JP3246066B2 - Semiconductor laser - Google Patents

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 in which a current is confined in a lateral direction of an active layer and a threshold current is reduced.

[0002]

2. Description of the Related Art As a semiconductor laser having a low threshold current, an SDH (Separated Double Hetero junction) type semiconductor laser which can be formed by a single crystal growth operation is disclosed in Japanese Patent Application No. Kaisho 61-183987
And Japanese Patent Laid-Open Publication No. 2-174287.

As shown in a schematic enlarged cross-sectional view of one example of this SDH type semiconductor laser in FIG. 2, a substrate 1 of a first conductivity type, for example, a p-type and a main surface 1S of which is a {100} crystal plane. A ridge 2 extending in the <011> crystal axis direction is formed thereon, and the entire surface including the ridge 2 is of the first conductivity type by methyl MOCVD (chemical vapor deposition method using an organic metal). a p-type cladding layer 3, an active layer 4, a second conductivity type, for example, an n-type first cladding layer 5, a current blocking layer 7, a second conductivity type, ie, an n-type second cladding layer 8, and a contact layer 9; Is epitaxially grown.

At this time, as described above, the main surface 1 of the substrate 1
When the crystal plane of S and the extending direction of the ridge 2 are selected, {111} B which is naturally generated from both side edges of the ridge 2 and forms approximately 54.7 ° with respect to the main surface 1S is formed.
An epitaxial layer having a triangular cross section sandwiched between the inclined surfaces 6A and 6B made of crystal planes grows, and is separated from the epitaxial layers growing in the grooves 2A on both sides of the ridge 2.

[0005] This is based on the fact that when MOCVD is performed using a normal or methyl-based organic metal as a source gas, once a {111} B crystal plane is formed, epitaxial growth is unlikely to occur on this plane. is there.

Further, by appropriately selecting the thickness of each layer, the active layer 4 having a triangular cross section on the ridge 2 is formed.
Is sandwiched between the current blocking layers 7 growing on both side grooves of the ridge 2 in the lateral direction, that is, the slope 6A of the active layer 4.
And 6B, the current block layer 7 can be configured to abut near the end face. Thereby, the active layer 4
The semiconductor laser in which the current is confined spontaneously in the lateral direction can be formed with good crystallinity by one crystal growth without forming the lateral end face of the semiconductor laser by etching or the like. Further, in this case, an npnp thyristor can be formed on the groove 2A, the current there is blocked, and the threshold current can be reduced.

Incidentally, when such an SDH semiconductor laser is actually incorporated into a semiconductor laser device such as an optical system, for example, as shown in a side view of FIG. The semiconductor laser 2 is mounted on the heat sink 20 with
One end face of the heat sink 20, that is, the end face on the side from which the emitted light L ₁ is obtained, is fixedly arranged by the solder 23 or the like along the end face of the heat sink 20. 22 shows a photodetector for detecting light L ₂ from the rear.

In a semiconductor laser having a configuration formed on a ridge like the above-described SDH type semiconductor laser, when the surface convex portion on the ridge is buried in the solder 23, the light emitting point also sinks in the solder 23. In some cases. In particular, if vignetting of the emitted light occurs due to the swelling of the solder 23 on the rear end surface side, there is a possibility that monitoring with the backward emitted light may not be performed with high accuracy.

On the other hand, S using a p-type substrate as described above
The DH type semiconductor laser has a p-type current blocking layer.
As described in Japanese Unexamined Patent Publication No. 322486, compared with the case of using an n-type substrate for forming an n-type current block layer,
When a mold substrate is used, generation of a leak current in the groove 2A can be more reliably prevented.

Considering the growth crystal plane of the epitaxial growth layer grown in the trench 2A, a {311} B crystal plane region 11 substantially consisting of a {311} B crystal plane near the ridge 2 and being separated from the ridge 2 A {100} crystal plane region 12 substantially consisting of a {100} crystal plane is formed on a flat surface in the formed groove 2A, and a higher-order crystal plane region 13 is formed between them. When the current blocking layer 7 is of p-type, the thickness of the higher-order crystal plane region 13 is particularly large compared to other portions when the current blocking layer 7 is of p-type. It depends on. Therefore, in this case, even if the thickness of the current blocking layer 7 itself is not relatively large,
A device capable of avoiding generation of a leak current in the vicinity of the higher-order crystal plane region 13, maintaining an npnp thyristor structure, and reliably reducing a threshold current. It is.

However, in a semiconductor laser using a substrate such as a p-type GaAs, the contact metal on the back side is A
An alloy metal such as uZn is used. These alloy-type metals have poor adhesion to the GaAs substrate,
Inconvenience also occurred in securing long-term reliability.

[0012]

On the other hand, it has been attempted to use a TiPtAu-based metal as a non-alloy type p-type contact metal. However, for this purpose, a p-type high concentration A so-called highly doped layer must be formed, and a step of diffusing a p-type impurity and a step of growing a crystal of the highly doped layer are indispensable, and it is difficult to apply a semiconductor laser to a p-type substrate.

According to the present invention, there is provided a semiconductor laser having a configuration formed on a ridge, which avoids vignetting of emitted light, facilitates incorporation into a device, and can be configured with a high yield. Improve productivity by reducing the number of manufacturing steps.

[0014]

According to the present invention, a stripe-shaped ridge extending in the <011> crystal axis direction is formed on a substrate having a {100} crystal plane as a main surface. At least a first conductive type clad layer, an active layer, a second conductive type clad layer, a current blocking layer, and a contact layer are epitaxially grown on the entire surface, and a slope having a {111} B crystal plane is provided on the ridge. The height of the bottom of the contact layer at a position away from the ridge is set to be smaller than the height of the active layer on the ridge at least from the bottom of the groove on both sides of the ridge, and The configuration is such that the height of the groove on the upper surface from the bottom surface is large.

Further, according to the present invention, in the above-mentioned structure, the thickness of the contact layer is set to 2 μm or more and less than 10 μm.

Further, the present invention provides the above-described configuration,
The substrate is p-type and its impurity concentration is 5 × 10 ¹⁸ cm ^−3.
The above is set to be less than 1 × 10 ²⁰ cm ⁻³ .

[0017]

According to the present invention, as described above, the contact layer 9 is formed on the bottom of the groove 2A on both sides of the ridge 2 as a reference.
Since the semiconductor laser is configured so that the position of the upper surface of the flat surface is higher than the position of the active layer 4, for example, when the upper part of the ridge 2 is mounted on the heat sink by so-called junction down with the bonding surface side as the bonding surface, The position of the light emitting point corresponding to the position of the active layer is set at a position sufficiently high from the upper surface of the heat sink, and it is possible to reliably avoid the vignetting of the emitted light due to the swelling of the solder and to provide such a semiconductor laser to the optical device. Yield when incorporating can be improved.

At this time, by setting the thickness of the contact layer 9 to about 2 μm to 10 μm, the position of the active layer can be optimized more reliably and without deteriorating the characteristics, and the device can be manufactured with higher yield. Can be embedded.

Further, in the present invention, the impurity concentration is 5 ×
A p-type substrate having a density of 10 ¹⁸ cm ⁻³ or more and less than 1 × 10 ²⁰ cm ⁻³ is used. By using such a high-concentration substrate, a contact metal can be easily deposited with a sufficiently low contact resistance value. It can be performed.

That is, a normal semiconductor laser is relatively small.
The area of the back side is 5 × 10 ^-Fourcm^TwoAbout
You. In general, is the backside of the substrate entirely an electrode?
Obtain enough area to form contact metal
be able to. To avoid deterioration of device characteristics,
Ohmic contact with electrode metal
Tact resistance is 1 × 10^-FourΩcm^TwoLess than
Is desirable.

As a result of intensive studies on the present invention and the like, when the ohmic metal is directly deposited by selecting the impurity concentration within the above range, it is possible to obtain a sufficiently low contact resistance of about 1 × 10 ⁻⁴ Ωcm ² or less. It turns out that it can be done.

Therefore, according to the present invention, the contact metal can be easily formed without forming a high-concentration surface region by diffusion or epitaxial growth and depositing a metal, or without performing a process such as alloying after vapor deposition of AuZn. Can be provided, and the productivity of the semiconductor laser can be improved.

[0023]

Embodiments of the present invention will be described below in detail with reference to the drawings. In this example, an AlGaAs III-V
A case in which a semiconductor laser using a group III compound is provided will be described.

A description will be given with reference to FIG. First, the concentration of a p-type impurity made of GaAs or the like is 5 × 10 ¹⁸ cm ⁻³ or more and 1 ×
Less than 10 ²⁰ cm ^-3 , in this example 5 × 10 ¹⁹ cm ^-3
Substrate 1 is prepared and its {100} crystal plane, for example, (1)
00) A ridge 2 extending in the <011> crystal axis direction, for example, the [011] crystal axis direction, is formed on the main surface 1S made of a crystal plane by applying photolithography or the like. That is, for example, although not shown, a resist pattern having an opening extending in the [011] crystal axis direction is formed by application of a photoresist and pattern exposure, and RIE (reactive ion etching), wet etching, or the like is performed using the resist as a mask. Form. At this time, the upper surface of the ridge 2 is made of a (100) crystal plane, and the main surface 1S
, The bottom flat surface is composed of a (100) crystal plane.

In FIG. 1, FIG.
The direction orthogonal to the paper surface of FIG. 1 is defined as the <011> crystal axis direction, and the direction indicated by the upward arrow z on the paper surface of FIG. 1 orthogonal to the main surface 1S is defined as the <100> crystal axis direction.

Then, the above-mentioned resist pattern was removed.
Thereafter, the entire surface of the ridge 2 is covered with a normal MOC.
VD, MOCV using methyl-based organic metal as source gas
D, the first conductivity type, that is, the p-type A
l_xGa_1-xA first made of As (eg, x = 0.45)
Clad layer 3, intrinsic Al_yGa_1-yAs (for example, y
= 0.14), the second conductive type, that is, the n-type
Al_xGa_1-xFirst cladding layer 5 made of As or the like, example
For example, p-type Al_xGa_1-xAs and n-type Al_xGa _1-xAs
And p-type Al_xGa_1-xCurrent block having a laminated structure with As
Lock layer 7, second conductivity type, that is, n-type Al_xGa_1-xAs
The second cladding layer 8 composed of
Lengthen.

At this time, (100) on the upper surface of the ridge 2
In this case, the inclined planes 6A and 6B composed of the (1-11) B crystal plane and the (11-1) B crystal plane of the {111} B crystal plane forming approximately 54.7 ° with respect to the crystal plane occur spontaneously, On the slopes 6A and 6B, since the epitaxial growth by the methyl MOCVD does not easily proceed, each layer 3,
4 and 5 are formed separately from each other on the ridge 2 and in the groove 2A.

By appropriately selecting the width and height of the ridge 2 and the thicknesses of the respective layers 3, 4 and 5, both sides of the n-type first cladding layer 5 on the active layer 4 can be formed during the growth. Are formed so that the inclined surfaces 6A and 6B intersect with each other, and an epitaxial layer having a triangular cross section composed of the respective layers 3, 4 and 5 can be formed on the ridge 2.

Further, in this case, the growth of the n-type first cladding layer 5 is performed so that the upper surface thereof is located on both side surfaces of the active layer 4 on the ridge 2, that is, on the lower layer side from both end surfaces facing both slopes 6A and 6B. And stop at this point, and as described above, p-type Al _x Ga _1-x As and n-type Al _x Ga _1-x
As, p-type Al _x Ga _{1 -x} As (for example, x = 0.45)
A current blocking layer 7 having a three-layer structure is epitaxially grown. In this case, in consideration of the film thickness of each laminated portion, the n-type Al _x Ga _{1 -x} As layer of the intermediate layer abuts at least the end faces of the active layer 4 on the ridge 2 facing both slopes over the entire thickness. Epitaxial growth.

As described in the above-mentioned Japanese Patent Laid-Open Publication No. 4-322486, the current block layer 7 having a three-layer structure is easily made n-type in the {311} crystal plane region along the ridge 2. Since a high-order crystal plane region between the region and the flat portion is likely to be p-type, epitaxial growth is performed so as to have a p-type thick single-layer structure particularly in a high-order crystal plane region as shown in the drawing.

In this example, the height of the ridge 2 from the bottom of the groove 2A is 3.5 μm, and the first conductivity type cladding layer 3 is formed.
The thickness of the active layer is 1 μm, and the thickness of the active layer is several tens nm to 0.1 μm.
m, for example, 0.1 μm, the thickness of the first cladding layer 5 of the second conductivity type is, for example, 1.1 μm, and the thickness of the current blocking layer 7 having a three-layer structure of pnp is 0.1 μm. 2μ
m, 0.1 μm, and 0.2 μm, and the thickness of the second cladding layer 8 of the second conductivity type thereon is set to 0.8 μm, whereby the above-described configuration can be obtained.

Further, a contact layer 9 made of high-concentration p-type GaAs or the like is entirely formed on the second conductive type second cladding layer 7 to a thickness of, for example, 2 μm or more and less than 10 μm, for example, 2 μm by MOCVD. It grows epitaxially.

When the thickness of each layer is selected as described above, the upper surface of the flat portion of the contact layer 9 at a position separated from the ridge 2 is located at a height of approximately 5.5 μm from the flat surface in the groove 2A. On the other hand, the active layer 4 is located at a height of approximately 4.5 μm from the flat surface of the groove 2A. That is, there is a height difference of about 1 μm between the active layer 4 and the upper surface of the flat portion of the contact layer 9 in a direction perpendicular to the main surface 1S of the substrate 1.

Further, a contact metal 10 having a three-layer structure of, for example, AuGe, Ni and Au is continuously formed on the upper surface of the contact layer 9 by sputtering or the like so as to have a total thickness of about 0.7 μm. The semiconductor laser according to the present invention can also be formed by applying a treatment such as polishing to the back surface side of 1 and then forming a contact metal 15 such as TiPtAu.

The semiconductor laser is bonded and fixed to the heat sink 20 on the ridge 2 side with the solder 14.
As described above, the height h of the active layer 4 from the surface of the flat portion of the semiconductor laser, that is, the height of the light emitting portion from the upper surface of the contact metal 10 on the flat surface of the groove 2A is 1 μm or more. By adding the thickness of 10, the thickness becomes about 1.7 μm, and vignetting of the emitted light due to the swelling of the solder can be reliably avoided.

Therefore, even when the semiconductor laser according to the present invention is incorporated as a light source for a CD (compact disk) player or the like, the laser can be fixedly arranged with a high yield.

Further, since a p-type substrate having a high impurity concentration is used as described above, the current block layer can be made p-type, and the generation of a leak current on the higher-order surface can be reliably avoided. In forming the p-side electrode, the p-side contact metal can be formed with good contact resistance only by depositing a metal such as TiPtAu without performing diffusion, epitaxial growth or alloying of a high concentration layer. Can be formed. Therefore, the manufacturing can be simplified as much as the manufacturing process of a semiconductor laser using a normal n-type substrate.

[0038] Although in the above embodiment using the substrate of a high impurity concentration of 5 × 10 ¹⁹ cm ^-3 as a p-type substrate, the impurity concentration, if 5 × 10 ¹⁸ cm ^-3 or more As described above, a sufficiently low contact resistance can be obtained by depositing a metal such as TiPtAu.
When the ^{thickness is} less than about 10 ²⁰ cm ⁻³ , a substrate having good crystallinity with few crystal dislocations can be obtained. Therefore, in the present invention, a p-type substrate having a concentration of 5 × 10 ¹⁸ cm ⁻³ or more and less than 1 × 10 ²⁰ cm ⁻³ is used.

Further, in the above-described example, the height difference between the upper surface of the contact layer 9 and the active layer 4 in the direction perpendicular to the main surface of the substrate is about 1 μm, but the contact layer 9 is higher than the active layer 4. Any position is acceptable. However, in order to fix and arrange this semiconductor laser on a heat sink or the like with a sufficiently high yield, as described above, the thickness of each layer and the height of the ridge are arranged so that the contact layer and the active layer are arranged with a height difference of about 1 μm or more. It is desirable that the height etc. be selected.

As described above, the thickness of the contact layer 9 is 2 μm.
With the above degree, for example, the second
As compared with the case where the thickness of the conductive type cladding layer is increased and the position of the active layer is increased, the deterioration of the characteristics can be further suppressed, and the height difference from the active layer can be sufficiently obtained. When the thickness of the contact layer 9 is 10 μm or more, the reliability is reduced due to the occurrence of distortion due to stress or the problem of thermal conductivity, and the life may be reduced by half or about 以下 or less. is there. For this reason, in the present invention, the thickness of the contact layer 9 is about 2 μm or more and less than 10 μm.

Further, the present invention is not limited to the above-described embodiment, and is disclosed, for example, in Japanese Patent Application No. 4-225992 filed by the present applicant.
As proposed in the above application, a stripe ridge is formed along a <01-1> crystal axis direction on a substrate having a {100} crystal plane as a main surface, and a methyl-based source gas at about 800 ° C. or more is used, for example. The present invention can also be applied to an SDH type semiconductor laser in which the lateral confinement is performed by being surrounded by a slope composed of a {111} A crystal plane by using epitaxial growth, and its material system is also AlGaAs.
It goes without saying that the present invention can be modified in various ways, for example, other III-V compounds can be used without being limited to the system.

[0042]

As described above, according to the present invention, when a semiconductor laser is incorporated in a device, vignetting of emitted light due to swelling of solder adhered to the upper surface can be reliably avoided, and a CD player can be used. In the case where the semiconductor laser according to the present invention is incorporated as a light source, the laser can be fixedly arranged with high yield.

Also, without increasing the thickness of the second conductivity type cladding layer on the active layer,
By setting the thickness to about μm or more and less than about 10 μm, it is possible to sufficiently obtain a height difference from the active layer without deteriorating characteristics and reliability and shortening the life, and to improve the yield when fixed in the device. Can be.

Further, since a p-type substrate having a high impurity concentration is used as described above, the current block layer can be made p-type, and generation of a leak current on the higher-order surface can be reliably avoided. In forming the p-side electrode, the p-side contact metal can be formed with good contact resistance only by depositing a metal such as TiPtAu without performing diffusion, epitaxial growth or alloying of a high concentration layer. Can be formed. Therefore, the manufacturing can be simplified as much as the manufacturing process of a semiconductor laser using a normal n-type substrate.

[Brief description of the drawings]

FIG. 1 is a schematic enlarged sectional view of an embodiment of the present invention.

FIG. 2 is a schematic enlarged cross-sectional view of an example of a conventional semiconductor laser.

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

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 substrate 2 ridge 2A groove 3 first conductivity type cladding layer 4 active layer 5 second conductivity type first cladding layer 6A slope 6B slope 7 current blocking layer 8 second conductivity type second cladding layer 9 contact layer 10 Contact metal 14 Solder 15 Contact metal

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-24977 (JP, A) JP-A-5-55692 (JP, A) JP-A-4-79282 (JP, A) JP-A-57-57 35391 (JP, A) JP-A-58-97887 (JP, A) JP-A-2-22879 (JP, A) JP-A-2-156588 (JP, A) JP-A-3-171790 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01S 5/00-5/50

Claims (3)

(57) [Claims] 1. A stripe-shaped ridge extending in the <011> crystal axis direction is formed on a substrate having a {100} crystal plane as a main surface, and at least the first conductivity type is covered over the ridge. A cladding layer, an active layer, a cladding layer of the second conductivity type, a current blocking layer, and a contact layer are epitaxially grown to provide a slope of {111} B crystal plane on the ridge, at least on both sides of the ridge. The height of the bottom surface of the contact layer from the bottom surface of the groove at a position apart from the ridge is smaller than the height of the active layer on the ridge from the bottom surface of the groove. A semiconductor laser, wherein the height of the upper surface from the bottom surface of the groove is large. 2. The method according to claim 1, wherein the thickness of the contact layer is 2 μm or more.
2. The semiconductor laser according to claim 1, wherein the thickness is less than 0 μm. 3. The substrate according to claim 1, wherein the substrate is of a p-type and has an impurity concentration of 5 × 10 ¹⁸ cm ⁻³ or more and less than 1 × 10 ²⁰ cm ⁻³ . Semiconductor laser.