JP3634564B2 - AlGaAs semiconductor laser device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an AlGaAs semiconductor laser element manufactured by MOCVD and used for an optical disk or the like.
[0002]
[Prior art]
As a method for producing a compound semiconductor crystal such as AlGaAs for a semiconductor laser, one of LPE (liquid phase epitaxy), MBE (molecular beam epitaxy), and MOCVD (metal organic vapor phase epitaxy) is mainly used. . The LPE method can produce a good quality semiconductor crystal with a relatively simple apparatus, but it is difficult to produce a uniform crystal over a large area. On the other hand, the MBE method and the MOCVD method are more suitable for mass production and are widely used today.
[0003]
The MBE method is a method in which each solid element constituting a compound semiconductor is heated and irradiated on a substrate in a high vacuum, and thus a pure crystal is easily obtained. On the other hand, the MOCVD method transports elements constituting a compound semiconductor in the form of a gas as an organic compound or hydride under normal pressure or a reduced pressure of about 1/10 atm. Form. Therefore, organic substances and hydrogen generated after the chemical reaction are easily taken into the compound semiconductor as impurities. In particular, C (carbon) in the organic substance is taken into the compound semiconductor as a p-type dopant.
[0004]
When a compound semiconductor is manufactured by the MOCVD method, Se, Si, or the like is generally used as the n-type dopant element, and Zn, Mg, C, or the like is generally used as the p-type dopant element. Although these dopants can be used relatively well by themselves, depending on the combination, when the adjacent layers are doped, complicated interdiffusion occurs.
[0005]
FIG. 6 shows a cross-sectional view of an AlGaAs semiconductor laser manufactured by a conventional MOCVD method. On the n-type GaAs substrate 101, an Se-doped n-type GaAs buffer layer 102, a Se-doped n-type AlGaAs cladding layer 103, an undoped AlGaAs active layer 104, a Zn-doped p-type cladding layer 105, and a Se-doped n-type AlGaAs block are formed by MOCVD. Layer 106 is formed. The n-type block layer 106 is removed in a stripe shape to form a current path 120, and a Zn-doped p-type cladding layer 108 and a Zn-doped p-type contact layer 109 are further formed. An n electrode 110 is formed on the lower surface, and a p electrode 111 is formed on the upper surface.
[0006]
[Problems to be solved by the invention]
Such a conventional semiconductor laser has the following defects, and has been a cause of yield reduction and reliability reduction. As a first defect, the Zn-doped p-type cladding layer 105 to be p-type does not necessarily become p-type, but the conductivity type is inverted due to the mutual diffusion of Zn as the p-type impurity and Se as the n-type impurity. In some cases, the n-type cladding layer 103 and the n-type block layer 106 may be electrically short-circuited. As a second defect, the n-type cladding layer 103 becomes p-type in the vicinity of the active layer 104 in the stripe portion 120, so that an increase in operating current (deterioration of reliability) occurs during the accelerated deterioration test. There is a case.
[0007]
In order to suppress the above-described interdiffusion, the n-type impurity is generally replaced from Se to Si. Si is a dopant that hardly diffuses impurities, and also has an effect of suppressing diffusion of p-type impurities into the n-type layer at the pn interface.
[0008]
However, the effect of suppressing the diffusion of the p-type impurity into the n-type layer may cause the device characteristics to deteriorate. The case is shown below.
[0009]
Consider a case where the n-type impurity in FIG. 1 is replaced from Se to Si. In this case, the n-type impurity Si stays in the n-clad layer and the n-block layer for the effect of suppressing the diffusion of Si, and the p-type impurity stays in the p-cladding layer except that it slightly diffuses into the active layer. For this reason, the carrier concentration of the p-clad layer is substantially the same under the current stripe portion and the current block. On the other hand, in the Se doped element, the carrier concentration under the current block is lower than that in the stripe portion due to diffusion. For this reason, the Si-doped laser element has a drawback that the operating current is increased because the resistance of the p-type cladding layer is reduced and the leakage current is increased as compared with the Se-doped laser element.
[0010]
The present invention aims to solve the above problems. That is, the present invention provides a semiconductor laser device structure that can reduce the operating current without causing the p-type cladding layer to be n-inverted in the AlGaAs semiconductor laser device.
[0011]
[Means for Solving the Problems]
The AlGaAs semiconductor laser device according to the present invention (invention 1) includes at least a Si-doped n-type cladding layer, an active layer, a first Zn-doped p-type cladding layer, and a current blocking layer on an n-type substrate by MOCVD. A semiconductor laser device in which a second p-type cladding layer is regrown after growing by a method and forming a stripe-shaped groove in the current blocking layer,
The current blocking layer achieves the above object by sequentially forming a Se-doped n-type first current blocking layer and a Si-doped n-type second current blocking layer.
The AlGaAs semiconductor laser device according to the present invention (invention 2) includes at least a Si-doped n-type cladding layer, an active layer, a first Zn-doped p-type cladding layer, and a second Zn-doped layer on an n-type substrate. Alternatively, an Mg doped p-type cladding layer is grown by MOCVD, a ridge is formed on the second cladding layer, and then a current blocking layer is regrown, wherein the current blocking layer includes Se The doped n-type first current blocking layer and the Si-doped n-type second current blocking layer are sequentially formed to achieve the above object.
[0012]
In the AlGaAs semiconductor laser device according to the present invention (invention 3), the amount of Zn impurity (set impurity concentration × film thickness of the first p-type cladding layer) of the first p-type cladding layer is the n-type first current. The above object is achieved by making the amount of Se impurity in the block layer larger than or equal to the amount of Se impurity (set impurity concentration × film thickness of the n-type first current 1 block layer).
[0013]
The AlGaAs-based semiconductor laser device according to the present invention (invention 4) achieves the above object by performing the regrowth using either the MOCVD method or the LPE method.
[0014]
That is, in the present invention, in an AlGaAs semiconductor laser fabricated by MOCVD, the cladding layer n-type dopant is Si, the n-type block layer is close to the pn interface, and the Se-doped n-type block is formed thereon. It is intended to be a double block of layers.
[0015]
Hereinafter, the operation of the present invention will be described.
[0016]
The conventional defect is caused by the fact that Se, which is an n-type dopant, and Zn or Mg, which is a p-type dopant, easily cause mutual diffusion. That is, Zn doped in the p-type first cladding layer diffuses into the n-type cladding layer beyond the n-type block layer and the active layer 105 due to the influence of thermal history and the like. Then, Se in the n-type block layer and the n-type cladding layer diffuses into the p-type first cladding layer.
[0017]
According to the present invention, first, Se, which is an n-type cladding dopant, is replaced with Si, thereby preventing the p-type cladding dopant from diffusing into the n-type cladding. In addition, by using Se as the dopant of the n-type first block layer on the p-type cladding layer and Si as the dopant of the n-type second block layer thereon, first, Zn is placed on the n-type block side under the block layer. A pile-up phenomenon occurs in which both the p-type dopant and the n-type dopant are concentrated on the n-type block layer side of the pn interface. Zn in the cladding layer is further diffused into the n block layer, and the Se impurity amount (Se impurity concentration × n-type first cladding layer thickness) of the n-type first block layer and the Zn impurity amount (set Zn impurity concentration × p-type cladding). Diffusion occurs until the layer thickness is equal. In addition, when the impurity amount of Zn in the p-type cladding layer is larger than the impurity amount of Se in the first n-type block layer, Se does not diffuse into the p-cladding layer. The current blocking function is maintained in the second n-type block layer. Therefore, with this structure, the carrier concentration of the p-type cladding is high in the stripe portion, and the carrier concentration is low under the block layer. Therefore, confinement of current in the stripe portion is increased, and the operating current is reduced.
[0018]
[Embodiments of the Invention]
<Example 1>
1 is a cross-sectional view of the semiconductor laser device of Example 1. FIG.
This is a structure called a self-aligned type, and an n-type GaAs buffer layer 2 (1.5 × 10 ¹⁸ / cm ^{3) having} a thickness on an n-type GaAs substrate 1 (carrier concentration 2 × 10 ¹⁸ / cm ³ ) by MOCVD. 0.5 μm setting), Si-doped n-type Al _0.5 Ga _0.5 As cladding layer 3 (carrier concentration 4 × 10 ¹⁷ / cm ³ , thickness 1 μm setting), undoped Al _0.14 Ga _0.86 As activity Layer 4 (thickness 0.04 μm), Zn-doped p-type Al _0.5 Ga _0.5 As cladding layer 5 (carrier concentration 4 × 10 ¹⁷ / cm ³ , thickness 0.3 μm setting), Se-doped n-type first AlGaAs Block layer 6 (carrier concentration 2 × 10 ¹⁸ / cm ³ , thickness 0.03 μm setting), Si-doped n-type second AlGaAs block layer 7 (carrier concentration 3 × 10 ¹⁸ / cm ³ , thickness 0.8 μm setting). The n blocking layers 6 and 7 are removed in the form of stripes having a width of 4 μm to form current paths 20. Further, a Zn-doped p-type Al _0.5 Ga _0.5 As second cladding layer 8 (1.5 × 10 ¹⁸ / cm ³ , thickness 1 μm setting) and a Zn-doped p-type GaAs contact layer 9 (4 × 10 ¹⁸ / cm ³ and a thickness of 1 μm setting). After that, an n-electrode 10 is formed on the lower surface and a p-electrode 11 is formed on the upper surface, and then divided into bars. A light-reflecting film on both sides of the bar is coated with a reflective film, and further divided into chips to form individual elements. As a result, a semiconductor laser with a wavelength of 780 nm and an output of 5 mW is obtained.
[0019]
Here, the group III material is TMG (trimethylgallium), TMA (trimethylaluminum), the group V material is AsH ₃ (arsine), the n-type dopant material is SiH ₄ (silane) and H ₂ Se (hydrogen selenide), p DEZ (diethyl zinc) was used as the type dopant. The growth temperature is 750 ° C., the growth pressure is 76 Torr, and V / III = 120.
[0020]
In order to examine the doping concentration in the stripe, a sample having a width of 1000 μm was prepared. Further, in order to examine the doping concentration outside the stripe, a sample in which up to the Si-doped n-type AlGaAs block layer 7 was grown in the above process was prepared. The doping concentration was measured by SIMS (secondary ion mass spectrometry) analysis. FIG. 2 shows the profiles of SIMS Zn and Si in the stripe. Zn diffuses into the active layer, but does not diffuse into the n-clad layer 3. FIG. 3 shows the profile of Zn, Si, and Se outside the stripe, and FIG. 4 shows an enlarged view of the Se and Zn profile in FIG. 3 near the first n block. Zn diffuses in the n-type first block layer 6, but does not diffuse in the n-type second block layer 7, and Se and Si do not diffuse. The impurity concentration of Zn in the p-type cladding layer under the block layer is 4 × 10 ¹⁶ / cm ³ , indicating that the impurity concentration is lower than that in the p-cladding under the stripe.
[0021]
When the operating current of the laser manufactured under these conditions was measured, it was 32 mA, and the characteristics were improved over the element (38 mA) in which the n-type block layer was prepared only by Si doping. The amount of increase in operating current when operating at an output of 5 mW · 70 ° C. for 200 hours was 0.1 mA, which was also better in characteristics than the Si-only block layer element (0.8 mA).
[0022]
In order to simplify the description of FIG. 1, some layers are omitted. Actually, there is an etching stop layer group consisting of two layers between the p-type first cladding layer and the n-type first block layer, and the n-type second block layer is an Si-doped layer having a mixed crystal ratio of about four layers. Although it is a group, illustration and description of the thin layers are omitted.
[0023]
The Al mixed crystal ratio of each layer is not limited to the values shown in the embodiments. For example, the active layer may be GaAs having an Al mixed crystal ratio of zero.
[0024]
Although a laser of 5 mW is used here, a 40 mW class high output laser can be obtained by slightly reducing the thickness of the active layer, and the optimum carrier concentration is almost the same.
[0025]
<Example 2>
In Example 2, the second growth in Example 1 was performed by the LPE method instead of the MOCVD method. This is the same until the layers up to the Si-doped n-type AlGaAs block layer 7 are formed and stripe-formed on the n-type GaAs substrate 2 by MOCVD. Further, an Mg-doped p-type second cladding layer 8 ′ (1.5 × 10 ¹⁸ / cm ³ , 1 μm) and an Mg-doped p-type contact layer 9 ′ (4 × 10 ¹⁸ / cm ³ , 1 μm) are formed by the LPE method. To do.
[0026]
As in Example 1, an experiment was performed in which the carrier concentrations of the n-type cladding layer and the p-type first cladding layer were changed, and almost the same result was obtained. The optimum value was obtained depending on whether the second growth was the MOCVD method or the LPE method. The variation was found to be slight.
[0027]
<Example 3>
FIG. 5 shows a cross-sectional view of an AlGaAs semiconductor laser manufactured by the MOCVD method of Example 3. This is a structure called a ridge type, and an Si-doped n-type GaAs buffer layer 52 (1 × 10 ¹⁸ / cm ^{3) having} a thickness is formed on an n-type GaAs substrate 51 (carrier concentration 2 × 10 ¹⁸ / cm ³ ) by MOCVD. 0.5 μm setting), Si-doped n-type Al 0.5 Ga 0.5 As cladding layer 53 (4 × 10 ¹⁷ / cm ³ , thickness 1 μm setting), undoped Al _0.14 Ga _0.86 As active layer 54 (thickness 0. 04 μm), Zn-doped p-type Al _0.5 Ga _0.5 As first cladding layer 55 (3 × 10 ¹⁷ / cm ³ , thickness 0.3 μm setting), Zn-doped p-type GaAs etching stop layer 56 (1 × 10 ¹⁸ / cm ^3, thickness 0.003μm setting), Zn-doped p-type _Al 0.5 _{Ga 0.5} As second cladding layer ^{58 (1.5 × 10 18 / cm} 3, a thickness of 1μ Setting), Zn-doped p-type GaAs cap layer ^{59 (3 × 10 18 / cm} 3, a thickness of 1μm setting) to form a. The cap layer 59 and the second cladding layer 58 are removed so that the striped ridge portion remains. Next, by MOCVD, Se-doped n-type first AlGaAs block layer 60 (1 × 10 ¹⁸ / cm ³ setting, thickness 0.03 μm setting), Si-doped n-type second AlGaAs block layer 65 (3 × 10 ¹⁸ / cm ^3). Setting) and those formed on the cap layer 59 are removed. Further, a Zn-doped p-type contact layer 61 (3 × 10 ¹⁸ / cm ³ setting) is formed by MOCVD. Thereafter, an n-electrode 63 is formed on the lower surface, and a p-electrode 64 is formed on the upper surface, and then divided into bars, and the light emitting surfaces at both ends of the bar are coated with a reflective film and further divided into chips.
[0028]
The operating current of the laser was measured and found to be 34 mA. There was no significant difference in characteristics between the self-aligned type and the ridge structure type.
[0029]
【The invention's effect】
The present invention provides a p-type cladding in an AlGaAs semiconductor laser in which a light emitting portion is fabricated by MOCVD, by making an n-type block layer a Se-doped and Si-doped double cladding layer in order from the side closer to the p-type cladding layer. This makes it possible to fabricate a semiconductor laser having good characteristics without n-type inversion of the layers with a high yield. As a result, cost reduction of semiconductor lasers and effective utilization of material resources were realized.
[Brief description of the drawings]
FIG. 1 is a structural cross-sectional view of a semiconductor laser of Examples 1 and 2. FIG.
FIG. 2 is a SIMS profile in a stripe structure of a semiconductor laser in Example 1.
FIG. 3 is a SIMS profile in the structure outside the stripe of the semiconductor laser in Example 1;
4 is an enlarged view of the SIMS profile of FIG. 3 in the vicinity of an n-type first current blocking layer.
5 is a structural sectional view of a semiconductor laser of Example 3. FIG.
FIG. 6 is a structural cross-sectional view of a conventional semiconductor laser.
[Explanation of symbols]
1 n-type GaAs substrate 2 n-type GaAs buffer layer 3 Si-doped n-type cladding layer 4 active layer 5 p-type first cladding layer 6 Se-doped n-type first block layer 7 Si-doped n-type second block layer 8 p-type second 2 Cladding layer 9 p-type contact layer 10 n-electrode 11 p-electrode 20 current path 51 n-type GaAs substrate 52 n-type GaAs buffer layer 53 Si-doped n-type cladding layer 54 active layer 55 p-type first cladding layer 56 p-type GaAs etching Stop layer 58 p-type second cladding layer 59 p-type GaAs cap layer 60 Se-doped n-type first block layer 61 p-type contact layer 63 n-electrode 64 p-electrode 65 Si-doped n-type second block layer 101 n-type GaAs substrate 102 n-type GaAs buffer layer 103 Si-doped n-type cladding layer 104 active layer 105 p-type first cladding layer 106 Se Doped n-type block layer 108 p-type second cladding layer 109 p-type contact layer 110 n-electrode 111 p-electrode 120 Current path

Claims (4)

On the n-type substrate, at least a Si-doped n-type cladding layer, an active layer, a first Zn-doped p-type cladding layer, and a current blocking layer are grown by MOCVD, and a stripe-shaped groove is formed in the current blocking layer. Then, a semiconductor laser element in which the second p-type cladding layer is regrown,
The AlGaAs semiconductor laser device, wherein the current blocking layer is formed by sequentially forming a Se-doped n-type first current blocking layer and a Si-doped n-type second current blocking layer. On the n-type substrate, at least a Si-doped n-type cladding layer, an active layer, a first Zn-doped p-type cladding layer, and a second Zn-doped or Mg-doped p-type cladding layer are grown by MOCVD, A semiconductor laser device in which a current blocking layer is regrown after forming a ridge in the second cladding layer,
The AlGaAs semiconductor laser element, wherein the current blocking layer is formed by sequentially forming a Se-doped n-type first current blocking layer and a Si-doped n-type second current blocking layer. The amount of Zn impurity in the first p-type cladding layer (set impurity concentration × film thickness of the first p-type cladding layer) is the amount of Se impurity in the n-type first current blocking layer (set impurity concentration × n-type first current 1). 3. The AlGaAs semiconductor laser element according to claim 1, wherein the AlGaAs semiconductor laser element is larger than or equal to a thickness of the block layer. 3. The AlGaAs semiconductor laser element according to claim 1, wherein the regrowth is performed using either MOCVD or LPE.

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