Optical semiconductor device and manufacturing method thereof

Abstract

The present invention is provided with: a substrate (16); an active layer (20) which is formed on the substrate (16) and generates laser light; a modulation layer (22) which is formed on the substrate (16), is adjacent to the active layer (20), and modulates the laser light; a cladding layer (24) formed on the active layer (20) and the modulation layer (22); and a contact layer (26) which is formed on the cladding layer (24), in which one protrusion (28) is formed on the upper surface of the modulation layer (22) and at the end on the active layer (20) side, and two protrusions (30) are formed on the upper surface of the cladding layer (24) and vertically above the one protrusion (28), and the contact layer (26) is separated by the two protrusions (30) in the optical axis direction of the laser light.

Description

Technical Field

[0001] The present disclosure relates to an optical semiconductor device and a method for manufacturing the same. Background Art

[0002] In recent years, in mobile communication systems and cloud services, the amount of data communication has been rapidly increasing. In order to process a huge amount of data communication at high speed and in large quantities, high-speed operation of optical semiconductor devices and a large number of optical semiconductor devices are required.

[0003] For example, Patent Document 1 discloses an optical semiconductor device in which a semiconductor laser and an optical modulator are integrated on the same semiconductor substrate and each has a contact layer. In this optical semiconductor device, a low-resistance contact layer as a p-type semiconductor layer is formed on the upper parts of the semiconductor laser and the optical modulator by an epitaxial growth method. An isolation trench is formed by removing, by etching, the part above the connection part between the semiconductor laser and the optical modulator in the contact layer, thereby disconnecting the contact layer and suppressing the flow of current therebetween.

[0004] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2000-275460

[0005] However, in the optical semiconductor device disclosed in Patent Document 1, a complex process of forming an isolation trench between the semiconductor laser and the optical modulator and then filling the isolation trench is required. As a result, the number of processes increases, which is an important factor hindering mass production. Summary of the Invention

[0006] The present disclosure has been made to solve the above problems, and an object thereof is to obtain an optical semiconductor device and a method for manufacturing the same that can disconnect a contact layer without increasing the number of processes.

[0007] The optical semiconductor device according to the present disclosure includes: a semiconductor substrate; an active layer formed on the semiconductor substrate and generating laser light; an optical modulation layer formed on the semiconductor substrate, adjacent to the active layer, and modulating the laser light; a cladding layer formed on the active layer and the optical modulation layer; and a contact layer formed on the cladding layer. A first protrusion is formed on the upper surface of the optical modulation layer and at an end on the active layer side, and a second protrusion is formed on the upper surface of the cladding layer and vertically above the first protrusion. The contact layer is disconnected by the second protrusion in the optical axis direction of the laser light.

[0008] The manufacturing method of the opto-semiconductor device according to the present disclosure includes: a step of forming an active layer that generates laser light on a semiconductor substrate; a step of forming an insulating film on the active layer; a step of using the insulating film as a selective growth mask to form an optical modulation layer that is adjacent to the active layer on the semiconductor substrate, has a first protrusion at an end portion on the active layer side of the upper surface, and modulates the laser light; a step of removing the insulating film; a step of forming a cladding layer having a second protrusion on the upper surface vertically above the first protrusion on the active layer and the optical modulation layer; and a step of forming a contact layer that is disconnected by the second protrusion in the optical axis direction of the laser on the cladding layer.

[0009] According to the present disclosure, an opto-semiconductor device and a manufacturing method thereof that can disconnect the contact layer without increasing the number of processes can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a perspective view of the opto-semiconductor device according to Embodiment 1.

[0011] Figure 2 It is a cross-sectional view of the opto-semiconductor device according to Embodiment 1.

[0012] Figure 3 It is a cross-sectional view for explaining the manufacturing method of the opto-semiconductor device according to Embodiment 1.

[0013] Figure 4 It is a cross-sectional view for explaining the manufacturing method of the opto-semiconductor device according to Embodiment 1.

[0014] Figure 5 It is a cross-sectional view for explaining the manufacturing method of the opto-semiconductor device according to Embodiment 1.

[0015] Figure 6 It is a cross-sectional view for explaining the manufacturing method of the opto-semiconductor device according to Embodiment 1.

[0016] Figure 7 It is a cross-sectional view for explaining the manufacturing method of the opto-semiconductor device according to Embodiment 1.

[0017] Figure 8 It is a cross-sectional view for explaining the manufacturing method of the opto-semiconductor device according to Embodiment 1.

[0018] Figure 9 It is a cross-sectional view for explaining the manufacturing method of the opto-semiconductor device according to Embodiment 1.

[0019] Figure 10 It is a cross-sectional view of the opto-semiconductor device according to Embodiment 2.

[0020] Figure 11It is a cross-sectional view for explaining the manufacturing method of the optical semiconductor device according to Embodiment 2.

[0021] Figure 12 It is a cross-sectional view of the optical semiconductor device according to Embodiment 3.

[0022] Figure 13 It is a cross-sectional view for explaining the manufacturing method of the optical semiconductor device according to Embodiment 3.

[0023] Figure 14 It is a cross-sectional view for explaining the manufacturing method of the optical semiconductor device according to Embodiment 3.

[0024] Figure 15 It is a cross-sectional view of the optical semiconductor device according to Embodiment 4.

[0025] Figure 16 It is a cross-sectional view for explaining the manufacturing method of the optical semiconductor device according to Embodiment 4. Detailed Embodiments

[0026] Embodiment 1

[0027] In Figure 1 a perspective view of the optical semiconductor device 10 according to Embodiment 1 is shown. In Figure 2 a cross-section taken along line A-A in Figure 1 is shown. The optical semiconductor device 10 is a ridge-type semiconductor laser with an optical modulator, and includes a laser section 12 and a modulator section 14 adjacent to the laser section 12. A striped mesa surface 18 is formed from the laser section 12 to the modulator section 14 in the optical semiconductor device 10. The mesa surface 18 has an active layer 20, a cladding layer 24, and a contact layer 26 in the laser section 12, and has an optical modulation layer 22, a cladding layer 24, and a contact layer 26 in the modulator section 14. In the laser section 12, laser light that resonates in the stripe direction of the mesa surface 18 is generated in the active layer 20. In the modulator section 14, the laser light from the active layer 20 is modulated by passing through and being absorbed by the optical modulation layer 22. The laser light modulated by the modulator section 14 is emitted from the end face on the modulator section 14 side of the mesa surface 18.

[0028] The optical semiconductor device 10 includes a semiconductor substrate 16. The semiconductor substrate 16 is made of, for example, n-type InP.

[0029] An active layer 20 is formed on the semiconductor substrate 16. The active layer 20 is made of, for example, InP and has a strained multiple quantum well structure. With this structure, high output and low distortion of the laser light output from the optical semiconductor device 10 can be achieved.

[0030] On the semiconductor substrate 16, an optical modulation layer 22 is formed adjacent to the active layer 20. The optical modulation layer 22 is made of, for example, InGaAsP and has a quantum well structure. On the upper surface of the optical modulation layer 22 and at the end on the active layer 20 side, a first protrusion 28 is formed. The first protrusion 28 protrudes to a position higher than the upper surface of the active layer 20.

[0031] On the active layer 20 and the optical modulation layer 22, a cladding layer 24 is formed. The cladding layer 24 is made of, for example, p-type InP doped with Zn, and the p-type concentration is 1×10 18 cm -3 , and the thickness is 1 μm. On the upper surface of the cladding layer 24, a second protrusion 30 is formed. The second protrusion 30 is formed vertically above the first protrusion 28. Here, the vertical direction refers to the vertical direction with respect to the upper surface of the semiconductor substrate 16.

[0032] On the cladding layer 24, a contact layer 26 is formed. The contact layer 26 is made of, for example, p-type InP doped with Zn, and the p-type concentration is 1×10 19 cm -3 , and the thickness is 400 nm. The contact layer 26 is disconnected by the second protrusion 30 in the optical axis direction ( Figure 2 the left and right directions) of the laser. The height of the second protrusion 30 is above the thickness of the contact layer 26 to improve the electrical separation of the disconnected contact layer 26. In addition, the thickness of the contact layer 26 needs to allow current to flow evenly in the active layer 20 and the optical modulation layer 22, and is preferably 400 nm or more in order to maintain the carrier concentration of the contact layer 26 itself.

[0033] A protective film 32 is formed to cover the upper surface and side surface of the mesa portion 18 and the upper surface of the semiconductor substrate 16. On the upper surface of the mesa portion 18, openings are respectively formed in the laser portion 12 and the modulator portion 14, and a laser electrode 34 and a modulator electrode 36 that are electrically connected to the contact layer 26 through the openings are formed. These electrodes are made of, for example, Ti / Pt / Au from the bottom. In addition, a back electrode 38 is formed on the back surface of the semiconductor substrate 16. The back electrode 38 is made of, for example, Au / Ge / Ni / Au from the side close to the semiconductor substrate 16.

[0034] Here, the manufacturing method of the optoelectronic semiconductor device 10 will be described.

[0035] First, as Figure 3 described above, the active layer 20 is formed on the semiconductor substrate 16. For the formation of the active layer 20, for example, the MOCVD (Metal Organic Chemical Vapor Deposition) method is used.

[0036] Next, using a method such as RIE (Reactive Ion Etching), the active layer 20 is dry-etched to the semiconductor substrate 16 with the insulating film 40 formed in a stripe shape on the active layer 20 as an etching mask, and the structure of Figure 4 is obtained. The insulating film 40 is made of, for example, SiO2 and is formed using a sputtering method and a photolithography technique.

[0037] Next, as Figure 5 shown, with the insulating film 40 as a selective growth mask, the optical modulation layer 22 is formed in a buried manner on the semiconductor substrate 16 by the MOCVD method. When forming the optical modulation layer 22, a part of the source gas flowing onto the insulating film 40 flows toward the optical modulation layer 22 side ( Figure 5 the right side), so overgrowth occurs at the end of the optical modulation layer 22 on the active layer 20 side. As a result, the first protrusion 28 is formed in the optical modulation layer 22.

[0038] Next, as Figure 6 shown, the insulating film 40 is removed.

[0039] Next, as Figure 7 shown, the cladding layer 24 is formed on the active layer 20 and the optical modulation layer 22. For the formation of the cladding layer 24, for example, the MOCVD method is used. At this time, the second protrusion 30 is formed vertically above the first protrusion 28 in the cladding layer 24.

[0040] Next, as Figure 8 shown, the contact layer 26 is formed on the cladding layer 24 using the MOCVD method. At this time, a chlorine-based gas (e.g., HCl) is added while growing. As a result, the growth layer formed on the second protrusion 30 is eliminated while the contact layer 26 grows, so the contact layer 26 is formed by being disconnected in the optical axis direction of the laser. In addition, the growth temperature range is set to 550 - 650 °C. Since it grows at such a high temperature, the mass transport effect is assisted, and the contact layer 26 does not grow relative to the 111B plane on the upper surface of the second protrusion 30. In addition, although it is shown in Figure 8 that there is no growth of the contact layer 26 anywhere on the upper surface of the second protrusion 30, the contact layer 26 sometimes grows at the top. However, since the contact layer 26 does not grow on the left and right inclined portions of the second protrusion 30, the situation where the contact layer 26 is disconnected by the second protrusion 30 in the left and right directions remains unchanged.

[0041] Next, a mesa insulating film is formed on the cladding layer 24 and the contact layer 26 by plasma CVD (Chemical Vapor Deposition), patterned into stripes through a transfer process, and dry-etched. Next, using the mesa insulating film as a mask, the contact layer 26, the cladding layer 24, the active layer 20, and the optical modulation layer 22 are dry-etched to the substrate by an ICP (Inductively Coupled Plasma) apparatus using a chlorine-based gas to form a striped mesa portion 18.

[0042] Next, after removing the mesa insulating film, as Figure 9 shown, a protective film 32 is formed on the second protrusion 30 and the contact layer 26 (and on the side surface of the mesa portion 18 and the semiconductor substrate 16). Next, openings are formed in the protective film 32 at the laser unit 12 and the modulator unit 14 respectively using a transfer process. Next, a laser electrode 34 and a modulator electrode 36 are formed in these openings respectively. Next, a back electrode 38 is formed on the back surface of the semiconductor substrate 16. Next, cleavage is performed at a right angle to the optical axis direction of the laser, and the cleavage surface is coated to obtain the optical semiconductor device 10.

[0043] Thus, according to this embodiment, since the second protrusion 30 is formed, the growth and disconnection of the contact layer 26 can be simultaneously performed in the MOCVD apparatus. Therefore, the contact layer 26 can be disconnected without increasing the number of processes.

[0044] Embodiment 2

[0045] In Figure 10 is shown a cross-section of the optical semiconductor device 50 according to Embodiment 2. Different from Embodiment 1, the thickness of the optical modulation layer 62 of the optical semiconductor device 50 increases not only near the connection portion with the active layer 20 but also as a whole. That is, the upper surface of the optical modulation layer 62 is higher than the upper surface of the active layer 20 at any position.

[0046] The manufacturing method of the optical semiconductor device 50 is not different from that of Embodiment 1 until the process of dry-etching the active layer 20 until reaching the semiconductor substrate 16 ( Figure 4 process). After the Figure 4 process, the optical modulation layer 62 is formed such that the upper surface of the optical modulation layer 62 is higher than the upper surface of the active layer 20 at any position, and the Figure 11 structure is obtained. The subsequent manufacturing processes are the same as those in Embodiment 1.

[0047] When the optical modulation layer 62 is thickened in this way, in addition to the effects described in Embodiment 1, manufacturing deviations in the height direction of the optical modulation layer 62 can also be allowed.

[0048] Embodiment 3

[0049] In Figure 12 FIG. shows a cross section of the optoelectronic semiconductor device 90 according to Embodiment 3. Different from Embodiment 1, the cladding 104 of the optoelectronic semiconductor device 90 is thicker above the optical modulation layer 22 than above the active layer 20.

[0050] The manufacturing method of the optoelectronic semiconductor device 90 is not different from that of Embodiment 1 until the step of removing the insulating film 40 ( Figure 6 step). After the step of Figure 6 , above the optical modulation layer 22, a first cladding 121 having a third protrusion 111 vertically above the first protrusion 28 is formed, and the structure of Figure 13 is obtained. Next, as in Figure 14 , a second cladding 122 is formed above the active layer 20 and the first cladding 121. The second cladding 122 has the third protrusion 111. The combination of the first cladding 121 and the second cladding 122 is the cladding 104. The subsequent manufacturing steps are the same as those in Embodiment 1.

[0051] By increasing the thickness of the cladding 104 at the modulator section 94 in this way, in addition to the effects described in Embodiment 1, since the distance between the contact layer 106 formed with a high carrier concentration and the optical modulation layer 22 becomes longer, the light loss is reduced and the light output becomes larger. In addition, the perturbation of the shape (far-field pattern) of the emitted laser is small.

[0052] In addition, the features of Embodiment 3 can also be added to Embodiment 2.

[0053] Embodiment 4

[0054] In Figure 15 FIG. shows a cross section of the optoelectronic semiconductor device 130 according to Embodiment 4. Different from Embodiment 1, the upper surface of the second protrusion 150 and the upper surface of the contact layer 146 of the optoelectronic semiconductor device 130 are in the same plane.

[0055] The manufacturing method of the optoelectronic semiconductor device 130 is not different from that of Embodiment 1 until the step of growing the contact layer 26 ( Figure 8 step). After the step of Figure 8 , planarization of the second protrusion 150 and the contact layer 146 is performed by wet etching using a liquid containing Br, and the structure of Figure 16 is obtained. The subsequent manufacturing steps are the same as those in Embodiment 1.

[0056] When the second protrusion 150 and the contact layer 146 are planarized in this way, in addition to the effects described in the first embodiment, leakage current and parasitic capacitance can be reduced. In this embodiment, the height of the second protrusion 150 becomes lower and the area of the side surface of the second protrusion 150 decreases. Therefore, the leakage current flowing out from the side surface of the second protrusion 150 toward the modulator section 134 from the laser section 132 side and the leakage current flowing out from the side surface of the second protrusion 150 toward the laser section 132 from the modulator section 134 side are reduced. Further, in this embodiment, since the area of the side surface of the second protrusion 150 decreases, the parasitic capacitance of the P-I-N (I stands for Intrinsic) structure formed by the cladding layer 144, the optical modulation layer 22, and the semiconductor substrate 16 is reduced.

[0057] In addition, in all embodiments, the semiconductor substrate may be of p-type. In this case, the cladding layer and the contact layer are of n-type. Further, the optical semiconductor device is not limited to a ridge type and may be a buried laser.

[0058] Description of Reference Numerals

[0059] 10, 50, 90, 130... optical semiconductor device; 16... semiconductor substrate; 20... active layer; 22, 62... optical modulation layer; 24, 64, 104... cladding layer; 26, 66, 106, 146... contact layer; 28... first protrusion; 30, 70, 110, 150... second protrusion; 40... insulating film; 111... third protrusion; 121... first cladding layer; 122... second cladding layer.

Claims

1. A semiconductor optical device, wherein, comprises: a semiconductor substrate; an active layer formed on the semiconductor substrate and generating laser light; an optical modulation layer formed on the semiconductor substrate, adjacent to the active layer, and modulating the laser light; a cladding layer formed on the active layer and the optical modulation layer; and a contact layer formed on the cladding layer, a first protrusion is formed on the upper surface of the optical modulation layer and at an end portion on the active layer side; a second protrusion is formed on the upper surface of the cladding layer and vertically above the first protrusion, and the contact layer is disconnected by the second protrusion in the optical axis direction of the laser light.

2. The semiconductor optical device according to claim 1, wherein, the upper surface of the optical modulation layer is at a higher position than the upper surface of the active layer at any position.

3. The semiconductor optical device according to claim 1, wherein, the cladding layer is thicker above the optical modulation layer than above the active layer.

4. The semiconductor optical device according to claim 1, wherein, the upper surface of the second protrusion and the upper surface of the contact layer are on the same plane.

5. A method for manufacturing a semiconductor optical device, wherein, comprises: a step of forming an active layer generating laser light on a semiconductor substrate; a step of forming an insulating film on the active layer; a step of using the insulating film as a selective growth mask to form an optical modulation layer on the semiconductor substrate, adjacent to the active layer, having a first protrusion at an end portion on the upper surface on the active layer side, and modulating the laser light; a step of removing the insulating film; a step of forming a cladding layer having a second protrusion on the upper surface vertically above the first protrusion on the active layer and the optical modulation layer; and a step of forming a contact layer disconnected by the second protrusion in the optical axis direction of the laser light on the cladding layer.

6. The method for manufacturing a semiconductor optical device according to claim 5, wherein, in the step of forming the optical modulation layer, the optical modulation layer is formed such that the upper surface of the optical modulation layer is at a higher position than the upper surface of the active layer at any position.

7. The method for manufacturing a semiconductor optical device according to claim 5 or 6, wherein, in the step of forming the cladding layer, after forming a first cladding layer having a third protrusion vertically above the first protrusion on the optical modulation layer, a second cladding layer is formed on the active layer and the first cladding layer, thereby forming the cladding layer formed by combining the first cladding layer and the second cladding layer.

8. The method for manufacturing a semiconductor optical device according to claim 5, wherein, comprises: after the step of forming the contact layer, by performing wet etching using a liquid containing Br, a step of planarizing the upper surface of the second protrusion and the upper surface of the contact layer such that the upper surface of the second protrusion and the upper surface of the contact layer are on the same plane.

9. The method for manufacturing a semiconductor optical device according to any one of claims 5 to 8, wherein, In the process of forming the contact layer, the contact layer is formed while adding a chlorine-based gas.

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