JPH08107247A - Semiconductor laser - Google Patents

Abstract

PURPOSE: To provide a semiconductor laser which has improved luminous efficiency by preventing current from leaking to areas other than a stripe groove formed on a current blocking layer. CONSTITUTION: A semiconductor laser has a double hetero junction structure provided with current blocking layers 7a, 7b and 7c which have a stripe groove to be a current path in at least one of top and bottom clad layers 4 and 6 that sandwich an active layer 5 from both top and bottom planes. The semiconductor laser is provided with separated two or more current blocking layers of a conductivity type different from that of the clad layer which surrounds the current blocking layers.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser having a double heterojunction structure. More specifically, the present invention relates to a semiconductor laser provided with a current blocking layer having a stripe groove serving as a current path, in which the leakage current is reduced and the light emission efficiency is improved.

[0002]

2. Description of the Related Art A semiconductor laser has a band gap energy larger than that of the material of the active layer on both sides of the active layer, and
A double heterojunction structure sandwiched between cladding layers made of a material with a small refractive index is used to form a resonator by concentrating current in the stripe portion with a current blocking layer in which stripe grooves are formed. It has a structure to take out. FIG. 4 shows an example of a semiconductor laser using a GaAs compound semiconductor having such a structure.

In FIG. 4, reference numeral 21 is, for example, an n-type G.
A semiconductor substrate made of aAs or the like, on which, for example, n
-Type lower cladding layer 22 made of Al _v Ga _1-v As (0.35 ≦ v ≦ 0.75), undoped or n-type or p-type Al _w Ga _1-w As (0 ≦ w ≦ 0.
3) active layer 23, p-type Al _v Ga _1-v As first upper cladding layer 24, n-type GaAs current limiting layer 25, p-type Al _v Ga _1-v As second layer
An upper clad layer 26 and a contact layer 27 made of p-type GaAs are sequentially laminated, and a p-side electrode 28 and an n-side electrode 29 are provided on the upper and lower surfaces, respectively, to form a semiconductor laser chip. In this structure, the current limiting layer 25 made of n-type GaAs is a conductivity type layer different from the surrounding p-type clad layer, and the gap energy of the pn junction is used to block the current, so that the injection current has a stripe shape with a width W. By limiting the active region and absorbing the light generated in the active layer, it serves to provide a difference in refractive index inside and outside the stripe. Therefore, light is confined in the lateral direction, and it is used as a red or infrared refractive index guided structure type semiconductor laser which stably guides light in a stripe-shaped active region having a width W.

Recently, a blue LED in which a gallium nitride-based compound semiconductor is laminated on a sapphire substrate has been developed, and a blue-emitting semiconductor laser using a gallium nitride-based compound semiconductor is also demanded for a semiconductor laser.

When forming a semiconductor laser using a gallium nitride based compound semiconductor, the active layer is sandwiched from both sides by a clad layer made of a material having a band gap energy larger than that of the active layer and a refractive index smaller than that of the active layer. for oscillating confine light in the active layer by the structure, in _1-y Ga _y N as an active layer (0 <y <1, for example y = 0.85), Al _r as both sides of the clad layer
It is possible to use Ga _1-r N (0 ≦ r <1, for example r = 0.2).

[0006]

In a conventional semiconductor laser having a current blocking layer, for example, the current blocking layer formed in the p-type cladding layer is a single n-type layer, so that a pn junction for blocking current is provided. Only one is formed. Therefore, once electrons or holes have passed the gap energy of the pn junction, they flow as it is as a leak current, and the current cannot be blocked even if the thickness of the current blocking layer is increased. As a result, there has conventionally been a problem that a leakage current of about 1 to 10% exists and the luminous efficiency is reduced.

The present invention solves such a problem and provides a semiconductor laser having a current blocking layer in which stripe grooves are formed, which prevents leakage of current to areas other than the stripe grooves and has improved luminous efficiency. The purpose is to provide.

[0008]

A semiconductor laser according to the present invention comprises a double heterostructure having a current blocking layer having a stripe groove serving as a current path in at least one of upper and lower clad layers sandwiching an active layer from both upper and lower surfaces. In the semiconductor laser having a junction structure, the current blocking layer includes two or more layers separated from each other with a conductivity type different from the conductivity type of the cladding layer around the current blocking layer.

A first conductivity type lower clad layer, an active layer, a second conductivity type upper clad layer, and a second conductivity type contact layer are sequentially formed as semiconductor layers on a substrate, and a current is formed in the upper clad layer. A plurality of current blocking layers in which stripe grooves serving as paths are formed are provided, and the plurality of current blocking layers are a first conductivity type layer, a second conductivity type layer, and a first conductivity type layer.
A layered structure is preferable because a semiconductor laser can be obtained with a simple structure.

Since the semiconductor layer is a gallium nitride-based compound semiconductor layer, the semiconductor bandgap energy is larger than that of the GaAs-based compound semiconductor, so that the semiconductor layer does not penetrate through the forbidden band of the semiconductor to leak and the gap energy of the pn junction. Limits the leakage current,
More effective.

The lower cladding layer is an n-type Al _r Ga _{1 -r}
N (0 ≦ r <1), and the active layer is In _1-y Ga
_y N (0 <y <1), and the upper clad layer is p
Type Al _r Ga _1-r N (0 ≦ r <1), and the current blocking layer is GaN, Al _p Ga _1-p N (0 ≦ p <1) and In _1-q Ga _q N (0 < The semiconductor laser of the present invention can be constituted by a laminated structure of at least one n-type layer, p-type layer and n-type layer selected from the group consisting of q ≦ 1).

[0012]

According to the semiconductor laser of the present invention, the current blocking layer for concentrating the current path in a stripe shape is formed with a conductivity type different from that of the surrounding cladding layer, and is separated into two or more layers. Therefore, two or more pn junctions for blocking the current are formed. Therefore, even if an electron or hole crosses the energy gap of one pn junction,
Furthermore, since there is still at least one pn junction, the energy gap of the next pn junction cannot be overcome and the reactive current is significantly reduced. If there is no current flowing over the current blocking layer, all the current is concentrated in the stripe portion, and the luminous efficiency is improved.

Further, in a GaAs-based compound semiconductor, the band gap energy (forbidden band width) is narrow in the energy band of the semiconductor, so that leakage may occur through the forbidden band without overcoming the energy gap of the pn junction. Since the gallium nitride compound semiconductor has a large band gap energy, such a phenomenon does not occur, and the number of pn junctions is increased, so that the reactive current is further prevented.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a semiconductor laser of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view showing a chip of an embodiment of the semiconductor laser of the present invention, FIG. 2 is a sectional view showing a process of manufacturing the same, and FIG. 3 is a sectional view of a chip of another embodiment of the semiconductor laser of the present invention. FIG.

As shown in FIG. 1, one embodiment of the semiconductor laser of the present invention is such that an n-type Al _t Ga _u In _{1-tu is formed} on a substrate 1 such as sapphire (Al ₂ O ₃ single crystal).
0.01 μm to 0.2 μm composed of N (0 ≦ t <1, 0 <u ≦ 1, 0 <t + u ≦ 1, for example, t = 0, u = 1)
Low-temperature buffer layer 2, high-temperature buffer layer 3 having a thickness of 2 to 5 μm, and n-type Al _r Ga _s In _1-rs N (0 ≦ t ≦ r
<1, 0 <s ≦ 1, 0 <r + s ≦ 1, for example r + s =
1) the lower clad layer 4 of about 0.1 to 0.3 μm, undoped or n-type or p-type Al _x Ga _y
In _1-xy N (0 ≦ x <r, 0 <y <1, 0 <x + y <
r + s, for example x = 0), and the lower cladding layer 4
An active layer 5 having a smaller bandgap energy and a larger refractive index of about 0.05 to 0.1 μm, an upper clad layer 6 having a p-type and the same composition as the lower clad layer 4 of about 0.1 to 0.3 μm, GaN or Al _p Ga _q In
_1-pq N (0 ≦ p <1, 0 <q ≦ 1, 0 <p + q ≦ 1,
For example, p = 0 or p + q = 1) and the like, and an n-type first current blocking layer 7a having a stripe groove formed therein, a p-type second current blocking layer 7b, an n-type third current blocking layer 7c, a buffer layer. 0.3 to 2μ, which is a low resistance layer with the same composition as 2 and 3
m-type p-type Al _t Ga _u In _1-tu N (0 ≦ t <
1, 0 <u ≦ 1, 0 <t + u ≦ 1 For example, t = 0, u =
The contact layer 8 composed of 1) is sequentially laminated, the p-side electrode 9 is provided on the surface of the contact layer 8, and the n-side electrode 10 is provided on the high temperature buffer layer 3 exposed by etching a part of the laminated semiconductor layers. The semiconductor laser chip of the present invention is formed.

The semiconductor laser of the present invention comprises a plurality of current blocking layers 7a, 7b and 7c each having a stripe groove for concentrating a current in the stripe portion of the active layer.
The feature is that at least two pn junctions that block current are formed. The current blocking layers 7a, 7b, 7c
Subsequent to the formation of the p-type cladding layer 6, for example, n-type G
aN is 0.05 to 0.2 μm and p-type GaN is 0.05 to 0.2 μm.
It can be obtained by forming 0.2 μm and n-type GaN by 0.05 to 0.2 μm each, and then taking out from the MOCVD apparatus and etching three layers by photolithography technique to form stripe grooves. This current blocking layer can be formed by stacking five or more layers of a p-type layer and an n-type layer in this order. If two pn junctions that block the current are formed, 90% of the conventional leakage current is blocked. It is possible to achieve the purpose. On the other hand, if the number of stacked layers is increased, it is possible to further prevent the leakage current, but it is not preferable because the number of film forming steps is increased, the distance to the p-side electrode is increased, and the resistance loss is increased. When the current blocking layer is formed of the above-mentioned three layers (n-type layer, p-type layer, n-type layer),
When the total thickness is about 0.1 to 0.4 μm, the current blocking layer can be formed to the same thickness as the conventional current blocking layer, and the current blocking efficiency can be improved.

In order to make the material of the current blocking layers 7a, 7b and 7c a complex refractive index waveguide structure in which light is completely confined in the stripe portion, the light of the active layer is absorbed by InGaN.
It is preferable to use a system, GaN, or the like. In order to form a refractive index waveguide structure in which light is not completely confined in the stripe portion, it is preferable to use AlN, AlGaN, or the like that does not absorb light in the active layer.

Further, in the above embodiment, the current blocking layers 7a, 7a
3 layers b and 7c are made of the same semiconductor material and are of n-type layer, p-type layer, and
However, it is not always necessary to use the same material, but if two or more layers of the conductivity type opposite to the clad layer where the current blocking layer is provided are provided separately, the materials of the respective semiconductor layers are different. Good.

Although the current limiting layer is provided in the upper p-type cladding layer in the above-mentioned embodiment, it may be provided in the lower n-type cladding layer. In this case, the current blocking layer has two p-type layers.
More layers will be provided. Further, in the case of a gallium nitride based compound semiconductor, it is preferable that the surface side be a p-type layer because it is necessary to anneal the p-type layer, but the n-type and p-type may be opposite to those in the above-mentioned embodiment.

Next, the semiconductor laser of the present invention will be described in more detail with reference to specific examples.

Example 1 First, as shown in FIG. 2A, a substrate 1 made of sapphire or the like was placed in a reaction tube, H ₂ as a carrier gas was set to 10 slm, and trimethylgallium (hereinafter referred to as T) as a reaction gas.
MG) 100 sccm and NH ₃ 10 sl
m and vapor-phase-grown at 400 to 700 ° C. by metalorganic vapor phase epitaxy (hereinafter referred to as MOCVD method) to 0.0
The low temperature buffer layer 2 which is a polycrystalline film made of GaN having a thickness of about 1 to 0.2 μm was formed. Then 700-12
The polycrystalline film of the low temperature buffer layer 2 becomes a single crystal by raising the temperature to 00 ° C. and leaving it for about 5 to 15 minutes, and the same raw material gas as described above is introduced onto it to form a gas phase at a high temperature of 700 to 1200 ° C. By reacting, a high temperature buffer layer 3 made of GaN single crystal was formed to a thickness of 2 to 5 μm.

Further, trimethylaluminum (hereinafter, T
MA) is mixed at a flow rate of 10 to 100 sccm to cause a gas phase reaction to form an n-type cladding layer 4 made of Al _0.2 Ga _0.8 N with a thickness of 0.1 to 0.3 μm.

Next, the dopant SiH ₄ is stopped and trimethylindium (hereinafter TMI) is used instead of TMA.
Is supplied at a flow rate of 10 to 200 sccm.
_The non-doped active layer 5 made of _0.15 Ga _0.85 N is formed into 0.0
A film having a thickness of about 5 to 0.1 μm is formed, and a raw material gas having the same composition as that of the n-type lower cladding layer 4 is supplied. The impurity raw material gas is replaced with SiH ₄ and biscyclopentadienyl magnesium (hereinafter referred to as Cp ₂ Mg). ) Or dimethylzinc (hereinafter referred to as DMZn) at a flow rate of 10 to 1000 sccm to form a p-type upper cladding layer 6 made of Al _0.2 Ga _0.8 N with a thickness of 0.1 to 0.3 μm, Then, the TMA is stopped and SiH ₄ as a dopant is supplied to form an n-type GaN layer as a first current blocking layer in an amount of 0.05
About ~0.2μm, 0.05~0.2μm about the p-type GaN layer for the second current blocking layer to supply further changing the dopant gas from SiH ₄ to Cp ₂ Mg, a further dopant gas In place of SiH ₄ , an n-type GaN layer for forming a third current blocking layer was formed to a thickness of about 0.05 to 0.2 μm.

After that, the temperature inside the furnace is lowered to about 30 ° C., the substrate on which the semiconductor layers are stacked is taken out from the MOCVD apparatus, and as shown in FIG. 2B, etching is performed by a photolithography process to form stripe grooves. Then, the current blocking layers 7a, 7b and 7c were formed.

After that, as shown in FIG. 2 (c), the substrate is put in the MOCVD apparatus again, and the temperature is set to 700 to 1200 ° C., and TMG, NH ₃ as the reaction gas and Cp ₂ Mg or DMZn as the dopant are used as described above. Supply p
-Type GaN contact layer 8 was formed to a thickness of about 0.2 to 3 μm. After that, a protective film such as SiO ₂ or Si ₃ N ₄ is provided on the entire surface of the semiconductor layer at 400 to 800 ° C. and 20 to 20 ° C.
Annealing was performed for about 60 minutes to activate the p-type cladding layer 6 and the contact layer 8.

Next, in order to form the n-side electrode, a mask is formed with a resist film or the like, and reactive ion etching is performed on a part of the stacked semiconductor layers under a Cl ₂ gas atmosphere to form an n-type layer. The n-type clad layer 4 or the high temperature buffer layer 3 is exposed, and Au, Au- is formed on the contact layer 8.
On the p-side electrode 9 made of Zn or the like, the n-type cladding layer 4 or the high temperature buffer layer 3, n made of Al, Au—Ge or the like is formed.
The side electrode 10 was formed and dicing was performed to form a semiconductor laser chip (see FIG. 1).

In the above-mentioned embodiment, a material obtained by substituting a part or all of N by As and / or P by the above-mentioned general formula Al _α Ga _β In _1-α-β N as a gallium nitride compound semiconductor is also used. The present invention can be similarly applied.

Embodiment 2 FIG. 3 is a sectional view showing a chip of another embodiment of the semiconductor laser of the present invention. In this embodiment, a GaAs compound semiconductor is used, and each semiconductor layer is MO as in the first embodiment.
It can be formed by a CVD method or a molecular beam epitaxy (MBE) method.

In FIG. 3, 11 is, for example, n-type Ga.
A semiconductor substrate made of As or the like and having a thickness of about 50 to 200 μm, on which, for example, n-type Al _v Ga _1-v As (0.
35 ≦ v ≦ 0.75), and the lower cladding layer 12 having a thickness of about 0.8 to 2 μm is formed in the lower clad layer 12 by non-doping or n-type or p-type, for example, Al _w Ga _1-w As (0 ≦ w ≦ 0.3).
And the active layer 13, p having a thickness of about 0.05 to 0.2 μm.
Type Al _v Ga _1-v As, 0.4-0.5 μm
Of the first upper clad layer 14 and n-type GaAs having a thickness of about 0.05 to 0.2 μm
a, p-type GaAs, a second current blocking layer 15b having a thickness of about 0.05 to 0.2 μm, and n-type GaAs.
Third current blocking layer 15c of about 05 to 0.2 μm, p-type A
l _v Ga consists of a _1-v As, the second of about 0.8~2μm
The upper clad layer 16 is made of p-type GaAs,
A contact layer 17 having a thickness of about 2 μm is sequentially laminated, and a p-side electrode 18 and an n-side electrode 19 are provided on the upper surface and the lower surface, respectively, to form a semiconductor laser chip. Each of the three current blocking layers 15a, 15b, 15c is formed by stacking the semiconductor layers as in the first embodiment and then etching the three layers to form stripe grooves.

According to the second embodiment, since the band gap energy (forbidden band width) of the GaAs-based semiconductor is small, there may be a leak that penetrates the forbidden band, but the leak that crosses the energy gap of the pn junction is surely reduced. It is possible to contribute to the improvement of luminous efficiency.

In Example 2, GaAs was used as the substrate, Al _v Ga _1-v As was used as the cladding layer, and Al _w Ga _1-w A was used as the active layer.
s, GaAs is used for the current blocking layer, but the same applies to the case where a part or all of Ga is further replaced with In or Al and / or the part or all of As is replaced with P.

[0033]

According to the semiconductor laser of the present invention, the current blocking layers are formed in a plurality of layers, and two or more energy gaps of the pn junction for blocking the current are formed. The leakage of current can be greatly reduced. As a result, the luminous efficiency is improved by 10% or more as compared with the conventional one, and a large output semiconductor laser can be obtained with a small input.

[Brief description of drawings]

FIG. 1 is a sectional explanatory view showing an embodiment of a semiconductor laser of the present invention.

FIG. 2 is an explanatory cross-sectional view of steps of a manufacturing method of an embodiment of the semiconductor laser of the present invention.

FIG. 3 is a sectional explanatory view showing another embodiment of the semiconductor laser of the present invention.

FIG. 4 is a cross-sectional explanatory view of a conventional GaAs compound semiconductor laser.

[Explanation of symbols]

 4 Lower Cladding Layer 5 Active Layer 6 Upper Cladding Layer 7a First Current Blocking Layer 7b Second Current Blocking Layer 7c Third Current Blocking Layer 12 Lower Cladding Layer 13 Active Layer 14 First Upper Cladding Layer 15a First Current Blocking Layer 15b Second 2 current blocking layer 15c third current blocking layer 16 second upper cladding layer

Claims (4)

[Claims] 1. A semiconductor laser having a double heterojunction structure, comprising a current blocking layer having a stripe groove serving as a current path in at least one of upper and lower clad layers sandwiching an active layer from both upper and lower sides, wherein the current A semiconductor laser in which the blocking layer has two or more layers separated from each other with a conductivity type different from the conductivity type of the cladding layer around the current blocking layer. 2. A first conductivity type lower clad layer on a substrate,
A plurality of current blocking layers in which an active layer, a second conductivity type upper clad layer, and a second conductivity type contact layer are sequentially formed of semiconductor layers, and stripe grooves serving as current paths are formed in the upper clad layer. And a plurality of current blocking layers having a three-layer structure of a first conductivity type layer, a second conductivity type layer, and a first conductivity type layer. 3. The semiconductor laser according to claim 2, wherein the semiconductor layer is a gallium nitride based compound semiconductor layer. 4. The lower cladding layer is n-type Al _r Ga.
_1-r N (0 ≦ r <1), and the active layer is In _1-y
Ga _y N (0 <y <1), the upper cladding layer is p-type Al _r Ga _1-r N (0 ≦ r <1), and the current blocking layer is GaN or Al _p Ga _1-p. N (0 ≦ p <1)
4. The semiconductor according to claim 2, which has a laminated structure of at least one type of n-type layer, p-type layer and n-type layer selected from the group consisting of and In _1-q Ga _q N (0 <q ≦ 1). laser.