JPH0936477A - Semiconductor light emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a semiconductor light emitting element excellent in the operational characteristics by constituting a sufficiently reliable etching stop layer with no restriction on the critical thickness thereof. SOLUTION: At least a clad layer 13 of first conductivity type, an active layer 14, a first clad layer 15A of second conductivity type, a strained etching stop layer 19 larger than the band gap of active layer 14, and a second clad layer 15B of second conductivity type are formed sequentially on a substrate 11 and a compensation layer 21 larger than the band gap of active layer 14 is formed contiguously to the strained etching stop layer 19 while being strained reversely thereto. Furthermore, grooves 17 to be filled with a current constriction layer 18 are made on the opposite sides of the stripe current path with a depth reaching the etching stop layer 19 from second clad layer 15B of second conductivity type.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light emitting device suitable for application to a semiconductor laser, particularly a compound semiconductor laser such as an AlGaInP semiconductor laser.

[0002]

2. Description of the Related Art Semiconductor light emitting devices such as AlGaInP
The semiconductor laser is, for example, as shown in FIG.
On the substrate 1 via a buffer layer 2, a clad layer 3 of a first conductivity type, for example, n-type AlGaInP 3, an active layer 4 having a multiple quantum well structure (hereinafter referred to as MQW), and a second conductivity type, for example, p-type AlGaInP A clad layer 5 and a cap layer 6 of the same conductivity type as that of GaAs, for example, are sequentially epitaxially grown, and the cap layer 6 is traversed on both sides of the clad layer 5 on both sides thereof, leaving a portion forming a central stripe current path. A groove 7 having a maximum depth is formed by etching, and a groove of the first conductivity type, for example, n, is formed in the groove 7.
The current confinement layer 8 that blocks the energization by the GaAs type is formed by the selective CVD (selective chemical vapor deposition) method.

In this AlGaInP-based semiconductor laser, the active layer 4 having the MQW structure as described above is a semiconductor laser of this kind which does not have the MQW structure.
635n, which has a shorter wavelength than the emission of 50 nm
There is an advantage that light emission in the m to 630 nm band can be performed.

By the way, as described above, the current confinement layer 8
When the structure for forming the current confinement layer 8 is formed, it is necessary to etch the groove 7 for embedding the current confinement layer 8. However, in actuality, when the etching groove 7 is formed, the cladding layer 5 has a required depth. It is difficult to perform etching to a uniform depth with good reproducibility, and the workability is poor.

[0005]

In a semiconductor light emitting device having the above-described structure, for example, a semiconductor laser, an etching groove for burying a current confinement layer can be accurately etched to a predetermined depth. However, as a method of setting the depth of the etching groove to a predetermined depth, as shown in FIG. 7, the second conductivity type clad layer 5 is a lower clad layer 5A and an upper clad layer 5A. Of the second clad layer 5B, and the clad layer 5 is provided between the first and second clad layers 5A and 5B.
The etching stop layer 9 having a significantly lower etching rate than that of the AlGaInP clad layer 5 is epitaxially grown.
An etching mask layer 10 is formed on the upper striped current path forming portion, and the cap layer 6 is formed using this as a mask.
Are etched, and thereafter, the cladding layer 5 is etched by exhibiting a high etching property with respect to the cladding layer 5 and the etching stop layer 9 with a low etching property. By doing so, as shown in FIG. 8, the etching progress is stopped or delayed when the etching stop layer 9 is exposed, so that the control for stopping the etching can be performed easily and accurately. Then, as shown in FIG. 6, a current narrowing layer 8 is buried and formed in the etching groove 7. 7 and 8, parts corresponding to those in FIG. 6 are designated by the same reference numerals, and redundant description will be omitted.

In this structure, the formation position of the etching stop layer 9, that is, the thickness of the first and second cladding layers 5A and 5B is set in advance,
The depth of the etching groove 7 and the distance from the active layer 4 can be set reliably and easily, with excellent reproducibility and uniformity.

In this case, the etching stop layer 9 is made of, for example, GaA of the substrate 1, like the other cladding layers 3 and 5 and the like.
The composition is selected so that the lattice constant matches the s single crystal substrate.

However, according to this structure, although it is theoretically possible to form a semiconductor laser having a wavelength of 635 or 630 nm, it is possible to emit light with excellent operating characteristics, that is, with a low operating voltage. It is impossible to obtain a kind of compound semiconductor laser.

As described above, it has been revealed that the reason why it is difficult to obtain a semiconductor laser having excellent operating characteristics in the AlGaInP semiconductor laser, for example, is that absorption of light emitted from the active layer by the etching stop layer is absorbed. That is, for example, in an AlGaInP-based semiconductor laser, when the cladding layer is made of AlGaInP, the GaInP layer may be used as the etching stop layer having a different etching property from that of the AlGaInP-based semiconductor laser. The band gap of the etching stop layer is equal to or smaller than the band gap of the quantum well portion of the MQW structure of the active layer, so that the light emission from the active layer 4 is absorbed. Will show sex. . To address this problem, the present applicant previously filed Japanese Patent Application No. 7-119.
In application No. 60 “semiconductor laser”, for example, AlGa
Provided is a semiconductor laser that prevents absorption of oscillation wavelength light from the active layer by the etching stop layer even when the above-described etching stop layer is formed in the InP compound semiconductor laser.

In the semiconductor laser according to the invention proposed in the above-mentioned application, the etching stop layer having a large bandgap is formed by forming a material layer having an etching stop effect as an etching stop layer and using this layer as a tensile strain layer. Also in the short wavelength semiconductor laser, absorption of the oscillation wavelength light by the etching stop layer is avoided, and a semiconductor laser having desired characteristics excellent in operation characteristics is configured.

However, according to this structure, in order to cause tensile strain in the etching stop layer, its lattice constant is mismatched with that of the substrate. In order to avoid the occurrence of defects, it is necessary to select the thickness below the critical thickness at which epitaxial growth is possible. On the other hand, in order to obtain a stable etching stop function and to form a highly reliable etching stop layer, It is necessary to secure a thickness of at least 200Å, which is extremely close to the above-mentioned critical thickness. That is, there may be a problem in that both the occurrence of crystal defects and the etching stop function are completely satisfied.

In the present invention, in the semiconductor light emitting device such as the semiconductor laser having the structure in which the tensile strain etching stop layer or the compressive strain etching stop layer is provided as described above, the critical thickness of the strain etching stop layer is not restricted. It is possible to construct an etching stop layer that is thick enough to obtain sufficiently high reliability as an etching stop layer, and to solve the problem of crystal defect occurrence, and to have excellent operating characteristics. (EN) A semiconductor light emitting device having high efficiency can be configured.

[0013]

A semiconductor light emitting device according to the present invention comprises a substrate, at least a first conductivity type cladding layer, an active layer, a second conductivity type first cladding layer, and an active layer. A strain etching stop layer having a larger band gap and a second conductivity type second clad layer are sequentially stacked, and are in contact with the strain etching stop layer to have a larger band gap than the active layer. A strain compensation layer due to strain opposite to that of the strain etching stop layer is laminated. Then, a groove in which a current confinement layer is buried is formed on both sides of the current path having a stripe shape so as to have a depth from the second conductivity type second cladding layer side to the etching stop layer.

According to the structure of the present invention, the depth of the etching groove for forming the current confinement layer is set by the etching stop layer. Especially, the etching stop layer is a strained layer. The effect of increasing the band gap is thereby obtained, and thus the band gap of the etching stop layer is selected to be larger than that of the active layer. By thus selecting the band gap of the etching stop layer to be larger than that of the active layer, it is possible to prevent absorption of oscillation light from the active layer in the etching stop layer.

Further, in the present invention, the strain opposite to the strain of the etching stop layer, that is, when the strain etching stop layer is a tensile strain layer, the strain compensation layer of compressive strain is compressed, and the strain etching stop layer is compressed. In the case of strain, since the strain compensation layer for tensile strain is provided in contact with the strain etching stop layer, the strain due to the etching stop layer can be relaxed and the generation of crystal defects due to this strain can be suppressed. .

Therefore, the strain etching stop layer is
The thickness can be made thick enough to fully exhibit the etching stop function, and in the manufacture of this semiconductor light-emitting device, a semiconductor light-emitting device, such as a semiconductor laser, having the desired characteristics can be reliably manufactured with high reliability and reproducibility. it can.

[0017]

1 is a schematic sectional view of an example of a semiconductor light emitting device according to the present invention. In this example, the active layer is an example of a semiconductor laser having a multiple quantum well structure, but the present invention can be applied to a semiconductor laser having a single-layer quantum well structure or a semiconductor laser not having a quantum well structure. .

In the example of FIG. 1, a buffer layer 12, a first conductivity type clad layer 13, and an active layer 14 having a multiple quantum well structure are formed on a first conductivity type single crystal compound semiconductor substrate 11.
And the first conductivity type first cladding layer 15A and the active layer 1
A strain compensation layer 21 having a band gap larger than 4;
A structure in which a strain etching stop layer 19 having a larger band gap than that of the active layer 14, a second clad layer 15B of a second conductivity type, and a cap layer 16 of a second conductivity type are sequentially stacked in contact with this And Then, to form a stripe-shaped current path, the groove 1 is formed on both sides of the current path so as to sandwich the current path.
7 is formed to a depth defined by the etching stop layer 19 and the current confinement layer 18 is formed by filling the groove 17. Although not shown, one electrode that makes ohmic contact is formed on the cap layer 16, and the other electrode ohmic contact is formed on the back surface of the substrate 11.

Further, in order to facilitate the understanding of this semiconductor laser, an example of the manufacturing method thereof will be described with reference to the schematic sectional views in each step of FIGS.

In this example, 630 nm light emission is performed, that is, the band gap in the active layer 14 is 1.968.
This is a case where the present invention is applied to an eV AlGaInP-based semiconductor laser.

In this case, as shown in FIG. 2, on the GaAs substrate 11 of the first conductivity type, for example, the n-type, a buffer layer 12 of the same conductivity type, for example, a GaAs layer is used to interpose the first conductivity type, for example, the n-type. Clad layer 13 made of AlGaInP
And an active layer 14 having a multiple quantum well structure (MQW) in which a plurality of well layers and barrier layers having a quantum well structure are alternately stacked, and a second conductivity type, for example, p-type AlGaI.
a first clad layer 15A made of nP, a strain compensation layer 21 made of a second conductivity type, for example, p-type AlGaInP,
Second conductivity type strain etching stop layer 19 and second clad layer 15A made of second conductivity type AlGaInP
And a cap layer 16 made of GaAs of the second conductivity type are sequentially formed, for example, by MOCVD (Metal Organic Chemical Vapor).
Deposition) causes continuous epitaxial growth.

Then, it serves as an etching mask on the stripe-shaped current path in the center of the epitaxial growth layer formed of each compound semiconductor layer formed on the substrate 11 described above, and also serves as a mask for the selective MOCVD method of the current confinement layer to be performed later, for example, SiO. A mask layer 20 of _{2 is} deposited.

This mask 20 is formed by forming the SiO ₂ layer into C
It can be formed by forming the entire surface by a VD method or the like and then performing pattern etching by photolithography to remove the groove forming portion by etching.

Then, using this mask layer 20 as an etching mask, the groove 17 is formed by etching both sides of the mask layer 20 while leaving a portion for forming the mask layer 20. This etching is performed with, for example, an etching solution of a mixed solution of H ₂ SO ₄ , H ₂ O ₂ and H ₂ O.

According to such etching, when the etching reaches the etching stop layer 19, the etching rate is lowered to such an extent that the etching is substantially stopped. Therefore, if the etching is stopped at this point, the etching stop layer 19 is not removed. The depth of the groove 17 is defined by the formation position.

Thereafter, as shown in FIG. 4, the mask layer 20 is formed.
Using the mask as a mask, the current confinement layer 18 made of GaAs of the first conductivity type, for example, n-type, is formed in the groove 17 in which the compound semiconductor is exposed without forming the mask layer 20 by the well-known selective MOCVD method.

Thereafter, although not shown, a flattening layer is formed on the entire surface, and the surface of the flattening layer is planarly etched, for example, and as shown in FIG. 1, the cap layer 16 and the current narrowing layer 18 are formed.
The surface of is flattened.

If necessary, the back surface of the substrate 11 is planarly polished, for example, by chemical or mechanical polishing to reduce the thickness of the substrate 11, and then one electrode (not shown) is formed on the polished surface. Then, the other electrode (not shown) is ohmicly formed on the cap layer 16.

Here, the well layer of the active layer 14 having the MQW structure is, for example, − with respect to the lattice constant of the GaAs substrate 1.
G with tensile strain due to lattice constant mismatch of 0.7%
constituted by a _{0.61 1} In _0.389 P layer, the barrier layer is composed of _{(Al 0.5 Ga 0.5) 0.516 In} 0. 484 P layer.

Each clad layer 13, 15A and 15B
When the substrate 11 is the above-mentioned GaAs, has a lattice constant that is well matched to the GaAs and has a composition without distortion, such as (A
l _X Ga _1-X ) _0.516 In _0.484 P, usually at x = 0.
7, the composition is, for example, 0 ≦ x ≦ 1.

The strain etching stop layer 19 is formed on the substrate 1.
In the case where 1 is a GaAs substrate, (Al _X Ga
_1-x ) InP, for example, by Ga _0.65 In _0.35 P at x = 0 -1.0% (that is, {(b-a) / a} x 100 =-
1.0%, a is the lattice constant of the substrate 11, b is the lattice constant of the strain etching stop layer 19)
A band gap larger than the substantial band gap of the active layer 14 can be obtained. The thickness is set to, for example, 300 Å or less, which exceeds 200 Å, which is a thickness at which an etching stop function described later can sufficiently be exhibited.

The strain compensating layer 21 is made of the same material as the cladding layer.
The band gap of the active layer 14 is
Of the strain etching stop layer 19 at the same time as the strain of the strain etching stop layer 19 described above, that is, when the strain etching stop layer 19 has tensile strain as described above. , And the composition to be the compression strain layer is selected. The strain compensation layer 21 in this case
May be, for example, a + 0.3% compressive strain layer. The strain compensation layer 21 is formed of, for example, (Al _X Ga _1-X ) _{0.46 9} In.
_It can be composed of _0.531 P.

According to the above-mentioned configuration of the present invention, the current confinement layer 1
Although the depth of the etching groove for forming 8 is set by the etching stop layer 19, the effect of enlarging the bandgap of the etching stop layer 19 is particularly achieved. Thus, the band gap of this etching stop layer is selected to be larger than that of the active layer. In this way, by selecting the band gap of the etching stop layer to be larger than that of the active layer,
It is intended to prevent absorption of oscillation light from the active layer in the etching stop layer.

Further, in the present invention, the strain opposite to the strain of the etching stop layer, that is, when the strain etching stop layer 19 is a tensile strain layer, the strain compensating layer 21 of compressive strain, and the strain etching stop layer are also used. When 19 is compressive strain, the strain compensating layer 21 for tensile strain is provided so as to be in contact with the strain etching stop layer 19, so that the strain due to the etching stop layer 19 can be relaxed and the generation of crystal defects due to this strain. Can be suppressed.

Therefore, the strain etching stop layer 19
Can be made thick enough to fully exhibit the etching stop function, and in the manufacture of this semiconductor light-emitting device, a semiconductor light-emitting device, such as a semiconductor laser, having the target characteristics can be reliably manufactured with high reliability and reproducibility. Can be manufactured with.

In the example shown in FIGS. 1 to 4, the strain compensating layer 21 is arranged under the strain etching stop layer 19, but as shown in FIG. 5, a schematic sectional view is shown. The strain compensation layer 21 may be arranged on the strain etching stop layer 19. 5, parts corresponding to those in FIG. 1 and FIG. 4 are assigned the same reference numerals and overlapping description will be omitted.

The present invention is not limited to the above-mentioned AlGaInP-based semiconductor laser, that is, a semiconductor light-emitting device, but can be applied to, for example, a GaInAsP-based or ZnSe-based semiconductor light-emitting device.

In the above example, the first conductivity type is n.
In this case, the conductivity type and the second conductivity type are p-type, but needless to say, these conductivity types may be opposite conductivity types. In the above example, the active layer has the MQW structure. In this case, a 630 nm semiconductor laser can be formed, but SQW (single-layer quantum well structure) is used regardless of MQW.
Alternatively, an active layer without a quantum well structure can be used.

Further, in the above-mentioned example, the so-called DH (Doub) in which the clad layers are directly arranged with the active layer 14 sandwiched therebetween.
This is the case of a so-called SCH (Separate Confinement Heterostructure) in which a cladding layer is arranged with a guide layer sandwiching an active layer.
The structure is not limited to the above-described examples, and various structures can be adopted.

[0040]

As described above, according to the structure of the present invention,
The depth of the etching groove for forming the current confinement layer 18 is set by the etching stop layer 19, and in particular, by using the etching stop layer 19 as a strained layer, the band gap is increased. Since the band gap of the etching stop layer is selected to be larger than that of the active layer, the band gap of the etching stop layer 19 is selected to be larger than that of the active layer. Therefore, it is possible to prevent absorption of oscillation light from the active layer in the etching stop layer 19.

Further, in the present invention, the strain opposite to the strain of the etching stop layer 19, that is, when the strain etching stop layer 19 is a tensile strain layer, the strain compensating layer 21 of compressive strain, and the strain etching stop are also used. When the layer 19 has a compressive strain, the strain compensating layer 21 for tensile strain is provided in contact with the strain etching stop layer 19, so that the strain due to the strain etching stop layer 19 can be relaxed, and the crystal defects caused by this strain can be relaxed. Can be suppressed.

Therefore, the strain etching stop layer 19 is formed.
Can be made thick enough to fully exhibit the etching stop function, and in the manufacture of this semiconductor light-emitting device, a semiconductor light-emitting device, such as a semiconductor laser, having the target characteristics can be reliably manufactured with high reliability and reproducibility. Can be manufactured with.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of an example of a semiconductor light emitting device according to the present invention.

FIG. 2 is a schematic cross-sectional view in one manufacturing process of a semiconductor light emitting device according to the present invention.

FIG. 3 is a schematic cross-sectional view in one manufacturing process of the semiconductor light emitting device according to the present invention.

FIG. 4 is a schematic cross-sectional view in one manufacturing process of the semiconductor light emitting device according to the present invention.

FIG. 5 is a schematic cross-sectional view of another example of the semiconductor light emitting device according to the present invention.

FIG. 6 is a schematic sectional view of a conventional semiconductor laser.

FIG. 7 is a schematic cross-sectional view in one manufacturing process of a conventional semiconductor laser.

FIG. 8 is a schematic cross-sectional view in one manufacturing process of a conventional semiconductor laser.

[Explanation of symbols]

 1,11 Substrate 2,12 Buffer layer 3,13 First conductivity type cladding layer 4,14 Active layer 5,15 Second conductivity type cladding layer 15A First cladding layer 15B Second cladding layer 6,16 Cap Layer 7,17 Groove 8,18 Current narrowing layer 9,19 Etching stop layer 19A First etching stop layer 19B Second etching stop layer

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[Procedure amendment]

[Submission date] October 3, 1995

[Procedure amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0003

[Correction method] Change

[Correction contents]

[0003] In this AlGaInP semiconductor laser, is due to its active layer 4 MQW structure as described above, the semiconductor laser of this type which does not depend on MQW structure 6
Compared with the emission of 50 to 680 nm , there is an advantage that light emission in the 635 nm to 630 nm band having a shorter wavelength can be performed.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0031

[Correction method] Change

[Correction contents]

The strain etching stop layer 19 is formed on the substrate 1.
In the case where 1 is a GaAs substrate, (Al _X Ga
_1-X) -1.0% by Ga _0.65 In _0.35 P of InP for example x = 0 (i.e. {(b-a) / a } × 100 = -
1.0%, a is the lattice constant of the substrate 11, b is the lattice constant of the strain etching stop layer 19)
A band gap larger than the substantial band gap of the active layer 14 can be obtained. The thickness is, for example, 300 Å or less, for example, exceeding 50 Å, which is a thickness capable of sufficiently performing the etching stop function described later.

Claims (1)

[Claims] 1. A strained etching stop layer having a cladding layer of at least a first conductivity type, an active layer, a first cladding layer of a second conductivity type, and a strain gap larger than a bandgap of the active layer on a substrate. And a second clad layer of the second conductivity type are sequentially laminated, contacting the strained etching stop layer, and having a strain larger than the band gap of the active layer, which is opposite to the strained etching stop layer. A strain compensation layer is laminated, and a groove in which a current constriction layer is buried is formed on both sides of a current path in a stripe shape at a depth from the second conductivity type second clad layer side to the etching stop layer. A semiconductor light emitting device characterized by the following.