JPS6017979A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To form a high performance semiconductor laser in good reproducibility by forming a GaAs substrate raised region to become a reflecting surface vicinity region, thereby obtaining a light beam of high quality having no astigmatism. CONSTITUTION:A raised region of approx. 1.5mum is formed on a GaAs substrate 1 to become a semiconductor laser refelcting vicinity region, and N type Al0.4Ga0.6As layer 2, an Al0.1Ga0.9As layer 3 to become an active layer, a P type Al0.4Ga0.6Ga layer 4, and a P type GaAs layer 5 are sequentially formed, the thickness of the layer 3 is increased to 0.1mum in the semiconductor laser central region, and decreased to 0.02mum in the semiconductor laser reflecting surface vicinity region. In this structure, the light intensity distribution of the layer thicknesswise direction is largely spread in the distribution in the vicinity of the reflecting surface, the light emitting sectional area increases to reduce the light output density, the damage of the reflecting surface can be prevented by the light outputting operation of 50mW or higher, and a semiconductor laser having high reliability can be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a buried semiconductor laser that eliminates reflection surface deterioration and enables high output operation. AJ Ga
Multilayer semiconductor lasers using materials such as As are capable of highly efficient laser oscillation and are used for applications such as optical fiber communications, but their optical output value is 5 to 10 mW.
It was of a certain extent.

The limit to the amount of light output that can be extracted is mainly due to the fact that the crystal arm-opening plane is damaged by the high-density light output.For example, if you try to obtain a light output of about 50 mW, the heat generation due to light absorption on the reflective surface will cause damage. It was unavoidable that the reflective surface of the crystal arm opening would instantly destroy the surface.

In order to eliminate such defects, there are methods of forming a -1GaAs layer (transparent to the oscillation wavelength) on the open face of the crystal arm, or applying high-concentration Zn diffusion to the active layer except for the light-emitting region near the reflective surface. By shifting the oscillation wavelength to the lower energy side, the area near the reflective surface becomes a transparent area, or by thinning the active layer of the semiconductor laser to about 0.04 μm, the light intensity distribution is expanded and the emission cross section is changed. It's getting thicker. However, in these methods, the manufacturing process is complicated, and it is difficult to obtain a high-performance semiconductor laser with good reproducibility. Although the refractive index waveguide effect is maintained, there is no refractive index waveguide effect in the direction perpendicular to it (direction parallel to the thickness of the layer C).
Semiconductor 1--The outgoing beam has the disadvantage that astigmatism occurs and cannot be narrowed down to a minute beam.Also, when forming a thin active layer, the confinement rate of light in the active layer is greatly reduced. However, disadvantages such as increasing the oscillation threshold current were unavoidable.

The purpose of the present invention is to eliminate the separation point of the conventional structure described above, and to provide a semiconductor laser which can obtain a high-quality light beam without astigmatism, including reliability by eliminating reflection surface deterioration even in high-output operation. be.

The semiconductor laser according to the present invention has a strip-shaped multilayer structure in which a first semiconductor layer serving as a light emitting region is sandwiched between second and third semiconductor layers having a larger forbidden band width, and the strip-shaped multilayer structure includes:
A semiconductor laser structure characterized in that the fourth semiconductor layer is embedded with a fourth semiconductor layer having a larger forbidden band width than the first semiconductor layer, and the thickness of at least the first semiconductor layer is varied over the longitudinal direction of the cavity. It is.

Embodiments according to the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view of the light emitting surface side of a semiconductor laser according to the present invention, and FIG. 2 is a cross-sectional view of the central portion of the laser. FIG. 3 shows a cross-sectional view of the central portion of another embodiment of the semiconductor laser according to the present invention.

FIG. 1 shows an example of a GaA semiconductor laser according to the present invention.
s, 1'! i (5) is formed.

Next, a stripe-like 8102 mask is formed on the crystal surface, and a T-groove is formed in the etching using H, PO, +H, 02+3CI (30H solution) to reach the GaAs substrate (1). Next, after cleaning the crystal surface again, a second liquid phase growth process is performed to form n-type AI!o.
,, Ga o, 7A, s layer (6), PQAeo, 3G
ao, 7As layer (7), n-type kI! . , 3Gao, 7A
After the s-layers (8) are sequentially formed so as not to be stacked on the top of the strip-shaped laminate, a P-type Ga, AS layer (9) is formed over the entire crystal surface.

Finally, an n-type contact electrode 1y (10) and a p-type contact electrode (+ +1) are formed to form the semiconductor laser according to the present invention.In this structure, Afo, . Ga o, As n-type, p-type,
N-type semiconductor layers are stacked, and the current blocking effect is large.
Current flows efficiently through the strip-shaped stacked body portion, making it possible to form a semiconductor laser with high oscillation efficiency.

Further, in the structure according to the present invention, AJ6.
, (ia6.g As layer (3) is MGaAs (2k (4), (7) K
Since it has a refractive index waveguide mechanism in both the ffl and vertical directions, the beam waist position of the output beam is at the reflective surface position due to the crystal arm opening, and there is no astigmatism. It also has the feature of obtaining high-quality laser light that can be narrowed down to a minute spot.

Furthermore, the fact that high output operation was achieved by the semiconductor laser according to the present invention will be explained with reference to FIG. FIG. 2 shows a central portion A of the semiconductor laser according to the present invention shown in FIG.
This figure shows a cross section at . In this semiconductor laser, as shown in Figure 2, the area near the reflecting surface is ()aA.
The structure is such that a convex region is formed on the s-substrate (1), and multilayer semiconductor layers are formed thereon by a crystal growth process.

Here, in the commonly used liquid phase crystal growth method, the layer thickness of the crystal grown thereon is thinner in the convex region than in other regions. By taking advantage of the characteristics of the crystal growth method, the thickness of the active layer in the region near the opposite surface of the semiconductor laser is made thinner than in other regions.

That is, in the present invention, a convex region of about 1.5 μm is formed on the GaAs substrate, which is a region near the opposite surface of the semiconductor laser, and an n-type Al! '0.4 (ho, 6
As layer (2), AI that becomes the active layer! 6. HGa6. g
By forming the Ass layer 3), the P-type AeO,4Ga0.6As layer (4), and the P,%IjGa,As layer (5), the A/? (,,,(1a6.gA
The thickness of the s-layer (3) in the central region of the semiconductor laser is as follows:
The thickness can be increased to 0.01 μm, and the thickness can be reduced to about 0.02 μm in the region near the single-conductor laser reflection surface.

Therefore, in this structure, as shown in the same figure, the light intensity distribution in the layer thickness direction becomes a distribution that is greatly spread near the reflective surface, and the light emission cross section vJ2 increases, reducing the optical output density.
Even in an optical output operation of 50 mW or more, destruction of the reflecting surface could be prevented, and a highly reliable semiconductor laser could be formed.

In addition, in this structure, t-1, the central region I of the semiconductor laser
t(7) Active layer t'l ZI Ato, t aaLl
,, The l'X difference in As l threat (3) is 0.1 μm, and the confinement coefficient of light in the active layer is about 0.2, which increases the threshold value for illumination and avoids an increase in bIC. We were able to obtain a low IW threshold of about 4.0 mA, and achieved stable operation with a light output of 40 rnW or more even in a wet sieve atmosphere at 90°C or higher.

Next, other embodiments of the present invention will be described. In this case as well, the cross-sectional view on the side of the laser beam emitting surface has the same shape as that of the above-described embodiment, as shown in FIG. fifj1.

Fig. 3 shows the "Al side view" facing the center part A of the same figure, but the difference from the actual f-fabric example described above is that the GaAs in the area near the semiconductor laser reflective surface is A groove having an inclined surface was formed on the substrate (1).The inclined surface was formed using an ammonia-based etching solution (111) A.
This is a surface, and when placed on this surface, the crystal growth method FW is slow compared to other regions r. Therefore,
As shown in Figure 3, GaA
, s substrate' 2 sequentially, n 3jjJAIo, 4. Ga
o,, As 14 (21, A7'O+ which becomes the active layer
.

oao,, As layer (3), P type Ay? o,, ()
When forming a Q, +1, AS layer (4), P type (JaAs layer), the crystal growth rate on the (11,1) A plane is slow, and the active layer thickness in the region near the reflective surface is set to about 0.02 μm. The light intensity distribution is greatly expanded in the region near the reflective surface, as in the above-mentioned embodiment.
The optical output density can be reduced, and destruction of the reflective surface can be prevented by 1υi even when the optical output is operated at 50+nW or more. In addition, even in this structure, the thickness of the active layer in the central region of the semiconductor laser can be reduced to about 0.1 μm, and the threshold current for oscillation can be reduced to about 40 mA. This is similar to the example.

In the above two embodiments, the thickness of the first semiconductor layer is gradually changed, but even if the thickness is changed stepwise, the same effect as in the actual sister example can be obtained.

As described above, the semiconductor laser structure according to the present invention can increase the light emission cross section L1 in the region 1 near the reflective surface (in the area L1), and can increase the optical output density to one region, and can achieve high output operation of FOmW or more. Even in this case, it is possible to prevent the destruction of the opposite surface, and furthermore, in the central region 1 of the semiconductor radar, the light emitting cross section is made smaller, and the confinement coefficient of light to the active tm is increased, so that the oscillation t:L<value current is Making it possible to reduce the amount of light and even emit light @
By surrounding the active layer, which serves as a castle, with an undyed external semiconductor 1 with a higher refractive index, a refractive index waveguide mechanism is incorporated in both the lateral and vertical directions, and an IA quality optical beam 11 with no astigmatism is created. It is possible to form high-performance semiconductor lasers with good reproducibility.

C and below, extra white)

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of the laser beam emitting surface side of a semiconductor laser according to the present invention, FIG. 21 is a schematic cross-sectional view at the center part A of FIG. 1, and FIG. 3 is a schematic cross-sectional view of another embodiment of the present invention. A schematic cross-sectional view is shown in each case. In the figure, 1: n-type GaAs substrate 2: n% A-eo, Ga(, 6As layer 3
: Ato, , GaO, , As active layer 4 : p-type k
l(,,,,Ga6.,N3 layer 5:p type GaAs layer 6:n type A/'6.3 Gao,7Aj II7e,type k16..Gao,,A 5f-8:n type M6.s
Ga 6,7A s layer 9; P-type GaAs 1iJ 10: n-type contact electrode 11; p-type contact 1! Each pole is shown.

Claims (1)

[Claims] A strip-shaped multilayer structure is provided in which a first semiconductor layer serving as a light-emitting region is sandwiched between second and third semiconductor layers having a larger forbidden band width, and the strip-shaped multilayer structure has a forbidden band width larger than that of the first semiconductor layer. In a semiconductor light emitting device having a structure in which the fourth semiconductor layer is embedded with a large fourth semiconductor layer, at least the first
A semiconductor laser characterized in that the thickness of the semiconductor layer is varied.