JP2013069945A - Nitride semiconductor laser element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a nitride semiconductor laser element excellent in luminous efficiency.SOLUTION: A nitride semiconductor laser element 100 comprises an n-side region 10, an active region 20, and a p-side region 30 in this order. The n-side region 10 has a hole blocking layer 11 capable of blocking holes. The p-side region 30 has an electron blocking layer 31 capable of blocking electrons. The hole blocking layer 11 is configured to have a band gap energy larger than that of the electron blocking layer 31.

Description

  The present invention relates to a nitride semiconductor laser device.

  In recent years, a nitride semiconductor laser element using a nitride semiconductor has been developed. As a nitride semiconductor laser element, a structure including a hole block layer and an electron block layer for confining carriers has been proposed (for example, Patent Document 1 and Patent Document 2).

JP 2010-021287 A JP 2010-251810 A

  However, there is a problem in that it is difficult to improve the light emission efficiency even if a hole block layer and an electron block layer are simply provided. The present invention has been made in view of the above problems, and an object of the present invention is to obtain a nitride semiconductor laser element mainly excellent in luminous efficiency.

  The nitride semiconductor laser device according to one aspect includes an n-side region, an active region, and a p-side region in this order. The n-side region has a hole blocking layer capable of blocking holes, and the p-side region has an electron blocking layer capable of blocking electrons. The hole block layer has a larger band gap energy than the electron block layer.

1 is a schematic cross-sectional view showing a nitride semiconductor laser device according to an embodiment of the present invention. 5 is a diagram for comparing the IL characteristics of Example 1 and Comparative Example 1. FIG. 6 is a diagram for comparing the IV characteristics of Example 1 and Comparative Example 1. FIG.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. However, the form shown below is the illustration for materializing the technical idea of this invention, Comprising: This invention is not limited to the following. In this specification, a “nitride semiconductor” is a semiconductor containing nitrogen, and can be typically represented by a general formula InxAlyGa1-xyN (0 ≦ x, 0 ≦ y, x + y ≦ 1).

  A sectional view of a nitride semiconductor laser device 100 according to an embodiment of the present invention is shown in FIG. The nitride semiconductor laser device 100 includes an n-side region 10, an active region 20, and a p-side region 30 in this order. The n-side region 10 has a hole blocking layer 11 that can block holes, and the p-side region 30 has an electron blocking layer 31 that can block electrons. The hole block layer 11 has a band gap energy larger than that of the electron block layer 31.

  Thereby, luminous efficiency (quantum efficiency) can be improved. Although details are unknown, by providing the hole blocking layer 11 and the electron blocking layer 31, carriers can be effectively confined in the active region 20, and the band gap energy of the hole blocking layer 11 is more than the electron blocking layer. This is considered to be because the hole can be confined more reliably by increasing the size. Hereinafter, main components constituting the nitride semiconductor laser element 100 will be described.

(N-side region 10)
In the present embodiment, the n-side region 10 includes, in order from the active region 20 side, a hole block layer 11, an n-side light guide layer 12, an n-side cladding layer 13, and an n-side contact layer 14. The The hole blocking layer 11 is a layer for blocking holes (holes) from the p-side region 30 and confining them in the active region 20, and is made of, for example, AlGaN. The hole blocking layer 11 can be configured to contact the active region 20 in order to efficiently block holes. The n-side light guide layer 12 is a layer for keeping light generated in the active region 20 in the vicinity of the active region 20, and is made of, for example, GaN. The n-side cladding layer 13 is a layer that is integrated with the n-side light guide 12 layer and keeps the light generated in the active region 20 in the vicinity of the active region 20, and is made of, for example, AlGaN. That is, by making the refractive index of the n-side light guide layer 12 larger than that of the n-side cladding layer 13, light can be easily confined inside (on the active region 20 side) with the interface between the two as a boundary. The n-side contact layer 14 is a layer for providing an n-electrode, and is made of, for example, GaN.

  Some of these layers can be omitted. For example, the n-side cladding layer 13 can be omitted when the n-side light guide layer 12 and the n-side contact layer 14 can sufficiently secure a difference in refractive index for confining light. On the contrary, it goes without saying that other layers may be provided.

(Active region 20)
The layer structure of the active region 20 is not limited, and various layers can be adopted. For example, a single quantum well structure (SQW) having one well layer and a multiple quantum well structure (MQW) having two or more well layers can be employed. When the active region 20 has a quantum well structure, the n-side can be the well layer and the p-side can be the barrier layer. By making the first layer of the active region 20 (the layer closest to the n-side region 10) a well layer, holes can be more reliably blocked by the hole blocking layer 11 in contact therewith. However, it goes without saying that the active region 20 may be configured to start from the barrier layer.

(P-side region 30)
In the present embodiment, the p-side region 30 includes, in order from the active region 20, an electron block layer 31, a p-side light guide layer 32, a p-side cladding layer 33, and a p-side contact layer 34. The electron blocking layer 31 is a layer for blocking electrons from the n-side region 10 and confining them in the active region 20, and is made of, for example, AlGaN. The electron blocking layer 31 can be configured to be in contact with the active region 20 in order to efficiently block electrons. The p-side light guide layer 32 is a layer for keeping the light generated in the active region 10 in the vicinity of the active region 20, and is made of, for example, GaN. The p-side cladding layer 33 is a layer that is integrated with the p-side light guide layer 32 and keeps the light generated in the active region 20 in the vicinity of the active region 20, and is made of, for example, AlGaN. That is, by making the refractive index of the p-side light guide layer 32 larger than that of the p-side cladding layer 33, it is possible to easily confine light inside (on the active region 20 side) with the interface between the two as a boundary. The p-side contact layer 34 is a layer for providing a p-electrode, and is made of, for example, GaN.

  Some of these layers can be omitted. For example, the p-side cladding layer 33 can be omitted when the p-side light guide layer 32 and the p-side contact layer 34 can ensure a sufficient difference in refractive index for confining light. On the contrary, it goes without saying that other layers may be provided.

<Example 1>
Hereinafter, the main structure of the nitride semiconductor laser element (oscillation wavelength of 405 nm) according to the present embodiment will be described. In this embodiment, a case where an MOCVD method (metal organic chemical vapor deposition method) is used as a growth method will be described.

(N-side contact layer 14)
First, as the n-side contact layer 14, a commercially available nitride semiconductor substrate made of n-type GaN and having a thickness of 400 μm was prepared.

(N-side cladding layer 13)
Next, Si-doped Al _0.03 Ga _0.97 N was grown to a thickness of 2 μm to form the n-side cladding layer 13.

(N-side guide layer 12)
Next, non-doped GaN was grown to a thickness of 150 nm, and Si-doped In _0.02 Ga _0.98 N was grown to a thickness of 14 nm to form an n-side guide layer 12 composed of two layers.

(Hall block layer 11)
Next, Si-doped Al _0.23 Ga _0.77 N was grown to a film thickness of 2.5 nm to form the hole block layer 11.

(Active region 20)
Next, in order from the n side, a non-doped In _0.06 Ga _0.94 N film having a thickness of 7 nm as a well layer and a Si-doped In _0.02 Ga _0.98 N film having a film thickness of 14 nm as a well layer are formed as a well layer. Non-doped In _0.06 Ga _0.94 N was grown to a thickness of 7 nm, and non-doped In _0.02 Ga _0.98 N was grown to a thickness of 14 nm as a barrier layer to form an active region 20. In other words, in this embodiment, the MQW active region 20 including the well layer / barrier layer / well layer / barrier layer is formed in order from the n-side region 10.

(Electronic block layer 31)
Next, Mg-doped Al _0.20 Ga _0.80 N was grown to a thickness of 10 nm to form the electron blocking layer 11.

(P-side guide layer 32)
Next, non-doped GaN was grown to a thickness of 0.15 μm to form the p-side guide layer 32.

(P-side cladding layer 33)
Next, an A layer made of non-doped Al _0.08 Ga _0.92 N was grown at a film thickness of 2.5 nm, and then a B layer made of Mg-doped GaN was grown at a film thickness of 2.5 nm. Then, the A layer and the B layer were laminated by repeating this operation in order, and the p-side cladding layer 33 made of a multilayer film (superlattice structure) having a total film thickness of 450 nm was formed.

(P-side contact layer 34)
Next, Mg-doped GaN was grown to a thickness of 15 nm to form the p-side contact layer 34.

(Other processes)
After the reaction was completed, ridges were formed in stripes by RIE (reactive ion etching). The ridge width is 2 μm. Next, an insulating film 40 made of ZrO ₂ was formed. Next, a p-electrode 50 made of Ni / Au / Pt / Ni / Pd / Au is formed on the p-side contact layer 34, and an n-electrode 60 made of Ti / Au / Pt / Au is formed on the n-side contact layer 34. did. The wafer having the above configuration was polished from the nitride semiconductor substrate side to 80 μm, and then the wafer was cleaved into a bar shape with the M plane as a cleavage plane to produce a resonator. A dielectric multilayer (not shown) film made of SiO ₂ , Al ₂ O ₃ and ZrO ₂ is formed on the laser beam emission surface side and the reflection surface side, and finally the bar is cut in a direction parallel to the ridge. The laser element oscillates at 405 nm.

<Comparative Example 1>
A nitride semiconductor laser element similar to that of Example 1 was manufactured except that the hole block layer 11 was not provided.
<Evaluation of characteristics>

  FIG. 2 shows a graph comparing the IL characteristics (current-light output characteristics) of the nitride semiconductor laser element of Example 1 and the nitride semiconductor laser element of Comparative Example 1. Here, the evaluation result of Example 1 is indicated by a solid line, and the evaluation result of Comparative Example 1 is indicated by a broken line. As is clear from FIG. 2, it was found that the IL characteristic improved in Example 1 as the drive current increased compared to Comparative Example 1. This is presumably because holes were more efficiently confined in the hole blocking layer 11 by providing the hole blocking layer 11 having a larger band gap than the electron blocking layer 31.

  FIG. 3 shows a graph comparing the IV characteristics (current-voltage) of the nitride semiconductor laser element of Example 1 and the nitride semiconductor laser element of Comparative Example 1. Here, the evaluation result of Example 1 is indicated by a solid line, and the evaluation result of Comparative Example 1 is indicated by a broken line. As is clear from FIG. 3, the IV characteristics of both were almost the same (in FIG. 3, only the solid line may be confirmed, but this is because the solid line and the broken line overlap). Thus, it was confirmed that the hole blocking layer 11 became a resistance component and did not increase the voltage. This is presumably because the thickness of the hole blocking layer 11 is thin enough to allow electrons to tunnel.

DESCRIPTION OF SYMBOLS 100 ... Nitride semiconductor laser element 10 ... n side area | region 11 ... hole block layer 12 ... n side light guide layer 13 ... n side clad layer 14 ... n side contact layer 20 ... active region 30 ... p side area 31 ... electron block layer 32 ... p-side light guide layer 33 ... p-side cladding layer 34 ... p-side contact layer 40 ... insulating portion 50 ... p electrode 60 ... n electrode

Claims (5)

A nitride semiconductor laser device comprising an n-side region, an active region, and a p-side region in order,
The n-side region has a hole blocking layer capable of blocking holes,
The p-side region has an electron blocking layer capable of blocking electrons,
The hole block layer has a band gap energy larger than that of the electron block layer.   The nitride semiconductor laser element according to claim 1, wherein the hole blocking layer and the electron blocking layer are in contact with the active region. The n-side region has an n-side light guide layer on a side away from the active region of the hole blocking layer,
3. The nitride semiconductor laser element according to claim 1, wherein the p-side region has a p-side light guide layer on a side away from the active region of the electron blocking layer. The n-side region has an n-side cladding layer on a side away from the active region of the n-side light guide layer,
4. The nitride semiconductor laser device according to claim 3, wherein the p-side region has a p-side cladding layer on a side away from the active region of the p-side light guide layer. The n-side region has an n-side contact layer on a side away from the active region of the n-side cladding layer,
5. The nitride semiconductor laser device according to claim 4, wherein the p-side region has a p-side contact layer on a side away from the active region of the p-side cladding layer. 6.

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