JP3075728B2 - Semiconductor laser - Google Patents

Description

The present invention relates to an AlGaInP-based semiconductor laser that emits visible light.

(B) Conventional technology AlGaInP has a wavelength in the 0.6 μm band and is used as a material for visible light semiconductor lasers.

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

In the figure, (20) is a substrate made of n-type GaAs having a (100) plane orientation, (21) is a buffer layer made of n-type GaInP,
(22) is an n-type cladding layer made of n-type AlGaInP, (23)
Is an active layer made of undoped GaInP, and (24) is a p-type AlG
This is a p-type cladding layer made of aInP. These layers are sequentially epitaxially grown on one main surface of the substrate (20) using a well-known MOCVD method. A stripe-shaped ridge (25) having a width of 5 μm is formed on the p-type cladding layer (24) by etching.

(26) is a block layer of n-type GaAs epitaxially grown on the p-type cladding layer (4) except for the top of the ridge (25), and (27) is the top of the ridge (25) of the exposed p-type cladding layer (24). A cap layer made of p-type GaAs epitaxially grown on the block layer (26); (28) a p-type electrode formed on the cap layer (27); (29) on the other main surface of the substrate (20) Are formed on the n-side electrode.

Mg or Zn is used as a p-type impurity in such an AlGaInP-based semiconductor laser. However, in the MOCVD method, Mg
Since a solid is used as a source, it is difficult to accurately control the amount of Mg added, and the 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.

(C) Problems to be Solved by the Invention On the other hand, there is a demand for further shortening the wavelength of such an AlGaInP-based semiconductor laser. Therefore, Al is added to the composition of the active layer to increase the band gap. It has been proposed.

However, if the band gap of the active layer is increased, the band gap of the cladding layer is also increased to maintain the carrier injection efficiency into the active layer, and a sufficiently large heterobarrier is formed at the interface between the active layer and the cladding layer. There is a need to. As a method of increasing such a 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, the band gap is maximized when the Al composition ratio to Ga is 0.7, and even if the Al composition ratio is increased, no further band gap can be obtained. Therefore, it is desirable to increase the band gap and the carrier concentration of each clad layer. However, in the case of Zn of the p-type impurity, it is generally difficult to obtain a large carrier concentration. In particular, the carrier concentration decreases as the Al composition ratio increases. Tend to be. That is, conventionally, it was not possible to obtain a p-type cladding layer having a large band gap and a high carrier concentration.

Accordingly, the present invention provides an AlGaInP-based semiconductor laser that can increase the carrier concentration even when the Al composition ratio of the active layer and the p-type cladding layer is large and can further shorten the wavelength.

(D) Means for Solving the Problems The present invention provides an n-type Al film on a main surface of a GaAs substrate having a main surface inclined 5 to 9 degrees in the <011> direction from the (100) plane.
An n-type cladding layer made of GaInP, an active layer having a layer made of AlGaInP, a p-type cladding layer made of p-type AlGaInP are provided, and the n-type cladding layer serves as a donor.
Si is added, and Zn is added to the p-type cladding layer as an acceptor, so that the carrier concentration of the p-type cladding layer is increased in combination with the inclination of the main surface.

(E) Function According to the present invention, by using a substrate having a surface inclined in the <011> direction from the (100) plane as a main surface, Zn added to the p-type cladding layer provided thereon is The carrier concentration of the p-type cladding layer is increased, and Si added to the n-type cladding layer suppresses a decrease in crystallinity of the active layer caused by increasing the Al composition ratio,
The carrier concentration obtained in the n-type cladding layer is a value at which a sufficient heterobarrier is formed with the active layer.

(F) Embodiment FIG. 1 shows an embodiment of the present invention.

In the figure, (1) indicates that one principal plane is <011> from the (100) plane.
A substrate made of n-type GaAs inclined at, for example, 7 degrees in the direction,
(2) a buffer layer made of n-type Ga _0.5 In _0.5 P having a thickness of 0.3 μm, and (3) a 1 μm-thickness doped with Si as a donor.
An n-type cladding layer made of m-type n-type (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P, and (4) is an undoped (Al _0.1 G
a _0.9 ) An active layer composed of _0.5 In _0.5 P, and (5) is a 1 μm-thick p-type (Al _0.6 Ga _0.4 ) doped with Zn as an acceptor.
_0.5 In _0.5 P p-type cladding layer, (6) 0.1 mm thick
It is a contact layer made of p-type Ga _0.5 In _0.5 P of μm.
These layers are sequentially epitaxially grown on one main surface of the substrate (1) using a well-known MOCVD method.

Further, a p-type cladding layer (5) and a contact layer (6)
Is selectively etched from the surface of the contact layer (6) until the thickness of the p-type cladding layer (5) becomes 0.2 μm,
As a result, a stripe-shaped ridge (7) having a width of 5 μm is formed in the p-type cladding layer (5).

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

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 ¹⁷ cm ⁻³ ,
The maximum ambient temperature at which continuous oscillation was obtained was about 80 ° C., and the oscillation wavelength was 635 nm. Also, for comparison, (100)
A comparative device having the same configuration as that of the device of this example was prepared except that each layer was laminated on the surface, and the characteristics thereof were measured. As a result, the carrier concentration of the p-type cladding layer was about 5 × 10 ¹⁷ cm ^-3 and the continuous oscillation was performed. Ambient temperature is about 50 ° C and oscillation wavelength is 650n
m.

From the above measurement effects, the carrier concentration can be increased even in the case of the p-type cladding layer having the same Al composition ratio as compared with the comparative device of the device of the present embodiment, whereby a larger heterobarrier can be obtained. Therefore, even if the carrier is easily excited, that is, even if the ambient temperature increases, the carrier can be efficiently confined in the active layer, and continuous oscillation can be obtained. Further, the difference between the two oscillation wavelengths is due to the fact that the principal surface of the substrate is an inclined surface as already disclosed by the present applicant in Japanese Patent Application No. 1-83107.

FIG. 2 shows the relationship between the inclination angle from the (100) plane of the main surface of the substrate (1) to the <011> direction and the carrier concentration obtained in the p-type cladding layer (5). It can be seen from the figure that the use of the inclined surface as the main surface provides a higher carrier concentration when the inclination angle is 0 degree, that is, as compared with 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) than in the conventional device, so that the band gap of the active layer can be 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.However, increasing the Al composition ratio decreases the crystallinity of the active layer. It is desirable to suppress the composition ratio 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.
FIG. 3 shows the thickness when an active layer made of undoped Ga _0.5 In _0.5 P is formed by adding Si or Se as a donor to an n-type cladding layer made of (Al _0.5 GA _0.5 ) _0.5 In _0.5 P. 4 shows a carrier concentration distribution in the vertical direction. In the figure, the solid line is the case where Si is used, and the broken line is the case where Se is used. The figure shows that in the case of using Se, a large amount of carriers are observed in the active layer, and thus it is understood that a large amount of Se in the n-type cladding layer is brought into the active layer during the growth of the active layer. That is, when a donor is introduced into the active layer, the crystallinity of the active layer is easily deteriorated, which causes a decrease in the reliability of a laser device to be manufactured, and a donor level is formed. Since the light-emitting recombination using the light-emitting element occurs, the wavelength becomes longer. On the other hand, in the case of using Si, it can be seen that a steep interface is obtained between the n-type cladding layer and the active layer, in which donors are less brought into the active layer.

Further, the carrier concentration obtained in the n-type cladding layer when Si is used as the donor is constant at about 1 × 10 ¹⁸ cm ⁻³ irrespective of the inclined surface of the substrate, and the active layer and the sufficient heterobarrier Was formed.

As described above, by using a substrate having a main surface inclined in the <011> direction from the (100) plane, Zn as an impurity to be added to the p-type cladding layer, and Si as an impurity to be added to the n-type cladding layer, A semiconductor laser that can increase the band gap of the active layer without lowering the crystallinity and efficiently confine carriers in the active layer can be obtained.

FIG. 4 shows the aging characteristics due to the 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 a solid line in the figure. For comparison, a comparative device having the same configuration as that of the device of this example was prepared except that Se was used instead of Si as the donor in the n-type cladding layer and Mg was used as the acceptor in the p-type cladding layer instead of Zn. A similar experiment was performed. The results are also shown in FIG. 4 by broken lines. From the figure, it can be seen that the device of the present embodiment has little deterioration and high reliability.

(G) Effects of the Invention According to the device of the present invention, Zn added as an acceptor to the p-type cladding layer is reduced by using a substrate having a main surface having a surface inclined in the <011> direction from the (100) plane. Since the carrier concentration of the p-type cladding layer can be increased, the band gap of the active layer can be further increased, the wavelength can be shortened, and the Al composition in the active layer can be further increased. Even when the ratio is increased, by adding Si as a donor to the n-type cladding layer, it is possible to suppress a decrease in the crystallinity of the active layer caused by increasing the Al composition ratio, and to reduce n.
Even when 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 heterobarrier is formed with the active layer, and carriers are efficiently placed in the active layer. Can be confined.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an embodiment of the present invention, 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, and FIG. , Se
FIG. 4 is a characteristic diagram showing a carrier concentration distribution in the thickness direction of the active layer when using GaN, FIG. 4 is a characteristic diagram showing aging characteristics, and FIG.
The figure is a sectional view showing a conventional device.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masayuki Shono 2-18-18 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Ryoharu Hiroyama 2-18-18 Keihanhondori, Moriguchi-shi, Osaka (56) References IEICE Technical Report Vol. 89, No. 284 (November 16, 1989) p. 57-64 Electronics Letters 1st February. 1990 Vol. 26 No. 3 Jpn. J. of Appl. Phys. Vol. 27, No. 12, Dec, 1988, pL2414 to L2416

Claims (1)

(57) [Claims] An n-type Al is formed on a main surface of a GaAs substrate having a main surface inclined at 5 to 9 degrees in the <011> direction from a (100) plane.
An n-type cladding layer made of GaInP, an active layer having a layer made of AlGaInP, a p-type cladding layer made of p-type AlGaInP are provided, and the n-type cladding layer serves as a donor.
A semiconductor laser, wherein Si is added, and Zn is added as an acceptor to the p-type cladding layer to increase the carrier concentration of the p-type cladding layer in combination with the inclination of the main surface. .