JP2956489B2 - Crystal growth method of gallium nitride based compound semiconductor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention is a light emitting diode, a gallium nitride-based compound is used in an electronic device such as a laser diode semiconductor _{(In X Al Y Ga 1-} XY N, 0 ≦ X, 0 ≦
Y, X + Y ≦ 1, hereinafter a gallium nitride-based compound semiconductor is referred to as a nitride semiconductor. In particular, the present invention relates to a method for growing a nitride semiconductor crystal on a substrate directly or via a buffer layer.

[0002]

2. Description of the Related Art Laser diodes emitting blue and ultraviolet light and nitride semiconductors (In _{X '}
Al _{Y ′} Ga _{1−X′−Y ′} N, 0 ≦ X ′, 0 ≦ Y ′, X ′ + Y ′ ≦ 1)
Recently, a blue light emitting diode with a luminous intensity of 1 cd has just been put to practical use with this material. As shown in FIG. 1, the blue light emitting diode has a buffer layer 2 made of GaN and a Ga layer on a surface of a substrate 1 made of sapphire.
An n-type layer 3 of N, an n-type cladding layer 4 of AlGaN, an active layer 5 of InGaN,
And a p-type contact layer 7 made of GaN.

[0003] A nitride semiconductor device is generally a MOVPE.
It is obtained by laminating a nitride semiconductor layer on the substrate surface using a vapor phase growth method such as (organic metal vapor phase epitaxy), MBE (molecular beam epitaxy), or HDVPE (hydride vapor phase epitaxy). Materials such as sapphire, ZnO, SiC, GaAs, and MgO are used for the substrate. N is provided on the surface of the substrate via a buffer layer.
Type nitride semiconductor (In _X Al _Y Ga _{1 -XYN} , 0 ≦ X, 0
≦ Y, X + Y ≦ 1, among which n-type GaN and n-type Al
Mostly GaN. ) Will be grown. Also, SiC, ZnO
When a substrate having a lattice constant close to that of a nitride semiconductor is used, an n-type nitride semiconductor may be directly grown on the substrate without forming a buffer layer. Basically, by first growing an n-type nitride semiconductor layer on the surface of the substrate,
A nitride semiconductor device such as a light emitting device and a light receiving device is manufactured.

For example, according to the MOVPE method, as a nitride semiconductor, an organic metal compound gas serving as a Ga source, an Al source, and an In source and an ammonia gas serving as an N source are used as source gases. By bringing these source gases into contact with the heated substrate surface, the source gases are decomposed, and a nitride semiconductor is epitaxially grown on the substrate. Normally G
aN, AlN, GaAlN, etc. are selected,
It is grown at a temperature of 00 ° C. with a thickness of 10 Å to 0.1 μm. The n-type nitride semiconductor layer grown on the buffer layer is usually at least 1 μm at a temperature of 900 ° C. or more.
It is grown with a thickness of less than μm.

[0005]

It is known that a nitride semiconductor is a crystal that is very difficult to grow epitaxially because there is no substrate that is perfectly lattice-matched. Therefore, conventionally, a substrate close to the lattice constant of the nitride semiconductor to be grown, such as a SiC substrate, has been used, or epitaxial growth has been forcibly performed via a buffer layer that reduces lattice mismatch.

FIG. 2 shows, as an example, a schematic cross-sectional view of an n-type nitride semiconductor crystal grown on the surface of a substrate that does not have lattice matching. This is the Journal of Crystal Growth, 115, (1991) P628−63.
3), n-type GaN is epitaxially grown on the surface of a sapphire substrate via a buffer layer made of AlN, and its cross section is TEM (transmission e).
(electron microscopy) and schematically shows the crystal structure from the TEM image. According to this figure, a buffer layer with poor orientation is grown on the substrate in a columnar shape, and when GaN is epitaxially grown on the buffer layer, a part of the buffer layer plays a role like a seed crystal. This shows that the GaN layer with improved crystallinity is grown by gradually adjusting the orientation of GaN.

However, Ga which is completely free from crystal defects
It is difficult to grow N, and many crystal defects as shown by broken lines in FIG. 2 extend from the interface between the buffer layer and the GaN layer until reaching the GaN layer surface. Some of these defects stop inside the crystal, but those reaching the surface of the GaN layer are, for example, 10 ⁷ to 10 ⁹ / cm ^{2 at} the surface. Similarly, in the light emitting diode element of FIG. 1, the same phenomenon occurs in the crystal of the n-type layer 3.

When a large number of crystal defects are present on the surface of the n-type nitride semiconductor layer grown on the surface of the substrate, the defects are inherited by all the semiconductor layers such as the cladding layer and active layer growing on the surface of the n-type layer. This has the problem of adversely affecting the entire element structure. An element having a large number of crystal defects has a disadvantage that, for example, when the above-described light emitting diode is used, the element performance such as light emission output and life is adversely affected.

In growing an n-type nitride semiconductor layer on the surface of a substrate, it is very important to grow an n-type crystal having few crystal defects. Since the number of crystal defects in the clad layer, active layer, and the like is reduced, the performance of any device made of a nitride semiconductor can be improved. Accordingly, the present invention has been made in view of such circumstances, and the MOV
When growing an n-type nitride semiconductor layer on the surface of a substrate that is not completely lattice-matched by a vapor phase growth method such as PE or MBE, the growth is performed by reducing lattice defects in the n-type nitride semiconductor layer. It is intended to provide a method for causing this to occur.

[0010]

According to the method of the present invention, a nitride semiconductor (In _X Al _Y Ga _{1 -XYN} , 0 ≦ 0) is directly formed on a substrate surface by a vapor phase growth method or via a first buffer layer. X,
In a method of growing a crystal satisfying 0 ≦ Y, X + Y ≦ 1),
After growing the first n-type nitride semiconductor layer, In _a Ga _1-a N (0
<A ≦ 1), Al _b Ga _1-b N (0 <b ≦ 1), or a multilayer film in which thin films of Al _b Ga _1-b N (0 ≦ b ≦ 1) having different compositions are stacked. The second containing any one of the following
A second buffer layer made of an n-type nitride semiconductor is grown at least one layer above, and on the second buffer layer,
An n-type nitride semiconductor layer having the same composition as the first n-type nitride semiconductor layer is grown, and further an InGaN
And growing an active layer.

[0011]

In the method of the present invention, when a second nitride semiconductor layer having a different composition is formed in an n-type nitride semiconductor layer, the second nitride semiconductor acts as a buffer layer, that is, a buffer layer. It is considered that crystal defects can be reduced by the buffer layer (hereinafter, the second nitride semiconductor layer is referred to as a second buffer layer in the present specification). Specifically, n
When the type nitride semiconductor layer is grown on a substrate, the mismatch between the substrate and the nitride semiconductor is large.
A crystal defect as shown by a broken line is generated in the crystal. However, by interposing, as an intermediate layer, a second buffer layer having a different composition from the n-type nitride semiconductor layer to be grown, continuous crystal defects of the n-type nitride semiconductor layer cause the second buffer layer having a different composition. Stops temporarily in the buffer layer. next,
When the n-type nitride semiconductor is grown on the surface of the second buffer layer, the second buffer layer acts like a substrate having a small mismatch, so that the n-type nitride semiconductor is grown on the second buffer layer. It is assumed that the crystallinity of the nitride semiconductor is improved.

The second buffer layer may be formed in one or more layers, and the thickness of one layer is in the range of 10 Å (0.001 μm) or more and 1 μm or less, more preferably 0.001 μm or more and 0.1 μm or less. It is desirable to adjust. If the thickness is smaller than 0.001 μm, it tends to be difficult to stop crystal defects in the second buffer layer. If the thickness is larger than 1 μm, new crystal defects tend to be easily generated from the second buffer layer. The second buffer layer may have a thickness of several tens angstroms, and may be a multilayer film in which two or more layers are stacked.

The second buffer layer is composed of In _a Ga _{1 -a} N (0 <
a ≦ 1), Al _b Ga _1-b N (0 <b ≦ 1), or a multilayer film in which thin films of Al _b Ga _1-b N (0 ≦ b ≦ 1) having different compositions are stacked. desirable. More preferably, In _a Ga _1-a N having an _a value of 0.5 or less or Al _b Ga _1-b N having a b value of 0.5 or less is grown. Because
In a nitride semiconductor, the ternary mixed crystal has better crystallinity than the quaternary semiconductor layer. In _a Ga _1-a N ternary mixed crystal Among them, the _{Al b Ga 1-b N,} a value, and the buffer layer a b value was adjusted to the range further for good crystallinity is obtained In addition, crystal defects of the second buffer layer are reduced, and crystal defects of the n-type nitride semiconductor layer grown on the second buffer layer are reduced. further,
When the second buffer layer is a multilayer film, crystal defects can be stopped very well. The most preferred combination is n
N-type GaN (GaN has the fewest lattice defects), and the second buffer layer is n-type In _a Ga _1-a N
(0 <a ≦ 0.5) or n-type Al _b Ga _1-b N
(0 <b ≦ 0.5) or Al _b Ga having a different composition
_1-b N (0 ≦ b ≦ 1) multilayer film (superlattice)
It is.

Further, the electron carrier concentration of the second buffer layer is substantially the same as that of the previously formed n-type nitride semiconductor layer.
Or it is desirable to adjust larger. FIGS. 3 and 4 show that an n-cladding layer 4 ', an active layer 5', a p-cladding layer 6 ', and a p-contact layer 7' are laminated on the n-type nitride semiconductor layer 3 "obtained by the method of the present invention. 3 is a cross-sectional view showing the structure of the light emitting device as an actual light emitting device, wherein the second buffer layer 33 is more active than the etched surface of the n-type layer for forming the negative electrode. 4 differs from the layer 5 'in that the second buffer layer 33 is formed closer to the substrate 1' than the etched surface.For example, a light emitting device as shown in FIG. In other words, when an element is realized in which the position of the second buffer layer 33 is closer to the active layer side than the etching surface on which the negative electrode is to be formed, the electron carrier concentration of the second buffer layer 33 is Is smaller than the n-type layer 3 ′, n is supplied from n to p in the second buffer layer. Electrons are blocked and p-type
Current hardly flows through the layer, and the performance of the device deteriorates. Conversely, if the electron carrier concentration of the second buffer layer 33 is higher than that of the n-type layer 3, electrons are likely to spread uniformly in the second buffer layer 33, so that uniform light emission can be obtained. On the other hand, in the device as shown in FIG. 4, even if the electron carrier concentration of the second buffer layer 33 is low, the current flows through the n-type layer 3 ″ having a high electron carrier concentration. Has almost no effect, but conversely, if the electron carrier concentration of the second buffer layer 33 is high, the current tends to flow toward the second buffer layer 33, and uniform light emission is obtained. The electron carrier concentration of the second buffer layer 33 is preferably adjusted to be substantially the same as or higher than that of the n-type nitride semiconductor layer formed earlier.

In the present invention, an n-type nitride semiconductor (In _X Al _Y Ga _{1 -XYN} , 0 ≦ X, 0 ≦
Y, X + Y ≦ 1) means Al _Y G in which the Y value is in the range of 0 ≦ Y ≦ 0.5.
a _1-Y N, more preferably 0.3 or less Al _Y Ga _1-Y
Grow N, most preferably Y = 0 GaN. This is because the ternary mixed crystal nitride semiconductor has fewer crystal defects than the quaternary mixed crystal nitride semiconductor as described above. Further, when an n-type nitride semiconductor is used as an electronic device such as a light-emitting element and a light-receiving element, first, an n-type nitride semiconductor grown on a substrate is made of AlGaN having a larger band gap than InGaN having a small band gap,
This is because GaN is more convenient for realizing various structures such as single hetero and double hetero. Among them, especially, AlGaN tends to have more crystal defects as Al is contained, and GaN has n which has the fewest crystal defects.
Type nitride semiconductor layers tend to grow.

Furthermore, in the present invention, a material such as sapphire, GaAs, Si, ZnO, or SiC can be used for the substrate, but sapphire is generally used. When sapphire is used as a substrate, it is preferable to grow a buffer layer on the substrate. However, depending on the plane orientation of the sapphire substrate, growth can be performed without a buffer layer. By preferably growing the buffer layer, it is possible to obtain a smooth and mirror-like n-type nitride semiconductor crystal capable of measuring lattice defects. The n-type nitride semiconductor can be realized in a non-doped state or by doping a donor impurity such as Si, Ge, or C during crystal growth.

[0017]

The method of the present invention by the MOVPE method will be described in detail below. [Example 1] First, a well-washed sapphire substrate is placed on a susceptor in a reaction vessel. After evacuating the container,
While flowing hydrogen gas into the container, the substrate is heated at 1050 ° C. for about 20 minutes to remove oxides on the surface, and the substrate is cleaned. Thereafter, the temperature of the susceptor was adjusted to 500 ° C., and at 500 ° C., TMG (trimethyl gallium gas) as a Ga source and ammonia gas as an N source were flowed over the surface of the substrate, and the buffer layer made of GaN was placed at 0.0 ° C.
It is grown to a thickness of 2 μm.

Next, the TMG gas is stopped and the temperature is set to 10
After the temperature is raised to 50 ° C., TMG gas and SiH ₄ gas are flowed to grow a Si-doped n-type GaN layer to a thickness of 2 μm.

Next, the TMG gas and the SiH ₄ gas are stopped and the temperature is set to 800 ° C. When the temperature reaches 800 ° C., the carrier gas is switched to nitrogen, TMG gas, TMI (trimethylindium), and SiH ₄ gas are flown, and a Si-doped n-type In0.1Ga0.9N layer is formed as a second buffer layer by 0.01.
It is grown to a thickness of μm.

After the growth of the In0.1Ga0.9N layer, the temperature is raised again to 1050 ° C., the carrier gas is returned to hydrogen, TMG gas and SiH ₄ gas are flown, and S
An i-doped n-type GaN layer is grown to a thickness of 2 μm. Note that the carrier concentration of the second buffer layer and the carrier concentration of this n-type GaN layer were almost the same.

After the growth, the substrate is taken out of the reaction vessel, the surface of the uppermost n-type GaN layer is measured by TEM, and its TE is measured.
When the number of crystal defects per unit area was measured from the M image, it was about 1 × 10 ⁴ / cm ² .

Example 2 In the step of forming the n-type nitride semiconductor layer,
Example 1 except that a second buffer layer was sandwiched by using G, TMA (trimethylaluminum), and SiH ₄ gas to grow Si-doped n-type Al0.3Ga0.7N layers to a thickness of 2 μm each. Perform in the same way as As a result, when the measurement was performed in the same manner, the Si-doped n-type Al0.3Ga0.7N
The number of crystal defects reaching the surface of the layer was about 5 × 10 ⁵ / cm ² . Note that Si-doped n-type Al0.3Ga0.7
The electron carrier concentration of the N layer was almost the same as that of the second buffer layer.

A Si-doped n-type GaN layer is grown to a thickness of 1 μm in the same manner as in the step of forming the n-type nitride semiconductor layer in the third embodiment. Next, a Si-doped n-type In0.1Ga0.9N layer is grown to a thickness of 50 angstroms as a second buffer layer in the same manner as the second buffer layer. Further, similarly to the step of the n-type nitride semiconductor layer,
An aN layer is sequentially grown to a thickness of 1 μm.

Further, in the same manner as in the step on the Si-doped n-type GaN layer, a Si-doped n-type In0.1Ga0.9N layer is grown once more as a third buffer layer to a thickness of 50 angstroms. As in the last step, a Si-doped GaN layer is grown to a thickness of 2 μm. That is, in Example 3, the GaN buffer layer 200 Å, the n-type GaN layer 1 μm,
An Si-doped n-type In0.1Ga0.9N second buffer layer 50 Å, an n-type GaN layer 1 μm, a Si-doped n-type In0.1Ga0.9N third buffer layer 50 Å, and an n-type GaN layer 2 μm were sequentially stacked.

As a result, the final layer of Si-doped n-type GaN
The number of crystal defects reaching the surface of the layer is approximately 1 × 10 ⁴
Pieces / cm ² . The electron carrier concentrations of the second buffer layer, the third buffer layer, and the Si-doped n-type GaN layer were almost the same.

[Embodiment 4] In the step of forming the second buffer layer in Example 4, TMG, TMA (trimethylaluminum), S
The same operation as in Example 1 is performed, except that a second buffer layer is formed by growing a Si-doped n-type Al0.3Ga0.7N layer to a thickness of 0.01 μm using iH ₄ gas. As a result, the number of crystal defects reaching the surface of the Si-doped n-type GaN layer was approximately 1 × 10 ⁴ / cm ^{2 as} measured in the same manner. Note that the electron carrier concentration of the second buffer layer is S
It was almost the same as the i-doped n-type GaN layer.

[Fifth Embodiment] In the step of forming the second buffer layer in the fifth embodiment, the TMG, TMA, and SiH ₄ gases are used without changing the growth temperature.
A doped n-type Al0.02Ga0.98N layer is grown to a thickness of 30 angstroms. Next, the TMA gas is stopped, and a Si-doped n-type GaN layer is grown to a thickness of 30 Å. Then, this operation is repeated five times, and 3
0 Å of Si-doped n-type Al0.02Ga0.98
A multilayer film is formed by alternately laminating five N layers and 30 Å n-type GaN layers. Example 1 except that the second buffer layer was formed as described above.
Perform in the same manner as described above. As a result, when the lattice defects were measured in the same manner, the number of crystal defects reaching the surface of the Si-doped n-type GaN layer was about 5 × 10 ³ / cm ² . In addition,
The electron carrier concentration of the multilayer film as the second buffer layer is:
It was almost the same as the Si-doped n-type GaN layer.

Example 6 In the process of Example 2, Si was used as the second buffer layer.
Similarly, except that a doped n-type Al0.1GaGa0.9N is grown to a thickness of 0.01 μm, a Si-doped n-type Al0.3
A Ga0.7N layer was grown. As a result, the uppermost n-type A
The number of lattice defects reaching the l0.3Ga0.7N layer is about 1
× 10 ⁵ / cm 2. The electron carrier concentration in this example was also substantially the same.

Comparative Example 1 In Example 1, the Si-doped n-type GaN layer was continuously grown to a thickness of 4 μm without growing the second buffer layer. The number of reached crystal defects was about 1 × 10 ⁷ / cm ² .

[Embodiment 7] An embodiment in which the structure of an actual light emitting element is used will be described. The following steps were added after the steps of Example 1. Si doped n
After the growth of the n-type GaN layer, a new TMA (trimethylaluminum) gas is added, and at 1050 ° C., a Si-doped n-type Al0.2Ga0.8N layer is formed as an n-cladding layer by 0.1 μm.
It grows with the film thickness of.

After growing the n-cladding layer, TMG, TM
A, the SiH ₄ gas was stopped, the temperature was set again to 800 ° C., and in addition to TMG, TMI, and SiH ₄ gas, DEZ (diethyl zinc) was flown, and an Si and Zn-doped In0.05Ga0.95N layer was formed as an active layer. It is grown to a thickness of 0.1 μm.

After growing the active layer, TMG, TMI, Si
After stopping H ₄ and DEZ gas and setting the temperature to 1050 ° C.,
TMG, TMA, and Cp2Mg (cyclopentadienylmagnesium) gas are flowed, and a Mg-doped p-type Al0.1Ga0.9N layer is grown as a p-cladding layer to a thickness of 0.1 .mu.m.

After growing the p-type Al0.1Ga0.9N layer, the TM
The A gas is stopped, and a Mg-doped p-type GaN layer is grown at 1050 ° C. as a p-contact layer with a thickness of 0.3 μm.

The device obtained as described above is etched and n-type GaN grown next to the second buffer layer is etched.
The layer was exposed, and electrodes were formed on the p-contact layer and the exposed Si-doped n-type GaN layer. That is, a light emitting diode element having a structure as shown in FIG. 4 was obtained. The device was mounted on a lead frame and molded with resin. This light-emitting diode had a Vf of 3.6 V, an emission wavelength of 450 nm, a luminous intensity of 3.0 cd, and an emission output of 3.5 mW at 20 mA.

Comparative Example 2 The same process as in Example 7 was performed on the Si-doped GaN layer grown in Comparative Example 1 to obtain a light emitting diode device having a structure as shown in FIG. Diode 2
At 0 mA, Vf was 3.6 V and the emission wavelength was 450 nm. The luminous intensity was 1.0 cd, and the emission output was 1.2 m.
There was only W.

As described above, according to the present invention, an n-type layer having few crystal defects can be obtained, so that crystal defects such as a clad layer and an active layer laminated thereon can be reduced. In particular, since the thickness of the active layer is as thin as about 0.2 μm or less, it is very important to grow a crystal having few crystal defects. Therefore, since a crystal having few crystal defects can be grown, it is possible to realize a light-emitting diode element having a luminous intensity of 1 cd or more and excellent in light-emission output as in the related art.

Example 9 Crystal growth was performed in the same manner as in Example 5 except that the thickness of the Si-doped n-type GaN layer was changed to 5 μm.
The number of crystal defects on the surface of the layer was about 5 × 10 ⁶ .

[Embodiment 10] In the process of Embodiment 5, a Si-doped n-type Al0.3Ga0.7N layer was continuously formed by 10 μm in the same manner as in Embodiment 2.
Crystal growth was performed in the same manner except that the crystal was grown to a thickness of m. As a result, the number of crystal defects on the surface of the n-type Al0.3Ga0.7N layer was approximately 3 × 10 ⁶ / cm ² .

Example 11 Example 7 was formed on the Si-doped GaN layer obtained in Example 5.
In the same manner as described above, the n clad layer, the active layer, the p clad layer,
When the p-contact layer was laminated to form a light emitting diode in the same manner, the characteristics were almost the same as those of the seventh embodiment.

[0040]

As described above, according to the method of the present invention, an n-type nitride semiconductor layer having few crystal defects can be grown on the surface of a substrate. Therefore, the method of the present invention is very useful for stacking crystals with few crystal defects and realizing electronic devices such as light-emitting elements and light-receiving elements for a nitride semiconductor having no lattice-matched substrate.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing one structure of a conventional light emitting diode element.

FIG. 2 is a schematic cross-sectional view showing a crystal structure when an n-type GaN layer is grown on a surface of a substrate via an AlN buffer layer.

FIG. 3 is a schematic cross-sectional view showing one structure of a light-emitting diode device having an n-type nitride semiconductor layer obtained by a method of the present invention.

FIG. 4 is a schematic cross-sectional view showing one structure of a light-emitting diode device having an n-type nitride semiconductor layer obtained by the method of the present invention.

[Explanation of symbols]

1, 1 '... substrate 2, 2'
..Buffer layers 3,3 ', 3 "... N-type nitride semiconductor layers 4,4'.
..N-type cladding layers 5, 5 '... Active layers 6, 6'
..P cladding layer 7, 7 '... p contact layer 33 ... second buffer layer (second nitride semiconductor layer)

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01L 33/00 H01S 3/18 JICST file (JOIS)

Claims (2)

(57) [Claims] 1. A gallium nitride-based compound semiconductor (In _X Al _Y Ga _{1 -XYN} , 0 ≦ X, 0 ≦ Y, X + Y ≦) directly on a substrate surface or via a first buffer layer by a vapor growth method.
In the method of growing a crystal according to 1), after growing a first n-type gallium nitride-based compound semiconductor layer, In _a Ga ₁ -aN (0
<A ≦ 1), Al _b Ga _1-b N (0 <b ≦ 1), or a multilayer film in which thin films of Al _b Ga _1-b N (0 ≦ b ≦ 1) having different compositions are stacked. The second containing any one of the following
A second buffer layer made of n-type gallium nitride-based compound semiconductor is grown at least one layer, and n having the same composition as the first n-type gallium nitride-based compound semiconductor layer is formed on the second buffer layer. A method for growing a gallium nitride-based compound semiconductor crystal, comprising: growing a gallium nitride-based compound semiconductor layer; and growing an active layer made of InGaN thereon. 2. The method of growing a gallium nitride-based compound semiconductor according to claim 1, wherein the thickness of one layer of the second buffer layer is 1 μm or less.