JP2000294883A - Nitride compound semiconductor laser element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nitride compound semiconductor laser element where double hetero structure is formed in a mesa-type structure on a semiconductor substrate and the double hetero structure part of mesa-type structure is buried in a semiconductor whose refractive index is smaller than an active layer, in the nitride compound semiconductor laser element having double hetero structure formed of two upper/lower clad layers formed to sandwich the active layer constituted of InXGa1-XN(0<=X<=1) formed on the upper part of the substrate. SOLUTION: An n-type clad layer 2, an n-type light containment layer 3, an undoped MQW layer 4, a cap layer 5, a p-type light containment layer 6, a p-type clad layer 7 and a p-type contact layer 8 are sequentially grown on an n-type GaN substrate 1, and LD structure is obtained. Then, undoped AlGaN burying layers 10 are formed at a temperature equal to the growing temperature of the undoped MQW layer 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a nitride-based compound semiconductor (In _X Al _Y Ga _{1 -XYN} , X ≧ 0, Y ≧ 0, X + Y ≦ 1) laser device, and a method for manufacturing the same. Prepared using the method, nitride-based compound semiconductor (In _X Al _Y Ga _1-XYN , X ≧ 0, Y ≧ 0, X + Y ≦ 1)
The present invention relates to a laser device.

[0002]

2. Description of the Related Art Conventionally, a method for confining light and current in a stripe width direction of a nitride-based compound semiconductor laser is disclosed in Applied Physics Letters.
YSISCSLETTERS) Vol. 68, p. 3269, 1996
Gain-guided stripe lasers such as those described in Applied Physics Letters (APPLIED PH
YSISCS LETTERS) Vol. 69, p. 1,477. Ridge structure as described in 1996 or JP-A-9-246.
No. 763, there is a laser with a buried cladding layer, and the like, and we have also realized continuous oscillation at room temperature with a ridge type laser as shown in FIG. FIG. 8 shows a cross-sectional structure of a typical ridge structure laser manufactured by a conventional technique. n
An n-type clad layer 102 made of Si-doped n-type Al _0.1 Ga _0.9 N (silicon concentration 4 × 10 ¹⁷ atoms / cm ³ , thickness 1 μm) on a Si-type n-type GaN (silicon concentration 4 × 10 N-type optical confinement layer 103 of ¹⁷ atoms / cm ³ , 0.1 μm in thickness, In _0.2 Ga _0.8 N (thickness 3 n
m) Undoped MQW active layer 104 (three wells) composed of a well layer and an In _0.05 Ga _0.95 N (thickness 5 nm) barrier layer, cap layer 105 composed of Mg-doped p-type Al _0.2 Ga _0.8 N, Mg-doped p-type GaN (Mg concentration ^{2 × 10 1 7 atoms / cm} 3, a thickness of 0.1μ
m), a p-type optical confinement layer 106 composed of Mg-doped p-type Al _0
.1 Ga _0.9 N (Mg concentration 2 × 10 ¹⁷ atoms / cm ³ , thickness 0.5μ)
m), a Mg-doped p-type GaN (M
g concentration 2 × 10 ¹⁷ atoms / cm ³ , thickness 0.1 μm)
A p-type contact layer 108 is sequentially grown to form a laser diode structure (hereinafter, referred to as an LD structure). The laser structure is grown by MOCVD equipment and the growth temperature is InGaN
The MQW active layer 104 was at 780 ° C., and all other layers were at 1050 ° C. After partially leaving the mesa 109 including the p-type cladding layer 107 and the p-type contact layer 108 by dry etching, the SiO ₂ insulating film 110 is formed.
Then, the ridge structure was formed by exposing the mesa portion to the crest by an exposure technique. An n-electrode 111 made of Ti / Al was formed on the back of the n-type substrate, and a p-electrode 112 made of Ni / Au was formed on the p-contact.

[0003]

However, the above-mentioned nitride-based compound semiconductor laser device is of a gain waveguide type having no actual refractive index step in the lateral direction, or has a flat active layer and a convex portion. It had a ridge or cladding layer buried structure formed of a cladding layer, in which light waves were confined and propagated in the projections. In a laser having such a structure, the gain distribution region in the stripe width direction is wider than the refractive index distribution region, and extra carriers that do not contribute to laser oscillation are lost, so that the threshold current increases and the output increases. Then, the gain outside the stripe (outside the waveguide) increases, and the difference in effective refractive index inside and outside the stripe decreases, so that the stability of the transverse mode deteriorates. Further, when it is desired to radiate heat from the p-electrode side, since the active region is buried with an insulator such as SiO _2, thermal conductivity is deteriorated, and there is a disadvantage that the life of the device is shortened due to a rise in temperature of the device. In order to solve these problems, it is necessary to fabricate a structure in which the gain region and the refractive index distribution region in the stripe width direction coincide with each other. As a technique, a mesa-type high refractive index region (waveguide) including an active layer is used. A laser structure in which a low-refractive index semiconductor is regrown and an active layer is buried has been proposed (JP-A-8-330678). However, according to the study of the present inventor, using this method, in a nitride semiconductor laser using InGaN as an active layer, an active layer grown at a low temperature during the manufacturing process is a buried layer which is formed at a relatively high temperature. It has been found that there are problems such as the atomic arrangement being disordered inside the active layer and the vaporization of atoms from the active layer due to exposure to high temperatures during the growth of. SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and to provide a nitride-based compound semiconductor laser device having a low threshold current, a stable transverse mode, and a long life.

[0004]

According to the present invention, there is provided an active layer comprising In _X Ga _{1 -X} N (0 ≦ X ≦ 1) formed on a substrate, Both of the cladding layers are present in the mesa-type stripe structure, and a nitride-based compound semiconductor laser device in which a buried layer made of a semiconductor having a lower refractive index than the active layer is present on the side surface of the mesa-type stripe structure. The method of manufacturing a nitride-based compound semiconductor laser device, wherein the buried layer is grown at a temperature not higher than 100 ° C. higher than the growth temperature of the active region.

As described above, conventionally, the growth temperature of the buried layer is often higher than the growth temperature of the active layer, which disturbs the arrangement of atoms in the active layer and causes vaporization of atoms from the active layer. For example, it causes the quality of the active layer to deteriorate. However, in the present invention, the buried layer can be formed without causing deterioration of the active layer by growing the buried layer at a temperature lower than the growth temperature of the active layer.

The buried layer is grown at a temperature not higher than 100 ° C. higher than the growth temperature of the active layer, preferably at a temperature not higher than 50 ° C. higher than the growth temperature of the active layer, and most preferably. This is performed at a temperature lower than the growth temperature of the active layer.

As the material of the buried layer, a II-VI group compound semiconductor can be used. For example, MgSe is 325
It is possible to grow at a very low temperature of ° C. and to protect the active layer from high temperatures.

[0008] Further, In _X Al _Y Ga _1-XY N
It is also possible to use a nitride compound semiconductor having a composition of (X ≧ 0, Y ≧ 0, X + Y ≦ 1) as a material. Also, the buried layer can be a multilayer film. In this case, by forming a reverse bias structure in the buried layer, it is possible to reduce the leak current of the device and to improve the withstand voltage characteristics of the device.

When the buried layer is a multilayer film,
-VI compound semiconductor and In _X Al _Y Ga _{1-X- Y} N (X ≧ 0, Y ≧ 0, X +
Y ≦ 1) may be combined to form a multilayer film.

A first buried layer is grown thinly on the surface of the mesa-type stripe structure at a temperature lower than the growth temperature of the active layer, and then the temperature is raised to a temperature higher than the growth temperature of the active layer. It is also possible to regrow the buried layer. In this case, the thin buried layer grown first functions as a protective film for preventing atoms from being lost from the surface of the active layer due to vaporization.

[0011] The term "grow thinly" means that when the second buried layer is grown at a temperature higher than the growth temperature of the active layer, a film thickness sufficient to suppress the vaporization of atoms from the active layer. It is to grow. Specifically, the material is In
_{When 0.1} Ga _0.9 N is used, the film thickness is preferably 5 to 1000 °.

Further, there is provided a high-quality nitride-based compound semiconductor laser device manufactured by using the above method.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described in detail based on embodiments with reference to the drawings. (Embodiment 1) FIG. 1 is a structural sectional view of a semiconductor laser according to an embodiment. In this example, the active layer is protected by regrowing the buried layer at a temperature lower than the growth temperature of the active layer.

On an n-type GaN substrate 1, Si-doped n-type Al _0.1 G
a _0.9 N (silicon concentration 4 × 10 ¹⁷ atoms / cm ³ , thickness 1μ)
m), an n-type optical confinement layer 3 made of Si-doped n-type GaN (silicon concentration 4 × 10 ¹⁷ atoms / cm ³ , thickness 0.1 μm), In _0.2 Ga _0.8 N (thickness 3 nm) ) Undoped MQW layer 4 (three wells) composed of well layer and In _0.05 Ga _0.95 N (5 nm thick) barrier layer, Mg-doped p-type Al _0.2 Ga _0.8 N
(Mg concentration ^{2 × 10 17 atoms / cm 3} , thickness 20 nm) cap layer 5 made of, Mg-doped p-type GaN (Mg concentration 2 × 10 ^{1 7} at
oms / cm ³ , 0.1 μm thick)
Mg-doped p-type Al _0.1 Ga _0.9 N (Mg concentration 2 × 10 ¹⁷ atoms /
a p-type cladding layer 7 of cm ³ and a thickness of 0.5 μm; Mg-doped p-type GaN (Mg concentration: 2 × 10 ¹⁷ atoms / cm ³ ; thickness: 0.2)
.mu.m), and a p-type contact layer 8 of
Form a D structure. The laser structure is grown in a MOCVD apparatus, and the growth temperature is 780 ° C. for the InGaN MQW active layer 4 and 1050 ° C. for all other layers. Mesa type 9 including MQW active layer 4, p-type optical confinement layer 6, p-type cladding layer 7, and p-type contact layer 8 by dry etching
Was partially left, and an undoped Al _0.2 Ga _0.8 N (0.75 μm thick) buried layer 10 was formed at a growth temperature of 780 ° C. by regrowth by MOCVD. An n-electrode 11 made of Ti / Al is formed on the back of the n-type substrate, and a p-electrode 12 made of Ni / Au is formed on the p-contact.

Although an n-type GaN substrate is used, an AlGaN substrate
A C substrate or a sapphire substrate may be used.
Or i-type. Further, in this embodiment, the buried layer 9 is undoped AlGaN, but the polarity may be n-type.

The filling material is also In _X Al _Y Ga _1-XY N (X
≧ 0, Y ≧ 0, X + Y ≦ 1).

(Embodiment 2) FIG. 2 is a structural sectional view of a semiconductor laser according to an embodiment.

[0018] p-type Al _0.1 Ga _0.9 N Mg-doped on the substrate 13 p-type Al _0.1 Ga _0.9 N (Mg concentration ^{2 × 10 17 atoms / cm 3} ,
A p-type cladding layer 14 of 1 μm thickness, Mg-doped p-type GaN (Mg concentration 2 × 10 ¹⁷ atoms / cm ³ , thickness 0.1
μm), a p-type optical confinement layer 15, Si-doped In
_0.2 Ga _0.8 N (Si concentration 2 × 10 ¹⁷ atoms / cm ³ , thickness 3 nm)
S consisting of a well layer and an In _0.05 Ga _0.95 N (5 nm thick) barrier layer
i-doped MQW layer 16 (three wells) Si-doped p-type Al _0.2 Ga
_A cap layer 17 of _0.8 N (Si concentration 2 × 10 ¹⁷ atoms / cm ³ , thickness 20 nm), Si-doped n-type GaN (Si concentration 4 × 1
N-type optical confinement layer 18 made of 0 ¹⁷ atoms / cm ³ and 0.1 μm in thickness; Si-doped n-type Al _0.1 Ga _0.9 N (Si concentration 4 × 1
N-type cladding layer 19 composed of 0 ¹⁷ atoms / cm ^{3 and} 2 μm ⁱⁿ thickness; Si-doped n-type GaN (Si concentration: 8 × 10 ¹⁸ atoms / c)
m ³ , thickness 0.05 μm)
Are sequentially grown to form an LD structure. Laser structure is MO
The growth is performed in a CVD apparatus. The growth temperature is 780 ° C. for the InGaN MQW active layer 16 and 1050 for all other layers.
Perform at ° C. MQW active layer 16, n by dry etching
After partially leaving the mesa 21 including the p-type optical confinement layer 18, the p-type cladding layer 19 and the p-type contact layer 20, the Si-doped n-type Al _0.2 Ga _0.8 at a growth temperature of 780 ° C. by MOCVD. N (Si concentration 7 × 10 ¹⁷ atoms / cm ³ , thickness 0.5 μm) buried layer 22, Mg-doped p-type Al _0.2 Ga _0.8 N
(Mg concentration 2 × 10 ¹⁷ atoms / cm ³ , thickness 0.5 μm) buried layer 23, Si-doped n-type Al _0.2 Ga _0.8 N (Si concentration 7 × 1
(0 ¹⁷ atoms / cm ³ , thickness 1.2 μm) The buried layer 24 is formed. A p-electrode 25 made of Ni / Au is formed on the back of the p-type substrate, and an n-electrode 26 made of Ti / Al is formed on the n-contact. In this embodiment, a p-type AlGaN substrate is used, but a GaN substrate, a SiC substrate, a sapphire substrate, or the like may be used, and the polarity may be n-type or i-type.

In this embodiment, there are three buried layers. This is to introduce a reverse bias structure in the buried layer. The reverse bias structure introduced into the buried layer reduces the leak current of the device and improves the withstand voltage characteristics of the device.

(Embodiment 3) FIG. 3 is a structural sectional view of a semiconductor laser according to an embodiment.

In this embodiment, the active layer is protected by dividing the buried layer into two layers and growing again. n-type Al
_0.1 Ga _0.9 N Si on the substrate 27 doped n-type Al _0.1 Ga _0.9 N (silicon concentration ^{4 × 10 1 7 atoms / cm} 3, a thickness of 1 [mu] m) n-type cladding layer 28 made of, Si-doped n-type GaN (silicon concentration An n-type optical confinement layer 29 of 4 × 10 ¹⁷ atoms / cm ³ and a thickness of 0.1 μm, an In _0.2 Ga _0.8 N (thickness of 3 nm) well layer and an In _0.05 Ga _0.95 N (thickness of 5 nm) barrier layer Undoped MQW layer 30 (three wells), Mg-doped p-type Al _0.2 Ga _0.8 N
(Mg concentration 2 × 10 ¹⁷ atoms / cm ³ , thickness 20 nm), a cap layer 31 made of Mg-doped p-type GaN (Mg concentration 2 × 10 ¹⁷ a
p-type optical confinement layer 3 consisting of toms / cm ³ and thickness of 0.1 μm)
2. Mg-doped p-type Al _0.1 Ga _0.9 N (Mg concentration 2 × 10 ¹⁷ atoms
/ cm ³ , 2 μm thick) p-type cladding layer 33, Mg-doped p-type GaN (Mg concentration 2 × 10 ¹⁷ atoms / cm ³ , thickness 0.0
An LD structure is formed by sequentially growing a p-type contact layer 34 of 5 μm). The laser structure was grown in a MOCVD apparatus, and the growth temperature was 780 for the InGaN MQW active layer 30.
C., and all other layers are performed at 1050.degree. MQW active layer 30 and p-type optical confinement layer 3 by dry etching
2. After partially leaving the mesa 35 including the p-type cladding layer 33 and the p-type contact layer 34, undoped In _0.05 Ga _0.95 N at a growth temperature of 780 ° C. by regrowth by MOCVD.
(Thickness 0.1 μm) buried layer 36 followed by undoped Al _0.2
A buried layer 37 of Ga _0.8 N (thickness 0.75 μm) is formed. Here, the reason _why In _0.05 Ga _0.95 N is used as the first buried layer is that a high quality film can be grown even at a low temperature. An n-electrode 38 made of Ti / Al is formed on the back of the n-type substrate, and a p-electrode 39 made of Ni / Au is formed on the p-contact 31. In this embodiment, an n-type AlGaN substrate was used, but a GaN substrate, a SiC substrate, a sapphire substrate, or the like may be used.
The polarity may be p or i type.

(Embodiment 4) FIG. 4 is a structural sectional view of a semiconductor laser according to an embodiment.

In this embodiment, the active layer is protected by regrowing the buried layer at a temperature lower than the growth temperature of the active layer.

P-type Al_0.1Ga_0.90Mg dope on N substrate 40
P-type Al_0.1Ga_0.90N (Mg concentration 2 × 10¹⁷ atoms / c
m^Three, A 1 μm thick p-type cladding layer 41, Mg
Doped p-type GaN (Mg concentration 2 × 10¹⁷ atoms / cm^Three,thickness
0.1 μm), p-type optical confinement layer 42, Si-doped
 In_0.2Ga_0.8N (Si concentration 2 × 10¹⁷ atoms / cm^Three, Thickness 3n
m) Well layer and In_0.05Ga_0.95N (5 nm thick)
Si-doped MQW layer 43 (3 wells), Si-doped p-type
Al_0.2Ga_0.8N (Si concentration 2 × 10¹⁷ atoms / cm^Three, Thickness 20n
m), a Si-doped n-type GaN (Si concentration
Degree 4 × 10¹⁷ atoms / cm^Three, Thickness 0.1μm)
Optical confinement layer 45, Si-doped n-type Al_0.1Ga_0.9N (Si rich
Degree 4 × 10¹⁷ atoms / cm^Three, Thickness 2 μm)
Cladding layer 46, Si-doped n-type GaN (Si concentration 8 × 10¹⁸a
toms / cm^ThreeN-type contact with thickness of 0.05 μm)
The layer 47 is sequentially grown to form an LD structure. Laser structure
The structure is grown by MOCVD equipment and the growth temperature is InGaN MQ
The temperature of the W active layer 43 is 780 ° C.
Perform at 050 ° C. MQW active layer 4 by dry etching
3, n-type optical confinement layer 45, p-type cladding layer 46, and
The mesa 48 including the p-type contact layer 47 is partially left.
After the growth, the growth temperature was 325 ° C by regrowth in the MBE method.
Undoped MgSe (thickness: 2.2 μm) buried layer 49 is formed.
You. Formation of Ni / Au p-electrode 50 on the back of p-type substrate
On the n-contact, an n-electrode 51 made of Ti / Al
To form In this example, a p-type AlGaN substrate was used.
However, using a sapphire substrate or the like for both GaN and SiC substrates
And the polarity may be n-type or i-type. In this embodiment,
Is MgSe which is a II-VI group compound semiconductor as a buried layer.
Using Al _0.1Ga_0.90Material with lower refractive index than N cladding layer
Any II-VI compound semiconductor may be used.
In this embodiment, the regrown film is formed by the MBE method.
However, the MOCVD method may be used.

(Embodiment 5) FIG. 5 is a structural sectional view of a semiconductor laser according to an embodiment. p-type Al _0.1 Ga _0.90 N substrate 52
Mg-doped p-type Al _0.1 Ga _0.90 N (Mg concentration 2 × 10 ¹⁷
atoms / cm ³ , 1 μm thick) p-type cladding layer 5
3. Mg-doped p-type GaN (Mg concentration 2 × 10 ¹⁷ atoms
/ cm ³ , a thickness of 0.1 μm).
Si doped In _0.2 Ga _0.8 N (Si concentration 2 × 10 ¹⁷ atoms / cm
^3. Si-doped MQW layer 55 (three wells) composed of a well layer and a barrier layer of In _0.05 Ga _0.95 N (thickness of 3 nm)
i-doped p-type Al _0.2 Ga _0.8 N (Si concentration 2 × 10 ¹⁷ atoms / c
m ³ , thickness of 20 nm)
Type GaN (Si concentration 4 × 10 ¹⁷ atoms / cm ³ , thickness 0.1 μm)
N-type optical confinement layer 57 composed of Si, n-type Al _0.1 G
a N-type cladding layer 58 of _0.9 N (Si concentration 4 × 10 ¹⁷ atoms / cm ³ , thickness 2 μm), Si-doped n-type GaN (Si concentration 8 × 10 ¹⁸ atoms / cm ³ , thickness 0.05 μm) Consisting of n
The mold contact layer 59 is sequentially grown to form an LD structure. The laser structure is grown in a MOCVD apparatus, and the growth temperature is 780 ° C. for the InGaN MQW active layer 55 and 1050 ° C. for all other layers. By dry etching
Mesa 60 including MQW active layer 55, n-type optical confinement layer 57, p-type cladding layer 58 and p-type contact layer 59
Is partially left, and then undoped n-type Al _0.2 Ga _0.8 N (having a thickness of _0.1 μm) at a growth temperature of 780 ° C. by regrowth of the MOCVD method.
m) After growing the buried layer 61, the growth temperature is set to 105
Raise the temperature to 0 ° C and undoped Al _0.2 Ga _0.8 N (thickness 2.1μ
m) The buried layer 62 is formed. The reason for growing the buried layer 62 having a low refractive index at a relatively high temperature (1050 ° C.) is as follows.
This is for obtaining a buried layer having high crystallinity and good film quality. A p-electrode 63 made of Ni / Au is formed on the back of the p-type substrate, and an n-electrode 64 made of Ti / Al is formed on the n-contact.
To form In this embodiment, a p-type AlGaN substrate is used, but a GaN substrate, a SiC substrate, a sapphire substrate, or the like may be used, and the polarity may be n-type or i-type.

(Embodiment 6) FIG. 6 is a structural sectional view of a semiconductor laser according to an embodiment.

On an n-type Al _0.1 Ga _0.9 N substrate 65, a Si-doped n
Type Al _0.1 Ga _0.9 N (silicon concentration 4 × 10 ¹⁷ atoms / cm ³ ,
N-type cladding layer 66 of 1 μm thickness, Si-doped n-type GaN (silicon concentration 4 × 10 ¹⁷ atoms / cm ³ , thickness 0.1
μm), n-type optical confinement layer 67, In _0.2 Ga _0.8 N
An undoped MQW layer 68 (three wells) consisting of a well layer (thickness 3 nm) and an In _0.05 Ga _0.95 N (thickness 5 nm) barrier layer, Mg-doped p-type Al _0.2 Ga _0.8 N (Mg concentration 2 × 10 ¹⁷ atoms) / cm ³ , 20 nm thick cap layer 69, Mg-doped p-type GaN
(Mg concentration 2 × 10 ¹⁷ atoms / cm ³ , thickness 0.1 μm), p-type optical confinement layer 70, Mg-doped p-type Al _0.1 Ga _0.9 N (M
a p-type cladding layer 71 having a g concentration of 2 × 10 ¹⁷ atoms / cm ³ and a thickness of 2 μm; an Mg-doped p-type GaN (Mg concentration 2 × 1
0 ¹⁷ , p-type contact layer 7 having a thickness of 0.05 μm)
2 are sequentially grown to form an LD structure. Laser structure
The growth was performed in a MOCVD apparatus, and the growth temperature was 780 ° C. for the InGaN MQW active layer 68, and 105 ° C. for all other layers.
Perform at 0 ° C. MQW active layer 68, p
After partially leaving the mesa 73 including the p-type light confinement layer 70, the p-type cladding layer 71, and the p-type contact layer 72, Mg-doped p-type In _0.05 Ga _0.95 at a growth temperature of 780 ° C. by MOCVD. N (Mg concentration 2 × 10 ^17, thickness 0.1 μm)
Buried layer 74, followed by increasing the growth temperature to 1050 ° C.
Si-doped n-type Al _0.2 Ga _0.8 N (silicon concentration 4 × 10 ¹⁷ at
oms / cm ³ , thickness 1.0 μm) buried layer 75 is formed, followed by Mg-doped p-type Al _0.2 Ga _0.8 N (Mg
A concentration of 2 × 10 ¹⁷ atoms / cm ³ and a thickness of 1.1 μm) is formed. Here, the thickness of the buried layer 74 is 0.1
μm, which is thinner than other buried layers.
This buried layer 74 is used for the buried layer 7 to be subsequently formed.
This is because atoms are prevented from evaporating from the surface of the active layer due to the high temperature (1050 ° C.) used for the growth of 5,76.

On the back of the n-type substrate, an n-electrode 77 made of Ti / Al
Is formed, and a p-electrode 78 made of Ni / Au is formed on the p-contact. In this embodiment, an n-type AlGaN substrate is used, but a GaN substrate, a SiC substrate, a sapphire substrate, or the like may be used, and the polarity may be p or i-type.

In this embodiment, there are three buried layers. This is to introduce a reverse bias structure in the buried layer. The reverse bias structure introduced into the buried layer reduces the leak current of the device and improves the withstand voltage characteristics of the device.

(Embodiment 7) FIG. 7 is a structural sectional view of a semiconductor laser according to an embodiment. n-type Al _0.1 Ga _0.9 N Si doped on the substrate 79 n-type Al _0.1 Ga _0.9 N (silicon concentration 4 × 10 ^{1 7}
atoms / cm ³ , 1 μm thick) n-type cladding layer 8
0, Si-doped n-type GaN (silicon concentration 4 × 10 ¹⁷ atom
s / cm ³ , 0.1 μm in thickness).
In _0.2 Ga _0.8 N (thickness 3 nm) well layer and In _0.05 Ga _0.95 N
(5 nm thick) Undoped MQW layer 82 (three wells) composed of a barrier layer, Mg-doped p-type Al _0.2 Ga _0.8 N (Mg concentration 2 × 10 ¹⁷
atoms / cm ³ , a thickness of 20 nm)
Mg-doped p-type GaN (Mg concentration 2 × 10 ¹⁷ atoms / cm ³ , thickness 0.
1 μm) p-type optical confinement layer 84, Mg-doped p-type A
l _0.1 Ga _0.9 N (Mg concentration 2 × 10 ¹⁷ atoms / cm ³ , thickness 2μ)
m), a p-type cladding layer 85 composed of Mg-doped p-type GaN (M
A p-type contact layer 86 having a g concentration of 2 × 10 ¹⁷ atoms / cm ³ and a thickness of 0.05 μm) is sequentially grown to form an LD structure. The laser structure is grown in a MOCVD apparatus at a growth temperature of 780 ° C. for the InGaN MQW active layer 82 and 1050 ° C. for all other layers. After partially leaving the mesa 87 including the MQW active layer 82, the p-type optical confinement layer 84, the p-type cladding layer 85 and the p-type contact layer 86 by dry etching, the growth temperature is 600 ° C. by regrowth by MOCVD. Undoped with In _0.05 Ga _0.95 N (0.03 μm thickness)
The first buried layer (not shown) is regrown. The material of the first buried layer does not need to be the same as that of the second buried layer, and is selected in consideration of a regrowth temperature, a vaporization temperature, a refractive index difference from the active layer, and the like. The first buried layer is formed for the purpose of preventing the active layer from evaporating from the surface during the subsequent formation of the second buried layer at a high temperature (1050 ° C.). Subsequently, the growth temperature is raised to 1050 ° C., and the sample is waited for 5 minutes. The temperature of the sample is raised to 1050 ° C. to be a constant temperature, and the unnecessary first burying layer is vaporized. Undoped Al _0.2 Ga _0.8 N when the first buried layer has been vaporized
(Buried layer 88 made of (thickness: 2.2 μm))
To form On the back of the n-type substrate, an n-electrode 89 made of Ti / Al
Is formed, and a p-electrode 90 made of Ni / Au is formed on the p-contact. In this embodiment, an n-type AlGaN substrate is used, but a GaN substrate, a SiC substrate, a sapphire substrate, or the like may be used, and the polarity may be p-type or i-type.

[0031]

As described above, according to the present invention, a mesa structure including an active layer is regrown at a growth temperature lower than the growth temperature of the active layer so that a semiconductor having a lower refractive index than the active layer sandwiches the mesa structure. This can prevent the quality of the active layer from deteriorating due to the high temperature. Specifically, the following three effects are obtained.

Since the refractive index distribution in the stripe width direction and the gain distribution can be matched, the extra carriers are reduced and the capability of confining the carriers in the lateral direction is improved as compared with the conventional structure having a wide gain distribution. A low threshold laser is obtained.

In the structure having a wide gain distribution of the conventional structure, the gain outside the oscillation region increases as the optical output increases, while the refractive index distribution in the stripe width direction and the gain distribution can be matched. Thus, the stability of the transverse mode is improved.

In the conventional method, the mesa stripe is made of SiO ₂
, Heat conduction was poor, and a sufficient cooling effect could not be obtained. However, according to the present invention, since the active region is buried with the semiconductor, heat dissipation is improved and the life of the element can be extended as compared with the conventional method.

As described above, according to the present invention, it is possible to manufacture a buried laser device in which a refractive index distribution and a gain distribution are made to match with a nitride semiconductor. It is considered that the nitride-based compound semiconductor laser device having a low threshold obtained by the present invention, having excellent stability of the transverse mode at the time of high output, and having a long life has a great industrial value.

[Brief description of the drawings]

FIG. 1 is a sectional view of a nitride-based compound semiconductor laser device according to a first embodiment.

FIG. 2 is a sectional view of a nitride-based compound semiconductor laser device according to a second embodiment.

FIG. 3 is a sectional view of a nitride-based compound semiconductor laser device according to a third embodiment.

FIG. 4 is a sectional view of a nitride-based compound semiconductor laser device according to a fourth embodiment.

FIG. 5 is a sectional view of a nitride-based compound semiconductor laser device according to a fifth embodiment.

FIG. 6 is a sectional view of a nitride-based compound semiconductor laser device according to a sixth embodiment.

FIG. 7 is a sectional view of a nitride-based compound semiconductor laser device according to a seventh embodiment.

FIG. 8 is a cross-sectional view of a conventional nitride-based compound semiconductor laser device.

[Explanation of symbols]

1: n-type GaN substrate 2, 19, 28, 46, 58, 66, 80, 102: n
Mold cladding layer 3, 18, 29, 45, 57, 67, 81, 103: n
Light confinement layer 4, 16, 30, 43, 55, 68, 82, 104: MQ
W active layer 5, 31, 69, 83, 105: p-type cap layer 6, 15, 32, 42, 54, 70, 84, 106: p
Mold light confinement layers 7, 14, 33, 41, 53, 71, 85, 107: p
Mold cladding layer 8, 34, 72, 86, 108: p-type contact layer 9, 21, 35, 48, 60, 73, 87, 109: mesa type 10, 49, 88: buried layer 11, 26, 38, 51 , 64, 77, 89, 111:
n-electrode 12, 25, 39, 50, 63, 78, 90, 112:
p electrode 13: p-type AlGaN substrate 17, 44, 56: n-type cap layer 20, 47, 59: n-type contact layer 22, 36, 61, 74: first buried layer 23, 37, 62, 75: Second buried layer 24, 76: Third buried layer 27: n-type Al _0.1 Ga _0.9 N substrate 40: p-type AlGaN substrate 52: p-type AlGaN substrate 65: n-type AlGaN substrate 79: n-type AlGaN substrate 101: n Type GaN substrate 110: SiO ₂ insulating film

Claims (7)

[Claims] An In _X Ga _1-X N (0 ≦ X
≦ 1), and both the first cladding layer above the active layer are present in the mesa-type stripe structure, and the side of the mesa-type stripe structure is In the method for manufacturing a nitride-based compound semiconductor laser device having a buried layer made of a semiconductor having a low refractive index, the buried layer is grown at a temperature of 100 ° C. or higher than the growth temperature of the active region. A method for manufacturing a nitride-based compound semiconductor laser device. 2. The method according to claim 1, wherein the buried layer is made of a II-VI compound semiconductor. 3. An In _X Al _Y Ga _1-XYN as said buried layer.
2. The method for manufacturing a nitride-based compound semiconductor laser device according to claim 1, wherein a semiconductor having a composition of (X≥0, Y≥0, X + Y≤1) is used as a material. 4. The method for manufacturing a nitride-based compound semiconductor laser device according to claim 1, wherein said buried layer is a multilayer film. 5. The semiconductor device according to claim 1, wherein both the II-VI group compound semiconductor and In _X Al _Y Ga _1-XY N (X ≧ 0, Y ≧ 0, X + Y ≦ 1) are used as the multilayer film. The method for manufacturing a nitride-based compound semiconductor laser device according to claim 4. 6. A first buried layer is grown thinly on the surface of the mesa-type stripe structure at a temperature equal to or lower than the growth temperature of the active layer, and then the temperature is increased to a temperature equal to or higher than the growth temperature of the active layer. The method for manufacturing a nitride-based compound semiconductor laser device according to claim 4, wherein the buried layer is grown again. 7. A nitride compound semiconductor laser device manufactured by the method according to claim 1. Description: