JPS61287290A - Semiconductor laser element - Google Patents

Abstract

PURPOSE:To enable a basic lateral mode operation to low threshold value oscillation and high output by approximating a carrier distribution in an active layer to a light intensity distribution. CONSTITUTION:An internal stripe 10 and a channel groove 9 by an N-type GaAs current blocking layer 2 on a P-type GaAs substrate 1 are formed by photolithography. Then, a P-type high resistance layer Ga1-zAlzAs layer 1 is grown by a liquid-phase epitaxial method so that the thickness becomes thinnest on the stripe 10. Further, a P-type clad layer Ga1-yAlyAs 3, an active layer Ga1-zAlxAs 4, an N-type clad layer Ga1-yAlyAs 5 and N-type cap layer GaAs 6 are further sequentially grown. Here, the alumium composition ratio (z) of the layer 11 is equal to or smaller than the aluminum composition ratio (y) of the layer 3. An N-type electrode (Au-Ge) 7 is formed on the surface of the layer 6, and a P-type electrode (Au-Zn) 8 is alloyed by depositing on the back surface of the substrate 1. Thus, a carrier distribution in the active layer can beapproximated to a luminous intensity distribution.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to the element structure of a semiconductor laser.

(Prior Art and Problems to be Solved by the Invention) Conventionally, as a structure for stabilizing the transverse mode of a semiconductor laser device and reducing the oscillation threshold, a channel grooved internal structure as shown in FIG. 2(A) has been used. There is a striped laser. This semiconductor laser has a current blocking layer 2 of the opposite conductivity type to the substrate 1.
deposited on top and forming grooves 9 by etching technique;
Next, the first cladding layer 3, the active layer 4, the second cladding layer 5,
It is fabricated by sequentially depositing cap layers 6. When a voltage is applied between the electrodes 7 and 8, a current flows through the current blocking layer 2.
and flows only within the inner stripe 10 of width S. Further, the laser beam is confined within the channel by the uniform refractive index waveguide formed by the channel groove 9 having the width W. The light intensity distribution I (y) at that time is shown in Figure 2 (
Shown in B). The same figure also shows the carrier distribution n in the active layer.
(y) is also shown. This n(y) becomes much wider than the width of the channel trench 9 due to carrier diffusion within the active layer.

In this way, the conventional channel grooved internal stripe laser has a carrier distribution n(y
) is sufficiently wider, there are many carriers that do not contribute to laser oscillation, and the disadvantage is that the single value current is large at times ν. This useless current is consumed by unnecessary spontaneous emission light and heat generation, which adversely affects the reliability of the laser device. In addition, when trying to increase optical output by passing a large amount of current, the internal light intensity at the center of the channel becomes strong, and the carrier density is low at that part (but high at both sides), which is called the Hall-no-Sooning effect. The phenomenon is likely to occur (1, as a result,
In high-output operation, the gain of the -order mode becomes larger than the gain of the transverse mode, causing -order mode oscillation, and the drawback of ν1 is that a bend called a kink occurs in the current-light output characteristics. there were.

As a solution to these shortcomings, as shown in FIG.
There is a method to make the width S of the channel groove 9 narrower than the width W of the channel groove 9. However, since the current injected from the internal stripe 10 spreads in the thick first cladding layer 3 in the channel groove 9, As shown in Figure (B), the carrier distribution n(
y) was narrower than the case of FIG. 1(A) in which the internal stripe width S was wide, but the effect was still insufficient.

The present invention aims to provide a novel semiconductor laser device that enables low threshold oscillation and fundamental transverse mode operation up to high output by making the carrier distribution in the active layer almost similar to the light intensity distribution. purpose.

(Means for Solving the Problems) A semiconductor laser device according to the present invention includes a substrate, a current blocking layer forming an internal stripe narrower than the channel width on the substrate, and a thin layer formed on the internal stripe. , a high-resistance layer formed on the current-blocking layer to have a large layer thickness on the current-blocking layer in the channel, and a first cladding layer formed on the high-resistance layer until the surface becomes flat. , this first
a flat active layer formed on the cladding layer; a second cladding layer formed on the active layer and having a conductivity type opposite to that of the high resistance layer and the first cladding layer; It consists of a cladding layer and a cap layer formed on the cladding layer.

(Function) The semiconductor laser device according to the present invention provides a high-resistance layer between the current blocking layer and the first cladding layer, and makes the layer thinner on the inner stripe and thicker on both sides of the inner stripe. It is characterized by suppressing the spread of current within the groove.

(Effects of the Invention) According to the present invention, in the channel grooved internal stripe laser element, the distribution of carriers accumulated in the active layer in the junction direction becomes close to the distribution of light intensity.

Therefore, the threshold current is reduced and reliability is improved. Even if you are careful about high power operation, the hole burning effect will not occur, and basic transverse mode operation will be possible at high power.

(Example) FIG. 1(A) shows a cross-sectional view of a semiconductor laser of the present invention. The internal stripe width S is narrower than the channel groove width W, which is the same as the conventional example shown in FIG. The difference is that it is interposed. The specific resistance value of the high resistance layer 11 is the first
It is made larger than the specific resistance value of the cladding layer 3. This high-resistance layer 11 can be formed thinly on the internal stripe 10 and thickly on both sides thereof by liquid phase epitaxial growth. A first cladding layer 3 is deposited on this high resistance layer 11 so that its surface is flat. After that, as usual,
An active layer 4, a second cladding layer 5 and a cap layer 6 are deposited.

The current injected from the internal stripe 10 is suppressed from spreading due to the change in the layer thickness of the high resistance layer 11 within the channel groove 9, and as shown in FIG. 1(B), the carrier distribution in the active layer n(y) is almost close to the light intensity distribution I (y). As a result, invalid carriers that do not contribute to laser oscillation, ie, current, are reduced. As a result, the threshold current is reduced, and reliability is also improved. Furthermore, the hole burning effect is less likely to occur, fundamental mode oscillation is possible up to high output, and no kink occurs in the current-optical output characteristics.

Hereinafter, an embodiment using a semiconductor laser device made of a GaAs-GaAlAs compound semiconductor will be described along with the manufacturing process with reference to FIG. 1(A).

The internal stripes 10 and channel grooves 9 formed by the n-type GaAs current blocking layer 2 on the p-type GaAs substrate 1 are formed by photolithography as described in another application by the present inventors (Japanese Patent Application No. 58-228124). Formed using lithography. Here, the width S of the stripe 10 is 1.5 μl and the width W of the channel groove 9 is 8 μm, and the p-type high resistance layer G a 1-2A is formed by liquid phase epitaxial method.
1 z A s (11) was grown such that its layer thickness was thinnest on the inner stripes 10. In addition, p-shaped? 7t! Ga1-yApAs (3), active layer G
a1-XA fXAs(4), n-type cladding layer G a
1-, A1 y A'' (5), and an n-type cap layer GaAs (6) were grown sequentially. (2≦y). (If z > y, the p-type cladding layer 3 becomes a curved optical waveguide layer,
Higher-order transverse modes are likely to occur. ) The specific resistance of the p-type high resistance layer 11 was 0.2 Ω·cl, and the specific resistance of the p-type cladding layer 3 was 0.05 Ω·elm.

Is there an n-type electrode on the surface of the cap layer 6? (Au-Ge), and a p-type electrode 8 (Au-Ge) is placed on the back surface of the p-type GaAs substrate 1.
Zn) was deposited and alloyed.

The A4 composition ratio of each layer is x=0.05, y=0.35, z=
o, 3s, this semiconductor laser oscillates at a threshold current of 30A, an oscillation wavelength of 820, and an optical output of 50+W.
No kink appeared in the current-light output characteristics up to W. Further, the external differential efficiency was 30% on one side.

Note that the material is not limited to GaAs-GaAlAs, and other semiconductors such as InP-InGaAsP may also be used. □

[Brief explanation of the drawing]

FIG. 1(A) is a schematic cross-sectional view of the semiconductor laser according to the present invention, and FIG. 1(B) is the light intensity distribution I (y).
and carrier distribution n(y). FIG. 2(A) is a schematic cross-sectional view of an example of a conventional semiconductor laser, and FIG. 2(B) is a light intensity distribution 1 (y).
and carrier distribution n(y). FIG. 3(A) is a schematic cross-sectional view of an example of a conventional semiconductor laser, and FIG. 3(B) is a graph of light intensity distribution I(y) and carrier distribution n(y). 1... Substrate, 2... Current blocking layer, 3
...first cladding layer, 4...active layer, 5...
Second cladding layer, 6... Cap layer, 7.8...
- Electrode, 9... Channel groove, 10... Internal stripe, 11... High resistance layer.

Claims (1)

[Claims] (1) a substrate, a current blocking layer forming internal stripes narrower than the channel width on the substrate; A high resistance layer formed on the blocking layer, and a first layer formed on this high resistance layer until the surface becomes flat.
a cladding layer; a flat active layer formed on the first cladding layer; the high-resistance layer and the first cladding layer have conductivity types opposite to each other;
A semiconductor laser device comprising a second cladding layer formed on the above active layer and a cap layer formed on the second cladding layer.