JP2005136274A - Method of manufacturing semiconductor laser diode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent an active layer from deteriorating due to the diffusion of impurities and to realize sufficiently low element resistance so as to obtain an AlGaInP semiconductor laser diode. <P>SOLUTION: The method of manufacturing an AlGaInP semiconductor laser diode comprises a process of growing an n-type AlGaInP clad layer 3, an active layer 4, a p-type Mg-doped AlGaInP clad layer 5, and an n-type Zn-doped GaAs contact layer 6 successively on an n-type GaAs substrate 1 through a MOVPE method. The growth temperature of the contact layer 6 is set at 500 to 600°C, preferably at 500 to below 600°C. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention uses Mg and Zn for controlling the conductivity of a p-type layer, and particularly relates to a method for manufacturing an AlGaInP-based semiconductor laser diode.

  AlGaInP semiconductor laser diodes (LDs) are widely used as reading light sources and writing light sources for digital versatile discs (DVDs). Since recent electronic devices perform high-density mounting, it is particularly important to reduce operating current at high temperatures. For this reason, measures such as increasing the doping amount of the p-type cladding layer of the LD and increasing the carrier concentration to reduce the leakage current at the heterointerface and reduce the series resistance component are being taken.

  Examples of the p-type dopant of the AlGaInP-based compound semiconductor include beryllium (Be), magnesium (Mg), and zinc (Zn). Among these, the Be raw material used in molecular beam epitaxy (MBE) can be doped with high concentration and low diffusion, but has a drawback of being extremely toxic. Zn is widely used as a p-type dopant in AlGaInP-based compound semiconductors, but has a relatively large diffusion constant and is known to cause adverse effects due to a thermal process or the like.

  FIG. 7 shows one disclosed in Japanese Patent Laid-Open No. 9-219567 (Patent Document 1) as an example of a conventional semiconductor laser diode (LD) using an AlGaInP-based semiconductor material. In the figure, 201 is an n-type GaAs substrate, and 202 is a buffer layer made of n-type GaAs formed on the substrate 201. Reference numeral 203 denotes a clad layer made of n-type AlGaInP. Reference numeral 205 denotes an active layer made of AlGaInP, which has a non-doped AlGaInP layer above and below it. 206 is a clad layer made of p-type AlGaInP. That is, it has a double hetero structure in which the AlGaInP active layers 204 to 206 are sandwiched between the AlGaInP cladding layer 203 and the p-type AlGaInP cladding layer 207.

  A p-type GaInP contact layer 208 and a p-type GaAs cap layer 209 have a stripe structure, and a current blocking layer 210 made of GaAs is provided on both sides of the stripe structure for the purpose of current confinement.

  The AlGaInP-based semiconductor laser diode is characterized in that the first portion 207a in contact with the non-doped AlGaInP layer 206 in the p-type AlGaInP cladding layer 207 is replaced with a conventionally used Zn as a p-type impurity. Mg, which is difficult to diffuse in the solid of the compound semiconductor as compared with Zn, is doped, and the remaining second portion 207b is doped with Zn.

  In the semiconductor laser configured in this way, the first portion on the active layer side of the p-type cladding layer is not doped with Zn, or even at a very low concentration even when Zn is doped. As a result, Zn in the p-type cladding layer can be effectively prevented from entering the active layer. Further, since it is not necessary to excessively separate the second portion of the p-type cladding layer from the active layer in order to prevent Zn in the p-type cladding layer from entering the active layer, the series resistance of the p-type cladding layer is reduced. It can be made low enough.

In general, the contact layer is often made of p-type GaAs (see, for example, Patent Document 2).
JP-A-9-219567 (FIG. 1) Japanese Patent No. 3053836 (FIG. 3)

  However, according to the investigation by the present inventors, it has been found that the following problems occur when Mg is used as the p-type dopant of the cladding layer and contact layer of the AlGaInP-based semiconductor laser diode.

First, it is difficult to obtain an Mg—GaAs layer having a sufficiently low resistance when the outermost contact layer is formed by Mg doping. Even when trying to obtain a carrier concentration of about 2 × 10 ¹⁸ cm ⁻³ to 5 × 10 ¹⁹ cm ⁻³ necessary for the contact layer, Mg does not enter uniformly in the film thickness direction of the GaAs layer, and particularly at the initial growth stage of the GaAs layer. This is because Mg is difficult to enter.

FIG. 3 shows an Mg-GaAs layer having a carrier concentration of 1 × 10 ¹⁹ cm ⁻³ grown on a GaAs substrate, and the Mg concentration distribution in the film thickness direction was examined by secondary ion analysis (SIMS). As is clear from this, Mg is not sufficiently contained in the initial stage of growth, and it is difficult to obtain a low-resistance Mg—GaAs layer. When the resistance is high, heat is increased when the laser element is driven, resulting in an increase in operating current and a decrease in reliability.

As a second problem, when the relationship between the Mg (or Zn) concentration in the gas phase and the carrier concentration is examined as shown in FIG. 4, GaAs is far more Zn in GaAs and AlGaInP at the same Zn gas phase concentration. However, GaAs and AlGaInP have the same ease of entering Mg at the same Mg vapor concentration. The contact layer needs a carrier concentration of around 1 × 10 ¹⁹ cm ^{−3 in} order to obtain good electrical contact. When the Mg-GaAs layer is grown while supplying the Mg raw material necessary for this, excess Mg remains in the growth furnace after the crystal growth of the laser diode is completed. As a result, Mg is unintentionally taken into the crystal at the beginning of the next growth. In particular, Mg tends to segregate near the interface between the substrate and the epitaxial layer or near the interface between the epitaxial layers, which causes an increase in device resistance, which is not preferable.

  The present invention has been made to eliminate the above-mentioned drawbacks, and it is possible to obtain a high-quality AlGaInP-based semiconductor laser diode by preventing deterioration of the active layer due to impurity diffusion and realizing a sufficiently low device resistance. It is aimed.

  In order to achieve the above object, the present invention is configured as follows.

  According to a first aspect of the present invention, there is provided a method for manufacturing a semiconductor laser diode, comprising: an n-type clad layer, an active layer, a Mg-doped p-type clad layer, and a Zn-doped p-type contact layer on an n-type substrate in order by a MOVPE method; In the method of manufacturing a semiconductor laser diode to be grown, the growth temperature for growing the contact layer is 500 ° C. or more and 600 ° C. or less, preferably 500 ° C. or more and less than 600 ° C.

  According to a second aspect of the present invention, there is provided a method of manufacturing a semiconductor laser diode comprising: an n-type substrate, an active layer, a p-type clad layer made of Mg-doped AlGaInP, and a p-type made of Zn-doped GaAs. In the method of manufacturing a semiconductor laser diode in which the type contact layer is grown sequentially, the growth temperature for growing the contact layer is 500 ° C. or more and 600 ° C. or less, preferably 500 ° C. or more and less than 600 ° C.

<Key points of the invention>
The use of Mg as the p-type dopant for the contact layer is not preferable because of the above-mentioned problems. Therefore, if the contact layer is made of Zn-GaAs using Zn, which has a diffusion constant larger than Mg but easily obtains a high carrier concentration. It is considered good. In general, Zn-GaAs contact layers have been widely used. However, in this case, Zn is not supplied during the growth of the p-type cladding layer, but the Zn in the contact layer diffuses to the p-cladding layer side even though it is grown while supplying Mg, and further to the inside of the active layer. There has been a problem that the device characteristics are significantly deteriorated by diffusion.

  Therefore, we formed contact layers at various growth temperatures, compared the Zn diffusion status of the contact layers, and found that Zn diffusion was remarkably suppressed in the growth temperature range below 600 ° C, preferably below 600 ° C. It was. On the other hand, there is a problem that the surface state of the contact layer deteriorates at a growth temperature of 500 ° C. or lower. Therefore, the optimum temperature range for growing the contact layer is 500 ° C. or more and 600 ° C. or less, preferably 500 ° C. or more and less than 600 ° C.

  The secondary ion analysis results in the vicinity of the active layer of the epitaxial wafer produced by changing the growth temperature of the contact layer at 580, 630, and 680 ° C. are shown in FIG. 2, FIG. 5, and FIG. When the growth temperature of the contact layer exceeds 600 ° C., it is clear that Zn doped only in the contact layer is diffused to the vicinity of the active layer.

  According to the present invention, the following excellent effects can be obtained.

  First, since the p-type cladding layer is Mg-doped, it is possible to reduce the deterioration of the active layer due to thermal history as compared with Zn having a large diffusion constant.

  Next, the contact layer is made of Zn-GaAs, and the growth temperature thereof is set to 500 ° C. or more and 600 ° C. or less, preferably 500 ° C. or more and less than 600 ° C., thereby minimizing the amount of Zn diffused from the contact layer. In addition, an epitaxial wafer capable of obtaining a low-resistance ohmic contact can be obtained.

  Therefore, according to the present invention, an AlGaInP-based semiconductor laser diode having a large light emission output and a small operating voltage can be easily manufactured by reducing the impurity diffusion in the crystal.

  Hereinafter, the present invention will be described based on the illustrated embodiments.

As shown in FIG. 1, an n-type GaAs buffer layer 2 and an n-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P clad layer 3 lattice-matched with the n-type GaAs substrate 1 are sequentially epitaxially grown, and an AlGaInP layer is formed thereon. An active layer 4 composed of a strained quantum well of the system and an Mg-doped p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P clad layer (p-type clad layer) 5 were grown to produce a double heterostructure. Further, a Zn-doped p-type GaAs contact layer 6 was grown on the p-type cladding layer 5. At that time, the Zn—GaAs contact layer 6 was grown at a temperature in the range of 500 ° C. to 600 ° C., preferably 500 ° C. to less than 600 ° C.

  By making the growth temperature of the Zn-GaAs contact layer 6 in the range of 500 ° C. or higher and 600 ° C. or lower, preferably 500 ° C. or higher and lower than 600 ° C., by this semiconductor laser diode manufacturing method, the amount of Zn diffused from the contact layer 6 It is possible to obtain an epitaxial wafer that can minimize the resistance and obtain a low-resistance ohmic contact.

A p-type cladding layer 5 made of an Mg-doped AlGaInP layer on an n-type substrate by MOVPE (metal organic vapor phase epitaxy) method, and a growth temperature in the range of 500 ° C. to 600 ° C., preferably 500 ° C. to less than 600 ° C. An epitaxial wafer for an AlGaInP-based semiconductor laser diode having a contact layer 6 made of the formed Zn-doped GaAs layer was produced. An n-type GaAs single crystal substrate was used as the substrate 1, and triethylgallium, trimethylgallium, trimethylaluminum, and trimethylindium were used as Ga, Al, and In materials. Phosphine (PH ₃ ) was used as the P raw material. Arsine (AsH ₃ ) was used as the As raw material. The composition of the active layer 4 which is a light emitting layer may be an appropriate composition according to the emission wavelength, or may be a quantum well structure.

First, a GaAs substrate 1 was placed in a growth furnace, and an Si-doped GaAs buffer layer 2 having an n-type conductivity and a thickness of 0.5 μm was formed at a substrate temperature of 700 ° C. Next, at substrate temperature, made of _{(Al 0.7 Ga 0.3) 0.5 In} 0.5 n -type cladding layer 3 made of P, the active layer 4 made of strained quantum well AlGaInP-based, Mg-doped _{(Al 0.7 Ga 0.3) 0.5 In} 0.5 P A p-type cladding layer 5 was formed. Next, after the substrate temperature was lowered from 500 ° C. to 600 ° C., a Zn—GaAs contact layer 6 was grown. The carrier concentration of the p-type cladding layer 5 was 1.0 × 10 ¹⁸ cm ⁻³ .

  For comparison, an epitaxial wafer for an AlGaInP semiconductor laser diode in which only the growth temperature of the contact layer 6 was 630 ° C. to 680 ° C. was also manufactured.

  The results of secondary ion analysis (SIMS) of the completed epitaxial wafer are as shown in FIG. 2 (this example) and FIGS. 5 to 6 (comparative example). When the growth temperature of the contact layer, which is a comparative example, is 630 ° C. and 680 ° C. (FIGS. 5 and 6), Zn changes from the p-type cladding layer (abbreviated as p-cladding layer in the figure) to the active layer. It was diffused and the active layer was deteriorated.

  Also, after removing the contact layer of the epitaxial wafer with a sulfuric acid-based etchant and removing about half of the p-type cladding layer with a hydrochloric acid-based etchant, the photoluminescence spectrum of the active layer is measured using an Ar laser having a wavelength of 488 nm. As a result, the contact layer 6 grown at 600 ° C. or less, preferably 500 ° C. or more and less than 600 ° C. (in this example) had a half width of 12 nm or less, but the contact layer was grown at 630 ° C. (Comparative Example 1) had a half-value width of 18 nm, and a result consistent with the Zn diffusion state by SIMS was obtained. That is, a good quality active layer was obtained when the growth temperature of the contact layer was 600 ° C. or lower, preferably 500 ° C. or higher and lower than 600 ° C.

  An LD chip was produced from the LD epitaxial wafer thus obtained. In this case, as in the case of FIG. 7, the second cladding layer 5 and the p-type contact layer 6 have a ridge structure, current blocking layers are provided on the left and right sides of the ridge structure, and the p-side electrode 11 and the n-side electrode 12 are arranged vertically. Was provided. In this LD, in the case where the growth temperature of the contact layer is 600 ° C. or lower, preferably 500 ° C. or higher and lower than 600 ° C. (this example), the threshold current was 120 (mA), but the contact layer was 630 ° C. (Comparative Example 1) was 210 (mA), and the relationship with the quality of the active layer obtained from secondary ion analysis and photoluminescence measurement clearly appeared.

It is the figure which showed the structure of the epitaxial wafer for semiconductor laser diodes manufactured with the method of this invention. It is a figure which shows the secondary ion analysis result of the epitaxial wafer which grew the contact layer with the growth temperature of 580 degreeC. It is a figure which shows the Mg dope GaAs profile (by secondary ion analysis) of thickness 1 micron. It is the figure which showed the taking-in efficiency of Mg and Zn in comparison. It is a figure which shows the secondary ion analysis result of the epitaxial wafer which grew the contact layer at the growth temperature of 630 degreeC. It is a figure which shows the secondary ion analysis result of the epitaxial wafer which grew the contact layer at the growth temperature of 680 degreeC. It is the figure which showed the structure of the conventional epitaxial wafer for semiconductor laser diodes.

Explanation of symbols

1 substrate 2 buffer layer 3 n-type cladding layer 4 active layer 5 p-type cladding layer 6 p-type contact layer 11 p-side electrode 12 n-side electrode

Claims (2)

In a method of manufacturing a semiconductor laser diode, an n-type cladding layer, an active layer, a Mg-doped p-type cladding layer, and a Zn-doped p-type contact layer are sequentially grown on an n-type substrate by a MOVPE method.
A method of manufacturing a semiconductor laser diode, wherein a growth temperature for growing the contact layer is in a range of 500 ° C. to 600 ° C. In a method for manufacturing a semiconductor laser diode, an n-type cladding layer, an active layer, a p-type cladding layer made of Mg-doped AlGaInP, and a p-type contact layer made of Zn-doped GaAs are sequentially grown on an n-type substrate by an MOVPE method.
A method of manufacturing a semiconductor laser diode, wherein a growth temperature for growing the contact layer is in a range of 500 ° C. to 600 ° C.

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