JP3348656B2 - Gallium nitride based compound semiconductor light emitting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gallium nitride compound semiconductor light emitting device.

[0002]

2. Description of the Related Art Conventionally, a gallium nitride-based compound semiconductor (Al _x Ga ₁ -xN; including x = 0) thin film is formed on a sapphire substrate by metalorganic compound vapor deposition (hereinafter referred to as “MOVPE”). There has been studied a light-emitting device in which a gallium nitride-based compound semiconductor thin film is used as a light-emitting layer. Since a single crystal wafer of a gallium nitride-based compound semiconductor cannot be easily obtained, a gallium nitride-based compound semiconductor is epitaxially grown on a sapphire substrate having a lattice constant close to that of the single crystal wafer.

[0003]

However, because of the lattice mismatch between sapphire and the gallium nitride-based compound semiconductor as the light emitting layer and the large difference between the vapor pressures of gallium and nitrogen, a high-quality gallium nitride-based compound semiconductor crystal can be obtained. Therefore, a light-emitting element with high blue light emission efficiency cannot be obtained.

Accordingly, the present invention has been made to solve the above-mentioned problems, and an object of the present invention is to improve the crystallinity of a gallium nitride-based compound semiconductor grown on a sapphire substrate. An object of the present invention is to provide a blue light emitting element having high luminous efficiency.

[0005]

According to a first aspect of the present invention, there is provided a gallium nitride-based compound semiconductor layer (Al _x Ga ₁ -xN; including X = 0) on a sapphire substrate.
In a light-emitting element having a thickness of 100 to 500 mm on a sapphire substrate at a growth temperature of 400 to 600 ° C, the crystal structure is present in an amorphous crystal.
With a mixture of microcrystals or polycrystals having a
A gallium nitride-based buffer composed of a buffer layer having a wurtzite structure made of luminium (AlN) and a plurality of gallium nitride-based compound semiconductor layers (Al _x Ga ₁ -xN; including X = 0) formed on the buffer layer It is a compound semiconductor light emitting device. Further, the invention according to claim 2 is a method in which nitrogen is deposited on a sapphire substrate.
Gallium arsenide compound semiconductor layer (Al _x Ga ₁ -xN ; X =
0), the sapphire substrate
Film thickness of 100 Å to 50 at growth temperature of 400 以上 C to less than 600 ℃ C
Crystal structure grown in amorphous crystal with thickness less than 0 mm
Microcrystals or polycrystals with a size of 0.1 μm or less
Aluminum nitride (AlN) with wurtzite structure
And a plurality of layers formed on the buffer layer
Gallium nitride based compound semiconductor layer (Al _x Ga ₁ -xN ;
X = 0) (including X = 0)
It is a light emitting element. The invention of claim 3 is the invention of claim 2
The proportion of microcrystals or polycrystals is 1 to 90%.
It is characterized by that. The invention of claim 4 is the invention of claims 1 to
The invention according to claim 3 , wherein the buffer layer is formed by an organic metal compound vapor deposition method.

[0006]

[Function and effect] A growth temperature of 400 ° C. on a sapphire substrate
At a temperature of not less than 600 ° C. and a thickness of not less than 100 ° and less than 500 °, the crystal structure having an abundance of 1 to 9 in the amorphous crystal.
Since the buffer layer made of aluminum nitride (AlN) having a wurtzite structure in which microcrystals or polycrystals are mixed at 0% was provided, the crystallinity of the gallium nitride-based compound semiconductor grown on the buffer layer was improved. Similarly,
On a fire substrate, at a growth temperature of 400 ° C or higher and lower than 600 ° C,
It is grown to a thickness of 100 Å or more and less than 500 、 and has a crystal structure
Of aluminum nitride having a size of 0.1 μm or less in an amorphous crystal
Since a buffer layer made of aluminum (AlN) was provided,
Gallium nitride-based compound semiconductor grown on a buffer layer
Has improved crystallinity. Further, in the light emitting device of the present invention, a blue light emitting characteristic was improved because the buffer layer having the same configuration was provided.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described based on specific embodiments. FIG. 1 is a sectional view showing a configuration of a vapor phase growth apparatus for carrying out the present invention. The quartz tube 10 is sealed at its left end with an O-ring 15 and abuts against the flange 14.
7 and nuts 48, 49, etc. at several places
It is fixed to. The right end of the quartz tube 10 is an O-ring 4
0 and are screwed to the flange 27 with the screw fasteners 41, 4
2 fixed.

A liner tube 12 for guiding a reaction gas is provided in an inner chamber 11 surrounded by a quartz tube 10. One end 13 of the liner tube 12 is held by a holding plate 17 fixed to a flange 14, and the bottom 18 of the other end 16 is held by the quartz tube 10 by holding legs 19. The cross section of the liner tube 12 perpendicular to the X-axis direction of the quartz tube 10 is shown in FIGS.
As shown in the figure, the value differs depending on the position in the X-axis direction. That is, the reaction gas flows in the X-axis direction, but has a circular shape on the upstream side of the gas flow, and moves toward the downstream side (X-axis positive direction).
The direction perpendicular to the paper surface (Y-axis direction) is the long axis, and the shape is an elliptical shape that is enlarged in the long axis direction and reduced in the short axis direction. It has a flat elliptical shape that is thin in the (axis) direction and long in the Y-axis direction. The length in the Y-axis direction of the opening in the sectional view taken along the line IV-IV at the position A is 7.0 cm, and the length in the Z-axis direction is 1.2 cm.

A susceptor 2 is provided downstream of the liner tube 12.
A sample mounting chamber 21 having a rectangular cross section perpendicular to the X-axis for mounting 0 is integrally connected. The sample mounting room 21
The susceptor 20 is placed on the bottom portion 22 of the susceptor. The susceptor 20 has a rectangular cross section perpendicular to the X axis, but has an upper surface 2
3 is gently inclined in the positive direction of the Z axis with respect to the X axis.
A sample, that is, a rectangular sapphire substrate 50 is placed on the upper surface 23 of the susceptor 20. The gap between the sapphire substrate 50 and the upper tube wall 24 of the liner tube 12 facing the sapphire substrate 50 is 12 mm upstream and downstream. 4mm on the side.

An operating rod 26 is connected to the susceptor 20. The flange 27 is removed, and the susceptor 20 on which the sapphire substrate 50 is mounted is placed in the sample mounting chamber 21 by the operating rod 26, and the susceptor 20 is used for crystal growth. When the process is completed, the susceptor 20 can be taken out of the sample mounting chamber 21. A first gas pipe 28 is opened on the upstream side of the liner pipe 12, and a second gas pipe 29 is sealed at an end to form a first gas pipe 29.
The gas pipe 28 is covered. And both of those tubes 28,
Reference numeral 29 denotes a coaxial double tube structure. First gas pipe 28
A number of holes 30 are formed in a portion protruding from the second gas pipe 29 and a side peripheral part of the second gas pipe 29, and the reaction gas introduced by the first gas pipe 28 and the second gas pipe 29 is formed. Is
Each of them is blown into the inside of the liner tube 12 through a number of holes 30. And inside the liner tube 12,
Both reaction gases are mixed for the first time.

The first gas pipe 28 is connected to the first manifold 3
1 and the second gas pipe 29 is connected to the second manifold 32.
It is connected to the. The first manifold 31 has an NH ₃ supply system H, a carrier gas supply system I, and a trimethylgallium (hereinafter referred to as “TMG”) supply system J.
And a supply system K for trimethylaluminum (hereinafter referred to as “TMA”), and a carrier gas supply system I and diethyl zinc (hereinafter “DE”) are connected to the second manifold 32.
Z ") is connected to the supply system L.

A cooling pipe 33 for circulating cooling water is formed on the outer periphery of the quartz tube 10, and a high-frequency coil 34 for applying a high-frequency electric field is provided on the outer periphery. The liner tube 12 is connected to an external tube 35 via the flange 14, and a carrier gas is introduced from the external tube 35. Also, the sample mounting chamber 2
1, a thermocouple 43 for measuring the temperature of a sample and its conducting wires 44 and 45 are disposed in the introducing tube 36 extending from the outside through the flange 14 from the side. , So that the sample temperature can be measured from the outside. With such an apparatus configuration, a mixed gas of NH ₃ , TMG, TMA, and H ₂ introduced through the first gas pipe 28,
A mixed gas of DEZ and H ₂ guided by the second gas pipe 29 is mixed near the outlets of those pipes, and the mixed reaction gas is guided to the sample mounting chamber 21 by the liner pipe 12, and the sapphire substrate 50 It passes through a gap formed between the liner tube 12 and the upper tube wall 24. At this time, the sapphire substrate 5
The flow of the reaction gas above zero becomes uniform, and a high-quality crystal with little location dependence grows.

In the case of forming an N _- type Al _X Ga _{1 -X} N thin film, a mixed gas may be discharged only from the first gas pipe 28 to form an I-type Al _X Ga _{1 -X} N thin film. In such a case, the mixed gas may be discharged from the first gas pipe 28 and the second gas pipe 29. I-type Al _X Ga _1-X N
When forming a thin film, the dopant gas DEZ
Is mixed with the reaction gas flowing out of the first gas pipe 28 for the first time in the liner space 12 near the sapphire substrate 50. DEZ is sprayed on the sapphire substrate 50 and thermally decomposed, and the dopant element is grown Al
_X Ga _1-X N doped into I-type Al _X Ga
_1-X N is obtained. In this case, the reaction gas and the dopant gas are separated by the first gas pipe 28 and the second gas pipe 29 and guided to the vicinity of the sapphire substrate 50, so that good doping is performed.

Next, the sapphire substrate 50 is
Crystal growth was performed on the above as follows. First, a single-crystal sapphire substrate 50 whose main surface is the (0001) plane cleaned by organic cleaning and heat treatment is mounted on the susceptor 20.
Next, the sapphire substrate 50 was subjected to vapor phase etching at a temperature of 1100 ° C. while flowing H ₂ at 0.3 liter / min through the first gas pipe 28, the second gas pipe 29, and the outer pipe 35 to the liner pipe 12. Next, the temperature is reduced to 650 ° C.
3 liter / min of H ₂ and 2 liter of NH ₃ from gas pipe 28
/ Minute, 15 ° C. TMA was supplied at 50 cc / minute for 2 minutes.

In this growth step, as shown in FIG.
An N buffer layer 51 was formed to a thickness of about 300 mm. The RHEED image of this buffer layer was measured. FIG. 7 shows the result. It is understood from the RHEED image of FIG. 7 that the crystal structure is non-single crystal, that is, amorphous, microcrystalline, and polycrystalline.

Using the above apparatus, various AlN buffer layers were formed on another sapphire substrate at a growth temperature of 650 ° C. and a film thickness of 50 to 1000 °. The RHEED image of the surface at that time was measured. The results are shown in FIGS. 8 (a) and (b). When the film thickness is less than 100 mm, the single crystallinity is strong and the film thickness is 500
Above Å, the polycrystallinity becomes stronger. Further, in the above various samples in which the thickness of the AlN buffer layer is in the range of 50 to 1000 °, the sample temperature is maintained at 970 ° C., and H ₂ is supplied from the first gas pipe 28 at 2.5 liter / min, and NH ₃ is / Min,-
TMG at 15 ° C. was supplied at 100 cc / min for 60 minutes, and an N layer 5 of N-type GaN having a thickness of about 7 μm was formed as shown in FIG.
2 were each formed. Then, the SEM image and the RHEED image of the N layer 52 were measured. The results are shown in FIGS. 10 (a) and (b).
These are shown in FIGS. 11 (a) and 11 (b). The magnification of the SEM image is 4100 times.
If the thickness of the buffer layer 51 is 100 ° or less, the N layer 52 is in a pit state, and the thickness of the buffer layer 51 is 500
Above {}, the N layer 52 is in the same state as below 100 °. Therefore, in order to obtain an N layer having good crystallinity, the thickness of the AlN buffer layer 51 is desirably in the range of 100 to 500 °.

As another sample, an AlN buffer layer having a thickness of 300 Å was grown on a sapphire substrate at a growth temperature of 300 ° C.
Various growths were performed by changing the temperature in the range of ~ 1200 ° C. Then, the RHEED image of the AlN buffer layer was measured in the same manner.
The results are shown in FIGS. 12 (a) and (b). This indicates that a desired film thickness of the AlN buffer layer cannot be obtained if the growth temperature is lower than 300 ° C., and that if the growth temperature is higher than 900 ° C., crystallization of AlN proceeds and a desired film quality cannot be obtained. I understand.

Further, with respect to various samples in which the AlN buffer layer having a thickness of 300 ° was grown at a growth temperature of 300 to 1200 ° C., a film thickness was further formed on the AlN buffer layer under the same conditions as described above. An N layer of about 7 μm N-type GaN was grown. Then, the SEM image and the RHEED image of the N layer were measured. The results are shown in FIGS. 13 (a) and (b) and FIGS. 14 (a) and (b). The magnification of the SEM image is 3700 times. When the growth temperature of the AlN buffer layer is lower than 400 ° C., the N layer made of N-type GaN becomes a pitted crystal, and when the growth temperature of the AlN buffer layer is 900 ° C. or higher, it has a hexagonal morphology. It becomes a crystal. From the results, in order to obtain an N layer with good crystallinity, the growth temperature of the AlN buffer layer should be 40
It turns out that 0 to 900 ° C is desirable.

According to the above experiment, when the crystal structure of the AlN buffer layer is a wurtzite structure in which polycrystals or microcrystals are mixed in an amorphous structure, the crystal structure of a GaN layer grown thereon It turned out to be better. Then, it was found that the content ratio of the polycrystal or microcrystal was preferably 1 to 90%, and the size was desirably 0.1 μm or less. The formation of the AlN buffer layer having such a crystal structure requires the thickness and the growth temperature besides the above conditions,
TMA at 15 ° C. is 0.1 to 1000 cc /
Min, NH ₃ is 100cc ~10liter / min, H ₂ is 1 liter to 50
The operation was performed in the range of liter / min, and in all cases, a wurtzite structure was obtained.

Next, a method for manufacturing a light emitting diode will be described. Next, using this device, the configuration shown in FIG.
Crystal growth was performed on the sapphire substrate 60 as follows. Similarly to the above, the single-crystal sapphire substrate 6
0, at a growth temperature of 650 ° C., H ₂ at ₃ liter / min, NH ₃ at 2 liter / min, and TMA at 15 ° C. from the first gas pipe 28.
Was supplied at 500 cc / min for 1 minute to form an AlN buffer layer 61 of 350 ° C. Next, when one minute has passed, TMA
Is stopped, and the temperature of the sapphire substrate 60 is set to 970 ° C.
, And 2.5 liter / min of H ₂ from the first gas pipe 28,
1.5 liter / min of NH ₃ and 100 cc / of TMG at −15 ° C.
And an N layer 62 made of N-type GaN having a thickness of about 7 μm was formed. The sapphire substrate 60 on which the N layer 62 is formed is taken out of the vapor phase growth apparatus, and the N layer 62 is removed.
A photoresist was applied to the main surface of the substrate, exposed using a mask having a predetermined pattern, and then etched to obtain a photoresist having a predetermined pattern.

Next, using this photoresist as a mask, an SiO ₂ film 63 having a thickness of about 100 ° was pattern-formed. Thereafter, the photoresist was removed, and the sapphire substrate 60 on which only the SiO ₂ film 63 was patterned was washed, and then mounted on the susceptor 20 again and subjected to vapor phase etching. Then, the temperature of the sapphire substrate 60 is maintained at 970 ° C., and the first gas pipe 2
From 8, 2.5 liter / min of H ₂ and 1.5 liter of NH ₃
/ Min, TMG at -15 ° C. is supplied at 100 cc / min, and DEZ at 30 ° C. is supplied at 500 cc / min from the second gas pipe 29 for 5 minutes to form an I-layer GaN made of I-type GaN. 1.0μm
Formed.

At this time, in the portion where GaN is exposed, single-crystal I-type GaN grows and an I layer 64 is obtained.
The upper part of i0 ₂ film 63 conductive layer 65 made of polycrystalline GaN is formed. Thereafter, the sapphire substrate 60 is taken out of the reaction chamber 20, and aluminum electrodes 66 and 67 are deposited on the I layer 64 and the conductive layer 65.
Was cut into a predetermined size to form a light emitting diode. In this case, the electrode 66 becomes an electrode of the I layer 64,
The electrode 67 becomes an electrode of the N layer 62 via the conductive layer 65 and the extremely thin SiO ₂ film 63. Then, the I layer 64 is replaced with the N layer 6
By setting a positive potential for 2, light is emitted from the bonding surface. The light emitting diode thus obtained had an emission wavelength of 485 nm and a luminous intensity of 10 mcd. In comparison with the case where the AlN buffer layer is formed of a single crystal, the luminous intensity is 1%.
A 0-fold improvement was seen.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a vapor phase growth apparatus used to carry out the present invention.

FIG. 2 is a sectional view of the liner tube of the embodiment.

FIG. 3 is a sectional view of the liner tube of the embodiment.

FIG. 4 is a sectional view of the liner tube of the embodiment.

FIG. 5 is a sectional view of the liner tube of the embodiment.

FIG. 6 is a sectional view showing a configuration of a semiconductor to be crystal-grown.

FIG. 7 is a photograph showing the crystal structure of an AlN buffer layer by RHEED.

FIG. 8 is a photograph showing the crystal structure of the AlN buffer layer by RHEED when the thickness of the AlN buffer layer is changed.

FIG. 9 is a cross-sectional view showing the structure of a semiconductor on which an N-type GaN layer has been grown.

FIG. 10 is a photograph showing a crystal structure by a microscope (SEM) of a GaN layer grown on an AlN buffer layer while changing the thickness of the buffer layer.

FIG. 11 is a photograph showing the crystal structure by RHEED of a GaN layer grown on an AlN buffer layer while changing the thickness of the buffer layer.

FIG. 12 is a photograph showing a crystal structure by RHEED of an AlN buffer layer grown by changing a growth temperature.

FIG. 13 shows various types of Al grown at different growth temperatures.
Photograph showing the crystal structure of the GaN layer grown on the N buffer layer by a microscope (SEM)

FIG. 14 shows various types of Al grown by changing the growth temperature.
Photo showing the crystal structure of the GaN layer grown on the N buffer layer by RHEED

FIG. 15 is a sectional view showing a crystal structure when a light emitting diode is formed.

[Explanation of symbols]

10 quartz tube 12 liner tube 20 susceptor 21 sample mounting chamber 28 first gas tube 29 second gas tube 50, 60 sapphire substrate 51, 61 AlN buffer layer 52, 62 N layer 53, 63─I layer 64─conductive layer 65,66─electrode H─NH ₃ supply system I─carrier gas supply system J─TMG supply system K─TMA supply system L─DEZ supply system

Continuing from the front page (73) Patent holder 396020800 Japan Science and Technology Corporation 4-1-8 Honcho, Kawaguchi-shi, Saitama (72) Inventor Katsuhide Mabe 1 Ochiai-Ochiai, Nagahata, Kasuga-mura, Nishikasugai-gun, Aichi Prefecture Toyoda Gosei Co., Ltd. Nagoya University (72) Inventor Kuki Kato Kagasaki Village, Nishi-Kasugai-gun, Aichi Prefecture, Ochiai, Nagahata 1 Toyota Toyoda Gosei Co., Ltd. (72) Inventor Isamu Akasaki, Furo-cho, Chikusa-ku, Nagoya, Aichi Prefecture Nagoya University ( 72) Inventor Kazumasa Hiramatsu, Nagoya City, Aichi Prefecture Nagoya-shi, Furo-cho (Nanbanashi) Inside Nagoya University (72) Inventor Hiroshi Amano, Nagoya-shi, Aichi Prefecture, Chigusa-ku, Furo-cho (Nabanashi) Nagoya University (56) Reference Literature Journal of the Japanese Association for Crystal Growth, Vol. 15, No. 3,4, pp. 334-342 (1988) Journal of the Japanese Association for Crystal Growth, Vol. 13, No. 4, pp. 218-225 (1986)

Claims (4)

(57) [Claims] 1. A light-emitting device having a gallium nitride-based compound semiconductor layer (Al _x Ga ₁ -xN; including X = 0) on a sapphire substrate, wherein a growth temperature is 400 ° C. or more and less than 600 ° C. on the sapphire substrate. A nitride having a wurtzite structure mixed with microcrystals or polycrystals having an amorphous crystal having a proportion of 1 to 90% in an amorphous crystal and having a thickness of 100 to 500 mm.
A gallium nitride based compound semiconductor light emitting device comprising: a buffer layer made of luminium (AlN) ; and a plurality of gallium nitride based compound semiconductor layers (Al _x Ga ₁ -xN; including X = 0) formed on the buffer layer. element. 2. A gallium nitride compound on a sapphire substrate.
Having a semiconductor layer (Al _x Ga ₁ -xN ; including X = 0)
In the light emitting device, a growth temperature of 400 ° C. or more and less than 600 ° C. on the sapphire substrate.
Crystal grown with a thickness of 100 mm or more and less than 500 mm
Microcrystals whose size is less than 0.1μm in amorphous crystal
Al nitride with a wurtzite structure containing polycrystals
A buffer layer made of minium (AlN), and a plurality of gallium nitride based layers formed on the buffer layer
Compound semiconductor layer (Al _x Ga ₁ -xN ; including X = 0)
A gallium nitride-based compound semiconductor light emitting device comprising: 3. The existence ratio of said microcrystal or said polycrystal is 1
The gallium nitride-based compound semiconductor light-emitting device according to claim 2 , wherein the content is about 90%. Wherein said buffer layer according to claim 1 or claims characterized in that it is formed by metal organic vapor phase epitaxy
Item 4. The gallium nitride-based compound semiconductor light emitting device according to any one of items 3 to 5.