JP3493920B2 - Semiconductor laser - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser, in particular an AlGaInP-based red visible light self-oscillation type semiconductor laser, a so-called pulsation semiconductor laser.

[0002]

2. Description of the Related Art Self-excited oscillation type lasers, that is, pulsation semiconductor lasers, are widely used as various light sources because return light noise can be effectively avoided. However, there remains a problem in performing stable self-oscillation.

A conventional AlGaInP-based red visible light self-oscillation type semiconductor laser is, for example, as shown in a sectional view of its schematic structure in FIG. 7, on a substrate 1 made of n-type GaAs.
An n-type clad layer 2 made of n-type AlGaInP, for example, a well layer made of GaInP and an active layer 3 having a multiple quantum well structure made of a barrier layer made of AlGaInP, a p-type clad layer 4 made of p-type AlGaInP, and a p-type Ga layer.
An intermediate layer 5 made of InP is sequentially epitaxially grown, and both sides of the intermediate layer 5 are etched in a stripe shape from the intermediate layer 5 to the p-type clad layer 4 to form a mesa groove. A block layer 5 is formed by n-type GaAs for current narrowing and light absorption, and a cap layer 7 made of p-type GaAs is epitaxially grown over the entire surface. One electrode 8 is ohmicly deposited on the cap layer 7, and the other electrode 9 is ohmicly formed on the back surface of the substrate 1.

In order to cause self-sustained pulsation in this semiconductor laser, as indicated by a solid arrow in FIG.
The central stripe sandwiched by the block layers 5 is used as a current path to restrict the current supply to the active layer 3 so that the active layer 3 is concentrated in the center. Moreover, regarding the light distribution, both sides of the current path, that is, the active layer. The light is spread and distributed on both sides in the plane direction of 3 so that the saturable absorber regions are formed on both sides of the central stripe portion of the active layer 3 therebetween.

However, when the temperature rises due to a long-time operation or a rise in the ambient temperature, the current passage expands laterally as shown by the broken line arrow in FIG. 7, and self-excited oscillation occurs. Is disturbed or self-sustained pulsation stops.

As a method for avoiding such current spreading, it is conceivable to reduce the distance D between the active layer 3 and the block layer 6 to increase the substantial resistance in the lateral direction. However, when the distance D is set to be small, the absorption of the oscillation light from the active layer 3 in the block layer 6 becomes large, the complex refractive index n _S under the block layer becomes small, and the complex at the central portion becomes small. refractive index between the refractive index n _c difference [Delta] n = n _c
There is an inconvenience that the −n _S becomes large, the confinement of light in the lateral direction becomes strong, the operation of the saturable absorber is disturbed, and stable self-excited oscillation does not occur.

As a method of reducing the difference Δn in refractive index, it is known to increase the light confinement coefficient Γ in the vertical direction (thickness direction) of the active layer. The number of wells that make up the active layer, that is, the thickness of the active layer is increased, and the light density in the active layer is increased by increasing the vertical light confinement coefficient. As a result, there is a problem in reliability, such as a rise in life and a decrease in life.

[0008]

The present invention is based on the above-mentioned A.
In an lGaInP-based self-excited oscillation type semiconductor laser,
Provided is a semiconductor laser capable of reliably sustaining a self-oscillation operation even at a high temperature of, for example, about 50 ° C. or higher, particularly an AlGaInP-based red visible light self-oscillation semiconductor laser.

[0009]

A semiconductor laser according to the present invention has at least an active layer, a p-type cladding layer, and an n-type cladding layer, and has a stripe-shaped current path on both sides of the active layer. In an AlGaInP-based semiconductor laser having a block layer in which current confinement and light absorption are performed, in the p-type cladding layer, a peak position of light distribution in the thickness direction of the active layer is shifted in a direction away from the block layer. The excited oscillation stabilizing layer is arranged.

According to the above-mentioned constitution of the present invention, since the peak position of the light distribution is shifted in the direction away from the block layer, the absorption of light by the block layer can be weakened. Even when the distance D between the block layer and the block layer is small, an increase in light absorption can be suppressed, and a decrease in the refractive index in the saturable absorber region due to this can be suppressed. It is possible to prevent the optical confinement of the light from becoming stronger and the distribution of light to the saturable absorber region from becoming smaller. In other words, since the distance D between the active layer and the block layer can be made sufficiently small, the lateral spread of the current due to the temperature rise can be made sufficiently small, and the lateral distribution of light can be maintained. Stable self-sustained pulsation occurs even at about ℃ or higher.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a semiconductor laser according to the present invention, particularly an AlGaInP-based red visible light self-excited oscillation type semiconductor laser, will be described.

An embodiment of the present invention will be described with reference to FIG. In the semiconductor laser shown in FIG. 1, an n-type cladding layer 2 made of (Al _Xn Ga _{1 -Xn} ) InP doped with n-type impurities is formed on an n-type substrate 1 made of, for example, GaAs, if necessary. Is epitaxially grown through a buffer layer (not shown), on which GaInP, for example, is formed.
An active layer 3 having a multiple quantum well structure composed of a well layer made of AlGaInP and a barrier layer made of AlGaInP.
Epitaxially grows continuously. Then, directly on the active layer 3 or as in FIG.
Of a lower p-type cladding layer 4 made of (Al _Xp Ga _{1 -Xp} ) InP doped with a type impurity and having a thickness t is epitaxially grown on the lower p-type cladding layer 4. The self-excited oscillation stabilizing layer 10 for shifting the peak position of the distribution is epitaxially grown. Further, subsequently, a p-type impurity was doped on this (Al _Xp Ga _{1 -Xp} )
An upper p-type cladding layer 4 made of InP is epitaxially grown, and an intermediate layer 5 made of p-type GaInP is epitaxially grown.

Then, both sides of the intermediate layer 5 are etched in a stripe shape from the intermediate layer 5 to the p-type clad layer 4 to form a mesa groove, and a current confinement by n-type GaAs is formed in the mesa groove. Then, the block layer 6 that absorbs light is formed, and the cap layer 7 made of p-type GaAs is epitaxially grown on the entire surface.

One electrode 8 is ohmicly deposited on the cap layer 7, and the other electrode 9 is ohmicly arranged on the back surface of the base 1.

In the semiconductor laser having the structure shown in FIG. 1, a self-excited oscillation stabilizing layer 10 is formed on the p-type cladding layer 4, and the self-excited oscillation stabilizing layer 10 is formed of (Al _yp Ga).
_1-yp ) InP, 0 <yp ≦ 1, and yp> xp (y
p and xp are atomic ratios), that is, the peak position of the light distribution in the thickness direction of the active layer 3 is constituted by a semiconductor layer having a high Al content and a low Ga content. Are shifted in a direction away from the block layer 6.

This self-excited oscillation stabilization layer 10 is composed of the active layer 3
You can also place the child in contact with, the thickness t is 100nm
Through the following lower clad layer 4, that is, the active layer 3
It is arranged and formed at a position where the distance between and is 100 nm or less.
If this thickness exceeds 100 nm, the confinement of light in the active layer is weakened, which causes a problem that the operating current is increased.

A reference example will be described with reference to FIG. 2. In FIG. 2, parts corresponding to those in FIG. In this semiconductor laser, a self-excited oscillation stabilizing layer 11 is arranged on the n-type cladding 2 side to shift the peak position of the light distribution in the thickness direction of the active layer 3 in the direction away from the block layer 6. And the self-excited oscillation stabilization layer 11 is (Al _yn
Ga _1-yn ) InP, and 0 ≦ yn ≦ 0.7 (y
n is an atomic ratio). If yn exceeds 0.7, it becomes difficult to shift the peak position of the above-mentioned light distribution in the direction away from the block layer 6.

Also in this case, the self-excited oscillation stabilizing layer 11 is also provided.
May be arranged directly below the active layer 3, or as shown in FIG. 2, the self-excited oscillation stabilizing layer 11 and the upper layer may be formed on the lower n-type cladding layer 2. The n-type cladding layer 2 may be arranged.

Epitaxial growth of each semiconductor layer constituting the semiconductor laser according to the present invention is carried out in the usual manner, for example, by MOCVD (Metal Organic Chemical Vapor Deposit).
ion: metalorganic chemical vapor deposition) method.

As described above, in the semiconductor laser according to the present invention, the self-excited oscillation stabilizing layers 10 and 11 are provided so that the peak position of the light distribution in the thickness direction of the active layer 3 is moved away from the block layer 6. Since the light is shifted, the absorption of the oscillation laser light by the block layer 6 can be reduced, so that the active layer 3
Even if the distance D between the block layer 6 and the block layer 6 is sufficiently small, the lateral light confinement can be weakened.

That is, in the semiconductor laser according to the present invention described with reference to FIG. 1, the p-type cladding layer 4 is stabilized by self-sustained pulsation by a semiconductor layer having a high Al content and a low Ga content. The layer 10 is provided.
AlGaInP having a large content of 1 has a refractive index of
Since the p-type cladding layer 4 is smaller than the p-type cladding layer 4, the refractive index of the self-excited oscillation stabilizing layer 10 is small, as indicated by the curve 31 in FIG. 3 showing the refractive index distribution in the depth direction (thickness direction). That is, since a layer with small light absorption is formed, when the self-excited oscillation stabilizing layer 10 does not exist, the broken line curve 32
As shown in FIG. 3, for example, a laser showing a light distribution with a peak located in the approximate center of the active layer 3 in the thickness direction is a curve 3
As shown by 3, the peak is on the n-type cladding layer 2 side,
In other words, it is shifted in the direction away from the block layer 6. Therefore, in this configuration, the block layer 6
Since the effect of absorbing light is reduced, the light confinement in the lateral direction is weakened, and the distribution of light in the lateral direction, that is, the surface direction can be increased, so that the effect of the saturable absorber is surely produced. Therefore, the self-sustained pulsation can be stabilized.

Since the self-excited oscillation stabilizing layer 10 having a low Ga content has a large specific resistance, it is possible to effectively suppress the spread of current in the lateral direction of carriers, that is, the surface direction. This makes it possible to ensure that the effect of the saturable absorber is produced.

Further, the self-excited oscillation stabilizing layer 10 is made of Al
The energy band gap is larger than that of the p-type cladding layer 4 due to the increased content of P, and therefore the conduction band of the energy band in the depth (thickness) direction is shown in FIG. As shown in the model (1), since a barrier is generated in the self-excited oscillation stabilizing layer 10, it is possible to suppress the generation of leakage current and to reduce the threshold current I _th. Occurs.

In addition, the n-type cladding layer 2 shown in FIG.
In addition, in the structure in which the self-excited oscillation stabilization layer 11 is formed, the self-excited oscillation stabilization layer 11 is (Al _yn G
a _1-yn ) InP, and 0 ≦ yn ≦ 0.7 (yn
Is the atomic ratio), and the refractive index of the self-excited oscillation stabilizing layer 11 is high, the curve 51 in FIG.
As shown by the refractive index distribution in the depth direction (thickness direction), the self-excited oscillation stabilizing layer 11 forms a layer having a large refractive index , that is, a large light absorption. When the stabilizing layer 11 is not present, as shown by a broken line curve 52, for example, a laser exhibiting a light distribution with a peak located at approximately the center of the active layer 3 in the thickness direction, as shown by a curve 53 in FIG. The peak is shifted toward the n-type cladding layer 2 side, that is, away from the block layer 6. Therefore, in this configuration, since the effect of light absorption by the block layer 6 is reduced, the light confinement in the lateral direction is weakened, and the light distribution can be increased in the lateral direction, that is, the surface direction. Therefore, the effect of the saturable absorber can be generated, and the self-oscillation can be stably generated.

Further, in the present invention, as shown in FIG. 6, the self-excited oscillation stabilizing layers 10 and 11 described in FIGS. 1 and 2 are arranged in the p-type cladding layer 4 and the n-type cladding layer 2, respectively. The above configuration can be adopted, and in this case, the above-described stabilization of the self-excited oscillation can be surely achieved. 1 and 2 in the configuration of FIG.
Corresponding parts in FIG.

As described above, according to the configuration of the present invention, in the self-excited oscillation type semiconductor laser, the effect of making the light distribution in the depth direction away from the block layer 6 having the light absorption effect is produced. Since the light absorption by the block layer 6 can be weakened, an increase in light absorption can be suppressed even if the distance D between the active layer 3 and the block layer 6 is small, and the refraction in the saturable absorber region is thereby suppressed. Since it is possible to suppress the decrease in the rate, it is possible to suppress the light confinement in the lateral direction due to the small distance D from becoming strong and the distribution of light to the saturable absorber region becoming small. In other words, since the distance D between the active layer and the block layer can be made sufficiently small, the lateral spread of the current due to the temperature rise can be made sufficiently small, and the lateral distribution of light can be maintained. Stable self-sustained pulsation occurs even at about ℃ or higher.

[0027]

As described above, in the structure of the present invention, the p-type cladding layer is provided with the self-excited oscillation stabilizing layer having a small refractive index, and / or the n-type cladding layer is provided with a self-excited oscillation stabilizing layer having a large refractive index. By providing the excited oscillation stabilization layer, the peak position of the light distribution in the thickness direction of the active layer is shifted in the direction away from the block layer, so that stable self-excited oscillation is achieved even at high temperature and It is possible to extend the life.

[Brief description of drawings]

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

FIG. 2 is a schematic sectional view of another example of a semiconductor laser used for explaining the present invention.

FIG. 3 is a diagram showing the refractive index distribution and the light distribution in the depth direction of the main part of the semiconductor laser, which is used for explaining the effect of the example of the semiconductor laser according to the present invention.

FIG. 4 is an energy band model (conduction band side) diagram of an example of a semiconductor laser according to the present invention.

FIG. 5 is a diagram showing a refractive index distribution and a light distribution in a depth direction of a main part of a semiconductor laser used for explaining the present invention.

FIG. 6 is a schematic sectional view of still another example of the semiconductor laser according to the present invention.

FIG. 7 is a schematic sectional view of a conventional semiconductor laser.

[Explanation of symbols]

1 substrate, 2 n-type clad layer, 3 active layer, 4 p-type clad layer, 5 intermediate layer, 6 block layer, 7 cap layer, 8, 9 electrode, 10, 11 self-excited oscillation stabilizing layer

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01S 5/00-5/50

Claims (3)

(57) [Claims] 1. An AlGaInP-based self-excited oscillation semiconductor laser, comprising at least an active layer, a p-type cladding layer, and an n-type cladding layer, wherein the active layer is provided on the p-type cladding layer side of the active layer. Blocking layers for current narrowing and light absorption forming a stripe-shaped current path with respect to the layer are formed on both sides of the stripe-shaped current path with the stripe-shaped current path interposed therebetween. A saturated absorber region is formed, and a self-excited oscillation stabilizing layer that shifts the peak position of the light distribution in the thickness direction of the active layer in the p-type cladding layer in a direction away from the block layer is provided. A semiconductor laser having a configuration arranged. 2. The p-type cladding layer is made of (Al _Xp Ga
_1-Xp ) InP, and the self-excited oscillation stabilizing layer disposed in the p-type cladding layer is (Al _yp Ga _1-yp )
2. The semiconductor laser according to claim 1, wherein the semiconductor laser is made of InP, and 0 <yp ≦ 1 and yp> xp (yp and xp are atomic ratios). 3. The semiconductor laser according to claim 1, wherein the self-sustained pulsation stabilizing layer arranged in the p-type cladding layer is arranged within a distance of 100 nm from the active layer.