JP2000261102A - Group iii element nitride laser diode and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent generation of a crack after formation of a p clad layer by providing a (p) crack preventing layer of p-type having a specific composition formula between a p-type light guide layer and the (p) clad layer. SOLUTION: A (p) crack preventing layer L consisting of InyGa1-yN is provided between a p-type light guide layer 6 and a (p) clad layer 7. The composition of the (p) crack preventing layer L is preferably such that 0.05<=y<=0.2. Further, the thickness of the (p) crack preventing layer L is preferably not less than 5 nm and not larger than 200 nm. The p crack preventing layer L is preferably a buffer layer consisting of GaN grown at a low temperature. Further, in a method for manufacturing this group III element nitride laser diode, the growing temperature of the (p) crack preventing layer L is preferably not lower than 700 deg.C and not higher than 900 deg.C. According to this construction, as the thermal expansion coefficient of the (p) crack preventing layer L is larger than that of the (p) clad layer 7, the thermal stress of the (p) clad layer 7 can be relieved and a crack is not generated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser diode comprising a sapphire substrate and a group III nitride thin film laminated thereon.

[0002]

2. Description of the Related Art It is possible to control n-type and p-type valence electrons by adding silicon (Si) or magnesium (Mg) by direct transition and controlling the optical energy gap in a range of 1.9 to 6.2 eV. Possible Al _X Ga _y In _1-xy N system II
Prototypes of laser diodes (hereinafter referred to as LDs) and light-emitting diodes have been made using group I nitride semiconductors.
A sapphire substrate, a spinel (MgAl ₂ O ₄ ) substrate, or the like is widely used for crystal growth of a group III nitride semiconductor because of good matching of lattice and thermal expansion coefficient.

A typical layer structure of a group III nitride LD in which the active layer is In _y Ga _1-y N is shown below. On a sapphire substrate 1, a low-temperature buffer layer made of GaN, n-type GaN with a thickness of 3 μm
Layer, 0.4 [mu] m n-cladding layer made of n-type Al _0.2 Ga _0.8 N having a thickness, the active layer comprising a 0.07μm thick In _0.2 Ga _{0. 8} N, 0.1
μm-thick p-type GaN optical guide layer, 0.4 μm-thick p
A p-cladding layer of Al _0.2 Ga _0.8 N and a p-contact layer of p-type GaN having a thickness of 0.1 μm are sequentially formed. The layer configuration is repeatedly subjected to fine processing several times to form an optical resonator and an n-side electrode connection portion, and to form a p-electrode and an n-electrode respectively, to obtain an LD chip.

[0004]

In the above LD structure ## 0005], important during the epitaxial growth of GaN constituting the semiconductor _{laser, Al x Ga 1-x N} , the heat between the multilayer film such as In _y Ga _1-y N The key is to prevent cracking of the epitaxial film caused by thermal stress or lattice irregularity caused by a difference in expansion coefficient. Table 1 shows the thermal expansion coefficient and lattice constant of the multilayer film used for the LD.

[0005]

[Table 1] From Table 1, it can be estimated that thermal stress due to a difference in thermal expansion coefficient or large stress due to lattice irregularity is generated between the respective epitaxial films of the LD structure. Among them, GaN
The thermal stress between the Al _0.2 Ga _0.8 N layer and the Al _0.2 Ga _0.8 N layer generates a large tensile stress on the Al _0.2 Ga _0.8 N layer side, which causes a serious problem of cracks in the Al _0.2 Ga _0.8 N layer, resulting in a low LD yield. Greatly affects reliability.

As a countermeasure against such a crack, In
_0.2 Ga _0.8 N layer is composed of n-type GaN layer and Al _0.2 Ga _0.8 N
There is known an example introduced for the purpose of relaxing thermal stress between clad layers. FIG. 3 shows a conventional structure having an anti-crack layer III.
It is sectional drawing of the layer structure for group nitride laser diodes.
On a sapphire substrate 1, a low-temperature buffer layer 2 made of GaN, an n-type GaN layer 3 having a thickness of 3 μm, In _0.2 Ga having a thickness of _0.1 μm
N crack prevention layer C1, consisting of _0.8 N, 0.4 μm thick n
N-cladding layer 4 of type Al _0.2 Ga _0.8, 0.07 μm thick In
Active layer 5 of _0.2 Ga _0.8 N, p-type GaN of 0.1 μm thickness
Light guide layer 6 made of p-type Al _0.2 Ga _0.8 N 0.4 μm thick
And a p-contact layer 8 made of p-type GaN having a thickness of 0.1 μm. In _0.2
Thermal expansion coefficient of Ga _0.8 N is utilized is greater than Al _0.2 Ga _0.8 N, it is obtained by such take Al _0.2 Ga _0.8 thermal stress of N layer to the compression effect is observed.

[0007] Actually, 100 LDs having such a layer structure were assembled and IV characteristics were measured by passing a current, and 23 devices were destroyed at a voltage of 12 V or more. Observation of the thus-broken devices by SEM confirmed that cracks existed in all devices after the p-type cladding layer made of p-type Al _0.2 Ga _0.8 N. On the other hand, no crack was observed in the device which could be measured normally. In this way
_0.2 Ga _0.8 n crack preventing layer consisting of N is Al _0.2 Ga _0.8 N
This was merely a measure for preventing cracks in the n-cladding layer made of

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a semiconductor device having good LD characteristics without cracks after a p-cladding layer made of Al _0.2 Ga _0.8 N.
An object of the present invention is to provide a group III nitride laser diode and a method for manufacturing the same.

[0009]

In order to achieve the above object, a sapphire substrate and at least a buffer layer, an n-type GaN layer, an n crack preventing layer, an Al _X Ga
_1-x N n-cladding layer consisting of an active layer made of _{In y Ga 1-y N,} p -type optical guide layer made of GaN, p-cladding layer and a p-contact layer made of GaN consisting Al _X Ga _{1- x} N A III-nitride laser diode having a p-type In _y Ga between the p-type light guide layer and the p-cladding layer.
_It has a p-crack prevention layer made of _1-yN .

It is preferable that the composition of the p-crack preventing layer made of In _y Ga _1-y N satisfies 0.05 ≦ y ≦ 0.2. The In _y Ga
The thickness of the p-crack prevention layer made of _1-y N is 5 nm or more and 200 n
m or less. The crack prevention layer is preferably a buffer layer made of GaN grown at a low temperature. III above
In the method for manufacturing a group III nitride laser diode,
The growth temperature of the p-crack prevention layer composed of In _y Ga _1-y N is 700
It is preferable that the temperature is not lower than 900 ° C and not lower than 900 ° C.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below in detail with reference to examples, and its operation and effects will be described. Example 1 FIG. 1 is a sectional view of a layer structure for a group III nitride laser diode having a p-crack preventing layer according to the present invention.

A GaN buffer layer 2 is formed on a sapphire substrate 1 by using an organic metal vapor deposition method (hereinafter referred to as MOCVD).
After growing at ℃, the temperature is raised to 1050 ℃, 3μm thick n-type
A GaN layer 3 is grown. Next, cool down to 700 ℃, 0.1 μm
Growing the crack preventing layer C1 having a thickness of In _0.2 Ga _0.8 N. Again the temperature was raised to 1050 ° C., of 0.4 [mu] m thick n-type Al _{0. 2} G
An n clad layer 4 of _0.8 N is grown. Then 700 ° C
Then, the active layer 5 made of In _0.2 Ga _0.8 N and having a thickness of 0.07 μm is grown. Then the temperature was raised again to 1050 ° C and 0.1 μm
After growing the light guide layer 6 made of p-type GaN thick,
The temperature was lowered to ℃ to grow a 0.1 μm thick p-crack prevention layer L made of In _0.2 Ga _0.8 N. Then raise the temperature to 1050 ° C and 0.4
A p-cladding layer 7 of p-type Al _0.2 Ga _0.8 N having a thickness of μm and a p-contact layer 8 of p-type GaN having a thickness of 0.1 μm are sequentially grown.

When the surface of the wafer thus prepared was observed with an optical microscope and an SEM, cracks had a density of 1,000 / cm ^{2 in} the conventional layer structure without the p-crack preventing layer L. No crack was observed in such a layer configuration. This is due to the In _0.2 of the p crack prevention layer.
Thermal expansion coefficient of Ga _0.8 N can be estimated to be because the thermal stress of the p clad layer is relaxed larger than that of Al _0.2 Ga _0.8 N of the p-cladding layer.

After 100 LDs were formed from the wafer and assembled, and VI measurement was carried out in the same manner as in the prior art, the device having the layer structure according to the present invention was found to have one device broken at a voltage of 12 V or more. And the yield greatly improved. It was also confirmed that the introduction of the p-type crack prevention layer L had no effect on the VI curve and had no effect on the LD characteristics. This is a result of the use of the present invention in which cracking of the crystal was completely prevented.

Further, the influence of the thickness of the p crack preventing layer L was examined. Crack, changing thickness from 1 to 200 nm, V
When the -I characteristics and LD characteristics were examined, no effect on cracks was observed below 5 nm, and LD characteristics exceeded 200 nm.
It was found that the characteristics were deteriorated.

Further, the growth temperature of the p-crack preventing layer was also examined. As a result of investigations in the growth temperature range from 300 ° C to 900 ° C, a good epitaxial film cannot be grown below 700 ° C, and if it exceeds 900 ° C, In is not taken into the crystal, so it is sufficient as an LD crack prevention layer. Turned out not to work.

Further, the In composition (y) of the p crack preventing layer was also examined. As a result of examining the In composition in the range of 0.01 to 0.3, it was found that if it was less than 0.05, it did not function sufficiently as a crack prevention layer. When it exceeds 0.2, it has been found that light absorption in the p-crack preventing layer is large and the characteristics of LD are deteriorated.

If a p-crack preventing layer is interposed,
Al_0.2Ga_0.8Even if the thickness of the cladding layer 7 made of N is increased
It was also found that cracks did not occur.
Even if the D characteristic needs to be improved, it can be dealt with. Example
2 FIG. 2 shows a group III nitride laser diode according to the present invention.
FIG. 3 is a cross-sectional view of a layer configuration for use. Example 1 refers to n-type Al_0.2G
a_0.8N-type In between the N cladding layer 4 and the n-type GaN layer 3 _0.2Ga
_0.8Instead of the n crack prevention layer C1 made of N,
An n low-temperature buffer layer C2 made of n-type GaN grown at low temperature is provided.
Digits are different. The growth temperature was 500 ° C.

When the growth temperature was 400 ° C. or more and 700 ° C. or less, the same test results as in Example 1 were obtained using the n low-temperature buffer layer C2 at any growth temperature. The group III element in the n low temperature buffer layer is one element, and the binary In _0.2 Ga _0.8
Thin film formation is simpler than N layer.

[0020]

According to the present invention, a sapphire substrate and a small
At least a buffer layer formed on it, n-type GaN
Layer, n crack prevention layer, Al_XGa_1-xN cracks consisting of N
Layer, In _yGa_1-yN active layer, GaN optical layer
Id layer, Al_XGa_1-xN clad p layer and GaN
III-nitride laser with p-contact layer composed of
In the diode, the p-type light guide layer and the p-type
P-type In between the pad layers_yGa_{1- y}Prevention of p crack consisting of N
Cracks in the layers after the p-cladding layer
-Free III-nitride laser diode with excellent characteristics
And the production yield of LD is improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a layer structure for a group III nitride laser diode having a p-crack preventing layer according to the present invention.

FIG. 2 is a sectional view of a layer structure for a group III nitride laser diode according to the present invention.

FIG. 3 is a cross-sectional view of a conventional layer structure for a group III nitride laser diode having an n crack preventing layer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sapphire substrate 2 Buffer layer 3 n-type GaN layer C1 n crack prevention layer C2 n low temperature buffer layer 4 n clad layer 5 active layer 6 light guide layer Lp crack prevention layer 7 p clad layer 8 p contact layer

Continuation of front page (72) Inventor Yasushi Shinmura 1-1, Tanabe-Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Inside Fuji Electric Co., Ltd. (72) Inventor Yoichi Shindo 1-1-1, Tanabe-Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Fuji F term (reference) in Denki Co., Ltd. 5F041 AA44 CA04 CA34 CA40 CA46 5F073 AA51 AA55 CA07 CB05 CB07 EA28

Claims (5)

[Claims] A sapphire substrate and at least a shape thereon.
Buffer layer, n-type GaN layer, n crack prevention
Layer, Al_XGa_1-xN cladding layer made of N, In_yGa_1-yN
Active layer of GaN, p-type light guide layer of GaN, Al_XGa
_1-xN-type p-cladding layer and GaN-type p-type
III-nitride laser diode with tact layer
Between the p-type light guide layer and the p-cladding layer.
In_yGa _1-yHaving a p-crack prevention layer composed of N
A group III nitride laser diode characterized by the above-mentioned. 2. The group III nitride laser diode according to claim 1, wherein the composition of the p-crack preventing layer made of In _y Ga _1-y N satisfies 0.05 ≦ y ≦ 0.2. 3. The group III nitride laser diode according to claim 1, wherein the thickness of the p-crack prevention layer made of In _y Ga _1-y N is not less than 5 nm and not more than 200 nm. 4. The n-crack preventing layer is formed of n grown at a low temperature.
4. The method for producing a group III nitride laser diode according to claim 1, wherein the low-temperature buffer layer is made of type GaN. 5. The group III nitride according to claim 1, wherein the growth temperature of the p-crack prevention layer made of In _y Ga _1-y N is 700 ° C. or more and 900 ° C. or less. Manufacturing method of laser diode.