JP3057188B2 - Independently driven multi-beam laser and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an independently driven multi-beam laser, and more particularly to an independently driven multi-beam laser made of an AlGaAs compound semiconductor and a method of manufacturing the same.

[0002]

2. Description of the Related Art Multi-beam semiconductor lasers having a plurality of independently controllable laser beams in one chip have been developed in response to demands for high integration and high-speed processing of semiconductor lasers. In such an independently controlled multi-beam laser, unlike a single element, a plurality of independent input terminals are required.For example, an independent electrode is patterned and formed for each laser beam, and furthermore, a depth traversing the active layer is set. A method is conceivable in which a groove is reached to such an extent that it is formed by dry etching such as RIE (reactive ion etching) to perform element isolation.

However, when dry etching is performed across the active layer as described above, there is a possibility that the crystal may be damaged, and there is a problem that characteristics are deteriorated and reliability is deteriorated.

On the other hand, the present applicant has previously disclosed in
In issue 87, SDH (Separated Double Hetero Junct
An ion) type semiconductor laser was proposed. As shown in a schematic enlarged cross-sectional view of an example of this SDH type semiconductor laser in FIG. 3, first, a first conductivity type, for example, n-type and one main surface is # 10.
For example, a GaAs compound semiconductor substrate 1 having a 0 ° crystal plane
<01> orthogonal to the paper surface in FIG.
1> A stripe-shaped ridge 2 extending in the crystal axis direction is formed, and a normal MOCVD method (a chemical vapor deposition method using an organic metal) is sequentially formed on one main surface of the substrate 1 having the ridge 2.
That is, the first conductivity type, for example, the n-type cladding layer 33, the low impurity concentration or undoped active layer 4 and the second conductivity type, for example, the p-type first
, A first conductive type, for example, an n-type current blocking layer 6, a second conductive type, for example, a p-type second clad layer 7, and a second conductive type cap layer 8, It is formed by one epitaxial growth.

Here, the first conductivity type cladding layer 33 and the second conductivity type
First and second conductive cladding layers 35 and 7;
The conductive type current blocking layer 6 is made of a material having a larger band gap, that is, a smaller refractive index than the active layer 4.

In this case, the crystal orientation with respect to the substrate 1 and the ridge 2, the width and height of the ridge 2, that is, the depth of the groove on both sides thereof, and the first conductive type clad layer 33, the active layer 4,
By selecting the thickness of the second conductive type first cladding layer 35 and the like, the first conductive type cladding layer 3 is formed on the ridge 2.
3, the active layer 4, the first cladding layer 35 of the second conductivity type,
A fault is formed by the slopes 9A and 9B so as to be separated from those on the mesa groove, and the striped epitaxial growth layer 1 separated by the slopes 9A and 9B is formed.
0 is formed in a ridge 2 shape.

[0007] In the case of MOCVD using a methyl-based organic metal as a source gas, once a {111} B crystal plane is formed, it is difficult to make epitaxial growth on this plane. The epitaxial growth layer 10 is formed. In this case, the current block layer 6 is divided on both sides of the stripe-shaped epitaxial growth layer 10 by sandwiching the current block layer 6, and both end surfaces generated by this division are separated from the other in the stripe-shaped epitaxial growth layer 10. Both end faces or slopes 9A and 9 of layer 4
It is made to abut against the end face facing B.

In this manner, the active layer 4 in the stripe-shaped epitaxial growth layer 10 on the ridge 2 is formed so as to be sandwiched by the current blocking layer 6 having a smaller refractive index, and confinement in the lateral direction is performed, so that light emission operation is performed. Region, and the current blocking layer 6
The stripe-shaped epitaxial growth layer 10
Of the second conductive type second cladding layer 7
, A block layer 6, and a first cladding layer 3 of the second conductivity type
5 and the first conductivity type cladding layer 33,
A pn thyristor is formed and the current there is blocked, whereby the current is concentrated on the active layer 4 of the stripe-shaped epitaxial growth layer 10 on the ridge 2 so as to reduce the threshold current. Has been made.

The applicant of the present invention has previously disclosed in Japanese Patent Application Laid-Open No. 4-98888 a plurality of ridges as shown in FIG. We proposed an independently driven multi-beam laser that drives independently by forming an active layer in the groove between them.
The semiconductor laser has a buffer layer 21 on an n-type semiconductor substrate 21 having a main surface of {100} crystal plane, for example.
In this case, a first cladding layer of the second conductivity type, in this case, a p-type first cladding layer is epitaxially grown, and a plurality of stripe-shaped grooves 32A having a depth reaching the buffer layer 22 across the first cladding layer of the second conductivity type. Is formed by anisotropic etching such as RIE in a direction perpendicular to the main surface of the base 21. The groove 32A is formed in a stripe shape as a pattern extending in the <011> crystal axis direction, and the ridge 22 sandwiched therebetween is provided as a stripe pattern extending in the <011> crystal axis direction. The n-type cladding layer 24, the active layer 25, and the second conductivity type, that is, the p-type second cladding layer 26 and the cap layer 27 are epitaxially grown by MOCVD in this order including the groove 32A. An insulating layer 28 is applied over the entire surface, an opening is provided at a position corresponding to each groove 32A by RIE or the like, and a metal such as Al is vapor-deposited and provided in each groove 32A. The electrodes 29 corresponding to the active layers 25 are respectively formed, and an independently driven multi-beam laser is formed.

In such a configuration, as described above, by selecting the crystal plane of the main surface and the crystal orientation in which the ridge extends, {111} B
The cladding layer 24 of the first conductivity type is epitaxially grown in a triangular cross section having a slope formed of a crystal plane. Further, by appropriately selecting the thickness of each of the cladding layers 23 and 24, the width of the ridge 32, and the like, on the ridge 32, only the first conductivity type cladding layer 24 is epitaxially grown and the groove 32A is formed. In the active layer 2
5 is epitaxially grown separately in each groove 32A so that its lateral end face abuts on the ridge 32. The active layer 25 is vertically and laterally clad with the cladding layer 2.
A buried structure surrounded by 3, 24, and 26 can be adopted, and an npn thyristor structure is formed on the ridge 2, current is concentrated on the active layer 25, and a lower threshold current is achieved.

Further, in this case, by appropriately selecting the thicknesses of the second conductive type second clad layer 26 and the cap layer 27, the cap layer 27 is divided into the clad layers 24 on the ridge 32. , Independent driving can be performed.

However, in such a configuration,
Since the lateral end face of the active layer 25 is abutted on the side face of the ridge 32 formed by etching, there is a possibility that crystal degradation may occur in this portion. In particular, when the length of the resonator is large, that is, when the length in the direction perpendicular to the plane of FIG. 4 is large, there is a problem in the flatness of the bottom and side surfaces of the groove 32A. The crystallinity of the epitaxially grown active layer 25 may be non-uniform, which may cause non-uniformity of the characteristics and lower reliability.

[0013]

SUMMARY OF THE INVENTION The present invention provides an independently driven multi-beam laser with improved uniformity and reliability.

[0014]

As an example of the independently driven multi-beam laser of the present invention, as shown in an enlarged schematic sectional view of FIG. 1, a principal surface of a compound semiconductor substrate 1 composed of a {100} crystal plane. On the 1S, a plurality of <011> inverted mesa-shaped ridges 2 extending in the crystal axis direction, which are made of a semiconductor layer having a conductivity opposite to that of the compound semiconductor substrate 1 and having, for example, a p-type and having a selectivity to the compound semiconductor substrate 1 and etching selectivity, Formed and configured,
The ridge 2 and the compound semiconductor substrate 1 are entirely covered with at least the same conductivity type as the compound semiconductor substrate 1, for example, n.
Type first cladding layer 3, active layer 4, reverse conductivity type, for example, p
A second clad layer 5 of a mold is provided, only the first clad layer 3 is formed on the ridge 2, and the active layer 4 is provided independently between the ridges 2.

According to the present invention, in the above-mentioned independent drive type multi-beam laser, the compound semiconductor substrate 1 is made of GaAs, and the ridge 2 is made of AlGaAs.

Further, according to the present invention, in the independently driven multi-beam laser shown in FIG.
It is configured as μm or more.

In the method of manufacturing an independently driven multi-beam laser according to the present invention, as shown in FIGS. 2A to 2C, an example of the manufacturing process is shown in FIG.
An inverted mesa-shaped ridge 2 made of AlGaAs and having a conductivity type opposite to that of the semiconductor substrate, for example, p-type and made of AlGaAs, is provided on the main surface 1S made of A first cladding layer 3 of the same conductivity type, for example, an n-type, an active layer 4, and a second cladding layer 5 of the opposite conductivity type, for example, a p-type, are sequentially laminated on the entire surface of the semiconductor substrate 1 at least over the compound semiconductor substrate 1. Formed on the ridge 2
Is formed, and the active layer 4 is
Are provided independently of each other.

[0018]

As described above, in the present invention, on the compound semiconductor substrate 1, a plurality of inverted mesa-shaped ridges 2 of the opposite conductivity type and extending in the <011> crystal axis direction are provided. Only the first cladding layer 3 is formed on the
Are provided independently between the ridges 2, so that the above-mentioned Japanese Patent Application Laid-Open No.
As in the case of the multi-beam laser disclosed in Japanese Unexamined Patent Application Publication No. H10-209, current constriction is performed to reduce the threshold value and to enable independent driving.

Particularly, in the structure of the present invention, since the semiconductor layer constituting the ridge 2 has a substrate material and etching selectivity, the main surface 1S of the compound semiconductor substrate 1 below the ridge 2 is exposed when the ridge 2 is formed. The main surface 1S is etched to the groove 2 between the ridges 2
A, that is, the bottom surface of the first cladding layer 3 epitaxially grown in the trench 2A is formed as a crystal plane having excellent flatness formed along the main surface 1S of the substrate 1. it can. At this time, since the side surface of the cladding layer 3 in the groove 2A naturally has a vertical surface 3V perpendicular to the main surface 1S of the substrate 1, the active layer 4 grown on the side surface is in a lateral direction. It is formed with good crystallinity also at the end face.

According to another aspect of the present invention, the material of the substrate 1 is made of GaAs and the material of the ridge 2 is made of AlGaAs, so that the inverted mesa-shaped ridge 2 can be reliably formed with etching selectivity as described above. The active layer 4 can be epitaxially grown with good crystallinity.

According to still another aspect of the present invention, by setting the height h of the ridge 2 to 2 μm or more, light can be reliably confined in the vertical (thickness) direction and the lateral direction in the groove 2A. Since a (double hetero) type laser can be formed, a semiconductor laser with a low threshold can be formed.

In another manufacturing method of the present invention, the ridge 2 made of AlGaAs having etching selectivity is provided on the GaAs substrate as described above. It can be formed with a crystal plane.

Therefore, according to the configuration and the manufacturing method of the present invention, even when the resonator length is increased in the above-described multi-beam laser, the active layer of each laser is formed with uniform crystallinity. The reliability can be improved by measuring the uniformity of each laser beam of the independently driven multi-beam laser.

[0024]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an example of an independent driving type multi-beam laser according to the present invention. In this example, AlGaAs
The case where a multi-beam laser using a system compound semiconductor is obtained will be described.

First, as shown in FIG. 1, on a main surface 1S of a {100} crystal plane of a compound semiconductor substrate 1 made of n-type GaAs or the like, a p-type Al
A <011> stripe-shaped inverted mesa-shaped ridge 2 extending in the crystal axis direction is formed of a semiconductor layer such as GaAs. On the ridge 2, the substrate 1 is formed of the same conductivity type, in this case, n-type AlGaAs. A first clad layer 3 is formed. In each groove 2A sandwiched between the ridges 2, the first clad layer 3, an active layer 4 made of intrinsic GaAs or the like, and a conductive type opposite to the substrate 1 are used. In this case, a second clad layer 5 made of p-type AlGaAs or the like is formed by lamination, and the active layers 4 are independently provided in the grooves 2A between the ridges 2, respectively.

In this case, when each of the layers 3, 4 and 5 is epitaxially grown by MOCVD using a methyl-based source gas, once a {111} B crystal plane is generated from the edge on the ridge 2, Since the epitaxial growth rate is extremely slow on the｝ B crystal plane, the semiconductor layer on the ridge 2 is formed in a triangular cross section surrounded by the slope 9 composed of the ｛111｝ B crystal plane.

The first cladding layer 3 is epitaxially grown in the groove 2A sandwiched between the ridges 2.
At this time, ｛1 orthogonal to the main surface 1S of the compound semiconductor substrate 1
Epitaxial growth is performed while generating a vertical plane 3V by a 10 ° crystal plane.

A method of manufacturing such a multi-beam laser will be described with reference to a manufacturing process diagram of FIG. First, FIG. 2A
As shown in FIG. 5, a p-type A is formed on a main surface 1S of a {100} crystal plane of a compound semiconductor substrate 1 of n-type GaAs.
The semiconductor layer 12 made of lGaAs is epitaxially grown by MOCVD or the like with a thickness (height) h of, for example, 2 μm. Then, a stripe-shaped resist 13 extending in the <110> crystal axis direction indicated by an arrow A in FIG. 2A is formed thereon by application of a resist, pattern exposure, or the like.

Then, etching is performed by wet etching or the like using the resist 13 as a mask, and FIG.
As shown in FIG. 5, a groove 2A having a depth reaching the main surface 1A of the substrate 1 and a ridge 2 sandwiched therebetween are formed. In this case, the ridge 2 is formed as a stripe pattern extending in the <011> crystal axis direction indicated by an arrow A along the resist 13 and having a height h of, for example, 2 μm.

Then, as shown in FIG. 2C, a first cladding layer 3 made of n-type AlGaAs or the like is epitaxially grown on the entire surface over the ridge 2 and the groove 2A by MOCVD. At this time, the height and width of the ridge 2 and the thickness of the first cladding layer 3 are appropriately selected, so that only the first cladding layer 2 forms a {111} B crystal plane on the ridge 2. An epitaxial layer having a triangular cross section surrounded by the slope 9 is formed.

At this time, in the groove 2A, the edge of the ridge 2 is perpendicular to the main surface 1S of the substrate 1 and is # 11
The first cladding layer 3 grows while a vertical plane 3V composed of a 0 ° crystal plane is spontaneously generated. Therefore, this first
The upper surface of the cladding layer 3 is surrounded by a vertical surface 3V, and the upper surface 1
4 is formed as a crystal plane having good flatness along the main surface 1S. At this time, when the upper surface 14 is at a position lower than the upper surface of the ridge 2, the epitaxial growth is stopped, and the active layer 4 made of intrinsic GaAs or the like, as shown in FIG. Second cladding layer 5 made of AlGaAs or the like, cap layer 8 made of p-type GaAs or the like
The thickness of each of the layers 4, 5 and 8 is selected so that the upper surface of the cap layer 8 is at a lower position than the top of the epitaxial layer composed of the first cladding layer 3 on the ridge 2.
Epitaxial growth is performed by the OCVD method. Then, at a position corresponding to the upper part of each active layer 4 on the cap layer 8, Al
A plurality of electrodes 11 formed by vapor deposition or the like;
Although not shown, a counter electrode is also formed on the back side of the substrate 1 to obtain an independently driven multi-beam laser according to the present invention.

With such a structure, each active layer 4 is independently provided between the ridges 2 by a single crystal growth, and a DH type laser in which the laser is confined in the lateral direction is formed. The element is separated by the cladding layer 3 on the substrate 2 and independent driving is possible. In this portion, an npn thyristor is formed by the first cladding layer 3, the ridge 2 and the substrate 1, and current concentration in the active layer 4 is increased. A low threshold multi-beam laser can be obtained. Further, in the present invention, the active layer 4 has a thickness of $ 10.
Since the first cladding layer 3 is grown on the upper surface 14 of the first cladding layer 3 which epitaxially grows along the 0 ° crystal plane, the first cladding layer 3 can be formed with good flatness. And formed with good crystallinity against the vertical surface 3V. Therefore, even if the length of the resonator is particularly large, the characteristics can be made uniform, and the characteristics of such an independently driven multi-beam laser can be made uniform and the reliability can be improved.

It is needless to say that the present invention is not limited to the above-described embodiment, but can be variously modified and changed, for example, the conductive type of each part is set to the opposite conductive type to that shown in the drawings.

[0034]

As described above, according to the present invention, the active layer can be formed with good crystallinity and good flatness in an independently driven multi-beam laser having a DH structure and a low threshold. Therefore, even when the length of the resonator is increased, laser light having uniform characteristics can be obtained, and the reliability of the independently driven multi-beam laser can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic enlarged cross-sectional view of an example of an independently driven multi-beam laser according to the present invention.

FIG. 2 is a manufacturing process diagram of an example of a method for manufacturing an independently driven multi-beam laser according to the present invention.

FIG. 3 is a schematic enlarged sectional view of an example of a conventional semiconductor laser.

FIG. 4 is a schematic enlarged cross-sectional view of an example of a conventional independently driven multi-beam laser.

[Explanation of symbols]

 Reference Signs List 1 compound semiconductor substrate 1S main surface 2 ridge 3 first cladding layer 4 active layer 5 second cladding layer 8 cap layer 9 slope

Claims (4)

(57) [Claims] 1. A compound semiconductor substrate having a conductivity type opposite to that of the compound semiconductor substrate on a main surface of a {100} crystal plane,
<011> A plurality of inverted mesa-shaped ridges extending in the direction of the crystal axis formed of a semiconductor layer having the etching selectivity and the material of the compound semiconductor substrate. At least a first cladding layer of the same conductivity type as the compound semiconductor substrate, an active layer, and a second cladding layer of the opposite conductivity type are provided, and only the first cladding layer is formed on the ridge. Wherein the active layer is independently provided between the ridges. 2. The independently driven multi-beam laser according to claim 1, wherein said compound semiconductor substrate is made of GaAs, and said ridge is made of AlGaAs. 3. The independently driven multi-beam laser according to claim 1, wherein the height of the ridge is 2 μm or more. 4. A semiconductor substrate made of GaAs having a thickness of $ 10
An inverted mesa-shaped ridge made of AlGaAs and having a conductivity type opposite to that of the semiconductor substrate and extending in the <011> crystal axis direction is provided on the main surface of 0 °, and covers the ridge and the compound semiconductor substrate. A first cladding layer of the same conductivity type as the compound semiconductor substrate, an active layer, and a second cladding layer of the opposite conductivity type are sequentially formed on the entire surface, and only the first cladding layer is formed on the ridge. A method of manufacturing an independently driven multi-beam laser, wherein the active layer is provided independently between the ridges.