JPH11145063A - Semiconductor device having gallium nitride semiconductor layer and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor device provided with GaN superior in crystallinity or a semiconductor layer which is mainly coutstituted of GaN on a sapphire substrate, and to provide its manufacture method. SOLUTION: A first buffer layer 2a of GaInN is provided on a sapphire substrate 1. A second buffer layer 2b constituted of AlGaInN containing Al is provided on the first buffer layer 2a. A third buffer layer 2c constituted of AlGaInN whose percentage content of Al is larger than the second buffer layer 2b is provided on the second buffer layer 2b. A clad layer 3 constituted of GaN is provided on the third buffer layer 2c.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light emitting device or a semiconductor device provided with a gallium nitride compound semiconductor layer having excellent crystallinity, and a method of manufacturing the same.

[0002]

2. Description of the Related Art Recently, a gallium nitride-based compound semiconductor Al
Attention has been paid to blue light emitting diodes using GaInN. When manufacturing a light emitting diode of this type, a single crystal wafer of a gallium nitride-based compound semiconductor cannot be easily manufactured, and therefore, a vapor growth method is used on a sapphire substrate having a lattice constant relatively close to that of the gallium nitride-based compound semiconductor. A gallium nitride-based compound semiconductor layer is formed. But,
Although sapphire and a gallium nitride-based compound semiconductor, for example, gallium nitride (GaN) have relatively close lattice constants, the lattice mismatch ratio is considerably large at 16.1%. Therefore, when a GaN layer is formed directly on a sapphire substrate by metal organic chemical vapor deposition (MOCVD) or the like,
Many distortions and defects occur in the GaN layer. These distortions and defects are propagated to the semiconductor layer formed above the GaN layer and reduce the crystallinity thereof, which causes a decrease in luminous efficiency and the like. In order to solve this problem, Japanese Patent Application Laid-Open No. H4-297023 discloses a method of forming a gallium nitride-based compound semiconductor layer by interposing a buffer layer made of aluminum gallium nitride (AlGaN) on the upper surface of a sapphire substrate. I have. According to this method, the crystallinity of the gallium nitride-based compound semiconductor layer grown above the buffer layer is expected to be remarkably improved by the interposition of the buffer layer.

[0003]

However, the fact is that even with the above-described method of providing the buffer layer, the crystallinity of the GaN layer cannot be improved to a sufficient level.

Accordingly, an object of the present invention is to provide a semiconductor device including sapphire substrate and GaN having excellent crystallinity or a semiconductor layer containing GaN as a main component, and a method of manufacturing the same.

[0005]

Means for Solving the Problems The invention of an apparatus for solving the above problems and attaining the above object comprises a sapphire substrate, a buffer layer formed on one main surface of the sapphire substrate, and a buffer layer. a semiconductor device comprising a semiconductor layer composed mainly of formed GaN or GaN over said buffer _{layer, Al x Ga y in 1-} xy N
(However, the value satisfies 0 ≦ x <1, 0 ≦ x + y <1), and the Al content increases stepwise or continuously from the sapphire substrate side toward the semiconductor layer side. The present invention relates to a semiconductor device characterized in that: Note that the buffer layer as shown in claim 2, a first buffer layer made of GaInN containing no Al (gallium indium nitride), Al including Al _x Ga _y In
_A second buffer layer made of _1-xy N, and Al _x Ga _{y ′} In _{1-x ′ -y ′} containing more Al than the second buffer layer.
N (where x '> x, 0 <x'<1, x '+ y'<1)
And a third buffer layer made of An invention of a method for achieving the above object includes a sapphire substrate, a buffer layer formed on one main surface of the sapphire substrate, and a G layer formed on the buffer layer.
a method of manufacturing a semiconductor device comprising: aN or GaN as a main component;
a, and a gas containing In and N is supplied.
At the same time as the start of the supply of the gas containing In, N and N or after a predetermined time from the start of the supply, the supply amount on the sapphire substrate is increased stepwise or continuously with the passage of time.
is supplied, and a GaInN layer adjacent to the sapphire substrate and an Al _x Ga layer adjacent to the GaInN layer are supplied.
_y In _1-xy N (where x is a value larger than 0 and smaller than 1 and is a value that increases stepwise or continuously from the sapphire substrate side toward the semiconductor layer side). buffer layer, or Al _x Ga _y In
_A buffer layer made of _1-xy N (where x is a value larger than 0 and smaller than 1 and continuously increases from the sapphire substrate side to the semiconductor layer side). Forming a GaN or G layer on the buffer layer by a vapor phase growth method.
forming a semiconductor layer containing aN as a main component. As described in claim 4, the gas containing Ga, In, and N may be composed of trimethylgallium gas, trimethylindium gas, ammonia gas, and carrier gas, and the gas containing Al may be composed of trimethylaluminum gas. desirable.

[0006]

According to the invention of each claim, it is possible to provide a semiconductor device having a good buffer layer for GaN or a compound semiconductor layer containing GaN as a main component. That is, since the region on the sapphire substrate side of the buffer layer does not contain Al or has a low content of Al, the flexibility of the crystal is greater than that of the region on the semiconductor layer side having a higher Al content. Therefore, even if distortion occurs when a GaN having a lattice constant different from that of the buffer layer made of AlGaInN or a semiconductor layer containing the same as a main component is formed on the buffer layer made of AlGaInN, a region on the sapphire substrate side where the Al content of the buffer layer is low is obtained. And a good buffering effect is produced, and it is possible to suppress the generation of crystal defects in GaN or a semiconductor layer containing GaN as a main component or another semiconductor layer formed thereon. In addition, since the region of the buffer layer on the semiconductor layer side has a high Al content, the buffer layer has a function of preventing the evaporation of InN in the buffer layer, and GaN or a semiconductor layer containing this as a main component is required. It is possible to provide a simple buffer layer. According to the third and fourth methods, the buffer layer and the semiconductor layer can be formed easily and well.

[0007]

Embodiments and Examples Next, embodiments and examples of the present invention will be described with reference to FIGS. FIG. 1 shows a blue light emitting diode as a gallium nitride based compound semiconductor device according to the embodiment. This blue light emitting diode comprises a sapphire substrate 1, a buffer layer 2, a first n-type cladding layer 3 comprising an n-type GaN compound semiconductor region, and an n-type AlGa
A second n-type cladding layer 4 composed of an N semiconductor region, a light emitting layer (active layer) 5 composed of a p-type GaInN semiconductor region, p
P-type cladding layer 6 made of p-type AlGaN semiconductor region, second p-type cladding layer 7 made of p-type GaN semiconductor region, and GaN semiconductor with higher impurity concentration than second p-type cladding layer 7 A semiconductor substrate 9 having a contact layer 8 composed of a region; a cathode electrode 10 in low resistance contact with the first n-type cladding layer 3 on one main surface side of the semiconductor substrate 9; And an anode electrode 11 having a low resistance contact with the contact layer 8 on the surface. The difference between the blue light emitting diode of FIG. 1 and the conventional blue light emitting diode is that the buffer layer 2 has first, second and third buffer layers 2a and 2a having different Al contents.
b, 2c. Hereinafter, this will be described in detail.

The first buffer layer 2 a is made of a GaInN semiconductor, and is arranged so as to be in contact with the sapphire substrate 1. The second buffer layer 2b is made of Al _0.1 Ga _0.7 In
_It consists of a _0.2 N semiconductor region and is adjacent to the first buffer layer 2a. The second buffer layer 2b is a composition formula _{Al x Ga y In 1-xy} N ( where, x is a numerical value for indicating the molar ratios of Al,
This value satisfies 0 ≦ x <1. Further, y is a numerical value for indicating the Ga molar ratio, and is a value satisfying 0 ≦ x + y <1. In this example, x is 0.1 and y is 0.7. The third buffer layer 2c is made of Al _0.2 G _0.6
In _0.2 N, the second buffer layer 2 b and the first n
It is arranged between the shaped cladding layer 3. The third buffer layer 2c, the composition formula _{Al x 'Ga y' In 1} -x '-y' N ( where, x 'is a numerical value for indicating the molar ratios of Al, x'> x, This value satisfies 0 <x <1 and y ′
Is a numerical value for indicating the Ga molar ratio, and 0 <x ′ +
This value satisfies y '<1. In this example, x 'is 0.2, and y' is 0.6 made of indium aluminum gallium nitride. Accordingly, the Al content in the buffer layer 2 increases stepwise from the sapphire substrate 1 to the first n-type cladding layer 3. It should be noted that the first, second and third buffer layers 2a, 2a
b and 2c are formed so as to cover the entire one main surface of the sapphire substrate 1. Further, the thicknesses of the first, second and third buffer layers 2a, 2b and 2c are substantially the same, and are about 200 angstroms.

Next, a method of manufacturing a blue light emitting diode having the first, second and third buffer layers 2a, 2b and 2c of FIG. 1 will be described. First, as shown in FIG. 2, a sapphire substrate 1 is prepared, and a first buffer layer 2a, a second buffer layer 2b, and a third buffer layer 2c are provided on the upper surface of the sapphire substrate 1.
They are sequentially formed by an OCVD method (metal organic chemical vapor deposition). That is, the sapphire substrate 1 whose surface has been sufficiently cleaned
Is disposed on an acceptor provided in a reaction chamber of a known MOCVD apparatus. Thereafter, the reaction chamber is sufficiently evacuated, and then the chamber is replaced with hydrogen gas. Subsequently, the sapphire substrate 1 is heated at 1200 ° C. for about 10 minutes while supplying hydrogen gas at a flow rate of 5 liter / minute at normal pressure, and the sapphire substrate 1 is subjected to gas phase etching. Next, the temperature of the sapphire substrate 1 is reduced to 600 ° C., and hydrogen gas is supplied at a flow rate of 10 liter / min. Subsequently, in order to form the first buffer layer 2a on the upper surface of the sapphire substrate 1, trimethyl gallium gas (hereinafter, referred to as TMG gas), trimethyl indium gas (hereinafter, referred to as TMI gas), N
H3 (ammonia) gas is supplied. In this step, the flow rate of TMG gas, that is, the supply rate of Ga, is about 22 × 10
^-6 mol / min, the flow rate of the TMI gas, ie, the supply rate of In, is about 5 × 10 ⁻⁶ mol / min, and the flow rate of the NH3 gas, ie, the supply rate of NH3, is about 0.11 mol / min. This first
During the first period for forming the buffer layer 2a, no trimethylaluminum gas (hereinafter referred to as TMA gas) is supplied into the reaction chamber. As a result, the first buffer layer 2a formed in the first period does not contain Al, and
nN.

After completing the formation of the first buffer layer 2a,
A TMA gas is supplied into the reaction chamber in addition to the TMG gas, TMI gas, NH3 gas, and hydrogen gas to form a second buffer layer 2b continuously on the upper surface of the first buffer layer 2a. The flow rates of the TMI gas and the NH3 gas in the second period for forming the second buffer layer 2b, that is, I
The supply amount of n, NH3, and the flow rate of hydrogen gas are the same as those in the first period. In addition, TMG gas, TM
The flow rate of A gas, that is, the supply amounts of Ga and Al
２０20 × 10 ⁻⁶ mol / min and 2 to 4 × 10 ⁻⁶ mol / min. The second buffer layer 2b formed in the second period
Is composed of AlGaInN containing Al.

Next, the flow rates of the TMI gas and the NH 3 gas, that is, the supply amounts of In and NH 3, are kept the same as those in the first and second periods, supplied to the reaction chamber, and the supply amount of the TMG gas, that is, the supply of Ga. The amount is reduced to 14-16 × 10 ⁻⁶ mol / min,
The supply amount of TMA gas, that is, the supply amount of Al is set to 6 to 8 × 10 mol
1 / min to form a third buffer layer 2c on the upper surface of the second buffer layer 2b. This third buffer layer 2c
Since the flow rate (supply amount) of the TMA gas in the third period for forming the second buffer layer 2b is larger than that in the second period for forming the second buffer layer 2b, the third buffer layer 2c is formed.
Is higher than the Al content of the second buffer layer 2b. The above first, second and third buffer layers 2
The formation of a, 2b, and 2c is performed in a series of continuous MOCVD processes, and the temperature of the sapphire substrate 1 is maintained at 600 ° C. during this process. The temperature of the sapphire substrate 1 is 5
It can be increased or decreased in the range of 00 ° C to 700 ° C.

After forming the first, second and third buffer layers 2a, 2b and 2c as described above, the temperature of the sapphire substrate 1 is increased to 1100 ° C. while supplying NH 3 gas, hydrogen gas and nitrogen gas. Let it. Subsequently, the TM was placed in the reaction chamber.
G gas and silane (SiH ₄ ) gas are supplied. Here, the silane gas is for introducing Si as an n-type impurity into the formed film. Thus, as shown in FIG. 3, a first n-type cladding layer 3 made of GaN is formed on the upper surface of the sapphire substrate 1 with the buffer layer 2 interposed therebetween.
Further, while maintaining the temperature of the sapphire substrate 1 at 1100 ° C., TMG gas, NH 3 gas, hydrogen gas,
Supply TMA gas in addition to silane gas and nitrogen gas,
As shown in FIG. 3, the upper surface of the first n-type
A second n-type cladding layer 4 made of GaN is formed.

After the formation of the first and second n-type cladding layers 3 and 4, the temperature of the sapphire substrate 1 is lowered to 800 ° C. while supplying nitrogen gas. Subsequently, TMG gas, TMI gas, ammonia gas, silane gas and biscyclopentadienyl magnesium gas (hereinafter referred to as Cp2
Mg gas) is supplied to form an active layer made of p-type GaInN, that is, a light-emitting layer 5 on the upper surface of the second n-type cladding layer 4 as shown in FIG. Here, Cp2 Mg gas is for introducing Mg as a p-type conductivity type impurity into the formed film. After the formation of the light emitting layer 5, the temperature of the sapphire substrate 1 is increased to 1100 ° C. while supplying only nitrogen gas. Subsequently, a TMG gas, an ammonia gas, a hydrogen gas and a Cp2Mg gas are supplied into the reaction chamber, and a first p-type clad layer 6 made of p-type AlGaN is formed on the upper surface of the light-emitting layer 5 as shown in FIG. Continue to form.

Next, the temperature of the sapphire substrate 1 is set to 1100
As shown in FIG. 5, a second p-type cladding layer 7 made of p-type GaN is formed on the upper surface of the first p-type cladding layer 6 while maintaining the temperature at ° C. Further, Cp2 M supplied into the reaction chamber
By increasing the flow rate of the g gas, a contact layer 8 made of p-type GaN having a higher content of Mg, which is a p-type impurity, is formed on the upper surface of the second p-type cladding layer 7. The first and second cladding layers 3 and 4 above the buffer layer 2 described above, the light emitting layer 5, the first and second p-type cladding layers 6,
7. Since the method for forming the contact layer 8 is the same as the method for forming the conventional blue light emitting diode, detailed description such as the flow rate of each gas is omitted.

Next, the contact layer 8, the first and second p
The upper portion of the semiconductor cladding layers 6 and 7, the light emitting layer 5, the second n-type cladding layer 4, and the first n-type cladding layer 3 on the right side of FIG. The first n-type cladding layer 3 is exposed on one main surface.

Finally, as shown in FIG. 1, the first n-type cladding layer 3 and the contact layer 8 are formed on one main surface of the semiconductor substrate 9 by using a well-known vapor deposition method and a lift-off method. The connected cathode electrode 10 and anode electrode 11 are formed to complete the blue light emitting diode device shown in FIG.

According to this embodiment, a GaN-based compound semiconductor layer having good crystallinity without crystal defects or distortion can be formed above the buffer layer 2. Therefore, a light-emitting element having excellent characteristics of luminous efficiency can be obtained. The reason why a GaN-based compound semiconductor layer having good crystallinity can be formed above the buffer layer 2 is considered as follows. The first buffer layer 2a is made of GaInN containing no Al,
The second buffer layer 2b is made of AlGaI having a low Al content.
Both have a lattice constant relatively close to that of the sapphire substrate 1, have flexibility, and function well as a buffer layer. However, Ga is placed on the first buffer layer 2a containing no Al or the second buffer layer 2b containing a low content of Al.
When N cladding layers 3 and 4 are successively formed, InN in the buffer layers 2a and 2b is easily evaporated, and a good nucleus for forming the cladding layer 3 is formed in the first buffer layer 2a or the second buffer layer. It becomes impossible to obtain the layer 2b, and the clad layer 3 cannot be formed well. On the other hand, according to the present invention, the third buffer layer 2 having a high Al content
c, the InN in the buffer layers 2a, 2b, 2c
Of the cladding layer 3 can be suppressed, and a good nucleus for the cladding layer 3 can be obtained, and the cladding layer 3 can be formed well. When a temperature change due to cooling or the like occurs after the semiconductor layers such as the cladding layers 3 and 4 are formed, the buffer layer 2
Is generated due to a difference in lattice constant between the semiconductor layer and the cladding layer 3, which causes crystal defects in the buffer layer 2, the cladding layers 3 and 4, and the semiconductor layer further thereon. Since the first and second buffer layers 2a and 2b having the above structure are provided, the strain is absorbed thereby, and crystal defects in the semiconductor layer are suppressed.

[0018]

[Modifications] The present invention is not limited to the above-described embodiment, and for example, the following modifications are possible. (1) When forming the second and third buffer layers 2b and 2c, the supply amount of the TMA gas containing Al is gradually increased with the passage of time, and the second and third buffer layers 2b and 2c are formed.
Instead of 2c, a layer whose Al content continuously increases from the sapphire substrate 1 side toward the clad layer 3 side can be formed. Further, in the example, Al was not contained in the first buffer layer 2a, but Al can be contained at a low level. Further, a TMA gas is supplied from the beginning when the buffer layer 2 is formed, and the supply amount is increased with time, and the cladding layer 3 is supplied from the sapphire substrate 1 side.
The buffer layer 2 can be formed such that the Al content gradually increases toward the side. (2) The Al content of the second and third buffer layers 2b and 2c can be changed. However, in order to obtain a good nucleus for the cladding layer 3, the molar ratio between Al and Ga in the third buffer layer 2c should be in the range of 15 to 50 mol% of Al and 50 to 80 mol% of Ga. Is desirable. Further, the molar ratio between Al and Ga of the second buffer layer 2b is set to 5 to 20 mol% of Al and 60 to 90 mol% of Ga.
It is desirable that (3) Instead of forming the cladding layer 3 made of GaN, a semiconductor layer containing GaN as a main component can be formed. On the cladding layer 3, the layers 4 to 8 shown in FIG.
Various other semiconductor layers can be formed.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a light emitting diode according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a buffer layer formed on a sapphire substrate for forming the light emitting diode of FIG.

FIG. 3 is a cross-sectional view showing a structure in which first and second n-type cladding layers are formed on the buffer layer of FIG. 2;

FIG. 4 is a cross-sectional view showing a light emitting layer and a first p-type cladding layer formed on the cladding layer of FIG. 3;

FIG. 5 is a cross-sectional view showing a structure in which a second p-type cladding layer and a contact layer are formed on the p-type cladding layer of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sapphire substrate 2 Buffer layer 2a, 2b, 2c 1st, 2nd, 3rd buffer layer 3 N-type cladding layer

Claims (4)

[Claims] 1. A semiconductor device comprising: a sapphire substrate; a buffer layer formed on one main surface of the sapphire substrate; and GaN or a GaN-based semiconductor layer formed on the buffer layer. a is, the buffer _{layer, Al x Ga y in 1-} xy N ( where,
It is a value satisfying 0 ≦ x <1, 0 ≦ x + y <1. Wherein the Al content increases stepwise or continuously from the sapphire substrate side toward the semiconductor layer side. 2. The method according to claim 1, wherein the buffer layer is formed of GaIn formed on one main surface of the sapphire substrate.
A first buffer layer made of N, Al _x was formed over the first buffer layer Ga _y I
a second buffer layer composed of n _1-xy (where 0 <x <1, 0 <x + y <1); and Al _x 'G formed on the second buffer layer.
a _y 'In _{1-x' -y} 'N (where x'> x, 0 <x '<
2. The semiconductor device according to claim 1, further comprising a third buffer layer comprising: 1, 0 <x '+ y'<1). 3. A semiconductor device comprising: a sapphire substrate; a buffer layer formed on one main surface of the sapphire substrate; and GaN or a semiconductor layer containing GaN as a main component formed on the buffer layer. Supplying a gas containing Ga, In, and N onto the sapphire substrate, and simultaneously with or after a predetermined time from the start of the supply of the gas containing Ga, In, and N, A gas containing Al is supplied so that the supply amount on the sapphire substrate increases stepwise or continuously over time, and the GaInN layer adjacent to the sapphire substrate and the GaInN
Adjacent to the N layer _{Al x Ga y In 1-xy} N ( 0 <
x <1, 0 <x + y <1), and x is a value that increases stepwise or continuously from the sapphire substrate side toward the semiconductor layer side. ) Or A
_{l x Ga y In 1-xy} N ( where, 0 <x <1,0 <x +
y <1) and x are values that increase continuously or stepwise from the sapphire substrate side to the semiconductor layer side. Forming a buffer layer consisting of) by vapor phase epitaxy; and forming the GaN layer on the buffer layer by vapor phase epitaxy.
Or a step of forming a semiconductor layer containing GaN as a main component. 4. The gas according to claim 3, wherein the gas containing Ga, In and N comprises trimethylgallium gas, trimethylindium gas, ammonia gas and carrier gas, and the gas containing Al is trimethylaluminum gas. A method for manufacturing a semiconductor device.