JPH0555692A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To surely maintain thyristor constitutions on both sides of a ridge, and reduce leak current, by forming semiconductor layers having carrier of the conductivity type different from that of a substrate, or insulative semiconductor layers, on both side surfaces of the ridge and in the bottoms of the trenches on both sides. CONSTITUTION:Both side surfaces 2S of a ridge 2 and the insides of trenches 3 on both sides are constituted so as to be surrounded by a semiconductor layer 4 having carrier of the conductivity type different from that of the substrate 1, or an insulative semiconductor layer. Thereby a leak current can be surely avoided when the leak current penetrating from a clad layer 5 of a first conductivity type on the ridge 2 to a current blocking layer 9 is generated, and a thyristor composed of a first conductivity type clad layer 6, a second conductivity type clad layer 7, a current blocking layer and a second clad layer 10 of a second conductivity type is turned on, because a P-N-P-N thyristor composed of the substrate 1, the semiconductor layer 4, the clad layer 6 of a first conductivity type and the clad layer 7 of a second conductivity type is constituted.

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 which has a current threshold in the lateral direction of an active layer to reduce a threshold current.

[0002]

2. Description of the Related Art As a semiconductor laser having a low threshold current I _th , an SDH (Separated Double Hetero Ju) which can be formed by one epitaxial growth operation is used.
A semiconductor laser is disclosed in
It has been proposed in the patent applications of 61-183987 and JP-A-2-174287.

In this SDH type semiconductor laser, as shown in FIG. 4 which is an enlarged schematic cross-sectional view of an example thereof, first, a first conductivity type, for example, n type, and one main surface 1S having {100} crystal faces, for example, (100) are used. ) A linear mesa protrusion or ridge 2 extending in, for example, the [011] crystal axis direction of the <011> crystal axis direction orthogonal to the paper surface of FIG. Is formed by sandwiching both sides of the groove 3 in the n-type substrate 1 including the ridge 2.
Of the first conductivity type, for example, the n-type clad layer 5 on the main surface 1S of the n-type cladding layer 5 in succession by a normal MOCVD (Chemical Vapor Deposition with Organic Metal) method, that is, a methyl MOCVD method.
A low impurity concentration or undoped active layer 6, a second conductivity type, for example, a p-type first cladding layer 7, a first conductivity type, for example, an n-type current blocking layer 8, and a second conductivity type, for example, p-type. The second clad layer 10 and the semiconductor layer of the second conductivity type cap layer 11 are formed by one epitaxial growth operation.

The first conductivity type clad layer 5, the second conductivity type first and second clad layers 7 and 10 and the first conductivity type current blocking layer 9 are compared with the active layer 6. And a material having a large band gap, that is, a small refractive index.

At this time, as described above, the main surface 1 of the substrate 1 is
The crystal plane of S and the crystal orientation of the ridge 2 are selected,
Further, the width and height of the ridge 2, that is, the depth of the groove 3 on both sides thereof, the n-type cladding layer 5, the active layer 6, and the p-type first layer.
By selecting the thickness of the clad layer 7 and the like, the faults are formed by the slopes 8a and 8b so as to divide the layers 5, 6 and 7 from each other on the ridge 2 and the groove 3, and the slopes 8a and 8b are formed. It is possible to form on the ridge 2 an epitaxial growth layer 20 having a triangular cross section divided by 8 and 8b and extending in a direction orthogonal to the paper surface of FIG.

This is because, in the case of the usual MOCVD method, that is, the MOCVD method in which a methyl-based organic metal is used as a source gas, once the (111) B crystal plane is generated, epitaxial growth is unlikely to occur on this plane. Is used to form the epitaxial growth layer 20 having a triangular cross section. In this case, the current blocking layer 9
Are divided by the epitaxial growth layer 20 on both sides of the same, and both end faces generated by this division are exactly in the vicinity of both end faces of the divided striped active layer 6 in the striped epitaxial growth layer 20, that is, the slopes 8a and 8b. It is made to abut in the vicinity of the end face facing the.

In this way, the active layer 6 in the epitaxially grown layer 20 on the ridge 2 is formed so as to be sandwiched by the current block layers 9 having a smaller refractive index than that, and confined in the lateral direction to form a light emitting operation region. And the presence of the current blocking layer 9 causes the p-type second cladding layer 10 and the blocking layer 9 to be formed on both outer sides of the striped epitaxial growth layer 20.
, P-type first clad layer 7, and n-type clad layer 5
And form a p-n-p-n thyristor,
The current is blocked here, so that the current is concentrated in the active layer 6 of the epitaxial growth layer 20 on the ridge 2 to lower the threshold current.

However, in the case of such a structure, as shown by an arrow i _a in FIG. 4, from the n-type cladding layer 5 on the ridge 2 to the n-type current blocking layer through the interface in contact with the slopes 8a and 8b. A leak current path is formed from 9 to the p-type second cladding layer 10, and leak current flows during operation. When the leak current becomes large, the p-type second cladding layer 10,
When the thyristor constituted by the current blocking layer 9, the p-type first cladding layer 7 and the n-type cladding layer 5 is turned on, and a large leak current flows as indicated by the arrow i _b. was there.

[0009]

SUMMARY OF THE INVENTION The present invention provides a ridge 2 in a semiconductor laser having the SDH structure as described above.
Stable holding of the thyristor structure in the grooves 3 on both sides,
An object of the present invention is to reliably prevent a large leak current from being generated when the thyristor is turned on.

[0010]

FIG. 1 is a schematic enlarged sectional view showing an example of a semiconductor laser of the present invention. According to the present invention, as shown in FIG. 1, a ridge 2 extending in the <011> crystal axis direction of this substrate is formed on a substrate 1 of the first conductivity type having a {100} crystal plane as a main surface 1S. At least the first conductivity type cladding layer 5, the active layer 6, the second conductivity type cladding layer 7, and the current blocking layer 9 are formed on the ridge 2 by vapor phase epitaxy and extend from both edges of the ridge 2. Consist of {111} B
The semiconductor layer 4 or the insulating type semiconductor is formed by growing so that the slopes 8a and 8b formed of crystal planes appear, and has carrier of a conductivity type different from that of the base 1 on the both side surfaces 2S of the ridge 2 and the bottoms of the grooves 3 on both sides. It is constructed by providing layers.

[0011]

As described above, in the semiconductor laser of the present invention, the ridge 2 extending in the <011> crystal axis direction of the substrate 1 is formed on the substrate 1 having the {100} crystal plane as the main surface 1S. On top of vapor phase growth method, that is, ordinary methyl-based MO
The cladding layer 5 of the first conductivity type, the active layer 6, the cladding layer 7 of the second conductivity type, the current blocking layer 9 and the like are deposited by the CVD method. When the extending direction of the ridge 2 is selected, once the {111} B crystal plane is formed on the ridge 2, it is difficult to grow on the {111} B crystal plane by the methyl MOCVD method. Then {111}
It grows in a triangular cross-section sandwiched on both sides by slopes 8a and 8b made of B crystal plane, and each layer grows on the ridge 2 and in the groove 3 while being separated from each other. Therefore, by appropriately selecting the width and height of the ridge 2 and the thicknesses of the layers 5, 6 and 7, the first conductivity type clad layer 5, the active layer 6 and the second conductivity type are formed on the ridge 2. Type clad layer 7
The epitaxial growth layer 20 having a triangular cross section is formed, and the current blocking layer 9 in the groove 3 is located near both sides of the active layer 6 on the ridge 2 facing both slopes 8a and 8b. it can. In the example of FIG.
The case where the end face of the active layer 6 is covered is shown.

Further, in the semiconductor laser of the present invention, both side surfaces 2S of the ridge 2 and the trenches 3 on both sides are surrounded by a semiconductor layer 4 having carriers of a conductive type different from that of the base 1 or an insulating semiconductor layer. As a result, as indicated by a broken line arrow a in the drawing, a leak current leaking from the first conductivity type cladding layer 5 on the ridge 2 to the current block layer 9 is generated, and the first conductivity type cladding layer 6 in the groove 3 is generated. , The second conductive type first cladding layer 7, the current blocking layer 9, and the second conductive type second cladding layer 10 are turned on, the substrate 1, the semiconductor layer 4, the first conductive layer 4 P-type cladding layer 6 of the second conductivity type and the cladding layer 7 of the second conductivity type
Since the npn thyristor is configured, as shown by the broken line arrow b, the flow from the substrate 1 to the semiconductor layer 4, the first conductivity type clad layer 5, and the second conductivity type clad layer 7 is larger than that. It is possible to reliably avoid the occurrence of a leak current.

Therefore, even if a large operating current is applied to the ridge 2 and a certain amount of leak current is generated on the ridge 2, the thyristor structure can be stably maintained in the groove 3. It is possible to reliably prevent the generation of a larger leak current.

[0014]

EXAMPLE 1 An example of a semiconductor laser of the present invention will be described in detail below with reference to the sectional view of FIG. 1 and the manufacturing process drawings of FIGS. 2A to 2C showing the manufacturing method thereof for easy understanding. To do. In this case, A
An example of an lGaAs type III-V group semiconductor laser will be shown.

In FIG. 1, reference numeral 1 denotes a base made of n-type GaAs or the like. A <011> crystal axis, for example, of a <1001> crystal axis, for example, on a {100} crystal face of the base 1, for example, a main surface 1S made of a (100) crystal face [011] Ridge 2 extending in the crystal axis direction
Are formed. A semiconductor layer 4 of a conductivity type different from that of the substrate 1, that is, p-type GaAs or AlGaAs in this case, is formed on the both sides 2S of the ridge 2 and on the bottoms of the grooves 3 on both sides of the ridge 2. .. On top of this, a clad layer 5 made of AlGaAs or the like of the first conductivity type, an active layer 6 made of intrinsic GaAs, etc. are sequentially formed.
Further, a first conductivity type cladding layer 5 and an active layer 6 are formed on the ridge 2 by sequentially depositing a first conductivity type cladding layer 7 of a second conductivity type such as p-type AlGaAs.
And the second clad layer 7 of the second conductivity type
1} B crystal plane In this case, the epitaxial growth layer 20 having a triangular cross section surrounded by the inclined surfaces 8a and 8b made of the (111) B crystal plane is formed.
Further, for example, n-type Al is formed on the conductivity type first cladding layer 7.
A current blocking layer 9 made of GaAs or the like and a second conductivity type second clad layer 1 made of p-type AlGaAs or the like in this case.
A cap layer 11 of 0, p-type GaAs or the like is sequentially deposited to form a semiconductor laser.

A method of manufacturing such a semiconductor laser is shown in FIG.
This will be described with reference to A to C. First, as shown in FIG. 2A,
For example, it extends in the [011] crystal axis direction, in this case, the direction orthogonal to the paper surface of FIG. 2A, on the main surface 1S made of, for example, the (100) crystal plane of the substrate 1 made of the first conductivity type, for example, n-type GaAs. The ridge 22 is formed by etching, for example, in an inverted mesa shape. Although not shown, this etching is performed by application of photolithography or the like using, for example, a hydrochloric acid-based or ammonia-based wet etching solution. Then, for example, p-type GaA is entirely covered to cover the ridge 2.
of the semiconductor layer 4 made of s or AlGaAs
OCVD method, that is, methyl-based MOCV using materials such as trimethylaluminum, trimethylgallium, and arsine
Epitaxial growth is performed by the D method. In this case, on both side surfaces 2S of the ridge 2, a surface 4F composed of {011} crystal faces is formed.
Occurs spontaneously, and the semiconductor layer 4 epitaxially grows on this surface 4F and on the surface along the (100) surface of the bottom of the groove 3. On the other hand, on the ridge 2, the {111} B crystal planes forming an angle of about 55 ° from the both edges of the ridge 2 with respect to the main surface 1S, in this case, the slopes 8a and 8b made of the (111) B crystal planes are spontaneously generated. Occurs in.

This is because once the conventional methyl-based MOCVD method is used, epitaxial growth is unlikely to occur on the above-mentioned {111} B crystal plane.
This is because when the 1} B crystal plane is generated, the ridge 2 and the groove 3 are separated from each other and epitaxially grown.

In this way, by selecting the extending direction of the ridge 2 and the crystal plane of the main surface 1S of the substrate 1, the ridge 2 and the side surfaces 2S of the ridge 2 and the groove 3 are mutually separated. The semiconductor layer 4 can be adhered and formed by dividing.

Next, as shown in FIG. 2B, this semiconductor layer 4 is formed.
For example, a liquid photoresist 21 is applied to cover the semiconductor layer 4 in the groove 3 only, and etching is performed using the photoresist 21 as a mask to form the ridge 2.
Only the upper semiconductor layer 4 is removed by etching.

After this, as shown in FIG. 2C, normal SDH
Similar to the semiconductor laser having a structure, for example, an n-type clad layer 5 made of AlGaAs or the like, an active layer 6 made of GaAs or the like, and a p-type first clad layer 7 made of AlGaAs or the like are sequentially epitaxially grown by a methyl-based MOCVD method. To do. At this time, by appropriately selecting the width of the ridge 2 and the film thickness of each of the layers 5, 6 and 7, each of these layers 5, 6 and 7 is surrounded on both sides by slopes 8a and 8b composed of (111) B crystal planes. The epitaxial growth layer 20 having a triangular cross section can be formed. Then, in the groove 3, the thickness of the p-type first cladding layer 7 is appropriately selected, and the upper surface of the first cladding layer 7 is formed on both slopes 8 of the active layer 6 on the ridge 2.
It is formed so as to be located below the end faces facing a and 8b, and is made of n-type AlGaAs or the like on the clad layer 7,
Current blocking layer 9 having a smaller refractive index than the active layer 6
Are epitaxially grown so that the current blocking layer 9 abuts both end faces of the active layers 6.

Then, as shown in FIG. 1, thereafter, a p-type second cladding layer 10 is epitaxially grown. At this time, epitaxial growth does not occur on both slopes 8a and 8b in the initial stage, but as growth in the groove 3 progresses, a face other than the (111) B crystal face occurs at the abutting portion, so that the p-type second The cladding layer 10 covers the epitaxial growth layer 20 and grows over the entire surface.

After that, although not shown, the semiconductor laser of the present invention can be obtained by depositing electrodes made of Al or the like on the cap layer 11 and the back surface of the substrate 1 by vapor deposition, sputtering or the like.

With this structure, the end faces of the epitaxial layer 20 on the ridge 2 facing the two slopes 8a and 8b of the active layer 6 are sandwiched by the current block layers 9 having a smaller refractive index, that is, An SDH type semiconductor laser can be obtained in the same manner as in the conventional case by laterally confining it so as to form a light emitting operation region. Moreover, in this embodiment of the present invention, the pn-layer formed by the second conductivity type first cladding layer 7, the first conductivity type cladding layer 5, the semiconductor layer 4 and the substrate 1 is formed below the current blocking layer 9. A pn thyristor structure is formed so that the current in the thyristor structure is blocked. That is, in this case, even if the leakage current shown by the broken line arrow a occurs from the first conductivity type cladding layer 5 on the ridge 2 to the current blocking layer 9 in the groove 3 and the current blocking layer 9 is turned on, Due to the thyristor structure, it is possible to reliably prevent generation of a large leak current from the substrate 1 to the layers 4, 5 and 7 in the groove 3 as indicated by the broken line arrow b.

Therefore, even if a large operating current is applied to the ridge 2 and a certain amount of leak current is generated on the ridge 2, the thyristor structure can be stably maintained in the groove 3, It is possible to reliably prevent the generation of a larger leak current.

Embodiment 2 With reference to the schematic enlarged sectional view of FIG. 3, an explanation will be given together with an example of a manufacturing method for facilitating the understanding thereof. In FIG.
Portions corresponding to those in FIG. 1 are designated by the same reference numerals, and duplicate description will be omitted. Although the groove 3 on both sides of the ridge 2 on the substrate 1 has a large width and the ridge 2 is provided substantially isolated on the substrate 1 in the first embodiment, this example has been described. In the case of forming the ridge 2 by etching, the grooves 3 on both sides are formed by etching with a required width.
The case where the step portion 22 having the main surface 1S extending in parallel to the ridge 2 is provided on both outer sides, that is, on the left and right in FIG.

Also in this example, AlGaAs III-
In an example of a group V compound semiconductor laser, a <011> crystal axis is applied to the {100} crystal plane of a substrate 1 made of n-type GaAs or the like on the main surface 1 made of, for example, a (100) crystal plane by photolithography or the like. Ridge 2 extending in the direction of, for example, the [011] crystal axis, and grooves 3 on both sides of the ridge 2 are formed by patterning with a required width using a wet etching solution such as hydrochloric acid-based solution or ammonia-based solution. Similar to the ridge 2, the case is shown in which the step portion 22 having the main surface 1S made of the (100) crystal plane is provided.

Also in this case, both side surfaces 2 of the ridge 2
S, the two immediate surfaces 22S of the step inside the groove 3 are surrounded by a semiconductor layer 4 made of GaAs or the like having a conductivity type different from that of the base body 1, for example, p-type GaAs. Similar to the first embodiment, the entire surface is epitaxially grown by the ordinary methyl-based MOCVD method and is divided into the ridge 2, the step portion 22, and the groove 3 to grow, and then, for example, a liquid photoresist is applied. Mask only the groove 3
It can be formed by etching away only the epitaxial layer on the ridge 2 and the step portion 22.

Then, the first layer is entirely formed on the semiconductor layer 4.
A clad layer 5 made of AlGaAs or the like having a conductivity type, an active layer 6 made of GaAs or the like, a second conductivity type such as p
Type AlGaAs or other second clad layer 7 and n-type AlGaAs or other current blocking layer 9 are sequentially epitaxially grown by the methyl-based MOCVD method.
1) Form an epitaxial growth layer 20 having a triangular cross section surrounded by slopes 8a and 8b composed of B crystal planes. In this case, the groove 2 is also formed on both the step portions 22 by the inclined surface 8 formed of the (111) B crystal plane extending from the edge of the groove 3.
The epitaxial growth layer 30 is formed separately from the inside.

Also in this case, by appropriately selecting the width and height (depth) of the ridge 2 and each groove 3, and the thickness of each layer 5, 6 and 7, the current blocking layer to be deposited thereon is formed. 9 can cover the end faces of the active layer 6 of the epitaxial growth layer 20 facing both the inclined surfaces 8a and 8b.

Also in this case, a second conductivity type second clad layer 10 of AlGaAs or the like and a cap layer 11 of p type GaAs or the like in this case are formed on the current blocking layer 9. Sequentially grow epitaxially. Similar to the first embodiment, the second cladding layer 10 does not grow on the slopes 8a, 8b and 8 in the initial stage, but as the growth proceeds, the second cladding layer 10 is formed at the abutting portion (11
1) The faces other than the B crystal face grow and are grown entirely.

Although not shown, this cap layer 11
The semiconductor laser of the present invention can be obtained by depositing electrodes made of Al or the like on the upper surface and the back surface of the substrate 1 by vapor deposition, sputtering or the like.

With such a structure, the groove 3
In the figure, the base 1, the semiconductor layer 4, the clad layer 5 of the first conductivity type, and the clad layer 7 of the second conductivity type are used as p-n-p.
A -n thyristor structure can be obtained, and even if a leak current leaking from the substrate 1 through the first conductivity type cladding layer 5 on the ridge 2 to the current block layer 9 is generated and the current block layer 9 is turned on, It is possible to reliably avoid generation of a large leak current in the groove 3.

Therefore, even when a large operating current is applied to the ridge 2 and a certain amount of leakage current is generated on the ridge 2, the thyristor structure can be stably maintained in the groove 3, It is possible to reliably prevent generation of a large leak current.

Further, in this case, since a so-called W-shaped ridge structure is provided in which the step portions 22 are provided on both sides of the ridge 2 with the groove 3 interposed therebetween, the epitaxial growth layer 30 formed on the step portions 22 is the epitaxial growth layer on the ridge 2. The surface of the cap layer 11 which is deposited at the same height as 20 and which is finally obtained can be formed as a substantially flat surface except for the concave portion formed by following the shape of the groove 3. When the surface is flattened in this manner, the upper surface of the semiconductor laser can be fixed to the heat sink as it is, so that heat can be efficiently radiated as compared with the semiconductor laser having the conventional SDH configuration. Has the advantage.

In each of the above-mentioned examples, when etching each ridge 2 and groove 3, wet etching of hydrochloric acid type or ammonia type is performed as an etching solution,
The case where a so-called inverted mesa-shaped ridge 2 or step portion 22 is formed in which the width of the ridge 2 becomes gradually smaller as it becomes deeper from the main surface 1S is shown. For example, a sulfuric acid-based wet etching solution is used to form the ridge 2. Various configurations can be adopted, such as forming a so-called forward mesa-shaped ridge 2 or step portion 22 whose width gradually increases as it becomes deeper from the main surface 1S.

Further, in each of the above-described examples, the case where the semiconductor layer 4 made of GaAs or the like having a conductivity type different from that of the substrate 1 is formed on both sides of the ridge 2 and in the groove 3 is shown. However, the semiconductor layer 4 may be made of intrinsic or insulating GaAs or the like.

Furthermore, in each of the above examples, AlGaA
The case of obtaining an s-based III-V group semiconductor laser has been shown.
The semiconductor laser of the present invention can use other InP-based materials, and can adopt various material configurations such as the conductivity types being opposite to those shown in the drawing.

[0038]

As described above, in the semiconductor laser of the present invention, by adopting the SDH type structure, the end faces of the active layer 6 facing both slopes 8a and 8b are formed into the current blocking layer 9 having a smaller refractive index than that. It is covered and laterally confined, and both side surfaces of the ridge 2 and the inside of the groove 3 are surrounded by a semiconductor layer 4 of a conductive type or an insulating type different from that of the base body 1. Even if the current blocking layer 9 is turned on due to a leak current flowing from the one conductivity type cladding layer 5 through the current blocking layer 9 to the second conductivity type second cladding layer 10, the base 1 and the semiconductor layer 4, a thyristor configuration including the first conductivity type cladding layer 5 and the second conductivity type first cladding layer 7 can prevent a large leak current from flowing there.

Therefore, even if a large operating current is applied to the ridge 2 and a certain amount of leak current is generated on the ridge 2, the thyristor structure can be stably maintained in the groove 3, It is possible to reliably prevent generation of a large leak current.

When a so-called W-shaped ridge structure in which the step portions 22 are provided on both sides of the ridge 2 with the groove 3 interposed therebetween,
As described above, since the upper surface of the cap layer is substantially flattened, it is possible to perform the planar treatment. For example, the upper surface can be directly bonded to the heat sink, and the heat dissipation efficiency can be improved.

[Brief description of drawings]

FIG. 1 is an enlarged schematic cross-sectional view of an example of a semiconductor laser of the present invention.

FIG. 2 is a manufacturing process diagram of an example of a semiconductor laser of the present invention.

FIG. 3 is a schematic enlarged cross-sectional view of another example of the semiconductor laser of the present invention.

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Base | substrate 2 Ridge 2S Side surface 3 Groove 4 Semiconductor layer 5 1st conductivity type cladding layer 6 Active layer 7 2nd conductivity type 1st cladding layer 8 Slope 8a Slope 8b Slope 9 Current block layer 10 2nd conductivity type 1st 2 Clad layer 11 Cap layer 20 Epitaxial growth layer 30 Epitaxial growth layer

Claims (1)

[Claims] 1. A ridge extending in the <011> crystal axis direction of this substrate is formed on a substrate having a {100} crystal plane as a main surface, and at least a first conductivity type is formed on the ridge by vapor phase epitaxy. The clad layer, the active layer, the second conductive type clad layer, and the current blocking layer are grown so that a slanted surface composed of {111} B crystal planes extending from both end edges of the ridge appears. A semiconductor laser comprising a semiconductor layer having a carrier of a conductivity type different from that of the base or an insulating semiconductor layer provided on both side surfaces of the ridge and groove bottom portions on both sides.