JP7517629B1 - Semiconductor Device - Google Patents

Abstract

The 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 including two or more undoped layers stacked in the vertical direction and having a different composition from the layers adjacent above and below, and a p-type cladding layer (16) formed on the diffusion prevention layer (16).

Description

The present disclosure relates to a semiconductor device.

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, which then generates light, which 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.

In such semiconductor lasers, the dopants injected into the p-type cladding layer can diffuse into the active layer. When the dopants diffuse into the active layer, the laser light characteristics and electrical characteristics deteriorate.

In the semiconductor laser element described in Patent Document 1, an undoped semiconductor layer is formed between the p-type cladding layer and the active layer to prevent Zn, the 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.

Japanese Patent Application Publication No. 4-320027

However, the semiconductor laser element described in Patent Document 1 has a problem in that it is not effective enough to prevent the dopant in the p-type cladding layer from diffusing into the active layer. In general, dopants have a strong tendency to localize near the heterointerface. In the semiconductor laser element described in Patent Document 1, the number of interfaces increased by inserting an undoped semiconductor layer is only one, so the effect of preventing dopant diffusion is limited.

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

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, from the side closest to the active layer, an undoped first diffusion prevention layer and a second undoped diffusion prevention layer having a composition different from that of the first diffusion prevention layer alternately stacked, and a p-type cladding layer formed on the diffusion prevention layer , and the second diffusion prevention layer is strained .

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

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. 1A to 1C are diagrams showing a method for manufacturing a semiconductor device according to a first embodiment; 1A to 1C are diagrams showing a method for manufacturing a semiconductor device according to a first embodiment; 1A to 1C are diagrams showing a method for manufacturing a semiconductor device according to a first embodiment; 1A to 1C are diagrams showing a method for manufacturing a semiconductor device according to a first embodiment; 1A to 1C are diagrams showing a method for manufacturing a semiconductor device according to a first embodiment; FIG. 13 is a cross-sectional view of a semiconductor device according to a modified example. 13A and 13B are diagrams showing a layer structure of a diffusion prevention layer in a modified example.

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

The semiconductor device 10 includes a semiconductor substrate 12. The semiconductor substrate 12 is made of an n-type semiconductor, for example, n-type InP. A first electrode 14 is formed under the semiconductor substrate 12.

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.

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.

A diffusion prevention layer 22 having a layer structure is formed on the active layer 18. Figure 2 shows the layer structure of the diffusion prevention layer 22.

The diffusion prevention layer 22 is formed by alternately stacking the first diffusion prevention layer 26 and the second diffusion prevention layer 28 from the bottom. In FIG. 2, three layers of the first diffusion prevention layer 26 and the second diffusion prevention layer 28 are stacked, but at least one layer of the first diffusion prevention layer 26 and the second diffusion prevention layer 28 may 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, for example, InP. The second diffusion prevention layer 28 is made of an undoped semiconductor that is lattice-matched with the first diffusion prevention layer 26. In the first embodiment, the dopant of the p-type cladding layer 20 is Zn, so the second diffusion prevention layer 28 is made of AlInAs that 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, etc., which are lattice-matched with InP. Since the electrical resistance increases with the thickness of the first diffusion prevention layer 26 and the second diffusion prevention layer 28, it is preferable that the thickness of each layer is 10 nm or less. From the viewpoint of preventing the diffusion of the dopant in the p-type cladding layer 20, it is preferable that the number of pairs of the first diffusion prevention layer 26 and the second diffusion prevention layer 28 is three or more.

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.

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.

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

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 the MOCVD (Metal Organic Chemical Vapor Deposition) method. From this point on, the MOCVD method will be used to stack the semiconductor layers. However, the stacking method is not limited to the MOCVD method.

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

Next, the 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, as shown in FIG. 5.

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

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

Next, the first electrode 14 and the second electrode 32 are formed under the semiconductor substrate 12 and on the contact layer 30, respectively. In this manner, the semiconductor device 10 shown in FIG. 1 is manufactured.

Here, the effect of the diffusion prevention layer 22 will be explained. If the diffusion prevention layer 22 is not present, the dopant in the p-type cladding layer 20 may diffuse into the active layer 18. If the dopant reaches the active layer 18, the laser light characteristics and electrical characteristics will 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 diffusion into the active layer 18 is suppressed.

Furthermore, since 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, the diffusion prevention effect of the dopant into the active layer 18 is high. In general, dopants tend to be localized at heterointerfaces. In the semiconductor device 10 according to the first embodiment, since the diffusion prevention layer 22 has a layer structure, there are multiple heterointerfaces. For example, as shown in FIG. 2, when the first diffusion prevention layer 26 and the second diffusion prevention layer 28 are stacked in three layers each, the number of interfaces is six more than when the diffusion prevention layer 22 does not exist. In this way, the number of interfaces increases due to the presence of the diffusion prevention layer 22, so in the semiconductor device 10 according to the first embodiment, the effect of preventing the dopant in the p-type cladding layer 20 from diffusing into the active layer 18 is enhanced.

The diffusion prevention layer 22 is not limited to two types of layers stacked alternately, but may be two or more undoped layers 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 inserting the diffusion prevention layer 22 becomes two or more, and the effect of preventing the dopant in the p-type cladding layer 20 from diffusing into the active layer 18 is enhanced.

In addition, it is preferable that the undoped layer of 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.

Embodiment 2.
The semiconductor device according to the second embodiment is similar to the semiconductor device 10 according to the first embodiment, but differs from the first embodiment in that the second diffusion prevention layer is strained to reduce the band gap difference with the first diffusion prevention 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 prevention layer is similar to that shown in FIG.

If the band gap difference between the first and second diffusion prevention layers is large, the electrical resistance increases, and there is a possibility that the light emission efficiency of the laser light will decrease. On the other hand, as in the semiconductor device of embodiment 2, when the second diffusion prevention layer is strained to reduce the band gap difference with the first diffusion prevention layer, the electrical resistance of the diffusion prevention layer decreases. For example, when the second diffusion prevention layer is made of AlInAs, the band gap difference with InP can be reduced by adjusting the composition ratio of Al and In to apply strain, thereby preventing a decrease in light emission efficiency.

Embodiment 3.
The semiconductor device according to the third embodiment is one in which a diffusion prevention layer is 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 Figs. 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 and band gap difference of the layers constituting the diffusion prevention layer.

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.

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

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 (8)

an n-type cladding layer;
an active layer formed on the n-type cladding layer;
a diffusion prevention layer formed on the active layer, the diffusion prevention layer being formed by alternately stacking, from the side closer to the active layer, an undoped first diffusion prevention layer and an undoped second diffusion prevention layer having a composition different from that of the first diffusion prevention layer;
a p-type cladding layer formed on the diffusion barrier layer;
Equipped with
The second diffusion prevention layer is subjected to a strain. 2 . The semiconductor device according to claim 1 , wherein at least one of the first diffusion prevention layer and the second diffusion prevention layer has a higher solid solubility of the dopant of the p-type cladding layer than that of the active layer. The semiconductor device according to claim 1 , wherein the first diffusion prevention layer and the second diffusion prevention layer have a thickness of 10 nm or less. The semiconductor device according to claim 1 , wherein the p-type cladding layer is doped with Zn. the n-type cladding layer is made of InP;
the active layer is made of InGaAsP;
the first diffusion barrier layer is made of InP ;
The semiconductor device according to claim 4 , wherein the p-type cladding layer is made of InP. 6. The semiconductor device according to claim 5, wherein the second diffusion prevention layer is made of any one of AlInAs, InGaAsP, InGaAs, and AlGaInAs. 6. The semiconductor device according to claim 5, wherein the diffusion prevention layer includes three or more pairs of the first diffusion prevention layer and the second diffusion prevention layer stacked together. 2. The semiconductor device according to claim 1, wherein the semiconductor device is a laser light modulation section of an EA modulator or an MZ modulator.

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