JP3490923B2 - Method of setting carrier concentration of semiconductor layer and method of setting carrier concentration of semiconductor laser - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates to relates to a method for increasing the carrier concentration of the method and a semiconductor laser increases the carrier concentration of the semiconductor layer used in a semiconductor laser of AlGaInP system for emitting visible light.

[0002]

2. Description of the Related Art AlGaInP has a wavelength of 0.6 μm band and is used as a material for visible light semiconductor lasers.

FIG. 5 shows a conventional AlGaInP type semiconductor laser, which is described in, for example, Japanese Patent Laid-Open No. 62-200786.

In the figure, (20) is in both positions (10
(21) n-type Ga
InP buffer layer, (22) n-type AlGaI
n-type cladding layer made of nP, (23) active layer made of undoped GaInP, (24) p-type AlGaI
It is a p-type cladding layer made of nP. These layers are sequentially epitaxially grown on one main surface of the substrate (20) using the well-known MOCVD method. In addition, the p-type clad layer (2
In 4), a stripe-shaped ridge (25) having a width of 5 μm is formed by etching.

(26) is a block layer made of n-type GaAs epitaxially grown on the p-type cladding layer (24) excluding the top of the ridge (25), and (27) is a ridge () of the exposed p-type cladding layer (24). 25) p-type GaAs epitaxially grown on top and block layer (26)
Is a p-side electrode formed on the cap layer (27), and (29) is an n-side electrode formed on the other main surface of the substrate (20).

Mg and Zn are used as p-type impurities in such an AlGaInP semiconductor laser. However, in the MOCVD method, since Mg is used as a solid source, it is difficult to accurately control the amount of Mg added, and reproducibility is poor. Therefore, Zn existing as an organic metal is mainly used as a p-type impurity because the amount of addition can be easily controlled.

[0007]

On the other hand, such AlGaI
There is a demand for even shorter wavelengths in nP-based semiconductor lasers. Therefore, it has been proposed to add Al to the composition of the active layer to increase its bandgap.

However, if the band gap of the active layer is increased, the efficiency of carrier injection into the active layer is maintained.
It is necessary to increase the band gap of the clad layer and form a sufficiently large hetero barrier at the interface between the active layer and the clad layer. As a method of increasing the hetero barrier, there are a method of increasing the Al composition ratio of the cladding layer and a method of increasing the carrier concentration of the cladding layer.

However, in AlGaInP,
When the Al composition ratio to Ga is 0.7, the band gap becomes maximum, and even if the Al composition ratio is increased, a band gap higher than this cannot be obtained. Therefore, it is desired to increase the band gap of each clad layer and increase its carrier concentration. However, it is generally difficult to obtain a large carrier concentration with p-type impurity Zn, and the carrier concentration decreases as the Al composition ratio increases. Tends to become. That is, conventionally, it was not possible to obtain a p-type clad layer having a large band gap and a large carrier concentration.

Therefore, an object of the present invention is to provide a method for setting the carrier concentration of a semiconductor layer which can increase the carrier concentration of the semiconductor layer made of p-type AlGaInP.

Further, the present invention provides a method for setting the carrier concentration of an AlGaInP-based semiconductor laser which can increase the carrier concentration even when the Al composition ratio of the active layer and the p-type clad layer is large, and can further shorten the wavelength. It is provided.

[0012]

The present invention is a p-type cladding layer of a semiconductor laser formed on the main surface of a GaAs substrate.
Increase the carrier concentration of a p-type AlGaInP semiconductor layer
A method of causing the addition of Zn as an acceptor in the semiconductor layer, the main surface of the GaAs substrate (100)
By tilting the plane in the <011> direction, characterized in that the carrier concentration of the semiconductor layer was made to be larger than the main surface is a (100) plane.

According to such a setting method, the carrier concentration can be increased even in a semiconductor layer made of AlGaInP having the same Al composition ratio.

[0014]

[0015] Between the p-type cladding layer and the active layer, it is possible to form a large hetero barrier, it is possible to increase the band gap of the active layer.

Further, according to the present invention, an n-type clad layer made of n-type AlGaInP and AlG are formed on the main surface of a GaAs substrate.
Active layer having a layer of aInP, p-type AlGaIn
A method of increasing the carrier concentration of a semiconductor laser in a semiconductor laser in which a p-type cladding layer made of P is sequentially formed, wherein Si is used as a donor in the n-type cladding layer.
Is added to the p-type cladding layer as an acceptor.
By adding n and inclining the main surface of the GaAs substrate in the <011> direction from the (100) plane, the carrier concentration of the p-type cladding layer is made larger than in the case where the main surface is the (100) plane. characterized in that set to be.

In this case, by using a substrate whose main surface is a surface inclined in the <011> direction from the (100) surface, Z added to the p-type clad layer provided thereon.
n increases the carrier concentration of the p-type cladding layer,
Moreover, Si added to the n-type clad layer suppresses the deterioration of the crystallinity of the active layer caused by increasing the Al composition ratio, and the carrier concentration obtained in the n-type clad layer provides a sufficient hetero barrier with the active layer. It is the value that is formed.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a semiconductor laser in which the carrier concentration of the cladding layer is increased according to the present invention (hereinafter referred to as the device of the present embodiment).

In the figure, (1) has one main surface of (100).
N-type GaA tilted in the <011> direction from the plane by, for example, 7 degrees
s substrate, (2) is 0.3 μm thick n-type Ga_0.5
In _0.5Buffer layer made of P, (3) as donor
Si-added 1 μm thick n-type (Al_0.6Ga_0.4)
_0.5In_0.5N-type clad layer made of P, (4) thickness
0.06 μm undoped (Al_0.1Ga_0.9)_0.5In
_0.5Active layer made of P, (5) Zn as an acceptor
1 μm thick p-type (Al_0.6Ga_0.4)_0.5I
n_0.5P-type clad layer made of P, (6) has a thickness of 0.1
μm p-type Ga_0.5In_{0 .Five}A contact layer made of P
It These layers are formed on the substrate using the well-known MOCVD method.
(1) Sequentially epitaxially grows on one main surface.

The p-type clad layer (5) and the contact layer (6) have a p-type clad layer (5) thickness of 0.2 μm.
The surface of the contact layer (6) is selectively etched until the thickness reaches m, so that the p-type cladding layer (5) has a width of 5
A stripe-shaped ridge (7) of μm is formed.

(8) is an n-type GaA epitaxially grown on the p-type cladding layer (5) except the top of the ridge (7).
(9) is a cap layer made of p-type GaAs epitaxially grown on the ridge (7) top of the exposed p-type cladding layer (5) and the block layer (8), and (10) is a cap layer. (9) A formed on
A p-side electrode made of an alloy of u and Cr, and (11) an n-side electrode made of an alloy of Au, Sn and Cr formed on the other main surface of the substrate (1).

When the characteristics of the device of this embodiment were measured, the carrier concentration of the p-type cladding layer (5) was about 9 × 10.
^{It is 17} cm ^-3 , and the maximum ambient temperature at which continuous oscillation is obtained is about 8
The oscillation wavelength was 0 ° C. and 635 nm. For comparison, a comparative device having the same structure as the device of this example except that each layer was laminated on the (100) plane of the substrate was manufactured, and its characteristics were measured. The carrier concentration of the p-type clad layer was about At 5 × 10 ¹⁷ cm ⁻³ , the maximum ambient temperature at which continuous oscillation was obtained was about 50 ° C., and the oscillation wavelength was 650 nm.

From the above measurement results, the device of this embodiment can increase the carrier concentration even with the p-type cladding layer having the same Al composition ratio as compared with the comparative device, and thereby a larger heterobarrier can be obtained. . Therefore, it is understood that the carriers can be efficiently confined in the active layer even if the carriers are easily excited, that is, the ambient temperature rises, and continuous oscillation is selected. In addition, the difference in the oscillation wavelength between the two is already disclosed in Japanese Patent Application No. 1-8310.
This is because the main surface of the substrate is an inclined surface as disclosed in No. 7.

FIG. 2 shows the inclination angle from the (100) plane of the main surface of the substrate (1) to the <011> direction and the p-type cladding layer (5).
The relationship of the carrier concentration obtained in the above is shown. From the figure, by using the inclined surface as the main surface, when the inclination angle is 0 degree,
That is, it can be seen that a larger carrier concentration can be obtained than in the conventional device having the (100) plane as the main surface.

As described above, in the device of the present invention, a larger heterobarrier can be formed between the p-type cladding layer (5) and the active layer (4) as compared with the conventional device, so that the bandgap of the active layer is increased. The wavelength can be further shortened.

On the other hand, the band gap of the active layer can be increased by increasing the Al composition ratio of the active layer.
Since increasing the composition ratio causes deterioration of the crystallinity of the active layer, it is desirable to suppress the Al composition ratio of the active layer as much as possible. For this purpose, it is preferable to use Si as a donor of the n-type cladding layer (3) as shown in the apparatus of this embodiment. In FIG. 3, (Al _0.5 Ga _0.5 ) _0.5 In _0.5
Si or Se is added as a donor to the n-type cladding layer made of P, and undoped Ga _0.5 In _0.5 P is added on top of this.
3 shows a carrier concentration distribution in the thickness direction when an active layer made of is formed. In the figure, when the solid line is made of Si, the broken line is Se.
Is the case of using. From the figure, in the case of using Se,
Since many carriers are found in the active layer, it can be seen that Se in the n-type cladding layer is much brought into the active layer during growth of the active layer. That is, when a donor is brought into the active layer, the crystallinity of the active layer is likely to deteriorate, which causes a decrease in the reliability of the laser device to be manufactured, and a donor level is formed. As a result of radiative recombination using, it becomes a cause of making the wavelength longer. On the other hand, Si
It can be seen that in the case of using, the steep interface between the n-type cladding layer and the active layer, in which the donor is not brought into the active layer, is obtained.

Further, n when Si is used as a donor
The carrier concentration obtained in the mold clad layer is constant at about 1 × 10 ¹⁸ cm ⁻³ regardless of the inclined surface of the substrate,
The value was such that a sufficient hetero barrier was formed with the active layer.

From the above, a substrate having a main surface inclined in the <011> direction from the (100) plane is used, and the impurity added to the p-type cladding layer is Zn and the impurity added to the n-type cladding layer is Si. As a result, a semiconductor laser can be obtained in which the band gap of the active layer can be increased without deteriorating the crystallinity and carriers can be efficiently confined in the active layer.

FIG. 4 shows the aging characteristics by a constant output operation at an ambient temperature of 40 ° C. and 3 mW, and the change of the apparatus of this embodiment shown in FIG. 1 is shown by the solid line in the figure. For comparison, a comparative device having the same configuration as that of the device of the present example was prepared except that Se was used as the donor in the n-type cladding layer instead of Si and Mg was used as the acceptor in the p-type cladding layer instead of Zn. , A similar experiment was conducted. The result is also shown in FIG. From the figure, it can be seen that the device of this embodiment has little deterioration and high reliability.

[0030]

According to the present invention, from the (100) plane to <0
Zn which is added as an acceptor to the semiconductor layer by using a substrate having a main surface inclined in the 11> direction
Can increase the carrier concentration of the semiconductor layer.

Moreover, the semiconductor layer is p of a semiconductor laser.
In the case of the type clad layer, the band gap of the active layer can be further increased, and the wavelength can be shortened.

Further, even when the Al composition ratio in the active layer is increased in order to further increase the band gap, the Al composition ratio is increased by adding Si as a donor to the n-type cladding layer. The decrease in crystallinity of the active layer caused by
Even if the type clad layer is formed on the main surface of the inclined substrate, the carrier concentration obtained in the n-type clad layer is a value at which a sufficient hetero barrier is formed with the active layer, and carriers are efficiently incorporated in the active layer. Can be confined.

[Brief description of drawings]

FIG. 1 Increases the carrier concentration of the cladding layer according to the present invention
It is sectional drawing which shows the made semiconductor laser.

FIG. 2 is a characteristic diagram showing the relationship between the tilt angle of the substrate and the carrier concentration of the p-type cladding layer.

FIG. 3 is a characteristic diagram showing a carrier concentration distribution in a thickness direction of an active layer when Si and Se are used as a donor of an n-type cladding layer.

FIG. 4 is a characteristic diagram showing aging characteristics.

FIG. 5 is a cross-sectional view showing a conventional semiconductor laser.

[Explanation of symbols]

1 substrate 3 n-type clad layer 4 Active layer 5 p-type clad layer

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masayuki Shono 2-5-5 Keihan Hondori, Moriguchi City, Osaka Prefecture Sanyo Electric Co., Ltd. (72) Inventor ▲ Hiro ▼ Ryoji Yama 2 Keihanhondori, Moriguchi City, Osaka Prefecture 5-5, Sanyo Electric Co., Ltd. (56) Reference JP-A-1-286482 (JP, A) IEICE Technical Report Vol. 89, No. 284 (November 16, 1989) P57-64 (58) Fields investigated (Int.Cl. ⁷ , DB name) H01S 5/00

Claims (2)

(57) [Claims] 1. A semiconductor device formed on a main surface of a GaAs substrate.
-Type AlGaInP half that is the p-type cladding layer of the body laser
A method of increasing the carrier concentration of a conductor layer , comprising adding Zn as an acceptor to the semiconductor layer,
The main surface of the As substrate from (100) plane by inclining the <011> direction, the main surface the carrier concentration of the semiconductor layer (100) to be greater than a surface
The carrier concentration of the semiconductor layer, characterized in that the increased
How to make . 2. An n-type AlGaI is formed on the main surface of a GaAs substrate.
n-type cladding layer made of nP, active layer, p-type AlGaI
A method for increasing the carrier concentration of a semiconductor laser in which a p-type clad layer made of nP is sequentially formed,
Si is added to the p-type cladding layer as a donor, Zn is added to the p-type cladding layer as an acceptor, and
The main surface of aAs substrate from (100) plane by inclining the <011> direction, that the carrier concentration of the p-type cladding layer was made to be larger than the main surface is a (100) plane A method for increasing the carrier concentration of a characteristic semiconductor laser.