JP2001274509A - Semiconductor laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser wherein generation of kink phenomenon is prevented, while mixed crystal ratio of Al in a current constriction layer is not so increased and a depletion layer due to a PN junction in the current constriction layer is prevented from reaching an active layer, and stable operation is obtained up to high power output. SOLUTION: This semiconductor laser is provided with a double hetero structuring part 11 wherein the active layer 3 clamped with an N-type clad layer 2 and a P-type clad layer 4 is arranged on a semiconductor substrate 1 composed of, e.g. N-type GaAs. For example, the current constriction layer 6 wherein a stripe trench 6c is formed of conductivity type (e.g. N-type) different from the conductivity type (e.g. P-type) of the clad layer 4 is formed in the P-type clad layer 4. A light confinement layer 10 whose refractive index is smaller than that of a P-type clad layer 4a is formed by using the same conductivity type as the P-type clad layer 4 or an undoped layer, on the active layer 3 side of the current constriction layer 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CD-ROM,
The present invention relates to a semiconductor laser used as a light source such as an optical disk device such as a DR and a DVD-ROM, a high-definition LBP (laser beam printer), and a laser pointer. More specifically, the present invention relates to a semiconductor laser capable of oscillating at a high output without causing kink by confining light as much as possible while confining current with a current confinement layer.

[0002]

2. Description of the Related Art A self-aligned semiconductor laser having a light confinement effect by a current confinement layer has a structure as shown in FIG. 2, for example. That is, in FIG. 2, an n-type cladding layer 22 made of, for example, n-type Al _0.6 Ga _0.4 As, an active layer 23 made of undoped Al _0.2 Ga _0.8 As, a p-type Al _0.6 P-type first cladding layer 24a made of Ga _0.4 As, etching stop layer 25, for example, current confinement layer 26 made of n-type Al _0.7 Ga _0.3 As, p-type A
a p-type second cladding layer 24b of l _0.6 Ga _0.4 As;
A GaAs p-type contact layer 27 is sequentially epitaxially grown, and a p-side electrode 28 is
The semiconductor laser (LD) chip having the structure shown in FIG. 2 is formed by forming an n-side electrode 29 on the back surface of the substrate 21 and forming the chip by cleavage or the like.

In this structure, in order to enhance the light confinement effect and increase the output, the current confinement layer 26 is brought closer to the active layer, or the current confinement layer 26 is increased in the mixed crystal ratio of Al to be refracted. A method of reducing the rate is used.

[0004]

As described above, in order to enhance the light confinement and increase the output, the position of the current confinement layer should be as close to the active layer as possible or the current made of the AlGaAs-based compound semiconductor should be increased. It is necessary to increase the mixed crystal ratio of Al in the constriction layer to decrease the refractive index. However, when the mixed crystal ratio of Al is increased, Al is very easily oxidized.
After the stripe groove is formed in the current confinement layer, the exposed surface is liable to corrode, and it is difficult to grow a clean single crystal semiconductor layer when growing the semiconductor layer again. In particular, a protective layer such as GaAs is formed on the uppermost surface of the current confinement layer, and can be cleaned by thermal etching at the time of regrowth. Cannot be performed, the semiconductor layer is likely to be polycrystallized, a leakage current flows to increase the threshold current value, or the resistance component increases due to polycrystallization, and the operating current increases. .

On the other hand, since the current confinement layer has a conductivity type different from that of the surrounding cladding layer, the current is blocked by the reverse bias of the pn junction, so that a depletion layer due to the reverse bias is formed at the pn junction. As shown in FIG. 2, when the current confinement layer 26 is formed so as to be too close to the active layer 23, the depletion layer A reaches the active layer 23.
When the depletion layer A reaches the active layer 23, as shown in FIG. 2, the current I flows to a part of the current confinement layer 26 where the stripe groove is not formed, and the current I cannot be confined. There is a problem that current flows.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and the depletion layer due to the pn junction of the current confinement layer is formed as an active layer without increasing the Al composition ratio in the current confinement layer. It is an object of the present invention to provide a semiconductor laser which operates stably up to a high output without causing a kink phenomenon while preventing the laser from reaching the maximum.

[0007]

A semiconductor laser according to the present invention has an active layer having a double heterostructure portion sandwiched between n-type and p-type cladding layers. A current confinement layer in which a stripe groove is formed in a conductivity type different from the conductivity type of the layer, and a light confinement layer having a smaller refractive index than the cladding layer on the active layer side of the current confinement layer is the same as the cladding layer; It is formed of a conductive type or undoped.

With this structure, the light confinement layer having a small refractive index is formed of the same conductivity type or undoped as the cladding layer, so that only the function of confining light without forming a reverse-biased pn junction is achieved. Can be made. Therefore, it is possible to approach the active layer as much as possible. On the other hand, since the current confinement layer of the conductivity type different from that of the cladding layer is provided on the side of the light confinement layer opposite to the active layer, the current confinement layer acts to block the current by the reverse bias of the pn junction. The depletion layer due to this reverse bias spreads to the light confinement layer, but the thickness of the light confinement layer can be adjusted so as not to reach the active layer. No leaks occur. As a result, the optical confinement is enhanced while the current is sufficiently blocked, and stable operation up to a high output can be achieved.

If the current confinement layer is formed of a semiconductor layer having the same refractive index as the light confinement layer, even if the thickness of the light confinement layer is small, light confinement is sufficiently performed together with the current confinement layer. However, the depletion layer due to the reverse bias can be prevented from reaching the active layer.

[0010]

Next, a semiconductor laser according to the present invention will be described with reference to the drawings. In a semiconductor laser according to the present invention, an active layer 3 is formed on an n-type and p-type cladding layer 2 on a semiconductor substrate 1 made of, for example, n-type GaAs as shown in FIG. Heterostructure part 1 sandwiched between the four heterostructures 4 (4a)
One. Then, for example, the p-type cladding layer 4
(4a, 4b) is provided with a current confinement layer 6 in which a stripe groove 6c is formed in a conductivity type (for example, n-type) different from the conductivity type (for example, p-type) of the cladding layer 4; On the active layer 3 side, a light confinement layer 10 having a smaller refractive index than the p-type cladding layer 4 is formed with the same conductivity type as that of the p-type cladding layer 4 or undoped.

In the example shown in FIG. 1, the double heterostructure portion 11 is, for example, an n-type Al _x Ga _{1 -x} As (0.3 ≦
an n-type cladding layer 2 of x ≦ 0.7, for example x = 0.6), undoped or n-type or p-type Al _y Ga
_The active layer 3 is made of _1-y As (0 ≦ y ≦ 0.3, for example, y = 0.15), and the p _-type first cladding layer 4a is made of Al _x Ga _1-x As. Has become. The material of the active layer 3 is determined by the band gap corresponding to a desired emission wavelength, and the cladding layers 2 and 4 made of a material having a larger band gap are formed so that carriers can be confined in the active layer 3. It has a structure sandwiched by. Therefore, depending on the desired wavelength, another semiconductor such as an InGaAlP-based compound is used instead of the AlGaAs-based compound.

The p-type cladding layer 4 includes a first cladding layer 4a.
And a second cladding layer 4b, between which a light confinement layer 10 and a current confinement layer 6 are provided via an etching stop layer 5. The etching stop layer 5
A stripe groove 6c is formed in the current confinement layer 6 and the light confinement layer 10.
Is a layer for stopping the etching with respect to the etching at the time of forming, and may be formed of a composition capable of selectively etching the current confinement layer 6 and the light confinement layer 10. Al _{a for} p-type
Ga _1-a As (y <a <1, a ≠ z, r) or InG
a _1-b Al _b P (0 ≦ b ≦ 0.5)

[0013] Light confinement layer 10 and the current confining layer 6, in the example shown in FIG. 1, both _{Al z Ga 1-z As (} 0.4 ≦
z ≦ 0.8, x <z, and stripe grooves 6 c (extending in the direction perpendicular to the plane of the drawing because of the cross section in the direction perpendicular to the stripes in the drawing) are formed in both layers. That is, since the mixed crystal ratio z of Al is formed to be larger than that of the cladding layer 4, the refractive index becomes small, and the light acts to confine light to the active layer 3 side.

On the other hand, the light confinement layer 10 has the same conductivity type as the surrounding clad layer, that is, p in the example shown in FIG.
The current confinement layer 6 is formed in the opposite conductivity type, that is, n-type, while being formed in the shape or undoped. Therefore, a reverse-biased pn junction surface is formed at the interface between the current confinement layer 6 and the light confinement layer 10, and the current is blocked. The current flows only through the portion where the stripe groove 6c is formed, so that the current flows. It has become stenotic. When a reverse bias is applied to this pn junction surface, FIG.
As shown by a broken line, depletion layers A are formed on both sides of the pn junction. The light confinement layer 10 is formed so that the depletion layer A does not reach the active layer 3. If the light confinement layer 10 is too thick, the current injection region tends to spread from the stripe groove, which is not preferable. For example, the light confinement layer 10 is formed to a thickness of about 0.05 to 0.3 μm, and the current confinement layer 6 is formed to a thickness of about 0.2 to 0.5 μm.

On the current confinement layer 6 and on the etching stop layer 5 exposed by the stripe groove 6c, a p-type first
A p-type second cladding layer 4b having the same composition as that of the cladding layer 4a is grown thereon, and a contact layer 9 made of p-type GaAs is further provided thereon. Each of the side electrodes 9 is provided and chipped by cleavage or the like, whereby a semiconductor laser having the structure shown in FIG. 1 is obtained.

To manufacture this semiconductor laser, first,
MOCV is applied to the surface of the semiconductor substrate 1 made of n-type GaAs.
According to the D method or the MBE method, the n-type cladding layer 2 made of n-type Al _0.6 Ga _0.4 As is about 1 μm, the active layer 3 made of undoped Al _0.15 Ga _0.85 As is about 0.1 μm, and the p-type Al _0.6 Ga _The p-type first cladding layer 4a made of _0.4 As is made to have a thickness of about 0.15 μm and undoped In _0.5 G
a _0.4 Al _0.1 P etching stop layer 5 of about several tens of nm, p-type Al _0.7 Ga _0.3 As, light confinement layer 10 of about 0.1 μm, n-type Al _0.7 Ga _0.3 As of current confinement. The layer 6 is sequentially stacked to a thickness of about 0.4 μm, and an anti-oxidation layer made of n-type GaAs (not shown) is stacked to a thickness of about 0.03 μm.

Then, a portion other than the portion where the stripe groove 6c is to be formed is masked with a photoresist, and is etched with, for example, a sulfuric acid-based aqueous solution to form the stripe groove 6c. In this aqueous solution, In _0.5 Ga _0.4 Al _0.1 P is not etched, so that the etching is stopped by the etching stop layer 5, the etching is not performed up to the p-type first cladding layer 4 a, and the current confinement layer 6 and the light confinement layer are not etched. Only 10 is etched by a predetermined width.

Thereafter, the reactor is again placed in a reaction vessel such as an MOCVD apparatus, and the second p-type cladding layer 4b made of p-type Al _0.6 Ga _0.4 As and the contact layer 7 made of p-type GaAs are each about 1 μm. Laminate.
Thereafter, the p-side and n-side electrodes 8, 9 are formed, for example, by vapor deposition, and then formed into chips by, for example, cleavage, thereby obtaining the semiconductor laser chip shown in FIG.

According to the present invention, apart from the current confinement layer 6,
A light confinement layer 10 that has the same conductivity type as the surrounding cladding layer 4 or has an undoped refractive index smaller than that of the cladding layer 4 and acts to confine light is formed on the active layer side. Therefore, even if the light confinement layer 10 is brought closer to the active layer 3 side, the depletion layer does not escape to the active layer.
Light confinement can be enhanced by approaching the active layer 3.
As a result, it is possible to sufficiently confine the light without increasing the mixed crystal ratio of Al in the current confinement layer 6 more than necessary and reducing the refractive index, thereby improving the crystallinity and the threshold current value. In addition to improving light emission characteristics such as reduction in light emission, the light confinement is strong and stable operation up to high output is achieved.

[0020]

According to the present invention, in a semiconductor laser which uses an AlGaAs-based compound semiconductor or an InGaAlP-based compound semiconductor to confine light in a self-aligned type and has a high output, the mixed crystal ratio of Al is increased more than necessary. Even if the light confinement layer is not strengthened, the light confinement layer is formed of the same conductivity type as the surrounding cladding layer or undoped separately from the current confinement layer. , And light confinement can be enhanced.
As a result, a stable high-output semiconductor laser can be obtained without causing kink.

[Brief description of the drawings]

FIG. 1 is an explanatory sectional view of an embodiment of a semiconductor laser according to the present invention.

FIG. 2 is an explanatory sectional view showing a conventional self-aligned semiconductor laser.

[Explanation of symbols]

 2 n-type cladding layer 3 active layer 4a p-type first cladding layer 4b p-type second cladding layer 6 current confinement layer 10 light confinement layer 11 double heterostructure

Claims (2)

[Claims] An active layer has a double heterostructure portion sandwiched between n-type and p-type cladding layers, and one of said cladding layers has a stripe groove having a conductivity type different from a conductivity type of said cladding layer. A semiconductor laser comprising: a current confinement layer formed with a layer; and a light confinement layer having a smaller refractive index than the cladding layer formed on the active layer side of the current confinement layer by the same conductivity type or undoping as the cladding layer. . 2. The semiconductor laser according to claim 1, wherein said current confinement layer is formed of a semiconductor layer having the same refractive index as said light confinement layer.