JPH0513872A - Hetero junction type semiconductor laser - Google Patents

Abstract

PURPOSE:To improve deterioration of characteristics, instability, and deterioration of reliability, by forming a layer containing little Al, in a p-type clad layer. CONSTITUTION:An upper clad layer 24 and a lower clad layer 22 have the respective first clad layers 1 on the side of an active layer 23. On each side opposite to the active layer 23, the respective second clad layers 2 are formed via the respective third clad layers 3. Thereby a lamination structure is constituted. The active layer 23 is constituted of, e.g. Al0.14Ga0.86As whose Al content is small. The p-type clad layers, i.e., at least a part of the p-type clad layer 24 out of the upper and the lower clad layers arranged so as to sandwich the active layer 23 is constituted of a layer wherein Al content is small and so thermal conductivity and electric conductivity are comparatively high. Hence problem of operating current of a semiconductor laser, increase of threshold current, instability, problem of reliability, and further impurity doping quantity can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heterojunction type semiconductor laser, and more particularly to a heterojunction type semiconductor laser having a cladding layer of a mixed crystal containing Al such as an AlGaAs type compound semiconductor.

[0002]

2. Description of the Related Art As shown in FIG.
The double heterojunction (DH) semiconductor laser is
This is formed on a base body 21 made of an electric type, for example, n type GaAs.
Equivalent electric type, for example, n type Al_xGa_1-xBelow composed of As
Layer Clad layer 22 and Al_yGa _1-yAs (0 ≦ y <x)
Of the active layer 23 of a second conductivity type, for example, p-type Al_x
Ga_1-xAn upper clad layer 24 made of As, and
Second conductive layer made of, for example, GaAs without Al on top
Type, for example, p-type cap layer 25 is sequentially epitaxial
Although not shown, the cap layer 25 is formed on the
Of the electrode and the substrate 21 which are ohmic-contacted in the shape of an ip.
It moves between the counter electrode that makes ohmic contact with the back side.
A working current is applied.

However, in the DH type semiconductor laser having this structure, when the confinement of the injection current into the active layer 23 by the cladding layers 22 and 24 is strengthened, the confinement of light also becomes sharp at the same time, and the divergence angle is increased and the optical confinement is suppressed. There is a problem in increasing the power due to the destruction of the end face due to the strengthening.

In order to improve this point, as shown in the schematic cross-sectional view of FIG. 4, the SCH (Separate
There is a Confinement Heterostructure) type semiconductor laser. This is because the band gap between the active layer 23 and both cladding layers 22 and 24 is smaller than that of the cladding layers 22 and 24, that is, the upper and lower guide layers made of Al _z Ga _1-z As (y <z <x). 26 and 27 are provided. In FIG. 4, parts corresponding to those in FIG. 3 are designated by the same reference numerals, and redundant description will be omitted.

However, even in the case of such an SCH type structure, the cladding layer 22 is formed similarly to the DH type structure.
And 24, to obtain the required confinement effect,
The band gap of the active layer is, for example, 0.2e
Since it is necessary to increase V or 0.3 eV or more, it is necessary to increase the Al content x.

In particular, when the bandgap of the active layer is increased in order to emit light of a short wavelength, it becomes necessary to increase the Al content x of the cladding layers 22 and 24 accordingly.

However, AlGaAs or AlGaI
In a compound semiconductor made of a mixed crystal containing Al such as nP, the larger the amount of Al, the lower the thermal conductivity and the electrical conductivity.

FIG. 3 shows A of an AlGaAs mixed crystal compound.
It shows the relation between 1 content (x value) and thermal resistance ρ (= 1 / σ) (Casey & Panish, HETEROSTRUCTURE LASERS, AC
It can be seen from ADEMIC PRESS) that a high thermal resistance is exhibited in a practical region for obtaining a bandgap as a cladding layer, for example, 0.3 <x <0.7.

The decrease in thermal conductivity due to the inclusion of Al is more remarkable in the p-type.

When the clad layer is made of such a mixed crystal containing Al, the thermal conductivity and the electric conductivity of the clad layer cannot be sufficiently increased, so that the characteristic, that is, the threshold current I _th , increase in operating current, etc., and there is a problem in reliability such as characteristic fluctuation and instability especially during continuous use for a long time, and a large amount of impurity doping is required to further improve electric conductivity. There is a problem.

[0011]

DISCLOSURE OF THE INVENTION The present invention provides a semiconductor laser of DH type, SCH type, etc., which is made of a mixed crystal compound semiconductor containing Al, and its characteristics, that is, thermal conduction for threshold current I _th , operating current, etc. And try to solve problems related to electrical conduction.

[0012]

The present invention provides a junction type semiconductor laser having cladding layers 22 and 24 made of a mixed crystal containing Al, as shown in FIG. 1 which is an enlarged schematic sectional view of an example thereof. At least the p-type clad layer, for example, the upper clad layer 24, is interposed between the first and second clad layers 2 and 3 having a large Al content, and is compared with the first and second clad layers 2 and 3. The third clad layer 3 has a small Al content and a large thickness.

[0013]

As described above, in the present invention, at least p
-Type clad layers, that is, at least p-type clad layers of the upper and lower clad layers that are arranged with an active layer sandwiched between them are formed by a layer having a small Al content and thus a relatively high thermal conductivity and electrical conductivity. Since it is configured, it is possible to solve the problems of the operating current of the semiconductor laser, the increase of the threshold current, the instability and the reliability, and the improvement of the impurity doping amount.

It should be noted that the cladding layer having the above structure can also sufficiently confine light in the active layer. This is because the light generated in the active layer oozes out of the active layer 23 in a Gaussian distribution, and therefore, a sufficient amount of Al is contained at a position separated by this leaching distance from the active layer through the third cladding layer 3. This is because the presence of the second cladding layer 2 sufficiently confines the light.

Regarding the confinement of carriers, the Al content on the side close to the active layer 23 is large and the band gap thereof is made sufficiently larger than the band gap of the active layer.
Due to the existence of the clad layer 1 of FIG.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of application to an SCH type semiconductor laser will be described with reference to FIG.

In this case, the first conductivity type, for example, n-type GaA
On the s substrate 21, similarly, if necessary, an n-type buffer layer (not shown) of the first conductivity type is also used to deposit a first conductivity type, for example, an n-type lower clad 22 and a lower guide layer 26, respectively. It grows axially and subsequently has an active layer 23 on it.
And a second conductivity type, for example, p-type upper guide layer 27, respectively.
Then, the upper clad layer 24 and the cap layer 25 are continuously epitaxially grown by, for example, MOCVD (metal organic chemical vapor deposition).

The upper and lower clad layers 22 and 24 are
The first clad layer 1 is disposed on the active layer 23 side (the side adjacent to the upper and lower guide layers 26 and 27 in the example of FIG. 1), and the third clad layer is provided on the side opposite to the active layer 23. A laminated structure in which the second clad layer 2 is arranged via 3 is adopted.

The active layer 23 has a thickness of, for example, 150Å
˜600Å GaAs or a small Al content, for example, Al _0.14 Ga _0.86 As.

The lower and upper clad layers 22 and 24 as a whole have a thickness of at least 1.2 μm or more so that the above-mentioned light confining effect can be obtained.
Each first clad layer 1 has a thickness of 500Å-100
By setting 0 Å, carriers can be sufficiently confined, and the thickness of each third cladding layer 3 can be selected to be, for example, 1 μm, and the second cladding layer 2 can have a thickness of, for example, 1. It can be selected to be 5 μm.

The first, second and third clad layers 1, 2 and 3 are each made of a mixed crystal compound semiconductor containing Al, for example, AlGaAs, but the third clad layer 3 is composed of the first and second clad layers. It is selected to be smaller than the content of Al in the second cladding layers 1 and 2. For example, first and second
The cladding layers 1 and 2 of Al _0.47 Ga _0.53 As,
The Al content of the third clad layer 3 is intermediate between the active layer 23 and the first and second clad layers 1 and 2. For example, Al _0.30 Ga _0.70 As.

The lower and upper guide layers 26 and 27 have a bandgap larger than the bandgap of the active layer 23 and smaller than the bandgap of the first cladding layer 1 facing the active layer 23, as in the case of a normal SCH laser. , Its thickness can be selected from 200Å to 500Å.

The cap layer 25 is made of GaA containing no Al.
s. The example shown in FIG.
SCH when applied to a CH type semiconductor laser
The ordinary DH type semiconductor laser described in FIG. 3 which does not depend on the type, that is, does not have a guide layer, may have a structure having at least the first to third cladding layers 1 to 3 described above in its cladding layer. ..

Although not shown in FIG. 1, one electrode is ohmicly deposited on the back surface of the base body 21 and formed in a stripe shape on the cap layer 25 corresponding to the resonator forming portion formed in the active layer 23. The other electrode that makes ohmic contact is deposited.

Although not shown in FIG. 1, for example, a p-n for narrowing a current path to the resonator forming portion is formed at a depth from the cap layer 25 to the cladding layer 24.
It is also possible to form the junction or the high resistance region by ion implantation, diffusion or implantation of protons of the first conductivity type impurity.

Besides, the present invention can be applied to not only the illustrated example but also heterojunction type semiconductor lasers of various structures.

In the above-mentioned example, the case of applying to an AlGaAs semiconductor laser is shown.
The present invention can be applied to various semiconductor lasers having a liquid crystal compound semiconductor layer containing Al as a cladding layer, such as P-based semiconductor lasers.

In the above example, the third cladding layer 3 having a small Al content is provided in both the n-type and p-type cladding layers, but this Al is only used for the p-type cladding layer. It is also possible to adopt a configuration in which the clad layer 3 having a small content is arranged.

[0029]

As described above, according to the present invention, the clad layer retains a thickness necessary for achieving the original function of the clad layer, that is, the effect of confining the active layer.
In particular, since at least the p-type clad layer, in which the thermal conductivity is remarkably reduced by including Al, is provided with a layer containing a small amount of Al, it is possible to improve the decrease in the thermal conductivity and the electrical conductivity in the clad layer. It is possible to effectively improve deterioration of characteristics, instability, and deterioration of reliability.

[Brief description of drawings]

FIG. 1 is an enlarged schematic cross-sectional view of an example of a heterojunction semiconductor laser according to the present invention.

FIG. 2 is a diagram showing a relationship between Al content and thermal resistance.

FIG. 3 is a schematic enlarged cross-sectional view of a conventional laser.

FIG. 4 is a schematic enlarged cross-sectional view of a conventional laser.

[Explanation of symbols]

 1 1st clad layer 2 2nd clad layer 3 3rd clad layer 22 lower clad layer 23 active layer 24 upper clad layer 26 lower guide layer 27 upper guide layer

Claims (1)

Claim: What is claimed is: 1. In a junction type semiconductor laser having a clad layer made of a mixed crystal containing Al, at least the p-type clad layer is composed of first and second clad layers having a large Al content. A heterojunction semiconductor laser which is interposed between them and is composed of a third clad layer having a smaller Al content and a larger thickness than the first and second clad layers.