrate, wherein the laser unit includes an electrode placed on the first terrace, and the groove is formed between the electrode and the first pad or the second pad which is closer to the electrode.
4 . The optical semiconductor device according to claim 1 , wherein the groove is formed along an outer periphery of at least one of the first pad and the second pad.
5 . The optical semiconductor device according to claim 1 , wherein the groove is formed in an entire region between the first pad and the second pad.
6 . The optical semiconductor device according to claim 1 , wherein the optical modulator includes a first optical modulator and a second optical modulator which are placed in a traveling direction of light and electrically connected in series.
7 . The optical semiconductor device according to claim 1 , wherein the optical modulator includes a plurality of optical modulators, and 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 , further comprising a dummy pad having the same height as the first pad and the second pad and placed on the second terrace.
9 . The optical semiconductor device according to claim 1 , wherein the groove is entirely filled with the insulating film.
10 . An optical semiconductor device comprising: a substrate; an optical modulator including a semiconductor layer having a first conductive type layer, an absorbing layer and a second conductive type layer which are formed in this order on the substrate, a first electrode connected to the first conductive type layer, and a second electrode connected to the second conductive type layer; a first pad connected to the first electrode; and a second pad connected to the second electrode, wherein the semiconductor layer includes a waveguide, a first terrace and a second terrace positioned on the opposite sides with respect to the waveguide, the first pad and the second pad are placed on the first terrace via an insulating film, and a high-resistance layer with increased resistance is formed between the first pad and the second pad by implantation of protons, silicon, helium or argon ions into the semiconductor layer.

Description

BACKGROUND OF THE INVENTION Field The present disclosure relates to an optical semiconductor device. Background An optical semiconductor device in which a laser unit and an optical modulator are monolithically integrated has been proposed (see, for example, Patent Literature 1). The optical modulator is differentially operated by the differential voltage applied between an anode pad and a cathode pad. By placing the anode pad and the cathode pad of the optical modulator on a terrace on the same side with respect to a waveguide, the lengths of wires connected to both the pads can be made equal. Patent Literature 1: JP 5891920 B2 SUMMARY When the optical modulator is differentially operated, since a leakage current flows between the two pads of the optical modulator, the voltage applied to an absorbing layer of the optical modulator decreases. The leakage current flows through a capacitance under the electrodes of the optical modulator, and, therefore, as the frequency increases, the leakage current increases and the extinction ratio decreases. As a result, there is a problem of reduction of the frequency band in which the optical modulator can operate normally. The present disclosure has been made to solve the problem mentioned above, and the purpose of the disclosure is to obtain an optical semiconductor device capable of preventing a reduction of the frequency band. Solution to Problem An optical semiconductor device according to the present disclosure includes: a substrate; an optical modulator including a semiconductor layer having a first conductive type layer, an absorbing layer and a second conductive type layer which are formed in this order on the substrate, a first electrode connected to the first conductive type layer, and a second electrode connected to the second conductive type layer; a first pad connected to the first electrode; and a second pad connected to the second electrode, wherein the semiconductor layer includes a waveguide, a first terrace and a second terrace positioned on the opposite sides with respect to the waveguide, the first pad and the second pad are placed on the first terrace via an insulating film, and a groove is formed in the semiconductor layer between the first pad and the second pad. Advantageous Effects of Invention In the present disclosure, the groove is formed in the semiconductor layer between the first pad and the second pad. Since this groove splits the leakage current path between them and reduces the leakage current, the response particularly in a high frequency range is improved. As a result, a reduction of the frequency band can be prevented. BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a top view showing an optical semiconductor device according to a first embodiment. FIG. 2 is a cross-sectional view of the laser unit taken along A-A′ in FIG. 1. FIG. 3 is a cross-sectional view of the optical modulator taken along B-B′ in FIG. 1. FIG. 4 is a cross-sectional view of the optical modulator taken along C-C′ in FIG. 1. FIG. 5 is a cross-sectional view taken along D-D′ in FIG. 1. FIG. 6 is a cross-sectional view taken along E-E′ in FIG. 1. FIG. 7 is a top view showing an optical semiconductor device according to the comparative example. FIG. 8 is a cross-sectional view taken along A-A′ in FIG. 7. FIG. 9 is a diagram showing the frequency response characteristics of the first embodiment and the comparative example. FIG. 10 is a top view showing an optical semiconductor device according to a second embodiment. FIG. 11 is a cross-sectional view taken along A-A′ in FIG. 10. FIG. 12 is a diagram showing the frequency response characteristics of the second embodiment and the comparative example. FIG. 13 is a top view showing an optical semiconductor device according to a third embodiment. FIG. 14 is a top view showing an optical semiconductor device according to a fourth embodiment. FIG. 15 is a top view showing an optical semiconductor device of a first modified example according to the fourth embodiment. FIG. 16 is a top view showing an optical semiconductor device of a second modified example according to the fourth embodiment. FIG. 17 is a top view showing an optical semiconductor device according to a fifth embodiment. FIG. 18 is a cross-sectional view of the first optical modulator taken along A-A′ in FIG. 17. FIG. 19 is a cross-sectional view of the second optical modulator taken along B-B′ in FIG. 17. FIG. 20 is a top view showing an optical semiconductor device according to a sixth embodiment. FIG. 21 is a top view showing an optical semiconductor device according to a seventh embodiment. FIG. 22 is a cross-sectional view showing an optical semiconductor device according to an eighth embodiment. FIG. 23 is a top view showing an optical semiconductor device according to a ninth embodiment. FIG. 24 is a cross-sectional view taken along A-A′ in FIG. 23. DESCRIPTION OF EMBODIMENTS An optical semiconductor device according to the embodiments of the present disclosure w