JPH08204277A - Semiconductor laser - Google Patents

Abstract

PURPOSE: To constitute a semiconductor laser having an excellent operating characteristic by avoiding the absorption of oscillation-wavelength light from an active layer by means of an etching stopping layer. CONSTITUTION: At least a clad layer 13 of first conductivity, active layer 14, first clad layer 15A of second conductivity, etching stopping layer 19, and second clad layer 15B of second conductivity are successively formed on a substrate 11 and a groove 17 in which current constricting layers 18 are buried on both sides of a stripe-like current passage. The etching stopping layer 19 is constituted so that the lattice constant of the layer 19 can be selected to a value at which tensile strains are formed and the band gap of the layer 19 can become larger than that of the layer 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser, and more particularly to a semiconductor laser suitable for application to an AlGaInP semiconductor laser which is a compound semiconductor laser.

[0002]

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

In this AlGaInP semiconductor laser, the active layer 4 of which has the MQW structure as described above has a shorter wavelength than the semiconductor laser of this kind which does not depend on the MQW structure, which emits light of 650 nm. Of 63
There is an advantage that light emission in the 0 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 the semiconductor laser having the above-described structure, it is desired that the etching groove for burying the current confinement layer can be accurately etched to a predetermined depth. As a method of setting the depth of the etching groove to a predetermined depth, a method shown in FIG.
As shown in FIG.
Of the first cladding layer 5A and the second cladding layer 5B of the upper layer, and the first and second cladding layers 5A
And 5B, an etching stop layer 9 having a different etching property from the cladding layer 5, that is, an etching rate significantly lower than that of the AlGaInP cladding layer 5 is epitaxially grown, and a striped current path forming portion on the cap layer 6 is formed. An etching mask layer 10 is formed on the upper surface, and the cap layer 6 is etched by using this as a mask, and then etching having a high etching property with respect to the cladding layer 5 and a low etching property with respect to the etching stop layer 9 is performed. The cladding layer 5 is etched. In this way, as shown in FIG. 8, the etching progress is stopped or slowed 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, easily and 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, in the case of this structure, absorption of the oscillation wavelength light from the active layer 4 in the etching stop layer 9, that is, the light of 630 nm occurs, and it is theoretically possible to form a semiconductor laser of this wavelength. However, it is not always possible to obtain a compound semiconductor laser of this kind that has excellent operating characteristics, that is, can emit light with a low operating voltage.

In the present invention, for example, AlG mentioned above is used.
In the aInP-based compound semiconductor laser, even when the active layer has the MQW structure, the etching stop layer is formed to surely form the etching groove for forming the current confinement layer, but the etching stop layer is formed. The layer avoids absorption of oscillation wavelength light from the active layer, and constitutes a semiconductor laser having excellent operating characteristics.

[0010]

That is, the inventors of the present invention absorb the light emitted from the active layer by the etching stop layer because the reason why it is difficult to obtain a semiconductor laser having excellent operating characteristics in the above-mentioned AlGaInP-based semiconductor laser, for example. It was determined that it was possible. For example, AlGaI
In the nP semiconductor laser, the cladding layer is made of AlGaI.
In the case of being composed of nP, it can be considered that the etching stop layer having a different etching property from that of GaP is a GaInP layer. In this case, however, if the composition is lattice-matched to the substrate, this etching stop layer is used. The bandgap of the layer is equal to or smaller than the bandgap of the quantum well portion of the MQW structure of the active layer, and thus exhibits absorption of light emitted from the active layer 4.

Therefore, according to the present invention, at least a first-conductivity-type cladding layer, an active layer, and a second-conductivity-type first layer are provided on a substrate.
Clad layer, an etching stop layer, and a second conductive type second clad layer forming a second conductive type clad layer together with the clad layer are sequentially laminated, and a striped current path is sandwiched between both sides of the clad layer. A groove in which the current confinement layer is buried is formed at a depth reaching the etching stop layer,
The etching stop layer is configured to have a band gap larger than that of the active layer 14 by being selected as a lattice constant with which tensile strain is formed.

[0012]

As described above, according to the present invention, the etching stop layer for setting the depth of the etching groove for forming the current confinement layer is provided. In particular, the etching stop layer is set so that strain is generated. The band gap is made larger than that of the active layer. By doing so, it is possible to prevent the etching stop layer from absorbing the oscillation laser light from the active layer by the etching stop layer.

Therefore, this etching stop layer 1
It is possible to avoid the deterioration of the operating characteristics of the semiconductor laser due to the provision of No. 9.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail with reference to FIG. 1. In this case, in order to facilitate understanding, reference will be made to schematic cross-sectional views in each step of FIGS. Then, an example of the manufacturing method will be described.

In this case, 630 nm light emission is performed, that is, the band gap in the active layer 14 is 1.968e.
In the case where the present invention is applied to a V AlGaInP semiconductor laser, in this case, as shown in FIG. Via a cladding layer 13 of a first conductivity type, for example, n-type AlGaInP,
For example, 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 AlGaInP
A first clad layer 15A made of a second conductive type and an etching stop layer 19 of a second conductivity type having a thickness of 100 to 300Å, for example.
And a second clad layer 15A made of AlGaInP of the second conductivity type and a cap layer 16 made of GaAs of the second conductivity type in order, for example, by MOCVD (Metal Organic Chem).
Epitaxial growth continuously by ical vapor deposition.

The etching stop layer 19 is formed on the substrate 11
In the case of a GaAs substrate, (Al _X Ga
_1-x ) InP (0 ≦ x ≦ 0.7) composition, for example GaI
nP.

When the lattice constant of the substrate 11 is a and the lattice constant of the etching stop layer 19 is b, the following relationship (Equation 1) is established.

[0018]

1> 0> (b−a) /a≧−0.02

Then, it becomes 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 further becomes 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.

The 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 the 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, for example, with an etching solution containing a mixed solution of HCl, H ₂ O ₂ and H ₂ O or an etching solution containing a mixed solution of H ₂ SO ₄ , H ₂ O ₂ and H ₂ O.

By such etching, the etching stop layer 19 is exposed to substantially stop the etching. When the etching is stopped at this point, the depth of the groove 17 is defined by the position where the etching stop layer 19 is formed. .

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 planarizing layer is formed on the entire surface, and the surface of the planarizing 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 has a negative lattice constant of, for example, the GaAs substrate 1.
It constituted by Ga _{0. 65} In _0.35 P layer having a tensile strain due to mismatch of 1.0% of the lattice constant, the barrier layer (A
1 _0.5 Ga _0.5 ) _0.516 In _{0.48 4} P layer.

The first conductivity type clad layer 13 and the second conductivity type clad layer 15 composed of the first and second clad layers 15A and 15B are made of (Al _0.7 Ga), respectively.
_0.3 ) _0.516 In _0.484 P

In this case, the etching stop layer 1
9 is selected as the lattice constant at which tensile strain is formed, that is, the above-mentioned (Equation 1), and more preferably the following (Equation 2).

[0029]

## EQU2 ## −0.016 ≦ (b−a) / a <−0.01

This etching stop layer 19 is made of (Al
_X Ga _1-x ) InP, 0 ≦ x ≦ 0.7, preferably G
a 0.5 _{+ y} In 0.5 _-y P, 0 <y <0.5, and in practice 0 <y <0.230 in this range. For example (ba)
/A=-0.016, the etching stop layer 19 is Ga _0.730 In _0.270 P, and the band gap at this time is 2.239 eV, and (b−a) / a =
When -0.12 is set, the etching stop layer 19
Is Ga _0.678 In _0.322 P, and the band gap at this time is 2.15 eV. Therefore, in either case, the band gap of the etching stop layer 19 is larger than the band gap of the active layer 14.

Therefore, in the semiconductor laser having this structure, despite the fact that the etching stop layer 19 exists between the first and second cladding layers 15A and 15B,
Absorption of light emitted from the active layer 14 is avoided.

When the above (Equation 1), especially (Equation 2) is selected, epitaxial growth of the etching stop layer 19 and the subsequent layers can be performed without growing crystal defects in the epitaxial growth layer.

According to the above-mentioned semiconductor laser of the present invention, the potential diagram of its conduction band is as shown in FIG.
The band gap of the etching stop layer 19 is set to the active layer 1
Since it can be made larger than that of 4, the absorption of the oscillated light from the active layer 14 in the etching stop layer 19 is avoided.

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 interposed therebetween is provided.
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.

[0036]

As described above, according to the present invention, since the etching stop layer 19 is formed in the portion where the current confinement layer 18 is formed, the depth of the groove 17 forming the current constriction layer 18 is
It can be set at the position where the etching stop layer 19 is formed, so that a semiconductor laser having excellent workability and excellent uniformity can be constructed.

Despite the provision of the etching stop layer 19 as described above, the band gap is adjusted by pulling the etching stop layer 19 so that strain is generated so that the band gap is made larger than that of the active layer. Therefore, it is possible to prevent the oscillation laser light from the active layer from being absorbed by the etching stop layer 15, and it is possible to avoid an increase in operating current due to this absorption and thus a decrease in operating characteristics.

Therefore, in particular, by making the active layer of the AlGaInP system, for example, the MQW structure, 630
Even in the case of a semiconductor laser whose wavelength is shortened to nm, it is possible to avoid the deterioration of its operating characteristics, so that the industrial benefit thereof is large in practical use.

[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 cross-sectional view in one manufacturing process of the semiconductor laser according to the present invention.

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

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

FIG. 5 is a potential model diagram for explaining a semiconductor laser 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 Layers 7,17 Grooves 8,18 Current narrowing layers 9,19 Etching stop layers

Claims (5)

[Claims] 1. A clad layer of at least a first conductivity type, an active layer, a first clad layer of a second conductivity type, an etching stop layer, and a second clad layer of a second conductivity type on a substrate. Are sequentially laminated, and a groove in which a current constriction layer is buried is formed on both sides of the stripe-shaped current path so as to reach the etching stop layer. The etching stop layer is a lattice in which a tensile strain is formed. A semiconductor laser characterized by being selected as a constant and having a bandgap larger than that of the active layer. 2. The substrate is a GaAs substrate, the cladding layer is an AlGaInP-based semiconductor laser made of AlGaInP, and the etching stop layer is (Al _x Ga _{1 -x} ) InP, and 0 ≦ x ≦ 0. . 7. The semiconductor laser according to claim 1, wherein 3. The etching stop layer is GaIn
The semiconductor laser according to claim 1, wherein the semiconductor laser is P. 4. The semiconductor laser according to claim 1, wherein the active layer has a quantum well structure. 5. When the lattice constant of the substrate is a and the lattice constant of the etching stop layer is b, 0> (b
5. The semiconductor laser according to claim 1, wherein the relationship is −a) /a≧−0.02.