JPH07106698A - Semiconductor light emitting element - Google Patents

Abstract

PURPOSE:To provide a highly reliable light emitting element by inhibiting unnecessary diffusion of impurities, especially to an active layer, during growth thereby controlling the position of impurities being present locally in the vicinity of the active layer. CONSTITUTION:At least a clad layer 2 of first conductivity type, an active layer 5, and a clad layer 8 of second conductivity type are formed on a semiconductor substrate 1 and strain layers 3, 7 are formed at least in one clad layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a semiconductor light emitting device, for example,
The present invention relates to a semiconductor light emitting device made of a III-V group compound semiconductor or the like, particularly a semiconductor laser.

[0002]

2. Description of the Related Art For example, in a light emitting device such as an AlGaAs semiconductor laser, p-type or n-type impurities are doped by MOCVD (metal organic chemical vapor deposition) or MBE (molecular beam epitaxy) during its manufacture. When epitaxially growing, the growth temperature is 600 to 7
If the temperature is relatively high at about 00 ° C., impurities such as Zn and Se may diffuse and move to a position deviated from a desired region in the growth layer.

For example, when p-type impurities such as Zn enter the active layer, an unnecessary energy level is generated, and the response of the light emitting element is deteriorated. For example, the pulse waveform and the optical waveform are deviated during pulse oscillation. It causes inconvenience such as being lost.

In order to prevent such diffusion of impurities, for example, as shown in an enlarged schematic cross-sectional view of an example thereof, a configuration in which non-doped layers 4 and 6 are set close to the active layer 5 is provided. Proposed. In FIG. 4, 1 is a semiconductor substrate, 2 is a first conductivity type, for example, n-type cladding layer, and 4 is a first
Conductive non-doped cladding layer, 5 is an active layer, 6 is a second layer
A conductive type, for example, p-type non-doped clad layer, 8 is a second conductive type clad layer, 9 is a cap layer, and 10 and 11 are electrodes.

However, in this case, if the thickness of the non-doping layer is increased, the characteristic temperature may be lowered and the series resistance may be increased. Furthermore, as the number of times of growth actually increases, even if core tube baking is performed, impurities remain in the entire system in the growth apparatus and the non-doping level of each grown element fluctuates, resulting in variations in characteristics. There is a problem that it may occur.

Further, if the growth temperature is lowered to suppress the diffusion of impurities, there arises a problem that the surface state of the grown semiconductor layer, that is, the smoothness is deteriorated. Further, a method of increasing the growth rate has also been proposed, but there is a disadvantage in that it is difficult to control the film thickness, and it becomes impossible to control the doping level of impurities, resulting in large variation in each growth.

[0007]

DISCLOSURE OF THE INVENTION The present invention more reliably suppresses the unnecessary diffusion of impurities during growth as described above, especially the diffusion reaching the active layer, and prevents the impurities localized in the vicinity of the active layer. A highly reliable semiconductor light emitting device is provided by controlling the position.

[0008]

According to the present invention, as shown in FIG. 1 which is an enlarged schematic sectional view of an example thereof, at least a first conductivity type cladding layer 2, an active layer 5 and a first conductivity type are provided on a semiconductor substrate 1. It has a clad layer 8 of two conductivity type, and strain layers 3 and 7 are provided in at least one clad layer. Further, the present invention is
In the above-mentioned structure, 50 is provided between the active layer 5 and the strained layers 3 and 7.
nm to less than 500 nm. Further, in the present invention, the strained layers 3 and 7 in the above-described structure are formed by compositional modulation of the clad layer. Furthermore, in the present invention, the semiconductor light emitting element is a semiconductor laser in each of the above configurations.

[0009]

As described above, in the present invention, the strained layers 3 and 7 are provided in at least one of the cladding layers. When the strained layer is provided in this way, impurities such as Zn tend to be concentrated in this strained layer. Therefore, it is possible to prevent impurities from entering the active layer 5.

Particularly, the distance between the active layer 5 and the strained layers 3 and 7 is set to 50.
The thickness of not less than 500 nm and less than 500 nm can reliably prevent the diffusion of impurities into the active layer 5.

Further, by constructing such a strained layer by compositional modulation of the cladding layer, it is possible to easily and accurately control the thickness and the like of the strained layer by switching the source gas in the growth apparatus or the like.

Further, by applying such a structure to a semiconductor laser, it is possible to obtain an element having higher reliability and good response.

[0013]

Embodiments of the present invention will now be described in detail with reference to the drawings. In this example, the present invention is applied to an AlGaAs-based compound semiconductor laser, and in particular, the strained layer is formed by modulating the Al concentration.

As shown in FIG. 1, for example, n-type GaAs
A semiconductor substrate 1 made of, for example, n-type
Al_0.45Ga_0.55The first layer made of As and doped with Se
1 conductivity type clad layer 2, Al concentration is the above clad layer 2
Al, which has a lower concentration than that of_0.30Ga_0.70
A non-doped strained layer 3 made of As, also a non-doped strained layer 3.
For example, n-type Al_0.45Ga_0.55First conductivity made of As, etc.
Type non-doped cladding layer 4, Al_0.10Ga_0.90As, etc.
Active layer 4 made of, for example, p-type Al_0.45Ga _0.55As
A second conductivity type non-doped cladding layer 6 of, for example,
If Al_0.30Ga _0.70Strained layer 7 made of As, Zn-doped
For example, p-type Al_0.45Ga_0.55Second conductivity made of As, etc.
Type clad layer 8 and a cap made of p type GaAs or the like.
The top layer 9 is sequentially formed, for example, by MOCVD or the like.
It will be grown up.

In these structures, the thickness of each layer is, for example, the first conductivity type and second conductivity type cladding layers 2,
8 is 1.5 μm, the strained layers 3 and 7 are around 30 nm, for example 50 nm, the first conductivity type and second conductivity type non-doped cladding layers 4 and 6 are, for example, 50 to 500 nm, for example 100 nm, and the active layer 5 is For example, it can be 50 nm.

As a result of investigating the manner of diffusion of the impurities with and without the strained layer using Zn, which is a p-type impurity, as shown in FIG. While the absolute amount of impurities can be reduced and the segregation amount and position can be controlled, in the comparative example in which the strained layer is not provided, the peak of the impurity concentration is near the active layer as shown in FIG. Therefore, it is difficult to control the impurity concentration and the segregation position in the active layer as described above.

Therefore, according to the present invention in which the strained layer is provided, the diffusion of the impurity into the active layer can be more surely suppressed by controlling the segregation position of the impurity, which is unnecessary in the active layer due to the entry of the impurity. It is possible to improve reliability by avoiding generation of various energy levels and deterioration of responsiveness.

In particular, as described above, by forming a non-doped layer between the strained layers 3 and 7 and the active layer 5, it is possible to reliably prevent diffusion of impurities into the active layer 5. In this case, the thickness of the non-doped layers 4 and 6, that is, the distance between the strained layer and the active layer is 50 nm or more and less than 500 nm, preferably 100 nm.
By setting the thickness to 200 nm or less, it is possible to reliably prevent the diffusion of impurities into the active layer 5 as described above, and it is possible to prevent the series resistance from increasing due to the increase in the film thickness of the non-doped layer.

Further, since it is possible to prevent the diffusion of impurities into the active layer 5 as described above, it is possible to prevent the lattice from being broken when a so-called artificial lattice in which, for example, a quantum well structure is applied as the active layer is produced. It is possible to obtain a highly reliable semiconductor laser with a low threshold and a high output.

Furthermore, in the above-described example in which the strained layer whose Al concentration is lower than that of the clad layer and therefore has a higher refractive index than that of the clad layer is provided, this strained layer has a function of pulling light. In the case of a laser performing a high power operation of several tens of mW or more, the distance from the active layer is set to 1 as described above.
When the thickness is 00 nm, it is desirable that the thickness of the strained layer be around 30 nm. When the distance is further increased, the film thickness can be increased, and when the distance is closer to the active layer, the film thickness can be further increased. Need to be small.

The Al concentration of the strained layer is set to a level not lower than the so-called light absorption layer, that is, the active layer. That is, the active layer is Al _x Ga _1-x As and the strained layer is Al _z Ga.
Assuming _1-z As, when x is 0.3, for example, z is preferably 0.1 to 0.2 as described above.

Furthermore, the strained layer can be formed by compositionally modulating the Al concentration to the high concentration side. For example, in the above composition, the same effect can be obtained when the Al concentration z of the strained layer is set to about 0.4 to 0.5.

The strained layer due to such compositional modulation can be easily formed by modulation of the flow rate ratio of the source gas at the time of epitaxial growth by MOCVD, MBE, etc. as described above. In addition to the above AlGaAs system, GaInP /
It goes without saying that it can be applied to various compound semiconductor light emitting devices and semiconductor laser devices such as AlGaInP based semiconductor lasers.

Further, in the above-mentioned example, the case where a single strained layer is introduced is shown. However, the present invention can be modified in various ways in its material constitution and the like. For example, the strained layer is only in the p-type cladding layer. It is needless to say that the same effect can be obtained in the case where the strained layer is provided, or the strained layer is formed by laminating a plurality of layers with a semiconductor layer having the same composition as that of the clad layer interposed therebetween, or when the strained layer has a concentration distribution in the strained layer. Nor.

[0025]

As described above, according to the present invention, by providing the strained layer in the cladding layer, the impurities can be concentrated in this strained layer, and thereby the segregation position of the impurity can be controlled. It is possible to suppress the entry of impurities into the layer and ensure higher reliability.

Since the diffusion of impurities into the active layer can be suppressed, the lattice can be prevented from being broken when an artificial lattice, that is, for example, a quantum well structure is applied to the active layer, and a higher output and a lower threshold value can be obtained. It is possible to realize a highly reliable semiconductor laser.

Further, by controlling the segregation position of impurities, the distribution of the impurities can be sharply modulated and controlled, so that the frequency characteristic can be improved.

[Brief description of drawings]

FIG. 1 is an enlarged schematic cross-sectional view of an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a function and effect of the present invention.

FIG. 3 is an explanatory diagram of a comparative example.

FIG. 4 is a schematic enlarged cross-sectional view of an example of a conventional semiconductor light emitting device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 2 1st conductivity type clad layer 3 Strain layer 4 1st conductivity type non-doped clad layer 5 Active layer 6 2nd conductivity type non-doped clad layer 7 Strain layer 8 2nd conductivity type clad layer 9 Cap layer 10 , 11 electrodes

Claims (4)

[Claims] 1. A semiconductor substrate having at least a first conductivity type cladding layer, an active layer, and a second conductivity type cladding layer, and a strain layer provided in at least one of the cladding layers. Semiconductor light emitting device. 2. The semiconductor light emitting device according to claim 1, wherein the distance between the active layer and the strained layer is 50 nm or more and less than 500 nm. 3. The strained layer is formed by compositional modulation of the cladding layer.
The semiconductor light-emitting device according to. 4. A semiconductor light emitting device, wherein the semiconductor light emitting device according to claim 1, 2 or 3 is a semiconductor laser.