JP2002043618A - Method for manufacturing nitride semiconductor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an MQW light emitting layer improved in light emitting efficiency by suppressing a deterioration of a well layer and improving crystallinity of a barrier layer, and to provide a method for manufacturing a light emitting element at a low cost by shortening a forming time of the MQW light emitting layer. SOLUTION: The method for manufacturing an MQW light emitting layer comprises the steps of growing parts of barrier layers 6, 8 and 10 while raising the temperature of the layers 6, 8 and 10 after the well layers 5, 7 and 9 are grown, and again repeating temperature raising and lowering steps after the parts of the layers 6, 8 and 10 are grown at a constant temperature. Thus, the MQW having excellent crystallinity and high light emitting efficiency can be formed. Further, the method for manufacturing the light emitting element comprises the steps of growing parts of the barrier layers 6, 8 and 10 while raising the temperatures of the layers 6, 8 and 10 after the well layers 6, 8 and 10 are grown, further accelerating the growth rate in the case of growing the parts of the layers 6, 8 and 10 at a constant temperature. Thus, a forming time of the MQW light emitting layer can be shortened, and a manufacturing cost of the emitting element can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a nitride semiconductor used for an optical device such as a light emitting diode or a semiconductor laser diode.

[0002]

2. Description of the Related Art A nitride semiconductor represented by AlGaInN containing a group III element such as Al, Ga, In and the like and containing a group V element such as N is a semiconductor material for a visible light emitting device or a high-temperature operating electronic device. It has been widely used in the fields of blue and green light emitting diodes and blue-violet laser diodes.

In the manufacture of a light emitting device using a nitride semiconductor, it has recently been the mainstream to grow a nitride semiconductor thin film crystal by metal organic chemical vapor deposition (MOCVD). According to this method, an organic metal compound gas (trimethylgallium (hereinafter, abbreviated as “TMG”), a trimethylaluminum (hereinafter, abbreviated as “TMG”) as a group III element source gas is placed in a reaction tube in which a substrate made of sapphire, SiC, GaN, or the like is installed. (TMA), trimethyl indium (hereinafter abbreviated as "TMI"), and ammonia or hydrazine as a group V element source gas, and the substrate temperature is increased to about 700C to 1100C. At a high temperature, an n-type layer, a light-emitting layer, and a p-type layer are grown on a substrate, and these layers are formed by lamination. During the growth of the n-type layer, monosilane (SiH
₄ ) or germane (GeH ₄ ), etc.
Cyclopentadienyl magnesium (Cp ₂ Mg) or dimethyl zinc (Zn (CH ₃ ) ₂ )
Are grown simultaneously with the flow of the group III element source gas.

After the growth and formation, an n-side electrode and a p-side electrode are formed on the surface of the n-type layer and the surface of the p-type layer, respectively, and separated into chips to obtain a light emitting device. it can.

[0005] The light-emitting layer is formed so that the desired emission wavelength can be obtained.
A double-hetero structure in which InGaN having a composition of n is adjusted and sandwiched by a cladding layer having a bandgap energy larger than that of the light emitting layer, and a quantum well structure in which the light emitting layer is formed of a thin layer that causes a quantum size effect, is used. Although generally used, recently, a quantum well structure having a higher luminous efficiency has become mainstream.

This quantum well structure is formed by sandwiching a layer having a small band gap energy called a well layer with a layer having a larger band gap energy than the well layer.

Further, a single quantum well having one well layer is used.
The multiple quantum well (MQW) with high luminous efficiency is In_x
Ga_1-xA well layer made of N (0 <x <1);_yAl
_zGa _1-yzN (0 ≦ y <1, 0 ≦ z <1, 0 ≦ y + z <
1, x> y) by alternately stacking barrier layers
The conventional MQW manufacturing method is as follows.
There are three main types.

[0008] The first prior art is disclosed in Japanese Patent Laid-Open No. 10-129.
No. 22 discloses this. This is a nitride semiconductor light emitting device made of MQW in which barrier layers made of AlGaN and well layers made of InGaN are alternately stacked.
Using a VD apparatus, a buffer layer made of AlN and a GaN layer doped with Si are sequentially laminated on a sapphire substrate, and then a light emitting layer composed of MQW is laminated, and a cladding layer doped with Mg is formed thereon. The contact layers are sequentially laminated.

The method for growing MQW in this light emitting device is described below.
First, the substrate temperature is kept at 1100 ° C._Twoor
Is H_Two, Ammonia, TMG and TMA to introduce Al
_0.05Ga _0.95Forming a 50 ° thick barrier layer made of N;
Subsequently, the substrate temperature is lowered to 800 ° C. and held,_TwoOr
H_Two, Ammonia, TMG, TMI, silicon
And zinc doped In_0.20Ga_0.80Thickness consisting of N
A well layer of 50 ° is formed. And the barrier layer and the
Well layers are grown alternately and the total thickness is 0.055 μm.
A light emitting layer made of MQW is formed. At this time, the barrier layer
It is the same as the growth rate of the door layer.

[0010] In this structure, since the MQW comprising a strained superlattice of a well layer and a barrier layer is used for the light emitting layer, a high quality crystal with few dislocations can be obtained, and the luminous efficiency of the nitride semiconductor light emitting device can be improved. It has been shown to improve.

A second prior art is disclosed in Japanese Unexamined Patent Publication No. 10-135.
No. 514. This is because, in the method of growing the MQW of the light emitting device, the substrate temperature is maintained at 900 ° C., and N ₃ , TMG, and ammonia are introduced to achieve a thickness of 3.5.
A barrier layer made of GaN having a thickness of nm is formed. Next, the substrate temperature was maintained at 750 ° C., and TMI was introduced in addition to N 2, TMG, and ammonia to form a 3.5 nm thick In _0.16 Ga.
_A well layer made of _0.84 N is formed. Then, the barrier layers and the well layers are alternately grown to form five barrier layers and well layers. Further, the substrate temperature is maintained at 900 ° C.
An uppermost barrier layer made of GaN with a thickness of nm is formed on the fifth quantum well layer. At this time, the growth rate of the barrier layer is the same as the growth rate of the well layer.

In this structure, the layer in contact with the Si-doped GaN layer and the Mg-doped clad layer is used as a barrier layer, and the thickness of each barrier layer is made uniform, so that the wavelength of the emitted light is increased. It is shown that the shift can be prevented. The third conventional technique is disclosed in Japanese Patent Application Laid-Open No. H11-224972. This is the MQW of the light emitting element.
In the growth method, the substrate temperature is maintained at 750 ° C.
A well layer made of In _0.2 Ga _0.8 N is formed with a thickness of 25 °. Next, a barrier layer made of In _0.01 Ga _0.95 N is formed at 50 ° _C. at the same substrate temperature only by changing the molar ratio of TMI.
It is formed with a film thickness of. This operation is repeated 13 times, and finally a well layer is formed to form an active layer having a multiple quantum well structure having a total thickness of 0.1 μm. At this time, the growth rate of the barrier layer is the same as the growth rate of the well layer.

In this example, the barrier layer is formed of InGaN having a bandgap larger than that of the well layer.
Since the crystal is softer than the crystal, cracks are less likely to occur in the cladding layer above the MQW and the cladding layer can be made thicker, which is particularly effective for improving the quality of a semiconductor laser made of a nitride semiconductor. It is shown that there is.

Further, when the barrier layer is also made of InGaN, the well layer and the barrier layer can be grown at the same temperature, so that the decomposition of the well layer formed earlier is suppressed. It has been shown that the growth time of MQW can be shortened because the layer and the barrier layer can be grown continuously.

[0015]

However, the above-described method for forming the MQW has the following problems.

First, in the first prior art, In
After growing the well layer made of GaN, the well layer is decomposed in the process of raising the temperature to the substrate temperature (1100 ° C.) for growing the barrier layer made of AlGaN. It is difficult.

Next, in the second conventional technique, In
After growing the well layer made of GaN, in the process of raising the temperature to the substrate temperature (900 ° C.) for growing the barrier layer made of GaN, at least the well layer is decomposed, so that a well layer having excellent crystallinity is grown. It is difficult.

On the other hand, in the third prior art, since the substrate temperature for growing the well layer and the barrier layer is the same, decomposition of the well layer is small. However, in MQW,
In order for the barrier layer to function sufficiently, the barrier layer needs to have a sufficiently lower In composition than the well layer. In this example,
The In composition of the barrier layer is 0.01, and such a low I
It is difficult to control the n composition.

The InGaN of the barrier layer is a crystal substantially similar to GaN. Thus, the barrier layer, which is a crystal close to GaN, has the same substrate temperature (750 ° C.) as the well layer.
Therefore, the crystallinity of the barrier layer is deteriorated as compared with the conventional technique 1 in which the barrier layer is grown at about 1100 ° C.

As described above, in the conventional MQW manufacturing method, when the substrate temperature for growing the barrier layer is raised above the substrate temperature for growing the well layer in order to improve the crystallinity of the barrier layer, the well layer deteriorates, If the barrier layer and the well layer are grown at the same substrate temperature, there is a problem that the crystallinity of the barrier layer becomes insufficient and the quality of the MQW deteriorates.

In order to manufacture a high quality MQW, the barrier layer needs to be formed thicker than the well layer. As is common to the three conventional techniques, in the method of growing the barrier layer and the well layer at the same growth rate, the growth time becomes longer when the barrier layer is made thicker or when the number of MQW cycles is increased, and the MQW becomes longer. Production cost increases, and MQ
There is a problem that the crystallinity of W decreases.

The problem to be solved in the present invention is to provide a method for manufacturing an MQW with improved luminous efficiency by suppressing the deterioration of the well layer and improving the crystallinity of the barrier layer, and forming the MQW. An object of the present invention is to provide a method for manufacturing a light emitting device made of a nitride semiconductor, in which the manufacturing cost is reduced by reducing the time.

[0023]

Means for Solving the Problems The present inventors have conducted intensive studies on a method of manufacturing an MQW (particularly, substrate temperature, growth rate, hydrogen concentration in atmosphere, and V / III ratio). As a result, after growing the entire well at a substrate temperature suitable for growing the well layer, a part of the barrier layer (hereinafter abbreviated as “barrier layer A”) is grown while the substrate is being heated, and further raised. After growing a part of the barrier layer (hereinafter abbreviated as “barrier layer B”) at a substantially constant substrate temperature after the temperature, the substrate temperature is lowered to a temperature at which the well layer is grown, and the well layer is grown. By repeating the process, MQ with excellent crystallinity and high luminous efficiency
It has been found that a W light emitting layer can be formed.

Next, when growing the barrier layer B, the hydrogen concentration in the atmosphere should be higher than when growing the barrier layer A, and the V / III ratio should be higher than when growing the barrier layer A. Has been found that the crystallinity of the barrier layer B can be improved.

When the barrier layer B is grown, the growth is performed at a higher growth rate than the well layer and the barrier layer A. When the barrier layer B is grown, the temperature is lowered to the substrate temperature at which the well layer is grown. In addition, it has been found that by adding a step of growing at least a part of the barrier layer, the MQW formation time can be further reduced even when the barrier layer is thick or the number of MQW cycles is large.

According to such a configuration, at the time of forming the MQW, the decomposition of the well layer can be suppressed, the crystallinity of the barrier layer can be improved, and the MQ with high luminous efficiency can be obtained.
A W light emitting layer can be manufactured. Further, since the formation time of the MQW light emitting layer can be shortened, it is possible to reduce the manufacturing cost of the light emitting element made of a nitride semiconductor.

[0027]

According to the first aspect of the present invention, a well layer made of a nitride semiconductor and a barrier layer made of a nitride semiconductor having a band gap energy larger than that of the well layer are formed on a substrate. A method for manufacturing a nitride semiconductor having a multiple quantum well structure alternately stacked, comprising: a first step of growing the well layer at a first substrate temperature;
A second step of growing the barrier layer while increasing the temperature from the substrate temperature to a second substrate temperature higher than the first substrate temperature, and changing the temperature from the second substrate temperature to the first substrate temperature. And a third step of lowering the temperature is repeated in order to form a multiple quantum well, thereby forming a nitride semiconductor.

According to this method, the barrier layer is grown while raising the temperature immediately after the growth of the well layer.
This has the effect that decomposition of the well layer made of GaN can be suppressed and the crystallinity of the barrier layer can be increased.

According to a second aspect of the present invention, after the growth of the barrier layer in the second step and before the third step, the substrate temperature is kept substantially constant. 2. The method for producing a nitride semiconductor according to claim 1, further comprising the step of: growing the barrier layer in a state where the temperature is maintained at a substrate temperature higher than the substrate temperature at which the well layer is grown. , Grow a part of the barrier layer,
This has the effect that the crystallinity of the barrier layer can be further increased.

The invention according to claim 3 is characterized in that the growth rate of at least a part of the growth of the barrier layer in the fourth step is higher than the growth rate of the barrier layer in the second step. 3. The method of manufacturing a nitride semiconductor according to claim 2, wherein a barrier layer relatively thicker than the well layer and an MQW having a large number of cycles can be grown in a short time, and the total MQW growth time can be shortened. Therefore, there is an effect that the manufacturing cost of the nitride semiconductor made of MQW can be reduced.

The invention according to claim 4, wherein the hydrogen concentration in the atmosphere in at least a part of the growth of the barrier layer in the fourth step is the same as that of the atmosphere in growing the barrier layer in the second step. 3. The method for producing a nitride semiconductor according to claim 2, wherein the concentration of hydrogen is higher than the concentration of hydrogen in the inside, and by increasing the hydrogen concentration in the fourth step, migration of atoms on the substrate surface is promoted. This has the effect that the crystallinity of the barrier layer can be further increased.

According to a fifth aspect of the present invention, in the fourth step, at least a part of the barrier layer at the time of growth is provided.
The ratio of the supply amount of Group V raw material to the supply amount of Group III raw material (hereinafter referred to as V
/ III ratio) is smaller than the V / III ratio at the time of growth of the barrier layer in the second step. Has the effect of significantly reducing the supply amount of ammonia without deteriorating the crystallinity of the barrier layer B, and reducing the manufacturing cost of a nitride semiconductor made of MQW.

[0033] In the invention described in claim 6, the well layer is formed of I
n _x Ga _1-x N (where, 0 <x <1) is, the barrier layer is _{In y Al z Ga 1-yz} N ( where, 0 ≦ y <1,0 ≦ z
6. The method for manufacturing a nitride semiconductor according to claim 1, wherein <1, 0 ≦ y + z <1, x> y). By limiting the material semiconductor material to the above-mentioned materials, it is possible to improve the quality of MQW and to produce a nitride semiconductor made of MQW having excellent optical characteristics.

[0034] In the invention described in claim 7, the barrier layer is formed of G
7. The method for producing a nitride semiconductor according to claim 6, wherein the nitride semiconductor is aN, wherein the crystallinity of the barrier layer can be further increased, and a nitride semiconductor made of MQW having excellent optical characteristics can be produced. Has an action.

The invention according to claim 8 is characterized in that the first substrate temperature is 500 ° C. to 900 ° C. and the second substrate temperature is 800 ° C. to 1200 ° C. 7. The method for manufacturing a nitride semiconductor according to claim 7, wherein the first substrate temperature and the second substrate temperature are limited to the above ranges, whereby the well layer and the barrier layer having excellent crystallinity are provided. Can be produced.

According to a ninth aspect of the present invention, the supply amount of Ga material at the start of growth of the barrier layer is less than the supply amount of Ga at the time of growth of the well layer.
The method for producing a nitride semiconductor according to any one of claims 6 to 8, wherein the amount of the raw material supplied is less than the amount of the raw material supplied. It has the effect of being able to.

According to a tenth aspect of the present invention, in the third step, the barrier layer is grown in at least a part of the second step.
9. The method for manufacturing a nitride semiconductor according to any one of items 1 to 9, wherein a part of the barrier layer is grown even when the temperature is lowered, so that the MQW is formed even when the thickness of the barrier layer is increased or the number of MQW cycles is increased. Can be shortened, and the manufacturing cost of a nitride semiconductor made of MQW can be reduced.

The invention according to claim 11, wherein the substrate contains sapphire or SiC, and a buffer layer containing a nitride semiconductor is formed on the substrate at a substrate temperature lower than the first substrate temperature; 11. The nitride semiconductor according to claim 1, wherein an underlayer containing a nitride semiconductor is formed on the buffer layer, and the multiple quantum well is formed on the underlayer. This is a manufacturing method, in which a base layer having high crystallinity can be manufactured, and the quality of the MQW grown thereon can be improved, so that the luminous efficiency of the nitride semiconductor light emitting device having the light emitting layer composed of the MQW can be improved. Has an action.

According to a twelfth aspect of the present invention, the substrate includes a nitride semiconductor, an underlayer including the nitride semiconductor is formed on the substrate, and the multiple quantum well is formed on the underlayer. The method for producing a nitride semiconductor according to any one of claims 1 to 10, wherein an underlayer having higher crystallinity can be manufactured, and the quality of MQW grown thereon can be improved. And a nitride semiconductor light-emitting device having a light-emitting layer made of MQW.

According to a thirteenth aspect of the present invention, when the substrate is G
13. The method for manufacturing a nitride semiconductor according to claim 12, wherein the substrate and the underlayer are made of the same material, so that an underlayer having higher crystallinity can be produced. Because the quality of MQW to be grown can be improved,
The nitride semiconductor light emitting device having a light emitting layer made of MQW has an effect of increasing the light emitting efficiency.

Hereinafter, specific examples of the embodiment of the present invention will be described.
This will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of M according to an embodiment of the present invention.
FIG. 1 is a cross-sectional view illustrating a layer structure of a nitride semiconductor light emitting device made of QW.

This light emitting device comprises a buffer layer 2 made of GaN, a first n-type clad layer 3 made of GaN, and a second n-type clad layer 4 made of AlGaN on a substrate 1 made of sapphire. Layer 5 made of InGaN
Having barrier layers 6 of GaN and GaN grown alternately
The W layer (5 to 10) and the p-type cladding layer 11 made of AlGaN are sequentially stacked. A light-transmitting electrode 12 and a p-side electrode 13 are sequentially formed on the surface of the p-type cladding layer 11, and the n-side electrode 1 is formed on the surface of the first n-type cladding layer 3.
4 are formed.

The MQW of this light emitting device is expressed as MOCV
It is produced by the following method using method D.

First, a substrate 1 made of sufficiently washed sapphire is charged into a reaction tube, and the substrate 1 is heated at about 1050 ° C. for 10 minutes while flowing nitrogen and hydrogen into the reaction tube to clean the surface of the substrate 1. Performing

Next, the temperature of the substrate 1 is lowered to 550 ° C., and nitrogen, TMG and ammonia are respectively flowed to form GaN.
The buffer layer 2 is formed on the substrate 1. After the buffer layer 2 is formed, the temperature of the substrate 1 is raised to 1050 ° C. while flowing nitrogen and ammonia respectively, and at this temperature, nitrogen, hydrogen, TMG, ammonia, and SiH ₄ are respectively flowed to form the first. The n-type GaN cladding layer 3 is formed.
After the formation of the first n-type GaN cladding layer 3,
At 050 ° C., nitrogen, hydrogen, TMG, TMA, and ammonia are respectively flowed to form the second n-type AlGaN cladding layer 4.

Next, the supply of hydrogen, TMG and TMA was stopped, the temperature of the substrate 1 was lowered to 750 ° C., and nitrogen, TM
G, TMI, and ammonia are flowed, respectively, and InGaN
Is formed.

Thereafter, only the supply of TMI was stopped, and subsequently, the barrier layer A was formed while the substrate temperature was raised from 750 ° C. to 1050 ° C. Further, at 1050 ° C., nitrogen, hydrogen, TMG and ammonia were respectively flowed. While
The barrier layer B is formed, and the barrier layer A and the barrier layer B are combined to form the barrier layer 6. Next, supply of hydrogen and TMG was stopped, and
Temperature to 750 ° C. Thereafter, the same procedure as that for the well layer 5 and the barrier layer 6 is repeated, and the well layer 7, the barrier layer 8, the well layer 9, and the barrier layer 10 are sequentially stacked to form the MQW. According to this method, decomposition of the well layer can be suppressed, and at the same time,
The crystallinity of the barrier layer can be increased.

According to the findings of the present inventors, it is desirable that the growth rate of the barrier layer B be higher than that of the barrier layer A. Specifically, the growth rate of the barrier layer A is 0.01 μm
/ H to 0.5 μm / h, whereas the growth rate of the barrier layer B is preferably 0.1 μm / h to 10 μm / h. If the growth rate of the barrier layer B is less than 0.1 μm / h, it takes too much time to form the MQW, and 10 μm / h.
If it is larger than h, the crystallinity of the barrier layer B deteriorates. The barrier layer must be formed thicker than the well layer. In particular, when the barrier layer B is grown at a higher growth rate than the barrier layer A, the growth at a high temperature (approximately constant temperature) is achieved. Since the speed is increased, the crystallinity of the barrier layer is improved, and at the same time, when the thickness of the barrier layer is increased or the number of MQW cycles is increased, the growth time can be shortened as compared with the conventional case.
The manufacturing cost of a nitride semiconductor made of QW can be reduced.

Next, it is desirable that the hydrogen concentration in the atmosphere when the barrier layer B is grown be higher than the hydrogen concentration in the atmosphere when the barrier layer A is grown. Specifically, while the hydrogen concentration in the atmosphere during the growth of the barrier layer A is 0% to 5%, the barrier layer B
The hydrogen concentration in the atmosphere during the growth of is preferably 5% to 70%. Here, the hydrogen concentration is a volume ratio of hydrogen gas. When the hydrogen concentration in the atmosphere during the growth of the barrier layer B is lower than 5%, the crystallinity of the barrier layer B deteriorates.
The uniformity of the film thickness and the like in the substrate surface is deteriorated.

In the barrier layer A, since it is important to suppress the decomposition of the well layer, the lower the hydrogen concentration in the atmosphere during the growth of the barrier layer, the more the decomposition of the well layer is suppressed. On the other hand, since it is important for the barrier layer B to improve the crystallinity of the barrier layer, by increasing the hydrogen concentration in the atmosphere at the time of growth at a higher temperature (1050 ° C.) than the barrier layer A, the barrier layer B has The migration can be promoted, and the crystallinity of the barrier layer can be improved.

Next, it is desirable that the V / III ratio when the barrier layer B is grown is smaller than the V / III ratio when the barrier layer A is grown. Specifically, the V / III ratio of the barrier layer A is 1 × 10 ⁴
２2 × 10 ⁵ , whereas the V / III ratio of the barrier layer B is 5
× 10 ² to 1 × 10 ⁴ is preferred. If the V / III ratio of the barrier layer B is less than 5 × 10 ^2, the pits are easily generated by nitrogen partial shortage of the growth surface during growth of the barrier layer B, a grown 1 × 10 ⁴ or more The surface morphology of the barrier layer B deteriorates when the polarity of the surface becomes the nitrogen surface.

Next, the MQW well layer is made of InxGa._1-xN
(0 <x <y), the barrier layer is In_yAl _zGa_1-yzN (0
≦ y <1, 0 ≦ z <1, 0 ≦ y + z <1, x> y)
Is desirable. Immediately after the growth of the well layer,
Since a part of the wall layer is grown, the material of the barrier layer is changed to nitride half.
Conductor, ie In_yAl_zGa_1-yzN (0 ≦ y <1,
0 ≦ z <1, 0 ≦ y + z <1, x> y)
As a result, the deterioration of the well layer is suppressed and
MQ with excellent light emission characteristics
A nitride semiconductor made of W can be manufactured.

When the barrier layer is made of GaN, the crystallinity of the barrier layer can be further improved.

Next, regarding the substrate temperature, the well layer
A range of 0 ° C to 900 ° C is desirable. In the well layer, decomposition occurs even during the growth. Therefore, when the temperature is higher than 900 ° C., the decomposition of InGaN is promoted and the well layer hardly grows. When the temperature is lower than 500 ° C., the crystallinity of the well layer deteriorates. On the other hand, the substrate temperature after the temperature rise is 800 ° C. to 1200 ° C.
Is desirable. When the substrate temperature is higher, the crystallinity of the barrier layer is improved. However, when the temperature is higher than 1200 ° C., the surface of the wafer is roughened and the load on the substrate heating source of the MOCVD apparatus is undesirably increased. When the substrate temperature is 800
If the temperature is lower than ℃, a barrier layer having sufficient crystallinity cannot be grown.

Next, it is desirable that the supply amount of the Ga source at least at the start of the growth of the barrier layer A be smaller than the supply amount of the Ga source in the well layer. Specifically, TMG during well layer growth
The supply amount is 2 μmol / min to 10 μmol / min, whereas the TMG supply amount at the start of the growth of the barrier layer A is 0.4 μmol / min.
mol / min to 4 μmol / min are preferred. If the supply amount of TMG at the start of the growth of the barrier layer A is smaller than 0.4 μmol / min, it becomes difficult to suppress the decomposition of the well layer when growing the barrier layer A, and is larger than 4 μmol / min. As a result, the crystallinity of the barrier layer A deteriorates. This is because when the supply amount of TMG of the barrier layer A is increased, the decomposition of the well layer is easily suppressed, but the barrier layer is grown at a relatively high growth rate at a low temperature, so that the crystallinity of the barrier layer is further deteriorated. To do that.

When growing the barrier layer A while increasing the substrate temperature, the growth rate of the barrier layer A can be gradually increased with the increase in the substrate temperature. In this case, Ga
The raw material supply amount is 0.4 μmol in the initial stage of the growth start of the barrier layer A.
/ Min to 4 μmol / min, and can be 20 μmol / min to 100 μmol / min immediately before the completion of the growth of the barrier layer A.

Next, after growing the barrier layer at a substrate temperature higher than the substrate temperature for growing the well layer, when lowering the substrate temperature to the temperature for growing the well layer, at least a part of the barrier layer is grown. It is desirable to reduce the growth time. Since the influence on the well layer (deterioration of crystallinity) at the time of the temperature decrease is lower than that at the time of the temperature increase after the well layer growth, there is an advantage that the growth rate can be increased as compared with the temperature increase. Since it is clear that the higher the temperature is, the better the crystallinity of the barrier layer is. Therefore, it is possible to increase the growth rate at the start of the temperature drop and gradually decrease the growth rate as the temperature decreases.
Thereby, the growth time of the MQW is shortened, and the manufacturing cost of the nitride semiconductor including the MQW light emitting layer can be reduced.

Next, the substrate is made of sapphire or SiC.
By laminating a buffer layer thereon and further growing an underlayer made of a nitride semiconductor, an underlayer having high crystallinity can be grown.
Since the quality of QW is improved, the luminous efficiency of the nitride semiconductor composed of MQW can be increased.

Further, the substrate can be a nitride semiconductor substrate. This makes it possible to reduce the difference between the lattice constant and the coefficient of thermal expansion between the substrate and the underlayer as compared with the related art, and to further enhance the crystallinity of the underlayer made of a nitride semiconductor. Thereby, the MQ grown on the underlayer is
Since the quality of W is further improved, the luminous efficiency of the nitride semiconductor composed of MQW can be increased.

Further, GaN is generally used for the underlayer of the MQW, and by using GaN for the substrate, the substrate and the underlayer are made of the same material, and the underlayer having excellent crystallinity can be grown. The quality of the MQW laminated thereon can be further improved, and the luminous efficiency of the nitride semiconductor comprising the MQW can be increased.

In addition to the above, sapphire, SiC, GaAs
A GaN laminated substrate in which a thick GaN is laminated on a substrate such as s may be used, or a GaN laminated substrate or the nitride semiconductor substrate patterned with a mask of SiO ₂ or the like may be used as the substrate. Similarly, the luminous efficiency of the nitride semiconductor made of MQW can be increased.

[0063]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a specific example of a method for manufacturing a gallium nitride-based compound semiconductor having an MQW structure according to the present invention will be described with reference to the drawings.

(Example 1) FIG. 2 is a sectional view showing a layer structure of a nitride semiconductor made of MQW according to Example 1 of the present invention, and FIG. 3 is a cross-sectional view showing the structure of the MQW according to Example 1 of the present invention. FIG. 3 is a view showing a growth profile (substrate temperature, growth rate, hydrogen concentration, ammonia flow rate) of a nitride semiconductor.

First, a sapphire substrate 1 having a mirror-finished surface is placed on a substrate holder in a reaction tube of an MOCVD apparatus. Then, the temperature of the substrate 1 is maintained at 1000 ° C., nitrogen is supplied at 5 l / min, and hydrogen is supplied. The substrate 1 was heated for 10 minutes while flowing at a flow rate of 5 liters / minute, thereby removing dirt and moisture such as organic substances adhering to the surface of the substrate 1.

Then, the temperature of the substrate 1 was lowered to 550 ° C., and 16 liters / minute of nitrogen, 4 liters / minute of ammonia, and 40 μmol / minute of TMG were used as carrier gases.
, The buffer layer 2 made of GaN is 25 n
m.

Next, after only the supply of TMG is stopped and the temperature of the substrate 1 is raised to 1050 ° C., ammonia is supplied while flowing nitrogen and hydrogen as carrier gases at 13 liter / min and 3 liter / min, respectively. The underlayer 22 made of undoped GaN was grown at a thickness of 2 μm by supplying TMG at 4 μl / min and 80 μmol / min.

After the growth of the underlayer 22, the supply of TMG is stopped, the temperature of the substrate 1 is lowered to 750 ° C., and this temperature is maintained, and nitrogen as a carrier gas is supplied at a rate of 14 liter / liter.
Min, ammonia 6 liter / min, TMG 4 μmol
The TMI was supplied at a rate of 5 μmol / min, and a well layer 5 having a quantum well structure made of undoped In _0.15 Ga _0.85 N was grown to a thickness of 2 nm.

After growing the well layer 5, the supply of TMI is stopped.
While supplying nitrogen at 14 L / min, ammonia at 6 L / min and TMG at 2 μmol / min as a carrier gas, and raising the temperature of the substrate 1 to 1050 ° C., the undoped GaN (barrier layer A ) Is 3 nm
When the temperature of the substrate 1 reaches 1050 ° C., while flowing nitrogen and hydrogen as carrier gases at 15 liters / minute and 3 liters / minute, respectively, ammonia is supplied at 2 liters / minute, and TMG is supplied at 40 μmol / minutes. Min, feed in
Subsequently, undoped GaN (barrier layer B) was grown to a thickness of 12 nm. Thus, a barrier layer 6 of undoped GaN having a thickness of 15 nm was formed. Then, 19 liter / min of nitrogen and 1 of ammonia were used as carrier gas.
The substrate temperature is again lowered to 750 ° C. while flowing at a rate of 1 liter / minute, and the same procedure as the method of manufacturing the well layer 5 and the barrier layer 6 is repeated, whereby the well layers 7, 8, 9, 9 are formed. 10 was formed.

After the growth of the barrier layer 10, the temperature of the substrate 1 is reduced to 1
While maintaining the temperature at 050 ° C. and continuously flowing nitrogen and hydrogen as carrier gases at 13 liters / minute and 3 liters / minute, respectively, ammonia was supplied at 4 liters / minute and TMG was supplied at 80 μm.
The cap layer 23 made of undoped GaN was grown to a thickness of 100 nm.

As described above, M having three well layers
QW was formed, and it was used as Sample 1.

(Comparative Example 1) In the step of forming an MQW in the manufacturing method of Example 1 described above, after growing the base layer 22, the supply of TMG was stopped, and the temperature of the substrate 1 was lowered to 750 ° C. At 750 ° C., 14 liters / minute of nitrogen as carrier gas, 6 liters / minute of ammonia,
By supplying TMG at 4 μmol / min and TMI at 5 μmol / min, a well layer 5 having a single quantum well structure made of undoped In _0.15 Ga _0.85 N was grown to a thickness of 2 nm. Next, while maintaining the substrate temperature at 750 ° C. and supplying nitrogen as a carrier gas at 14 L / min, ammonia is supplied at 6 L / min, TMG is supplied at 2 μmol / min, and undoped GaN is deposited at a thickness of 15 nm. To form a barrier layer 6.

Thereafter, the same procedure as the method of manufacturing the well layers 5 and the barrier layers 6 was repeated to form the well layers 7, the barrier layers 8, the well layers 9, and the barrier layers 10 in this order.

Next, while flowing nitrogen at a rate of 14 liters / minute and ammonia at a rate of 1 liter / minute as a carrier gas,
The temperature of the substrate 1 was raised to 1050 ° C., and after the temperature was raised, nitrogen and hydrogen were respectively used as carrier gases at 13 liter / min.
While flowing at a rate of 4 liters / minute,
Then, TMG was supplied at a rate of 80 μmol / min, and the cap layer 23 was laminated to a thickness of 100 nm.

As described above, the third embodiment having the same structure as the first embodiment
An MQW composed of a plurality of well layers was formed and used as a sample 2.

First, the optical characteristics of Sample 1 of Example 1 and Sample 2 of Comparative Example 1 were compared using a photoluminescence (PL) measuring apparatus. The excitation light used in the PL measurement device was a He-Cd laser (wavelength: 325 nm), and the excitation intensity was 10 mW.

FIG. 4 is a diagram showing the photoluminescence spectra of Sample 1 and Sample 2. The PL spectrum 31 of the sample 1 had an emission intensity about four times that of the PL spectrum 32 of the sample 2. This is probably because the barrier layer was grown at a higher temperature in Sample 1 and the crystallinity of MQW was improved. After the temperature is raised (a constant temperature of 1050 ° C.), the growth rate of the barrier layer is increased by 20 times so that the MQW growth time of sample 1 is about 30 times longer than that of sample 2.
Minutes.

Embodiment 2 A method for manufacturing a light emitting device using a nitride semiconductor according to a second embodiment of the present invention is shown in FIG.
This will be described with reference to FIG.

First, a sapphire substrate 1 whose surface has been mirror-finished is placed on a substrate holder in a reaction tube of an MOCVD apparatus. Then, the temperature of the substrate 1 is maintained at 1000 ° C., nitrogen is supplied at 5 liter / min, and hydrogen is supplied. The substrate was heated for 10 minutes while flowing at a flow rate of 5 liters / minute to remove dirt and moisture such as organic substances adhering to the surface of the substrate 1.

Next, the temperature of the substrate 1 was lowered to 550 ° C., and nitrogen was supplied at a flow rate of 16 liters / minute while supplying ammonia at a rate of 4 liters / minute and TMG at a flow rate of 40 liters / minute.
The buffer layer 2 made of undoped GaN was grown at a thickness of 25 nm at a rate of μmol / min.

Next, after the supply of TMG was stopped and the temperature was raised to 1050 ° C., ammonia was added at 4 L / min and TMG was supplied at 13 L / min and 3 L / min as carrier gas, respectively. Is 80 μmol / min,
The first n-type cladding layer 3 made of Si-doped GaN was grown at a thickness of 2 μm by supplying 10 ppm / minute of SiH ₄ diluted at 10 ppm.

After growing the first n-type cladding layer 3, the substrate 1
At a temperature of 1050 ° C., while flowing nitrogen and hydrogen as carrier gases at 15 liters / minute and 3 liters / minute, respectively, ammonia at 2 liters / minute and TMG at 40 μm.
The second n-type cladding layer 4 made of undoped Al _0.05 Ga _0.95 N was grown to a thickness of 20 nm by supplying ol / min and TMA at 3 μmol / min.

After growing the second n-type cladding layer 4, TMG
And the supply of SiH ₄ were stopped, the substrate temperature was lowered to 750 ° C., and at 750 ° C., nitrogen was flowed as a carrier gas at 14 liters / minute, while 6 liters / minute of ammonia, 4 μmol / minute of TMG, and TMI 5 μmol
Per minute, a well layer 5 having a quantum well structure made of undoped In _0.15 Ga _0.85 N was grown to a thickness of 2 nm.

After growing the well layer 5, the supply of TMI is stopped.
While supplying nitrogen at 14 L / min, ammonia at 6 L / min and TMG at 2 μmol / min as a carrier gas, and raising the temperature of the substrate 1 to 1050 ° C., the undoped GaN (barrier layer A ) Is 3 nm
When the temperature of the substrate 1 reaches 1050 ° C., while flowing nitrogen and hydrogen as carrier gases at 15 liters / minute and 3 liters / minute, respectively, ammonia is supplied at 2 liters / minute, and TMG is supplied at 40 μmol / minutes. Min, feed in
Subsequently, undoped GaN (barrier layer B) was grown to a thickness of 12 nm. Thus, a barrier layer 6 of undoped GaN having a thickness of 15 nm was formed. Then, 19 liter / min of nitrogen and 1 of ammonia were used as carrier gas.
The substrate temperature is again lowered to 750 ° C. while flowing at a rate of 1 liter / minute, and the same procedure as the method of manufacturing the well layer 5 and the barrier layer 6 is repeated, whereby the well layers 7, 8, 9, 9 are formed. 10 were formed in order.

After forming the barrier layer 10, the temperature of the substrate 1 is reduced to 1
While maintaining the temperature at 050 ° C. and continuously flowing nitrogen and hydrogen as carrier gases at 15 liters / minute and 3 liters / minute, respectively, ammonia was supplied at 2 liters / minute, and TMG was supplied at 40 μm.
ol / min, TMA 3 μmol / min, Cp ₂ Mg 0.
Mg-doped Al supplied at 4 μmol / min.
_The p-type cladding layer 11 made of _0.05 Ga _0.95 N
m.

After growing the p-type cladding layer 11, TMG and T
The supply of MA and Cp ₂ Mg was stopped, and nitrogen was reduced to 18 liters /
Then, while flowing ammonia at a rate of 2 liters / minute, the temperature of the substrate was cooled to about room temperature, and a wafer having a nitride semiconductor laminated on the substrate was taken out of the reaction tube.

Incidentally, TMG which is an organometallic compound, TM
I, TMA, and Cp ₂ Mg were all supplied to the reaction tube by being vaporized by a hydrogen carrier gas.

The thus-formed laminated structure made of a gallium nitride-based compound semiconductor is not separately annealed, and nickel (Ni) and gold (Au) are each deposited on the surface by 5 nm by vapor deposition. Then, the light-transmissive electrode 12 was formed by photolithography and wet etching.

Thereafter, an insulating film (not shown) made of SiO ₂ is deposited on the translucent electrode 12 and the exposed p-type cladding layer 11 to a thickness of 0.5 μm by the CVD method, And reactive ion etching,
A mask made of an insulating film that covers the translucent electrode 12 and at the same time exposes a part of the surface of the p-type cladding layer 11 was formed.

Next, using the above-mentioned mask, the p-type cladding layer 11 is exposed from the exposed surface of the p-type cladding layer 11 by a reactive ion etching method using a chlorine-based gas.
, The MQW layers (5 to 10) and the second n-type cladding layer 4 are removed at a depth of about 0.4 μm, and the first n-type cladding layer 3 is removed.
Surface was exposed.

After the above steps, the insulating film is once removed by a wet etching method, and a portion on the surface of the light transmitting electrode 12 is removed by a vapor deposition method and a photolithography method.
A part of the exposed surface of the first n-type cladding layer 3;
Titanium (Ti) having a thickness of 0.1 μm and Au having a thickness of 0.5 μm were laminated to form a p-side electrode 13 and an n-side electrode 14, respectively. Thereafter, an insulating film (not shown) made of SiO _{2 having a} thickness of 0.2 μm and covering the surface of the translucent electrode 12 was formed by a plasma CVD method and a photolithography method.

Thereafter, the back surface of the sapphire substrate 1 was polished to a thickness of about 100 μm and separated into chips by scribing. After bonding this chip to the stem with the electrode formation surface side facing upward, the p-side electrodes 13 of the chip and n
Each of the side electrodes 14 is connected to an electrode on the stem with a wire, and then resin-molded to produce a light emitting element.
And When this light-emitting device was driven by a forward current of 20 mA, light was emitted in blue with a peak wavelength of 470 nm. At this time, the light emission output was 4 mW, and the forward operation voltage was 3.8 V.

(Embodiment 3) A method of manufacturing a light emitting device using a nitride semiconductor according to a third embodiment of the present invention will be described with reference to the drawings.

FIG. 5 is a sectional view showing a layer structure of a light emitting device made of a nitride semiconductor having an MQW structure according to a third embodiment of the present invention.

In the light emitting device made of the nitride semiconductor having the MQW structure shown in the second embodiment, a prototype was manufactured for the case where the substrate was a nitride semiconductor, and the light emission output was examined. As an example,
A light emitting device in which the nitride semiconductor substrate was GaN was manufactured.
The substrate is formed by HVPE (hydride vapor phase epitaxy).
After laminating GaN having a thickness of 100 μm on the sapphire substrate, polishing was performed to a depth of 10 μm using diamond slurry to remove irregularities on the substrate surface. After polishing, the GaN surface was removed by removing the damage layer generated on the GaN surface by machining, and finally the sapphire substrate was removed.
It was set to 1. The GaN substrate 21 was subjected to organic cleaning and ultrapure water cleaning to remove organic substances and impurities such as lubricating oil and wax during polishing, and after drying, was placed on a substrate holder in a reaction tube of a MOCVD apparatus.

First, after the temperature of the GaN substrate 21 was directly raised from room temperature to 1050 ° C., ammonia was supplied at a flow rate of 13 liters / minute and 3 liters / minute as carrier gases, and ammonia was supplied at a rate of 4 liters / minute. , TMG to 80
μmol / min, 10 ppm of 10 ppm diluted SiH ₄
And a first layer of Si-doped GaN
Was grown with a thickness of 2 μm.

Thereafter, the second n-type cladding layer 4, well layer 5, barrier layer 6, well layer 7, barrier layer 8, well layer 9, barrier layer 10, Mg layer 10 A doped AlGaN cladding layer 11 is sequentially stacked, and a light-transmitting electrode 12, a p-side electrode 13, and an n-side electrode 14 are formed as electrode processes.
Was formed to produce a light-emitting element, which was used as Sample 4. When this light-emitting device was driven by a forward current of 20 mA, light was emitted in blue with a peak wavelength of 470 nm. At this time, the light emission output was 4 mW, and the forward operating voltage was 3.4 V.
In this case, a light emission output of a level equivalent to that of the light emitting element (sample 3) using the sapphire substrate shown in Example 2 was obtained. As a result, it was confirmed that when the substrate was GaN, the luminous efficiency of the light emitting device was significantly improved as in Example 2, and the forward operating voltage was further reduced.

In the above-described embodiment, an example in which the present invention is mainly applied to a light emitting diode has been described. However, the present invention is not limited to a light emitting diode, but is applied to various semiconductor devices such as a semiconductor laser using a nitride semiconductor. It is also possible.

[0099]

As described above, according to the present invention, in a nitride semiconductor having a multiple quantum well structure (MQW), the barrier layer is grown while the temperature of the substrate is raised immediately after the growth of the well layer. And at the same time, the crystallinity of the barrier layer can be improved, and the luminous efficiency of the light emitting element made of the nitride semiconductor can be improved.

Further, when the barrier layer is formed thick or the number of MQW cycles is increased, the time for forming the MQW light emitting layer can be shortened as compared with the conventional case, and the production of a light emitting device made of a nitride semiconductor can be achieved. Costs can be reduced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a layer structure of a nitride semiconductor light emitting device including an MQW according to an embodiment of the present invention.

FIG. 2 is a sectional view showing a layer structure of a nitride semiconductor made of MQW according to a first embodiment of the present invention.

FIG. 3 is a view showing a growth profile (substrate temperature, growth rate, hydrogen concentration, ammonia flow rate) of a nitride semiconductor made of MQW according to Example 1 of the present invention.

FIG. 4 is a diagram showing photoluminescence spectra of Sample 1 and Sample 2.

FIG. 5 is a cross-sectional view illustrating a layer structure of a light emitting device including a nitride semiconductor having an MQW structure according to a third embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 substrate 2 buffer layer 3 first n-type cladding layer 4 second n-type cladding layer 5, 7, 9 well layer 6, 8, 10 barrier layer 11 p-type cladding layer 12 light-transmitting electrode 13 p-side electrode 14 n-side electrode 21 GaN substrate 22 underlayer 23 cap layer 31 PL intensity of sample 1 32 PL intensity of sample 2

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shuichi Shinagawa 1006 Kazuma Kadoma, Osaka Prefecture F-term in Matsushita Electric Industrial Co., Ltd. (reference) 4K030 AA11 AA13 AA17 AA18 BA08 BA11 BA38 BB12 CA04 CA05 DA03 FA10 HA01 JA06 JA10 JA12 LA11 LA12 LA18 5F041 AA03 AA40 CA05 CA33 CA34 CA40 CA46 CA57 CA65 CA74 CA82 CA88 CA92 DA07 5F045 AA04 AB17 AB18 AC01 AC08 AC12 AC19 AD09 AD10 AD11 AD12 AD13 AD14 AD15 AD16 AF02 AF04 AF09 BB12 BB13 CA10 CA12 DA53F07 AE12 CB07 DA05 DA25 DA35 EA28

Claims (13)

[Claims] 1. A nitride having a multiple quantum well structure in which a well layer made of a nitride semiconductor and a barrier layer made of a nitride semiconductor having a larger band gap energy than the well layer are alternately stacked on a substrate. A method of manufacturing a semiconductor, comprising: growing a well layer at a first substrate temperature;
A step of growing the barrier layer while increasing the temperature from the first substrate temperature to a second substrate temperature higher than the first substrate temperature; and And a third step of lowering the temperature to the first substrate temperature to form a multiple quantum well by sequentially repeating the steps. 2. After the growth of the barrier layer in the second step, before the third step, the barrier layer is further grown at a substrate temperature that keeps the second substrate temperature substantially constant. 2. The method according to claim 1, further comprising the step of: 3. The method according to claim 2, wherein a growth rate of at least a part of the growth of the barrier layer in the fourth step is higher than a growth rate of the barrier layer in the second step. A method for manufacturing a nitride semiconductor. 4. The hydrogen concentration in the atmosphere in at least part of the growth of the barrier layer in the fourth step is higher than the hydrogen concentration in the atmosphere of the growth of the barrier layer in the second step. The method for producing a nitride semiconductor according to claim 2, wherein: 5. The method according to claim 4, wherein a ratio of a group V source supply amount to a group III source supply amount (hereinafter referred to as a V / III ratio) in at least a part of the growth of said barrier layer in said fourth step is said second ratio. 3. The method according to claim 2, wherein the V / III ratio during the growth of the barrier layer in the step is smaller than the V / III ratio. 6. The method according to claim 1, wherein said well layer is made of In _x Ga ₁ -xN (where 0 <
a x <1), the barrier layer is _{In y Al z Ga 1-yz} N
(However, 0 ≦ y <1, 0 ≦ z <1, 0 ≦ y + z <1, x
> Y), the method for producing a nitride semiconductor according to any one of claims 1 to 5. 7. The method according to claim 6, wherein the barrier layer is GaN. 8. The temperature of the first substrate is 500 ° C. to 900 ° C.
The method according to any one of claims 1 to 7, wherein the second substrate temperature is 800C to 1200C. 9. The nitride according to claim 6, wherein a supply amount of the Ga source at the start of growth of the barrier layer is smaller than a supply amount of the Ga source at the time of growth of the well layer. Of manufacturing semiconductor products. 10. The nitride semiconductor according to claim 1, wherein, in the third step, the barrier layer is grown in at least a part of the second step. Production method. 11. A substrate comprising sapphire or SiC, forming a buffer layer containing a nitride semiconductor on the substrate at a substrate temperature lower than the first substrate temperature, and forming a nitride layer on the buffer layer. The method for manufacturing a nitride semiconductor according to claim 1, wherein an underlayer containing a semiconductor is formed, and the multiple quantum well is formed on the underlayer. 12. The semiconductor device according to claim 1, wherein said substrate contains a nitride semiconductor, an underlayer containing a nitride semiconductor is formed on said substrate, and said multiple quantum well is formed on said underlayer. 11. The method for producing a nitride semiconductor according to any one of 1 to 10. 13. The method according to claim 12, wherein the substrate is GaN.