Semiconductor device

Abstract

This semiconductor device comprises: an n-type cladding layer (16); an active layer (18) formed on the n-type cladding layer (16); a diffusion prevention layer (12) formed on the active layer (18) and in which two or more undoped layers having different compositions from vertically adjacent layers are laminated in the vertical direction; and a p-type cladding layer (16) formed on the diffusion prevention layer (12).

Description

Semiconductor Devices

[0001] The present disclosure relates to semiconductor devices.

[0002] In semiconductor lasers, light amplification occurs in the active layer. The active layer is usually made of an undoped compound semiconductor such as InGaAsP, and light is generated when electrons and holes are injected into the active layer, where it is amplified and emitted to the outside as laser light. P-type cladding layers and n-type cladding layers are formed above and below the active layer. These cladding layers sandwich the active layer from above and below to form a laser diode, and serve to confine light within the active layer.

[0003] In such semiconductor lasers, the dopant implanted in the p-type cladding layer may diffuse into the active layer, causing degradation of the laser light characteristics and electrical characteristics.

[0004] In the semiconductor laser device described in Patent Document 1, an undoped semiconductor layer is formed between the p-type cladding layer and the active layer to prevent Zn, which is a dopant in the p-type cladding layer, from diffusing into the active layer. The undoped semiconductor layer prevents the dopant from diffusing into the active layer, thereby suppressing deterioration of the laser light characteristics and electrical characteristics.

[0005] Japanese Patent Application Publication No. 4-320027

[0006] However, the semiconductor laser device described in Patent Document 1 has a problem in that it is insufficient in preventing the dopant in the p-type cladding layer from diffusing into the active layer. In general, dopants tend to be localized near the heterointerface. In the semiconductor laser device described in Patent Document 1, the insertion of the undoped semiconductor layer increases the number of interfaces by only one, so the dopant diffusion prevention effect is limited.

[0007] The present disclosure has been made to solve the above problems, and aims to provide a semiconductor device that is highly effective in preventing the dopant in the p-type cladding layer from diffusing into the active layer.

[0008] The semiconductor device according to the present disclosure comprises an n-type cladding layer, an active layer formed on the n-type cladding layer, a diffusion prevention layer formed on the active layer and including two or more undoped layers stacked in the vertical direction, each having a composition different from that of adjacent layers above and below, and a p-type cladding layer formed on the diffusion prevention layer.

[0009] According to the present disclosure, a semiconductor device can be obtained that is highly effective in preventing dopants in a p-type cladding layer from diffusing into an active layer.

[0010] FIG. 1 is a diagram showing a cross section of a semiconductor device according to a first embodiment; FIG. 2 is a diagram showing a layer structure of a diffusion prevention layer; FIG. 3 is a diagram showing a manufacturing method of a semiconductor device according to a first embodiment; FIG. 4 is a diagram showing a manufacturing method of a semiconductor device according to a first embodiment; FIG. 5 is a diagram showing a manufacturing method of a semiconductor device according to a first embodiment; FIG. 6 is a diagram showing a manufacturing method of a semiconductor device according to a first embodiment; FIG. 7 is a diagram showing a cross section of a semiconductor device according to a modified example; FIG. 8 is a diagram showing a layer structure of a diffusion prevention layer according to a modified example.

[0011] First Embodiment A semiconductor device 10 according to a first embodiment is shown in Figure 1. The semiconductor device 10 is a semiconductor laser, and Figure 1 shows a cross section perpendicular to the direction in which laser light resonates. Note that the drawings including Figure 1 are intended to explain the embodiments, and the dimensional ratios of the components may differ from the actual ones.

[0012] The semiconductor device 10 includes a semiconductor substrate 12. The semiconductor substrate 12 is made of an n-type semiconductor, such as n-type InP. A first electrode 14 is formed under the semiconductor substrate 12.

[0013] An n-type cladding layer 16 is formed on the semiconductor substrate 12. The n-type cladding layer 16 is made of an n-type semiconductor, for example, n-type InP. The n-type cladding layer 16 may be integral with the semiconductor substrate 12.

[0014] An active layer 18 is formed on the n-type cladding layer 16. The active layer 18 is made of an undoped semiconductor, for example, InGaAsP.

[0015] A diffusion prevention layer 22 having a layer structure is formed on the active layer 18. The layer structure of the diffusion prevention layer 22 is shown in FIG.

[0016] The diffusion prevention layer 22 is formed by alternately stacking first diffusion prevention layers 26 and second diffusion prevention layers 28 from bottom to top. While FIG. 2 shows three layers of the first diffusion prevention layers 26 and three layers of the second diffusion prevention layers 28, it is sufficient that at least one layer of the first diffusion prevention layers 26 and one layer of the second diffusion prevention layers 28 be stacked. The top layer may be either the first diffusion prevention layer 26 or the second diffusion prevention layer 28. The first diffusion prevention layer 26 is made of an undoped semiconductor, such as InP. The second diffusion prevention layer 28 is made of an undoped semiconductor that is lattice-matched to the first diffusion prevention layer 26. In the first embodiment, since the dopant of the p-type cladding layer 20 is Zn, the second diffusion prevention layer 28 is made of AlInAs, which satisfies the above conditions. The material of the second diffusion prevention layer 28 is not limited to AlInAs, but may be InGaAsP, InGaAs, AlGaInAs, InGaAsP, InGaAs, or the like, which are lattice-matched to InP. Furthermore, since the electrical resistance increases as the thickness of the first diffusion prevention layer 26 and the second diffusion prevention layer 28 increases, it is preferable that the thickness of each layer be 10 nm or less. Furthermore, from the viewpoint of preventing the diffusion of dopants in the p-type cladding layer 20, it is preferable that there are three or more pairs of the first diffusion prevention layer 26 and the second diffusion prevention layer 28.

[0017] A p-type cladding layer 20 is formed on the diffusion prevention layer 22. The p-type cladding layer 20 is made of a p-type semiconductor doped with Zn, for example, p-type InP.

[0018] A contact layer 30 is formed on the p-type cladding layer 20. The contact layer 30 is made of a p-type semiconductor, for example, p-type InGaAs.

[0019] A second electrode 32 is formed on the contact layer 30 .

[0020] Here, a method for manufacturing the semiconductor device 10 according to the first embodiment will be described. First, as shown in FIG. 3, an n-type cladding layer 16 is formed on a semiconductor substrate 12. The n-type cladding layer 16 is formed using a metal organic chemical vapor deposition (MOCVD) method. Note that hereafter, the MOCVD method will be used to stack semiconductor layers. However, the stacking method is not limited to the MOCVD method.

[0021] Next, as shown in FIG. 4, an active layer 18 is formed on the n-type cladding layer 16 .

[0022] Next, a diffusion prevention layer 22 is formed on the active layer 18. To form the diffusion prevention layer 22, first a first diffusion prevention layer 26 is formed on the active layer 18. Then, a second diffusion prevention layer 28 is formed on the first diffusion prevention layer 26. If necessary, the first diffusion prevention layer 26 is formed on the second diffusion prevention layer 28. These steps are repeated until the desired number of diffusion prevention layers 22 are formed, forming the diffusion prevention layer 22 as shown in FIG.

[0023] Next, as shown in FIG. 6, the p-type cladding layer 20 is formed on the diffusion prevention layer 22 .

[0024] Next, as shown in FIG. 7, a contact layer 30 is formed on the p-type cladding layer 20 .

[0025] Next, the first electrode 14 and the second electrode 32 are formed respectively under the semiconductor substrate 12 and on the contact layer 30. In this manner, the semiconductor device 10 shown in FIG.

[0026] Here, the effect of the diffusion prevention layer 22 will be described. If the diffusion prevention layer 22 were not present, the dopant in the p-type cladding layer 20 would diffuse into the active layer 18. If the dopant reaches the active layer 18, the laser light characteristics and electrical characteristics would deteriorate. However, in the semiconductor device 10 according to the first embodiment, the diffusion prevention layer 22 is inserted between the p-type cladding layer 20 and the active layer 18, so that the dopant that diffuses from the p-type cladding layer 20 remains in the diffusion prevention layer 22 and is prevented from diffusing into the active layer 18.

[0027] Furthermore, the diffusion prevention layer 22 has a layer structure in which the first diffusion prevention layer 26 and the second diffusion prevention layer 28 are alternately stacked, thereby providing a high effect of preventing the diffusion of dopants into the active layer 18. Generally, dopants tend to localize at heterointerfaces. In the semiconductor device 10 according to the first embodiment, the diffusion prevention layer 22 has a layer structure, resulting in the presence of multiple heterointerfaces. For example, as shown in FIG. 2 , if the first diffusion prevention layer 26 and the second diffusion prevention layer 28 each have three layers stacked, the number of interfaces is six more than in the case where the diffusion prevention layer 22 is not present. Because the presence of the diffusion prevention layer 22 thus increases the number of interfaces, the semiconductor device 10 according to the first embodiment is more effective in preventing the diffusion of dopants in the p-type cladding layer 20 into the active layer 18.

[0028] The diffusion prevention layer 22 is not limited to a structure in which two types of layers are alternately stacked, but may be a structure in which two or more undoped layers are stacked vertically. In this case, each undoped layer may have a different composition from the layers adjacent thereto. In this way, if two or more undoped layers having different compositions from the layers adjacent thereto are stacked vertically, the number of interfaces increased by the insertion of the diffusion prevention layer 22 becomes two or more, thereby enhancing the effect of preventing the dopant in the p-type cladding layer 20 from diffusing into the active layer 18.

[0029] Furthermore, it is preferable that the undoped layer included in the diffusion prevention layer 22 is made of at least one semiconductor layer in which the solid solubility of the dopant in the p-type cladding layer 20 is higher than that of the active layer 18. If such a semiconductor layer is used, the dopant in the p-type cladding layer 20 remains in this undoped layer, and diffusion into the active layer 18 is suppressed.

[0030] Second Embodiment A semiconductor device according to a second embodiment is similar to the semiconductor device 10 according to the first embodiment, but differs from the first embodiment in that strain is applied to the second diffusion barrier layer to reduce the band gap difference with the first diffusion barrier layer. The cross section of the semiconductor device according to the second embodiment is similar to that shown in FIG. 1, and the layer structure of the diffusion barrier layer is similar to that shown in FIG.

[0031] If the band gap difference between the first diffusion barrier layer and the second diffusion barrier layer is large, the electrical resistance increases, which may reduce the luminous efficiency of the laser light. On the other hand, if the band gap difference with the first diffusion barrier layer is reduced by applying strain to the second diffusion barrier layer, as in the semiconductor device according to the second embodiment, the electrical resistance of the diffusion barrier layer is reduced. For example, if the second diffusion barrier layer is made of AlInAs, adjusting the Al and In composition ratio to apply strain can reduce the band gap difference with InP, thereby preventing a reduction in luminous efficiency.

[0032] Third Embodiment A semiconductor device according to a third embodiment has a diffusion prevention layer formed in the laser light modulation section of an EA (Electro Absorption) modulator or an MZ (Mach-Zehnder) modulator. The structure of the semiconductor device according to the third embodiment is the same as that of the first embodiment, and the cross section and the layer structure of the diffusion prevention layer are the same as those in Figures 1 and 2, respectively. In the laser light modulation section of the modulator, it is only necessary to apply a voltage between the first electrode and the second electrode, so there is no need to consider the film thickness or band gap difference of the layers that make up the diffusion prevention layer.

[0033] Although each embodiment has been described above, the semiconductor device in each embodiment may have a mesa structure in which the region including the active layer is formed in a stripe shape extending in the resonance direction of the laser light.

[0034] The semiconductor substrate may also be p-type. A cross section of the semiconductor device 40 in this case is shown in FIG. 8. Unlike FIG. 1, FIG. 8 depicts the semiconductor substrate as if it were on top for convenience. When the semiconductor substrate is p-type, a Zn-doped p-type cladding layer 50 is formed below the semiconductor substrate 42, and a diffusion prevention layer 52 is formed below the p-type cladding layer 50. The layer structure of the diffusion prevention layer 52 is shown in FIG. 9. The layer structure of the diffusion prevention layer 52 is such that the bottom layer is a first diffusion prevention layer 56, with a second diffusion prevention layer 58 formed above it. If necessary, the first diffusion prevention layer 56 and the second diffusion prevention layer 58 are further repeated above that. An active layer 48, an n-type cladding layer 46, and a contact layer 60 are formed below the diffusion prevention layer 52, with a first electrode 44 and a second electrode 62 formed above and below. In this way, even when the semiconductor substrate is p-type, the diffusion prevention layer is inserted, so that a semiconductor device can be obtained which is highly effective in preventing the dopant in the p-type cladding layer 50 from diffusing into the active layer 48 .

[0035] 10, 40: semiconductor device; 16, 46: n-type cladding layer; 18, 48: active layer; 20, 50: p-type cladding layer; 22, 52: diffusion prevention layer; 26, 56: first diffusion prevention layer; 28, 58: second diffusion prevention layer.

Claims

1. An n-type clad layer, an active layer formed on the n-type clad layer, a diffusion prevention layer formed on the active layer and having two or more undoped layers with different compositions from the layers adjacent above and below stacked in the vertical direction, and a p-type clad layer formed on the diffusion prevention layer.

2. The semiconductor device according to claim 1, wherein at least one of the undoped layers of the diffusion prevention layer has a higher solubility of the dopant of the p-type clad layer than the active layer.

3. The semiconductor device according to claim 1 or 2, wherein the film thickness of the undoped layer is 10 nm or less.

4. The semiconductor device according to any one of claims 1 to 3, wherein the p-type clad layer is doped with Zn.

5. The n-type clad layer is made of InP, the active layer is made of InGaAsP, the diffusion prevention layer is composed of a first diffusion prevention layer made of InP and a second diffusion prevention layer lattice-matched with InP alternately stacked from the side closer to the active layer, and the p-type clad layer is made of InP. The semiconductor device according to claim 4.

6. The semiconductor device according to claim 5, wherein the second diffusion prevention layer is made of any one of AlInAs, InGaAsP, InGaAs, AlGaInAs, InGaAsP, InGaAs.

7. The semiconductor device according to claim 5 or 6, wherein in the diffusion prevention layer, three or more sets of a combination of the first diffusion prevention layer and the second diffusion prevention layer are stacked.

8. The semiconductor device according to any one of claims 5 to 7, wherein strain is applied to the second diffusion prevention layer.

9. The semiconductor device according to any one of claims 1 to 8, wherein the semiconductor device is a laser light modulation unit of an EA modulator or an MZ modulator.

Images