JP3035979B2 - Semiconductor laser - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in the following order.

A Industrial Fields B Overview of the Invention C Prior Art D Problems to be Solved by the Invention E Means for Solving the Problems F Action G Example H Effects of the Invention A Industrial Field of Application The present invention relates to semiconductors. Lasers, especially for example AlGaInP or GaI
Embedded heterojunction type (BH
Type) semiconductor laser.

B SUMMARY OF THE INVENTION The present invention provides a compound semiconductor having stripe-shaped mesa protrusions formed on one main surface thereof, a compound semiconductor layer on each of the main surfaces, at least a cladding layer of the first conductivity type, and an active layer. And a second conductivity type clad layer are sequentially epitaxially grown, and separated from the others on the stripe-shaped mesa projection by a first conductivity type clad layer, an active layer, and a second conductivity type clad layer. Is formed, and a semi-insulating compound semiconductor layer and a contact layer of the second conductivity type are sequentially epitaxially grown by embedding the stripe-shaped epitaxial growth layer grown on the mesa projections. An impurity of the second conductivity type is selectively introduced into a position corresponding to the stripe-shaped epitaxial growth layer of the conductive compound semiconductor layer, By second conductivity type cladding layer and a second conductivity type contact layer is formed by electrically conductive, balance a reduction in the threshold current I _th by suppressing the leakage current, improving the properties.

C Prior Art As a semiconductor laser having a low threshold current I _th ,
There are buried heterojunction (BH) semiconductor lasers that confine light and carriers in the lateral direction of the active layer, that is, in the direction orthogonal to the plane direction of the active layer.

When manufacturing this type of BH semiconductor laser, a double heterostructure is generally formed by sequentially epitaxially growing a first conductivity type cladding layer, an active layer, and a second conductivity type cladding layer in the first crystal growth. Then, etching is performed across the active layer to form stripe-shaped protrusions including a stripe-shaped active layer, so-called ridges, and then, on both sides of the ridges in a second crystal growth, a BH-type semiconductor laser is obtained. Is adopted.

However, according to this method, in the operation of removing a part of the active layer by the etching, the remaining end face of the active layer itself is oxidized, which has a great adverse effect on characteristics and reliability.

For the purpose of avoiding such problems of characteristics and reliability and further complicating workability, the applicant of the present invention was able to form all layers in one epitaxial growth as described in, for example, JP-A-61-183987. SDH (Separ
ate Double Hetero Junction) type semiconductor laser.

D. Problems to be Solved by the Invention Further, the applicant of the present invention has proposed, in Japanese Patent Application No. 63-330136, such a semiconductor laser as shown in FIG. did. This is because, for example, a GaAs compound semiconductor substrate (11) of the first conductivity type, for example, n-type and one principal plane having a (100) crystal plane, the [100] crystal axis direction orthogonal to the paper plane in FIG. Stripe-shaped mesa protrusions (2) are formed extending on the main surface of the substrate (11) having the protrusions (2).
By D (Metal Organic Chemical Vapor Deposition), that is, a metal-based MOCVD, a first conductivity type, for example, an n-type cladding layer (3) and a low impurity concentration or undoped active layer (4) are continuously formed. ) And a second conductive type, for example, a p-type first cladding layer (1).
5) and a current blocking layer of the first conductivity type, for example, n-type (16)
And a second cladding layer (17) of a second conductivity type, for example, a p-type.
And the second conductive type cap layer (18) has one semiconductor layer.
It is formed by multiple epitaxial growths.

Here, the first conductive type clad layer (3), the second conductive type first and second clad layers (15) and (17),
The conductive type current blocking layer (16) 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 (11) and the mesa protrusion (2), the width and height of the protrusion (2), ie, the depth of the mesa groove on both sides thereof, and the first conductivity type clad layer (3) , The active layer (4) and the second conductive type first clad layer (15) by selecting the thickness of each layer, the first conductive type clad layer (3) on the mesa protrusion (2), The active layer (4) and the second conductive type first cladding layer (15) are formed with a slope by a slope (9) so as to be separated from those on the mesa groove, and the stripe separated by the slope (9) is formed. The epitaxial growth layer (10) is formed on the mesa protrusion (2). This is a normal MOCV
D, that is, in the case of MOCVD using a methyl-based organic metal as a source gas, once a (111) B crystal is formed, it is difficult to cause epitaxial growth on this surface. To form. In this case, the current block layer (16) is divided on both sides by the stripe-shaped epitaxial growth layer (10), and both end faces generated by the division are separated from the other in the stripe-shaped epitaxial growth layer (10). The both sides of the striped active layer (4), that is, the end faces facing the slope (9) are abutted.

In this way, the active layer (4) in the stripe-shaped epitaxial growth layer (10) on the mesa projection (2) is formed so as to be sandwiched by the current blocking layer (16) having a smaller refractive index, and the lateral confinement is performed. The current blocking layer (16) allows the second cladding layer (17) of the second conductivity type to be formed on both sides of the stripe-shaped epitaxial growth layer (10). A pnpn thyristor is formed by the block layer (16), the second conductive type first clad layer (15), and the first conductive type clad layer (3), and the current flowing therethrough is reduced. There is blocked, thereby being made so that the current is concentrated in the active layer (4) of the mesa projection (2) striped epitaxial layer on (10), a reduction in threshold current I _th I have to mow so.

However, in the case of the above-mentioned SDH structure, as shown by a broken line arrow in FIG. 2, the stripe-shaped epitaxial growth layer (10) passes through the current blocking layer (16) from the second conductivity type second cladding layer (17). operation active layer as a region (4) first cladding layer below (3) that is considered leakage current flows, which may inhibit the reduction in adequate I _th. Further, this leakage current triggers the above-mentioned thyristor to be turned on, and by turning on the thyristor, the characteristic which should be shown by a broken line is shown by a solid line as shown in the light output-current characteristic curve diagram in FIG. Thus, the problem of exhibiting the saturation characteristic occurs.

The present invention prevents the thyristor from being turned on by the leakage current generated through the current blocking layer in the SDH semiconductor laser as described above, and improves the saturation of the optical output characteristics.

E Means for Solving the Problems FIG. 1 is a schematic enlarged cross-sectional view of a main part of a semiconductor laser according to the present invention.

According to the present invention, at least one stripe-shaped mesa projection (2) is formed on one main surface (1A) of a compound semiconductor (1), and at least one compound semiconductor layer is formed on the main surface (1A) side of the compound semiconductor (1). A first conductivity type clad layer (3), an active layer (4), and a second conductivity type clad layer (5) are sequentially epitaxially grown and separated from the others on the stripe-shaped mesa projections (2). The first conductivity type cladding layer (3)
, An active layer (4), and a second conductive type clad layer (5) laminated on a striped epitaxial growth layer (10)
The semi-insulating compound semiconductor layer (6) and the second conductivity type contact layer (7) are sequentially epitaxially grown by embedding the striped epitaxial growth layer (10) grown on the mesa protrusion (2). An impurity of the second conductivity type is selectively introduced into the semi-insulating compound semiconductor layer (6) at a position corresponding to the stripe-shaped epitaxial growth layer (10), and the second conductivity type clad layer (5) is formed. And the second conductivity type contact layer (7) are electrically connected.

F function As described above, according to the present invention, in the SDH type semiconductor laser, since the lateral buried layer of the active layer is constituted by a semi-insulating compound semiconductor layer, each compound semiconductor such as a current blocking layer is conventionally used. Does not adopt a thyristor structure composed of layers.

Therefore, a leakage current does not flow through the current blocking layer and the like to the first conductivity type cladding layer below the active layer as an operation region during the light emission operation, and it is possible to avoid an increase in I _th . Further, it is possible to prevent such a leak current from being a trigger for turning on the thyristor, thereby improving the saturation and obtaining a good light output characteristic.

The formation of the semi-insulating compound semiconductor layer is performed, for example,
When a semiconductor laser is manufactured using an InP substrate, a semi-insulating compound semiconductor layer can be easily formed using an InP layer doped with iron (Fe). Therefore, when this semiconductor laser is manufactured by MOCVD, it can be manufactured by one crystal growth.

Further, in the above semiconductor laser, when the p-type contact layer is made of an organic arsenic material such as triethyl arsenic or trimethyl arsenic material without using arsine AsH ₃ , As
It is possible to avoid inactivation of the acceptor in the p-type cladding layer by the H group in H ₃ , thereby reducing the resistance between the p-type contact layer and the active layer and controlling the p-type carrier. , And the characteristics can be improved.

Further, as the organic arsenic raw material, if a raw material having an H group such as diethylarsine and tertiarybutylarsine and having a low decomposition temperature is used, the semiconductor laser can be used without inactivating the acceptor by the H group. Can be made.

Further, in this case, since the organic arsenic material is used only for growing the p-type contact layer, even if a material having low purity is used, adverse effects such as a change in characteristics due to impurities and a decrease in device reliability may be exerted. And a highly reliable semiconductor laser can be manufactured.

G Example Hereinafter, an example of a semiconductor laser according to the present invention will be described in detail with reference to the cross-sectional view of FIG.

In the case of manufacturing a GaInAsP-based III-V compound semiconductor laser, first, as shown in FIG. 1, a compound semiconductor (1) such as a first conductivity type, for example, an n-type InP substrate is provided. The compound semiconductor (1) has one principal surface (1A) formed of a (100) crystal plane, and both side surfaces (23) are gently curved concave surfaces on the main surface (1A) of the compound semiconductor (1). Then, a stripe-shaped mesa protrusion (2) close to the normal mesa is formed.

In the method of forming the mesa projection (2), for example, an etching mask on a stripe is selectively formed with a required width w on the main surface (1A) of the compound semiconductor (1). This mask can be formed, for example, by applying a photoresist film, pattern exposure, and development. In this case, the plane along the paper surface is selected as the (011) plane, and the extending direction of the mask stripe is selected in a direction perpendicular to this plane. Next, with respect to the compound semiconductor (1), H ₂ SO ₄ , H ₂ O _2, and H ₂ O, for example, a sulfuric acid-based etchant were mixed at a ratio of 3: 1: 1 from the surface (1A) side. Perform crystallographic etching with an etchant.
In this case, the etching proceeds from a portion not covered by the mask to form a mesa groove (22),
The above-mentioned mesa projection (2) can be obtained.

Thereafter, the etching mask is removed, and an n-type buffer layer (not shown) is formed on the uneven surface of the compound semiconductor (1) by MOCVD (not shown) if necessary.
A first conductivity type cladding layer (3) of InP or the like is epitaxially grown. In this case, as the epitaxial growth progresses, a slope (9) composed of a (111) B crystal plane at an angle of about 55 degrees with respect to the (100) plane is spontaneously formed on both sides on the upper surface of the mesa projection (2). Come up. Then, the epitaxial growth of the n-type cladding layer (3) is stopped in a state where the slope (9) due to the (11) B plane exists. Subsequently, an active layer (4) made of undoped GaInAsP is epitaxially grown by continuous MOCVD, including an n-type cladding layer (3) having a trapezoidal cross section on the mesa projection (2).

In this case, since an epitaxially grown layer by MOCVD is unlikely to be formed on the (111) B crystal plane of the slope (9), the active layer (4) hardly grows on the slope (9), and It can be selectively formed only on the projection (2) and on the bottom surface of the mesa groove (22) on both sides thereof.

Next, a second semiconductor layer made of, for example, InP is formed on the compound semiconductor (1).
A conductive type, for example, a p-type cladding layer (5) is epitaxially grown by MOCVD. In this case, the growth of the p-type cladding layer (5) proceeds to grow the p-type cladding layer (5) to a position where the slopes (9) on both sides of the mesa projection (2) cross each other. On the groove (22), the p-type clad is formed so that both side surfaces (23) of the mesa protrusion (2) are buried, and particularly so as not to contact the end surface of the active layer (4) on the stripe-shaped epitaxial growth layer (10). Grow layer (5).

Thus, on the mesa protrusion (2) of the compound semiconductor (1), the first conductivity type, that is, the n-type cladding layer (3), the active layer (4), and the second conductivity type, that is, the p-type cladding layer ( 5) is formed to form a striped epitaxial growth layer (10).

Thereafter, a semi-insulating compound semiconductor layer (6) made of, for example, InP doped with iron Fe is epitaxially grown by MOCVD. This doping of Fe is, for example, ferrocene Fe
By adding (C ₅ H ₅ ) ₂ to the organic compound raw material of InP, it can be continuously performed by MOCVD. In this case, the semi-insulating compound semiconductor layer (6) does not grow on the slope (9) initially, but (11)
1) When a crystal plane other than the B plane is generated, it grows over the entire surface including the slope (9).

Then, a p-type contact layer (7), that is, a cap layer is entirely formed on the semi-insulating compound semiconductor layer (6) which entirely covers the stripe-shaped epitaxial growth layer (10) on the mesa projection (2). Is formed.

This p-type contact layer (7) contains As, for example.
Made of GaInAsP or InGaAs, etc.
It is formed using triethyl arsenic or trimethyl arsenic having no group, or diethyl arsine, tertiary butyl arsine or the like having an H group but having a low decomposition temperature. Since the arsenic material in this case is used only for forming the p-type contact layer (7), even if a relatively low-purity material is used,
An element semiconductor laser having high reliability as before can be formed without affecting various characteristics of the semiconductor device.

Thereafter, the second conductivity type, ie, p-type, is placed on the p-type contact layer (7) at a position corresponding to the stripe-shaped epitaxial growth layer (10) of the semi-insulating compound semiconductor layer (6).
An impurity of a type such as Zn is selectively introduced to form an impurity introduction layer (8), and the p-type cladding layer (5) and the p-type contact layer (7) are electrically connected.

Although not shown, p including the impurity introduction layer (8) is used.
Electrodes are ohmic-coated on the mold contact layer (7) and on the back surface of the compound semiconductor (1), respectively, to obtain a semiconductor laser (30) according to the present invention.

Here, each layer (3), (4), (5), (6),
(7) can be formed by one operation, that is, one crystal growth, by switching the supplied source gas by a series of MOCVD.

In the above example, the cladding layers (3) and (5) of each conductivity type are respectively composed of InP, the active layer (4) is composed of GaInAsP, and the contact layer (7) is composed of GaInAsP. May be variously configured, for example, by using GaInAs.

Incidentally, if necessary, the optical waveguide layer can be formed by continuous MOCVD in contact with the active layer (4).

The conductivity type of each layer may be the conductivity type opposite to that shown in the figure. However, especially when the above-mentioned contact layer (7) containing arsenic is p-type, organic arsenic having no H group is used. By forming a p-type contact layer (7) using a raw material or a raw material such that the H group does not cause inactivation of the acceptor due to its low decomposition temperature, the p-type contact layer (7 ) And the active layer (4), a semiconductor laser with small resistance and good control of p-type carriers can be obtained.

H Effect of the Invention As described above, according to the present invention, in the SDH type semiconductor laser, the lateral buried layer of the active layer (4) is constituted by the semi-insulating compound semiconductor layer (6). A thyristor structure composed of each compound semiconductor layer such as a current block layer is not used.

Therefore, a leakage current does not flow through the current blocking layer or the like to the first conductivity type cladding layer below the active layer (4) as an operation region through the current blocking layer or the like, and it is possible to avoid an increase in I _th . Further, it is possible to prevent such a leak current from being a trigger for turning on the thyristor, and it is possible to obtain good light output characteristics.

The formation of the semi-insulating compound semiconductor layer (6)
For example, when manufacturing a semiconductor laser using an InP substrate,
The semi-insulating compound semiconductor layer (6) can be easily formed by the InP layer doped with iron Fe. Therefore MOCV
When this semiconductor laser is manufactured by D, it can be manufactured by one crystal growth.

Further, in the semiconductor laser of the present invention, when the p-type contact layer is made of an organic arsenic material such as triethyl arsenic or trimethyl arsenic without using arsine AsH ₃ , the acceptor in the p-type cladding layer by the H group is formed. Inactivation can be avoided, and characteristics can be improved by lowering the resistance between the p-type contact layer and the active layer and improving controllability of the p-type carrier.

As the organic arsenic raw material, if a raw material having an H group such as diethylarsine and tertiarybutylarsine but having a low decomposition temperature is used, a semiconductor laser can be manufactured without the H group inactivating the acceptor. can do.

Further, in this case, since the organic arsenic raw material is used only for growing the p-type contact layer, a highly reliable element can be manufactured even if a raw material having low purity is used.

[Brief description of the drawings]

FIG. 1 is a schematic enlarged sectional view showing an example of a semiconductor laser according to the present invention, FIG. 2 is an enlarged schematic sectional view showing an example of a conventional semiconductor laser, and FIG. 3 is a light output of the conventional semiconductor laser. It is a characteristic curve figure which shows a characteristic. (1) is a compound semiconductor, (1A) is a main surface, (2) is a mesa protrusion, (22) is a mesa groove, (23) is a side surface, (3) is a first conductivity type cladding layer, and (4) is An active layer, (5) a second conductivity type cladding layer, (6) a semi-insulating compound semiconductor layer,
(7) is a contact layer of the second conductivity type, (8) is an impurity introduction layer, (9) is a slope, (10) is a stripe-shaped epitaxial growth layer, (11) is a substrate, and (15) is a second conductivity type. First
(16) is the current blocking layer, (17) is the second
The conductive type second clad layer, (18) is a cap layer, (3
0) is a semiconductor laser.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H01S 5/00-5/50

Claims (1)

(57) [Claims] 1. A semiconductor device comprising: a main surface of a compound semiconductor having stripe-shaped mesa protrusions formed thereon; a cladding layer of at least a first conductivity type comprising a compound semiconductor layer on each of the main surfaces of the compound semiconductor; A cladding layer of the second conductivity type is sequentially epitaxially grown and separated from the others on the stripe-shaped mesa projections, the cladding layer of the first conductivity type, the active layer, and the cladding layer of the second conductivity type. Are formed, and a semi-insulating compound semiconductor layer and a contact layer of the second conductivity type are sequentially epitaxially grown by embedding the stripe-shaped epitaxial growth layer grown on the mesa protrusion. An impurity of the second conductivity type is selectively guided to a position of the insulating compound semiconductor layer corresponding to the stripe-shaped epitaxial growth layer. Is, the semiconductor laser, characterized in that said second conductivity type cladding layer and the second conductive type contact layer is formed by electrically conductive.