JP2007066957A - Semiconductor laser element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor laser element of higher output by enhancing th COD level. <P>SOLUTION: The semiconductor laser element 10 comprises a first conductivity type clad layer 2, an active layer 3, and a second conductivity type clad layer 4 formed sequentially on the upper surface S of a first conductivity type semiconductor substrate 1, and a pair of resonator surfaces A1 and A2 wherein free carrier absorption loss is set in the range of 10-13 cm<SP>-1</SP>in the active layer portion forming a part of the pair of resonator surfaces A1 and A2, and the active layer portion Z located in the vicinity of the active layer portion. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a semiconductor laser device, and more particularly to a resonator type semiconductor laser device.

A resonator type semiconductor laser element is used in an optical pickup device for recording and / or reproducing an optical disk such as a CD (Compact Disk) and a DVD (Digital Versatile Disk). Such a semiconductor laser element is desired to have a higher output in response to a further improvement in sensitivity of a conventional optical pickup device or the like.
However, in a high-power semiconductor laser device, optical damage called COD (Catastrophic Optical Damage) has been a problem, resulting in a decrease in reliability.
This COD occurs when the vicinity of the resonator surface of the active layer that generates laser light is an absorption region for the laser light generated inside the device.
In the element manufacturing process, the cleavage plane is usually obtained as a resonator plane by cleaving in the atmosphere. At this time, since the cleavage is performed in the atmosphere, a natural oxide layer is formed on the resonator surface by reacting with oxygen in the atmosphere.
Since the band gap of this natural oxide layer is smaller than the band gap of the active layer inside the device and becomes an absorption region, the temperature rises, and this temperature rise further narrows the band gap near the resonator surface, and the absorption of laser light is reduced. Increasingly more likely. As a result, the above phenomenon is repeated, and finally, the cavity surface is melted and the semiconductor laser element is destroyed.

Therefore, Patent Document 1 describes a method for improving the COD level (referred to as light emission output when COD occurs).
According to this Patent Document 1, by setting the impurity concentration in at least the active layer in the vicinity of the resonator surface to about 5 to 15 × 10 ¹⁷ cm ⁻³ or more, a highly reliable and high output semiconductor laser device can be obtained. It can be realized.
Japanese Patent No. 2758598

  However, in the semiconductor laser element described in Patent Document 1, it is difficult to sufficiently improve the COD level, so that a high output, for example, a light emission output of 300 mW or more cannot be obtained. As a reason why the COD level cannot be sufficiently improved, the influence of carrier loss can be considered.

  Accordingly, the problem to be solved by the present invention is to provide a semiconductor laser device with higher output by improving the COD level.

In order to solve the above problems, the present invention has the following means.
1) A first conductivity type cladding layer (2), an active layer (3), and a second conductivity type cladding layer (4) are sequentially laminated on the upper surface (S) of the first conductivity type semiconductor substrate (1). A semiconductor laser device (10) having a pair of resonator surfaces (A1, A2), the active layer portion forming the part of the pair of resonator surfaces (A1, A2) and the active layer The semiconductor laser device (10) is characterized in that a free carrier absorption loss in the active layer portion (Z) located in the vicinity of the portion is in a range of 10 to 13 cm ⁻¹ .

According to the present invention, the COD level is improved by setting the free carrier absorption loss of the active layer in the vicinity of each face of the pair of resonator faces within the range of 10 to 13 cm ⁻¹ , so that the high output semiconductor There is an effect that a laser element can be obtained.

The preferred embodiments of the present invention will be described with reference to FIGS.
1 to 4 are schematic cross-sectional views for explaining the first to fourth steps in the embodiment of the semiconductor laser device of the present invention. Each figure corresponds to each process.

<Example>
(First step) [See FIG. 1]
First, an n-type cladding layer made of (Al _0.4 Ga _0.6 ) _0.5 In _0.5 P having a dopant concentration of about 5 × 10 ¹⁷ cm ⁻³ is formed on the upper surface S of an n-type substrate 1 made of GaAs. 2, active layer 3 made of non-doped Ga _0.5 In _0.5 P, and (Al _0.4 Ga _0.6 ) _0.5 In _0.5 with a dopant concentration of about 5 × 10 ¹⁷ cm ^−3. A p-type cladding layer 4 made of P and a P + -type cap layer 5 made of GaAs are sequentially laminated by a MOVPE (Metal Organic Vapor Phase Epitaxy) method.

In this first step, Si (silicon) was used as the n-type dopant, and Zn (zinc) was used as the p-type dopant. As another p-type dopant, Be (beryllium), C (carbon), Mg (magnesium), or the like may be used.
In the first step, the substrate heating temperature when forming each layer was set to about 650 ° C.

(Second step) [See FIG. 2]
On the surface of the P + type cap layer 5, for example, a diffusion source layer 7 made of ZnO (zinc oxide) and having a width w1 of about 40 μm is formed in a stripe shape having a predetermined interval d1. In FIG. 2, two of the plurality of diffusion source layers 7 are shown.
In the embodiment, the distance d1 is about 1.5 mm.
Further, in FIG. 2, for easy understanding, the dimension of the interval d1 is compressed with respect to the width w1.

Next, the n-type substrate 1 on which the diffusion source layer 7 is formed is heated to about 600 ° C., which is lower than the substrate heating temperature in the first step, to thereby obtain Zn (zinc) in the diffusion source layer 7. Is diffused as an impurity into a region from the interface between the diffusion source layer 7 and the P + -type cap layer 9 to the middle of the n-type cladding layer 2. A region where Zn, which is an impurity, is diffused is referred to as an impurity diffusion region Z.
In the example, the heating time was adjusted so that the Zn concentration of the active layer 3 in the impurity diffusion region Z was about 2 × 10 ¹⁷ cm ⁻³ . The width w2 of the impurity diffusion region Z is about 40 μm.
The reason for setting this Zn concentration will be described in detail later.
Further, the Zn concentration of the p-type cladding layer 4 in the impurity diffusion region Z is about 2 × 10 ¹⁷ cm ⁻³ .

(Third step) [See FIG. 3]
The diffusion source layer 7 is removed.
Next, an Au (gold) -based p-type electrode 8 is formed on the surface of the P + type cap layer 9, and an Au (gold) -based n-type electrode 9 is formed on the surface opposite to the stacking direction of the n-type substrate 1. Form.

(4th process) [Refer FIG. 4]
The n-type substrate 1 on which the p-type and n-type electrodes 8 and 9 are formed is cleaved along a plane that substantially bisects the impurity diffusion region Z in the extending direction, and the cleaved surface is the resonator plane A1. , A2 is formed.
This bar is divided at a predetermined interval by a plane orthogonal to the surface of the n-type substrate 1 that has undergone the above-described steps, to obtain the semiconductor laser device 10 of this example.
Therefore, the width w3 of the impurity diffusion region Z of the semiconductor laser element 10 is about 20 μm.

  This semiconductor laser element 10 injects a forward current from the p-type electrode 8 side to the n-type electrode 9 side, and when this current exceeds the oscillation threshold value, the active layer 3 causes laser oscillation, Laser light is emitted from one of the resonator surfaces A1 and A2 of the active layer 4.

Here, the Zn concentration of the active layer 3 in the impurity diffusion region Z in the second step of the embodiment will be described.
The inventor first focused on the free carrier absorption loss in the active layer 3 in the impurity diffusion region Z. The greater the absorption loss due to free carriers, the more heat is generated by the absorption loss during laser oscillation, causing problems such as a decrease in COD level and an increase in threshold value. For example, in order for the produced semiconductor laser device to obtain a light output of 300 mW or higher, which is a high output, the COD level must be higher.
Therefore, as a result of intensive experiments by the inventors, it was found that the free carrier absorption loss should be 13 cm ⁻¹ or less in order to make the COD level 300 mW or more.

Next, the inventor paid attention to the relationship between the free carrier absorption loss and the concentration of Zn which is one of the impurities in the active layer 3 in the impurity diffusion region Z.
FIG. 5 shows the results of intensive experiments on the relationship between the free carrier absorption loss and the Zn concentration. FIG. 5 is a diagram showing the relationship between the free carrier absorption loss and the Zn concentration in the active layer 3 in the impurity diffusion region Z.
Referring to FIG. 5, for example, when the Zn concentration is 5 × 10 ¹⁷ cm ⁻³ or more as in the conventional example, the free carrier absorption loss increases corresponding to the Zn concentration (15 cm ⁻¹ or more).

When the Zn concentration is lower than 1 × 10 ¹⁶ cm ⁻³ , the energy difference between the band gap energy in the active layer 3 in the impurity diffusion region Z and the band gap energy in the active layer 3 other than the impurity diffusion region Z is small. Therefore, when laser oscillation is performed, laser light is absorbed in the impurity diffusion region Z, the element generates heat, and the COD level is lowered and the threshold value is raised.
From FIG. 5, when the Zn concentration is 1 × 10 ¹⁶ cm ⁻³ , the free carrier absorption loss is 10 cm ⁻¹ .

Therefore, by setting the Zn concentration in the active layer 3 in the impurity diffusion region Z to 1 × 10 ¹⁶ cm ⁻³ or more and less than 5 × 10 ¹⁷ cm ⁻³ , free carrier absorption loss in the active layer 3 in the impurity diffusion region Z is reduced. The amount can be in the range of 10-13 cm ⁻¹ .
As a result of intensive experiments by the inventors, a COD level of 300 mW or higher, that is, a light emission output of 300 mW or higher, in the range of 10 to 13 cm ⁻¹ of the free carrier absorption loss in the active layer 3 of the impurity diffusion region Z. It was confirmed that

Therefore, in this example, by setting the Zn concentration to 2 × 10 ¹⁷ cm ⁻³ , the amount of this free carrier absorption loss was set to 12 cm ⁻¹ .
Further, as a result of measuring the COD level of the semiconductor laser elements of the conventional example and the example, the COD level of the semiconductor laser element of the conventional example is about 280 mW, whereas it is about 320 mW in the example.

  The embodiment of the present invention is not limited to the configuration and procedure described above, and it goes without saying that modifications may be made without departing from the scope of the present invention.

For example, in the fourth step of the embodiment, the width w3 of the impurity diffusion region Z of the semiconductor laser element 10 is set to about 20 μm. However, the present invention is not limited to this.
However, when the width w3 exceeds 60 μm, there may be a problem that the threshold value increases. Further, if the width w3 is smaller than 10 μm, there may be a problem that the COD level is lowered.
Therefore, it is desirable to set the width w3 within the range of 10 to 60 μm.

It is typical sectional drawing for demonstrating the 1st process in the Example of the semiconductor laser element of this invention. It is typical sectional drawing for demonstrating the 2nd process in the Example of the semiconductor laser element of this invention. It is typical sectional drawing for demonstrating the 3rd process in the Example of the semiconductor laser element of this invention. It is typical sectional drawing for demonstrating the 4th process in the Example of the semiconductor laser element of this invention. FIG. 4 is a diagram showing a relationship between Zn concentration and free carrier absorption loss in an active layer of a Zn diffusion region Z.

Explanation of symbols

1 n-type substrate, 2 n-type clad layer, 3 active layer, 4 p-type clad layer, 5 P + type cap layer, 7 diffusion source layer, 8 p-type electrode, 9 n-type electrode, 10 semiconductor laser element, A1, A2 Resonator surface, S upper surface, Z impurity diffusion region, w1, w2, w3 width, d1 interval

Claims (1)

A semiconductor laser device having a pair of resonator surfaces, wherein a first conductivity type cladding layer, an active layer, and a second conductivity type cladding layer are sequentially laminated on an upper surface of a first conductivity type semiconductor substrate,
The free carrier absorption loss in the active layer portion forming part of the pair of resonator surfaces and in the active layer portion located in the vicinity of the active layer portion is in the range of 10 to 13 cm ^−1. Semiconductor laser element.

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