JPH11297628A - Group III nitride semiconductor - Google Patents

Abstract

(57) [Problem] To provide a semiconductor device on a group IV semiconductor substrate having a (111) plane orientation.
Epitaxially growing a nitride layer of a group I element
A group II nitride semiconductor is obtained. A silicon substrate having a (111) plane orientation is provided.
For example, an Al _x Ga _{1 -x} As buffer layer 2a is grown by MOCVD, and a group III nitride layer such as an n-type GaN contact layer 3 is epitaxially grown thereon. In particular, the Al composition x of the Al _x Ga _{1 -x} As buffer layer 2a is set to 0.1.
2 or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention is, (hereinafter referred to as _{Al x Ga y In 1-x-} y N, where x = 0~1, y = 0~1) aluminum gallium indium nitride produced by such an epitaxial method The present invention relates to a group III nitride semiconductor.

[0002]

2. Description of the Related Art Al _x G which is a direct transition and whose optical energy gap can be controlled in the range of 1.9 to 6.2 eV.
Semiconductor lasers and light emitting diodes using a _y In _1-xy N have been prototyped. Al _x G with wurtzite structure
a _y an In the _1-xy N good quality is large substrate crystals not been obtained, hence the semiconductor laser or a light emitting device using the _{Al x Ga y In 1-xy} N, lattice constant and thermal expansion Heteroepitaxial growth must be performed on substrates with different coefficients. So far, sapphire (Al ₂ O ₃ ), spinel (MgAl ₂ O ₄ ), silicon carbide (hereinafter abbreviated as SiC), and the like have been used as substrates for epitaxial growth because of their good lattice constants and good thermal expansion coefficients. A silicon (hereinafter, referred to as Si) substrate is used. And silicon (Si) and magnesium (Mg)
Control of n-type and p-type valence electrons by adding
_x Ga by _y In composition control for changing the x and y of _1-xy N to control the optical energy gap is achieved, the laser hetero (DH) structure to double is prototype.

[0003] Among the above-mentioned various substrates for epitaxial growth, sapphire does not have a conductive substrate, and its cleavage plane is different from the group III nitride grown thereon.
Therefore, when manufacturing a group III nitrogen compound semiconductor laser diode (hereinafter referred to as LD), the cavity end face cannot be formed by the cleavage method. Therefore, for example, the cavity end face is formed by a dry etching method, but there are serious problems in mass productivity and element life.

[0004] Further, the SiC substrate, like the sapphire substrate, has a cleavage plane different from that of the grown group III nitride and is expensive and unsuitable for mass production. On the other hand, in the case of a Si substrate having a (111) plane orientation, the interatomic distance is 0.1 mm.
384 nm, for example, 0.31 interatomic distance of GaN.
A group III nitride having a (0001) plane orientation close to 9 nm can be epitaxially grown thereon. The cleavage plane of the silicon substrate is a (111) plane, and can be a continuous plane sharing a ridge with the cleavage plane (1, -1, 00) plane of the grown group III nitride. In addition, since it is inexpensive and can supply a low-resistance substrate, it is expected to be industrially promising.

FIG. 2 is a schematic sectional view of an LD chip using a Si substrate. An n-type gallium nitride (hereinafter abbreviated as GaN) contact layer 3 and an n-type aluminum gallium nitride (hereinafter abbreviated as GaN)
_0.2 Ga _0.8 N) cladding layer 4, indium gallium nitride (hereinafter abbreviated as In _0.2 Ga _0.8 N) active layer 5,
The p-type Al _0.2 Ga _0.8 N cladding layer 6 and the p-type GaN contact layer 7 are formed, for example, by metal organic vapor deposition (hereinafter referred to as MOC).
(Referred to as VD method)). The plane orientation of the epitaxial layer is the (0001) plane. On the p-type GaN contact layer 7, there is a silicon oxide film (hereinafter, referred to as SiO ₂ ) 10 as a current confinement layer for passing a current through a part of the active layer, and through the gap, the p-side electrode 8 is p-type. It is in contact with the GaN contact layer 7. On the back surface side of the Si substrate 1, a back electrode 9 is provided. The resonator end face of the LD chip is formed by, for example, a cleavage method. When cleaved on a (111) oriented Si substrate, the cleavage plane forms an angle of about 70.5 degrees. On the other hand, the cleavage plane of the group III nitride is split almost perpendicularly to the growth plane.

[0006]

In the above-mentioned LD, the surface morphology often deteriorates partially when the group III nitride is epitaxially grown on Si. This is because, while Si is cubic, group III nitride is hexagonal, and although an AlN buffer layer is inserted as a buffer layer to reduce the difference in crystal morphology, defects occur at the interface. It is thought that it is easy to do.

Actually, the LD manufactured in this way is
When zero devices were assembled and a current was passed, current-voltage characteristics were measured. As a result, 76 devices were broken at a voltage of 12 V or more. Scanning electron microscope (SEM) for normal and broken elements
Observed and compared. The normal element had a smooth surface morphology, whereas the broken element had a rough surface morphology and a part of the surface was missing. Thus, the deterioration of the surface morphology leads to a decrease in the yield.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has as its object to provide a group III nitride semiconductor which has been epitaxially grown with good surface morphology and is suitable for manufacturing a semiconductor device having excellent quality. Is to do.

[0009]

In order to solve the above-mentioned problems, a group III nitride semiconductor according to the present invention is provided on a group IV semiconductor substrate having a (111) plane orientation by using aluminum gallium arsenide (Al _x Ga _{1 -x} As). , X = 0-1) layer, and a group III nitride layer is epitaxially grown on the aluminum gallium arsenide (Al _x Ga _{1 -x} As) layer.

[0010] By inserting the Al _x Ga _1-x As layer as the buffer layer, defects is suppressed at the interface between the substrate and the epitaxial layer as shown in the Examples below, it is improved morphology of the epitaxial growth layer . In particular, aluminum gallium arsenide (Al _x Ga _1-x
The Al composition x of As) is set to 0.2 or more.

Since AlGaAs has a strong bond between Al and As, evaporation of As is small and generation of defects at the interface is suppressed. It is assumed that the group IV semiconductor substrate is silicon. Silicon is most commonly used as a semiconductor substrate, is easily available, and has a low price, so that it is suitable as a substrate for epitaxial growth.

The group III element is aluminum, gallium,
It shall contain any of indium. Actually, epitaxial growth of aluminum nitride, gallium nitride, indium nitride and their mixed nitrides was performed, and it was confirmed that a high-quality epitaxial layer was obtained.

The semiconductor substrate is to be cleaved. For example, if a large number of semiconductor elements can be obtained by cleavage, such as a group III nitride semiconductor laser having a cleavage plane as a light-emitting surface, it is easy to manufacture and suitable for mass production.

[0014]

Embodiments of the present invention will be described below. Embodiment 1 FIG. 1 is a sectional view of an LD using a Si substrate according to the present invention. 20 nm thick n-type Al _0.5 Ga _0.5 As buffer layer 2 on n-type Si (111) substrate 1
a, through the n-type GaN contact layer 3 having a thickness of 500 nm, n-type Al _0.2 Ga _0.8 N cladding layer 4 having a thickness of 150nm, In _0.2 Ga _{0. 8} N active layer 5 having a thickness of 80 nm, a film thickness of 150nm A DH structure composed of a p-type Al _0.2 Ga _0.8 N cladding layer 6 and a 100-nm-thick p-type GaN contact layer 7 are laminated. AlGaAs buffer layer 2
Is an underlayer for enabling a group III nitride epitaxial film to be grown on the silicon substrate 1;
The contact layer 3 is a layer for improving the crystallinity of the epitaxial film after the n-type Al _0.2 Ga _0.8 N clad layer 4 thereon. A 50 nm-thick silicon oxide (Si) film is used as a current confinement film for flowing a current through a part of the active layer.
O ₂ ) film 10 is provided, and the contact portion of p electrode 8 is narrowed. Each of the p electrodes 8 has a thickness of 20 by a sputtering method.
It consists of three layers of nickel (Ni) / molybdenum (Mo) / gold (Au) of 0, 50 and 300 nm. On the back surface of the Si substrate 1, a thickness of 100,
200, 500 nm titanium (Ti) / nickel (N
A back electrode 9 composed of three layers of i) / gold (Au) is provided.

Hereinafter, a method of manufacturing the same will be described. First about thickness
500 μm low resistivity (15 mΩ · cm) n-type Si base
The plate is carried into a MOCVD apparatus, and the temperature is raised to 550 ° C.
_xGa_1-xThe As buffer layer 2a is grown. Al, G
a and As are each source of trimethyl aluminum
[Al (CH_Three)_Three], Trimethylgallium [Ga (C
H _Three)_Three], Arsine [AsH_Three]. Al composition
x was set to 0.5. Also, doping is performed to make the conductivity type n-type.
Si as punt (source is monosilane, SiH _Four)
And the carrier concentration is 1 × 10¹⁸cm^-3And (1
11) Al growing on silicon substrate 1 with plane orientation_0.5G
a_0.5The As buffer layer 2a also has a (111) plane orientation.

[0016] Then the temperature was raised to 1050 ° C., to grow an n-type GaN contact layer 3, n-type Al _0.2 Ga _{0. 8} N cladding layer 4. Next, the temperature is lowered to 700 ° C., and In _0.2 Ga _0.8
A N active layer 5 is grown. Then, the temperature was raised again to 1050 ° C., and the p-type Al _0.2 Ga _0.8 N cladding layer 6 and the p-type GaN
The contact layers 7 are sequentially grown. The sources of In and N are trimethylindium [In (CH ₃ ) ₃ ],
Ammonia [NH ₃ ]. Mg was used as the p-type dopant.

Here, the SiO ₂ film 10 is taken out of the MOCVD apparatus, a SiO ₂ film 10 is formed by a sputtering method, and a stripe is formed by photolithography. Next, SiO ₂ 1
Ni / Mo / as the upper p-side electrode 8 by sputtering.
An ohmic electrode made of Au is formed. To facilitate cleavage, the epitaxial film side is attached to a polishing sample support, and the thickness is reduced to about 50 μm from the back surface of the Si substrate 1 by ordinary mechanical polishing. Then, on the back surface (the polished Si substrate surface) washed with pure water,
Back electrode 9 made of Ti / Ni / Au by sputtering
Was formed. Thereafter, the cavity was cleaved to a width of 200 μm to form a cavity facet, and further scribed to obtain a group III nitride semiconductor LD chip, which was assembled.

One hundred LDs manufactured as described above were prepared.
A screening test at 12 V was performed as in the past. In the LD of this embodiment, the number of destroyed elements is 32,
The non-defective rate was greatly improved compared to the conventional one. SEM observation revealed that the surface morphology was also improved. This is probably because the use of the AlGaAs buffer layer 2a suppressed the occurrence of defects at the interface. Although the details of the mechanism for suppressing the occurrence of defects are not clear, the reason is that the interatomic distance of the AlGaAs buffer layer 2a having the (111) plane orientation is about 0.39 and (000).
1) The inter-atomic distance of the n-type GaN contact layer 3 in the plane orientation is close to 0.32, and the hardness of AlN is as high as 9, whereas the hardness of GaAs is about 5 which is soft and the bonding between atoms is loose. It is mentioned. [Experiment] An LD was manufactured in the same manner as in the above example by changing the Al composition x of Al _x Ga _{1 -x} As used as a buffer layer, and a similar screening test was performed. Table 1 shows the results. The non-defective rate in the table is the number of elements which did not break at 12 V or more when 100 elements were manufactured.

[0019]

[Table 1] From Table 1, it can be seen that the non-defective rate is significantly improved when the Al composition is 0.2 or more, but not so much when the Al composition is 0.3 or more.

When the Al composition is low, As evaporates and escapes during the growth of GaN at a high temperature, so that defects are likely to occur at the interface. It is considered that this is due to the fact that evaporation of As becomes difficult to occur due to the strongness. The surface morphology also shows that the Al composition is 0.
Significant improvement was seen at 2 and above.

[0021]

As described above, according to the present invention,
An aluminum gallium arsenide (Al _x Ga _1-x As, x = 0 to 1) layer is grown on a (111) plane group IV semiconductor substrate, and the aluminum gallium arsenide (Al _x Ga
By epitaxially growing a group III nitride layer on the _1-x As) layer, a group III nitride semiconductor having a high quality epitaxial layer with few interface defects can be obtained.

In particular, aluminum gallium arsenide (Al _x G
By setting the Al composition x of a _1-x As) to 0.2 or more, the yield of the group III nitride semiconductor can be significantly improved, for example, as shown in the examples. According to the method of the present invention using a general and inexpensive group IV semiconductor as a substrate,
The mass production of group III nitride semiconductors becomes possible, which greatly contributes to the development and spread of group III nitride lasers and the like.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a group III nitride semiconductor LD chip according to the present invention.

FIG. 2 is a cross-sectional view of a conventional LD chip.

[Explanation of symbols]

1 n-type Si substrate 2 n-type AlN buffer layer 2a n-type Al _X Ga _1-x As buffer layer 3 n-type GaN contact layer 4 n-type Al _X Ga _1-x N cladding layers 5 In _y Ga _1-y N activity Layer 6 p-type Al _x Ga ₁ -xN cladding layer 7 p-type GaN contact layer 8 p-side electrode 9 back electrode 10 SiO ₂ film

Claims (5)

[Claims] 1. A group II nitride layer epitaxially grown on a group IV semiconductor substrate having a (111) plane orientation.
In a group I nitride semiconductor, aluminum gallium arsenide (Al _x Ga _{1 -x} As, x = 0 to 1) is formed on a silicon substrate.
A layer is grown and its aluminum gallium arsenide (Al _x G
a group III nitride semiconductor, wherein a group III nitride layer is epitaxially grown on a _1-x As) layer. 2. An aluminum gallium arsenide (Al _x G)
2. The group III nitride semiconductor according to claim 1, wherein the Al composition x of a _1-x As) is 0.2 or more. 3. The group III nitride semiconductor according to claim 1, wherein the group IV semiconductor substrate is silicon. 4. The method according to claim 1, wherein the group III element is aluminum, gallium,
2. The method according to claim 1, wherein the alloy contains any of indium.
4. The group III nitride semiconductor according to any one of items 1 to 3. 5. The group III nitride semiconductor according to claim 1, wherein the semiconductor substrate is cleaved.