JP2000261099A - Group iii nitride laser diode and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a group III nitride laser diode, in which no cracking occurs even in a p-side Al0.2Ga0.8N clad layer and a method for manufacturing the laser diode. SOLUTION: In a group III nitride laser diode having a sapphire substrate 1 and at least a buffer layer 2, an n-type GaN layer 3, a crack-preventing layer C1, an n-type AlxGa1-xN clad layer 4, an InyGa1-yN active layer 5, a p-type GaN light guide layer 6, a p-type AlxGa1-xN clad layer 7, and a p-type GaN contact layer 8, all of which are formed on the substrate 1, a p-type low temperature GaN buffer layer L1 is interposed between the p-type light guide layer 6 and the p-type clad layer 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a group III nitride laser diode made of GaN, AlGaN, InGaN or the like.

[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 30nm thick GaN, 3 [mu] m thick n-type GaN layer, Al _0.2 of n-type 0.4 [mu] m thick Ga _0.8 n cladding layer, a 0.07μm thick an In _{0. 2} Ga _0.8 N active layer, 0.1 μm thick p-type GaN optical guide layer, 0.4 μm
m thick p-type Al _0.2 Ga _0.8 N cladding layer and 0.1
A contact layer made of p-type GaN having a thickness of μm is sequentially formed.

The layer structure is subjected to fine processing several times to form an optical resonator and an n-side electrode connection,
After forming the p-electrode and the n-electrode respectively, an LD chip is obtained.

[0005]

In the above-described LD layer structure, an important problem during epitaxial growth is thermal stress or thermal stress caused by a difference in thermal expansion coefficient between multilayer films such as GaN, AlGaN, and InGaN constituting a laser diode. And how to prevent cracks in the epitaxial film caused by lattice irregularities. Table 1 shows the thermal expansion coefficient and lattice constant of the thin film used in the above-described LD layer configuration.

[0006]

[Table 1] From Table 1, it can be seen that between each epitaxial layer of the conventional LD layer structure, thermal stress at the time of lowering the epitaxial temperature due to a difference in thermal expansion coefficient to room temperature or large stress due to lattice irregularity is generated. Can be estimated.

[0007] Among them, thermal stress between the GaN layer and the Al _0.2 Ga _0.8 N layer causes a large tensile stress on the Al _0.2 Ga _0.8 N layer side, which causes a serious problem that cracks occur in the Al _0.2 Ga _0.8 N layer. This greatly affects the LD yield, reliability, and the like.

As a measure against such cracks, In
There is known an example in which a _0.2 Ga _0.8 N layer is introduced for the purpose of relaxing thermal stress between a GaN layer and a cladding layer made of Al _0.2 Ga _0.8 N. FIG. 4 is a cross-sectional view of a conventional layer structure for a group III nitride laser diode having an n-type crack preventing layer. On a sapphire substrate 1, a low-temperature buffer layer 2 made of GaN having a thickness of 30 nm, an n-type GaN layer 3 having a thickness of 3 μm, and an n-type In layer having a thickness of 0.1 μm
Crack preventing layer L1 made of _0.2 Ga _0.8 N, n-type cladding layer 4 of 0.4 μm thick Al _0.2 Ga _0.8 n, active layer 5 of 0.07 μm thick In _0.2 Ga _0.8 N, p-type 0.1 μm thick
Optical guide layer 6 composed of GaN, 0.4 μm thick p-type Al _0.2 Ga
_0.8 N cladding layer 7 and 0.1 μm thick p-type GaN
Are formed sequentially. In
_0.2 thermal expansion coefficient of Ga consisting _0.8 N layer using the greater than Al _0.2 Ga _0.8 N layer, which was set to take Al _0.2 Ga _0.8 thermal stress of N layer to the compression effect is observed.

However, as a result of actually assembling 100 LDs having this layer structure and measuring IV characteristics by applying a current, 23 LDs were destroyed at a voltage of 12 V or more. Thus the element that is destroyed was observed by SEM, the existence of cracks was confirmed in the cladding layer after consisting also p-type Al _0.2 Ga _0.8 N to any of the elements. On the other hand, no crack was observed in the device which could be measured normally. Thus, In
_The anti-crack layer made of _0.2 Ga _0.8 N is n-side Al _0.2 Ga
_This was only a measure for preventing cracking of the n-cladding layer of _0.8 N.

The present invention has been made to solve the above-mentioned problem, and an object of the present invention is to provide a p-side Al _0.2 Ga _0.8 N
It is an object of the present invention to provide a group III nitride laser diode having no cracks in a layer after the p-cladding layer made of and having a simple crack prevention layer, and a method of manufacturing the same.

[0011]

In order to achieve the above object, a sapphire substrate and at least a buffer layer, an n-type GaN layer, a crack prevention 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 And a low-temperature buffer layer made of p-type GaN between the p-type light guide layer and the p-cladding layer.

It is preferable that a low-temperature buffer layer made of p-type GaN is further provided between the p-cladding layer and the p-contact layer. The crack preventing layer is preferably a low-temperature buffer layer made of n-type GaN. The thickness of the low-temperature buffer layer made of the p-type or n-type GaN is 5 nm or more and 100 n
m or less.

In the method for manufacturing a group III nitride laser diode described above, the growth temperature of the low-temperature buffer layer made of p-type or n-type GaN is preferably 400 ° C. or more and 700 ° C. or less.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below in detail with reference to examples. Example 1 FIG. 1 is a sectional view of a layer structure for a group III nitride laser diode having a low-temperature buffer layer made of p-type GaN according to the present invention.

A buffer layer 2 made of GaN is formed on a sapphire substrate 1 by metal organic chemical vapor deposition (MOCVD).
After growing at 0 ° C., the temperature was raised to 1050 ° C., and a 3 μm thick n
The GaN layer 3 is grown. Next, cool down to 700 ℃, 0.1 μm
Crack prevention layer C1 made of thick n-type In _0.2 Ga _0.8 N
Grow. The temperature is raised again to 1050 ° C, and 0.4 μm thick n-type
A cladding layer 4 made of Al _0.2 Ga _0.8 N is grown. Then 70
The temperature is lowered to 0 ° C., and an active layer 5 made of In _0.2 Ga _0.8 N having a thickness of 0.07 μm is grown. Then the temperature was raised again to 1050 ° C.
After growing the optical guide layer 6 made of 1 μm thick p-type GaN,
The temperature is lowered to 500 ° C., and a low-temperature buffer layer L1 made of p-type GaN having a thickness of 30 nm is grown. Then, the temperature was raised to 1050 ° C., and a cladding layer 7 made of 0.4 μm thick p-type Al _0.2 Ga _0.8 N, 0.1 μm thick p
Type GaN contact layers 8 are grown in order.

The wafer on which the group III nitride layers are laminated in this manner is placed on an optical microscope or a scanning electron microscope (SEM).
In the conventional layer configuration without the low-temperature buffer layer L1, cracks had a density of 1000 / cm ² .
No cracks were observed in the layer structure according to the present invention.

After 100 LDs were formed into chips from this wafer, they were assembled into devices, and VI measurement was performed in the same manner as in the prior art. As a result, the yield of the device measured using the present invention was greatly improved, with only one device broken at a voltage of 12 V or more.

A low-temperature buffer layer L made of p-type GaN
1 has no effect on the VI characteristics, and furthermore, L
It was also confirmed that there was no effect on the D 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 low-temperature buffer layer L1 made of p-type GaN was examined. 1 to 200 nm thickness
When the thickness was 5 nm or less, no effect on cracks was observed. On the other hand, when the thickness was 100 nm or more, the LD characteristics deteriorated.

The growth temperature of the p-type GaN low-temperature buffer layer L1 was also studied. Investigations at growth temperatures from 300 ° C to 900 ° C indicate that p-type GaN does not grow below 400 ° C, and that crystallization of GaN proceeds too much above 700 ° C and does not function sufficiently as a crack prevention layer. found. Further, it was also found that cracks did not occur even if the thickness of the p-type Al _0.2 Ga _0.8 N clad layer 7 was increased, and it became possible to cope with a structural design change for improving LD characteristics.

The p-type GaN low-temperature buffer layer L1 is amorphous at a substrate temperature of 500 ° C. during growth, but crystallizes in the course of raising the temperature to 1050 ° C., which is the growth temperature of the p-type Al _0.2 Ga _0.8 N clad layer 7. Goes on. The p-type GaN buffer layer L1 contains some crystal defects such as dislocations and acts as a cushion, and the stress that the p-type GaN optical guide layer 6 receives from the p-type Al _0.2 Ga _0.8 N clad layer 7 directly. It is presumed that the growth is relaxed as compared with the growth on the p-type GaN optical guide layer 6 and no crack is generated. In addition, it is found that the layer above the p-type GaN buffer layer 61 tends to have more defects such as dislocations than usual, but has no effect on the light emission characteristics because it is above the active layer. Example 2 A low-temperature buffer layer made of n-type GaN was inserted in place of the crack prevention layer made of n-type In _0.2 Ga _0.8 N in Example 1. FIG. 2 is a sectional view of a layer structure for a group III nitride laser diode having a low-temperature buffer layer made of n-type GaN according to the present invention. Crack prevention layer C1 in FIG.
However, since only the low-temperature buffer layer C2 made of n-type GaN is used, the description of the other symbols is omitted.

Since the low-temperature buffer layer C2 made of n-type GaN having a thickness of 30 nm has an amorphous and flexible structure, the thermal stress of the n-cladding layer 3 to be grown next is relaxed, and cracks occur in the n-cladding layer 3. Absent. The low-temperature buffer layer is composed of a single group III element, and is easier to form a thin film than In _0.2 Ga _0.8 N.

As a result, although a slight decrease in the luminous efficiency was observed, the characteristics were hardly affected, and a good LD epitaxial layer without cracks was obtained. Embodiment 3 FIG. 3 is a sectional view of a layer structure for a group III nitride laser diode further having a low-temperature buffer layer made of p-type GaN according to the present invention.

A low-temperature buffer layer was further added to the layer structure of Example 1. That is, the contact layer 8 cladding layer 7 made of p-type Al _0.2 Ga _{0 .8} N and consists of 0.1 [mu] m thick p-type GaN
Low temperature buffer layer L2 made of p-type GaN with a thickness of 30 nm
Was inserted. The effects of the growth temperature and film thickness of the buffer layer were the same as in Example 1.

In order to protect the active layer of the LD chip from the impact of wire bonding during LD assembly, a p-type Ga
It is preferable to increase the thickness of the contact layer 8 made of N 2. In this case, a p-type cladding layer 7 made of p-type Al _0.2 Ga _0.8 N
It is also necessary to consider the stress received from the p-contact layer 8 made of p-type GaN having an increased thickness. In such a case, the low-temperature buffer layer L4 made of p-type GaN
Is valid. In the case where the low-temperature buffer layer L2 is not provided (Example 1), when the thickness of the p-contact layer 8 exceeds 0.1 μm, some cracks occur. However, in the present embodiment, cracks were completely prevented. The occurrence of defects due to wire bonding impact was reduced.

[0026]

According to the present invention, a sapphire substrate, a buffer layer formed thereon, an n-type GaN layer, a crack prevention layer, an n-cladding layer made of Al _X Ga _1-x N, In _y Ga
_1-y N active layer, GaN p-type light guide layer,
In a group III nitride laser diode having a p-cladding layer made of Al _X Ga _1-x N and a p-contact layer made of GaN, a low-temperature buffer layer made of p-type GaN is provided between the p-type light guide layer and the p-cladding layer. Intervening, the thermal stress in the p-layer stack after the p-cladding layer is reduced, cracks do not occur, crack-free LD epitaxial films can be formed, LD yield improves, and laser characteristics are stabilized. Can be achieved.

Further, since a low-temperature buffer layer made of p-type GaN is further interposed between the p-cladding layer and the p-contact layer, the thickness of the p-contact layer can be increased, and the impact during wire bonding can be reduced. The assembly yield can be improved.

[Brief description of the drawings]

FIG. 1 is a sectional view of a layer structure for a group III nitride laser diode having a low-temperature buffer layer made of p-type GaN according to the present invention.

FIG. 2 is a sectional view of a layer structure for a group III nitride laser diode having a low-temperature buffer layer made of n-type GaN according to the present invention.

FIG. 3 is a cross-sectional view of a layer structure for a group III nitride laser diode further including a low-temperature buffer layer made of p-type GaN according to the present invention.

FIG. 4 is a cross-sectional view of a conventional layer structure for a group III nitride laser diode having a crack prevention layer.

[Explanation of symbols]

Reference Signs List 1 sapphire substrate 2 GaN buffer layer 3 n-type GaN layer C1 n-type In _0.2 Ga _0.8 N crack prevention layer C2 n-type GaN low-temperature buffer layer 4 n-cladding layer 5 active layer 6 optical guide layer L1 p-type GaN low-temperature buffer layer 7 p Cladding layer 8p contact layer

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yasushi Shinmura 1-1 1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki City, Kanagawa Prefecture Inside Fuji Electric Co., Ltd. (72) Inventor Yoichi Shindo 1st Tanabe Nitta, Kawasaki-ku, Kawasaki City, Kanagawa Prefecture No. 1 Fuji Electric Co., Ltd. F term (reference) 5F073 AA51 AA55 CA07 CB05 CB07 CB10 EA28

Claims (5)

[Claims] A sapphire substrate and at least a shape thereon.
Buffer layer, n-type GaN layer, crack prevention layer,
Al_XGa_1-xN cladding layer made of N, In_yGa _1-yFrom N
Active layer, p-type light guide layer made of GaN, Al_XGa_1-x
N p-cladding layer and GaN p-contact
III-nitride laser diode with
Between the p-type light guide layer and the p-cladding layer.
It has a low-temperature buffer layer made of GaN.
III-nitride laser diode. 2. The group III nitride laser diode according to claim 1, further comprising a low-temperature buffer layer made of p-type GaN between said p-cladding layer and said p-contact layer. 3. The group III nitride laser diode according to claim 1, wherein said crack preventing layer is a low-temperature buffer layer made of n-type GaN. 4. The group III nitride laser diode according to claim 1, wherein the low-temperature buffer layer made of p-type or n-type GaN has a thickness of 5 nm or more and 100 nm or less. 5. The II according to claim 1, wherein a growth temperature of the low-temperature buffer layer made of p-type or n-type GaN is 400 ° C. or more and 700 ° C. or less.
Manufacturing method of group I nitride laser diode.