JPH04167477A - Semiconductor element - Google Patents

Abstract

PURPOSE:To enable a large-area and single-crystal 2H-type substrate to be produced with SiC by including a growth layer of mixed crystal of aluminum nitride and silicon carbide and providing a multilayer structure. CONSTITUTION:When SiC is allowed to grow on 0001 face of AlN, a single crystal can be allowed to grow since lattice constant is close. AlN and SiC can be turned into an alloy as one semiconductor. In the case of a mixed crystal, AlN and SiC can be mixed in any ratio and they also change in terms of physical properties. Especially, the band structure, forbidden band width, etc., can change. On the other hand, the grown crystal structure shows Wurtzeit structure, it is equivalent to what is called 2H type in the SiC semiconductor, and it cannot grow easily in crystal growth of SiC alone. By producing a pn junction at the above semiconductor, each kind of semiconductor device can be created. By forming a single crystal 22 of AlN on a sapphire substrate 11 and then mixed crystal layers, namely a p layer 23 and an n layer 24, on it, quality of crystal of the mixed crystal layer can be improved drastically.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a semiconductor device used for environment-resistant devices, high-power devices, blue light-emitting devices, visible short wavelength and ultraviolet light-emitting devices, and the like.

(Prior Art) Currently, light emitting elements using semiconductors have been put into practical use and emit light up to red and green, and are used as various display elements. but,
Since blue is not yet available as a primary color, it is not sufficient for use as a display for displaying images. For this reason, blue and red,
Research is also progressing into light-emitting elements that have a luminous intensity equal to that of green.

Until now, light-emitting elements from red to green were made of Ga(1)As,
Semiconductors such as GaN have been used, but the forbidden band width of these semiconductors makes it impossible to produce blue color.

Materials for such regions include I such as Zn5e and ZnS.
There are I-VI group semiconductors, GaN, cubic type BN semiconductors, and group II semiconductors such as 5iC1 diamond.

However, it is difficult to control the conduction type of such a wide forbidden band material in the -shell, and cubic type B is the only material that can form pn junctions.
There are only N and ■ group raw conductors. However, ■ type semiconductor is SiC
Since both diamond and diamond have an indirect transition type forbidden band, they have the disadvantage that the luminous efficiency is essentially not high. Furthermore, since cubic BN can only be produced under high pressure, it has the disadvantage that large crystals that are suitable for practical use cannot be obtained.

Next, in the structure of blue light emitting devices, silicon carbide has a wide forbidden band width (2.2 to 3.3 eV), and among such wide forbidden band materials, it is the only material that can easily form pn junctions and MO5 structures. It is. It is also chemically stable and resistant to radiation. For this reason, high temperature operating elements,
It is expected to be used as a high-power device, a radiation inspection device, and a visible short wavelength light-emitting device.

In particular, as a visible light-emitting element, it is expected to be applied to full-color displays as a blue light-emitting diode. On the other hand, SiC is characterized by having many crystal polymorphisms. To date, only the 6H type, which is one of the hexagonal crystal polymorphisms, has been produced for practical use.6 However, when considering short wavelength light emitting devices, , 6H type crystal has a forbidden band width of only 2.8 eV at room temperature, so it can only emit blue light, and even in blue light emission, it cannot be used because light is emitted through shallow impurities, so the light emission efficiency is poor and bright light emission is not possible. It was not possible to create an element. For this reason, the forbidden band width is larger than 4.
It is expected that light-emitting devices can be manufactured using single crystals with an H-type or 2H-type hexagonal structure. I haven't been able to do it so far. The main reason for this is that crystals other than the 6H type are not thick enough to make practical devices, and also have drawbacks such as difficulty in producing single crystal substrates with few crystal defects.

Conventional methods for manufacturing single crystal substrates include: 1) Acheson method: carbon and silica sand are mixed and heated. 2) Lely method;
SiC powder is sublimated and recrystallized. 3) CVD method, Si,
Attempts have been made to mix C raw material gases and thermally decompose them. However, in method 1), the polishing S
Although this method is commonly used to fabricate iC, it has drawbacks such as not being able to produce large substrates and being easily contaminated with impurities. For this reason, current research is mainly based on methods 2) and 3).

However, the single crystal structure that can be made using these three methods is the 6H type or the 3C type crystal, which has a cubic crystal structure with a smaller forbidden band width, and it is difficult to create other crystals. However, sometimes only crystals with other crystal structures could be obtained that contained many crystal defects and were of poor quality.

One attempt to solve this problem was the Special Publication No. 1-437.
SiC on a sapphire substrate as shown in No. 20
However, even in this method, the crystal system grown is 3C type, and 2H type SiC, which is expected to be used as a light emitting device, could not be grown.

Next, regarding blue light-emitting elements with high luminous efficiency, currently used full-color displays include those using cathode ray tubes and liquid crystals, but in order to obtain a large screen, the device itself must be extremely large. However, depending on the angle from which you view the screen, it can be very difficult to see what is depicted on the screen. Therefore, displays using semiconductor light emitting devices are being actively developed.

However, for this to happen, we must wait for the development of a high-brightness blue light-emitting element. Silicon carbide is one of the materials being researched as a material for this blue light emitting element. #
Silicon dioxide has an energy gap of 2.4 to 3.4e.
Due to its high V and thermal stability, it has recently attracted attention as a material for blue light emitting devices. In particular, a silicon carbide crystal called 6H type has an energy gap of 2.86e.
Silicon carbide crystals with V type and so-called 4H type have an energy gap of 3.27 eV, and both are attracting attention as materials for short wavelength light emitting devices. Among these, blue light emitting devices using 6H type silicon carbide crystals and ultraviolet light emitting devices using 4H type silicon carbide crystals are being researched and prototyped at several research institutions.

However, a light emitting element using this 6H type silicon carbide crystal has a problem in that the emission intensity is low. This is due to the following reasons.

This 6H type silicon carbide crystal is an indirect transition type. Therefore, in a light emitting element using 6H type silicon carbide, light is usually emitted by recombination of carriers trapped by a donor and an acceptor, that is, a so-called D-A pair. However, the 6H type silicon carbide crystal has energy
The gap is 2.86 eV.

Therefore, in order to obtain an emission wavelength of 470n, which is a typical blue emission wavelength, impurities that can be added have a so-called shallow impurity level of about 220meV in total on the donor side and acceptor side. Limited. Impurities with such shallow impurity levels, such as aluminum as an acceptor impurity or nitrogen as a donor impurity, can conduct carriers (electrons in the case of donor impurities and holes in the case of acceptor impurities). The size for trapping from the band or valence band to the impurity level (capture cross section for carriers of the impurity) is small, so fewer carriers are trapped at the impurity level.

Therefore, the intensity of light emitted by recombination of carriers trapped by donors and acceptors is reduced. As a comparative example for the eighth embodiment, which will be described later, FIG. 9 shows a schematic cross-sectional view of the structure of a conventional silicon carbide light emitting device. All the layers in FIG. 9 are composed of 6H type silicon carbide. and each aluminum is lXl0”
Layer 101 containing 3 / C 3, aluminum I
1017 lC■3 and nitrogen I x 10'' pieces/c
layer 102 containing nitrogen at a concentration of 1×10” nitrogen/cma.

(Problems to be Solved by the Invention) As stated above, with the conventional technology, it is not possible to obtain a high-quality, large-area crystal that emits light in a wavelength region shorter than blue, so it is difficult to produce various devices using this. I couldn't.

Therefore, the first object of the present invention is to solve the above-mentioned problems, and is aimed at making it possible to manufacture a semiconductor element having a large area and capable of emitting light in a wavelength range shorter than that of blue.

Furthermore, with conventional techniques, it is not easy to produce a large-area, high-quality single crystal of 2H type SiC, and it has not been possible to produce various devices using this.

Therefore, the purpose of the present invention is to solve the above problems.
The purpose is to make it possible to manufacture a 2H type large area single crystal substrate using SiC.

Furthermore, as mentioned above, in the conventional blue light emitting device using silicon carbide, since silicon carbide is of the 6H type, the trapping cross section for carriers of impurities that can be added to silicon carbide is small, and the emission intensity is low. The problem was that the quantum efficiency was low.

Therefore, an object of the present invention is to provide a silicon carbide blue light-emitting device with high quantum efficiency.

[Structure of the invention]

(Means for Solving the Problems) A semiconductor device according to the present invention has a multilayer structure including a grown layer of a mixed crystal of aluminum nitride and silicon carbide. In addition, in blue light-emitting devices using silicon carbide, impurities such as
This is a semiconductor element having a structure containing at least - atoms selected from Group atoms and Group II atoms.

(Function) First, according to the present invention, a semiconductor layer with a large area and high quality can be grown. That is, ^QN single crystal is S
It has a lattice constant in the a-axis direction that is very close to iC.

Further, the iN single crystal has a single crystal structure called a wurtzite type, which is a crystal structure equivalent to the 2H type in SiC. Therefore, Si on the (0001) plane of AQN
When C is grown, a single crystal can be grown because the lattice constants are close to each other. AQN has a direct transition type band structure and is expected to have a high efficiency of interband transition accompanied by light emission, but it is a material that is difficult to make into a large single crystal. Furthermore, it is difficult to control the conductivity type by adding impurities. On the other hand, S
Although the conductivity type of iC is easy to control, it has an indirect transition type band structure, so the luminous efficiency is low, and the nature
, Vol., 275. As shown in pp. 435 (1978), it is known that SiC and AQN mix relatively easily. Until now, only minute crystals could be formed, so it was not possible to create a bond, but AQ, 0.
By growing it on another substrate such as SiC and controlling the conduction type, it became possible to create a direct transition type semiconductor that can control the conduction. Here, mixed crystal refers to JP-A-58-1
This is different from adding A12 and N to SiC as in No. 21690. In the present invention, both AQN and SiC are alloyed together as one semiconductor.

On the other hand, Al1. When N is added, it enters as an element and becomes an impurity. This also makes a big difference in the actual crystal growth phenomenon. When added as an element, there is a limit to the amount of AQ added, whereas when mixed crystal, AQN and SiC can be mixed in any ratio. On the other hand, in the case of mixed crystals, physical properties also change. Especially the band structure.

Forbidden band width etc. change. The present invention utilizes this change in band structure. On the other hand, the crystal structure grown according to the present invention exhibits a wurtzite structure.

This is equivalent to what is called a 2H type in SiC semiconductors, and cannot be easily grown by crystal growth of SiC alone. In this way, the semiconductor crystal of the present invention is SiC
to Al1. This is a completely different invention from the one in which N is added, and can be distinguished by the abundance ratio of AΩ in the crystal. The AQ abundance ratio applicable to the present invention is approximately 1
% or more. The present invention enables various semiconductor devices by creating a pn junction in the above-mentioned semiconductor.

Secondly, according to the present invention, 2H type SiC can be grown over a large area and with high quality. That is, the IQN single crystal has a lattice constant in the a-axis direction that is very similar to that of SiC. Further, the AΩN single crystal has a single crystal structure called a wurtzite type, which is a crystal structure equivalent to the 2H type in SiC. For this reason, when SiC is grown on the (0001) plane of AρN, the lattice constants are close, so a single crystal can be grown. However, AfiN is a material in which it is difficult to make large single crystals. For this reason, the current method to reliably grow AQN is to grow it on a sapphire substrate. At this time, if AQN is grown on the (0001) plane of sapphire, WIN can also be grown on the (0001) plane. This middle layer is special fairness 1 in AΩN alone.
As shown in No. 43720, only the 3C type containing many twins can be grown. However, AIIN and SiC
The inventor's research has discovered that the mixed crystal has few defects and forms a 21 (type) crystal.Furthermore, on top of this, SiC
When grown, it inherits the properties of the layer below and can grow with good reproducibility.

Thirdly, as mentioned above, when group Ⅰ or group Ⅰ atoms are added to silicon carbide, in the case of group Ⅰ atoms, a deep acceptor level is created in silicon carbide, and group Ⅰ atoms In this case, create a deep donor level in silicon carbide. Atoms that create such a deep impurity level have a large trapping cross section for carriers. Therefore, by adding atoms with such a large trapping cross section into a silicon carbide crystal, quantum efficiency can be increased. Moreover, by using a 4H type crystal with an energy gap of 3.278 V as the silicon carbide crystal, blue light emission with high luminous intensity can be obtained.

(Example) Next, an example of a light emitting device using the present invention will be described.

First Embodiment FIG. 1 shows a cross-sectional view of a SiC:AQN light emitting diode which is an embodiment of the present invention.Metalorganic chemical slow growth (MOCVD) method was used as the growth method. First, (00
01) MOCVD the sapphire crystal 11 cut into planes
After the temperature is lowered to the growth temperature (1500°C), nitrogen (N) is used as the AQ raw material trimethylaluminum (TMA) diluted with carrier gas, ammonia gas (NH3) as the raw material, and Si Silane gas, which is the raw material for carbon, and propane gas, which is the raw material for carbon, are introduced. First, when growing the second layer 12, a raw material gas containing a group Ⅰ element is introduced. In this embodiment, dimethyl zinc (DMZ) was used. Next, cut the DMZ and make one layer 13
In this embodiment, dimethyl selenium (DMSe), which is a source gas for selenium, is introduced.The semiconductor layer made in this embodiment contains 10% AQN. After growth, the negative and n layers are removed by etching to expose the second layer. After that, AlI3 is deposited on the second layer and Ni15 is deposited on the n layer, and alloying treatment is performed at 1000 degrees.
The light-emitting device manufactured according to the present invention in which an ohmic electrode was formed emits purple light, and the luminescence intensity is significantly higher than that of a conventional SiC blue light-emitting device.

Second example A second embodiment of the present invention is shown and explained in FIG.

A single crystal 22 of AQH is formed on a sapphire substrate 21.

Thereon, two layers 23 and zero layers 24 of the mixed crystal layer of the present invention are formed. By doing so, the crystal quality of the mixed crystal layer was significantly improved.

Third embodiment FIG. 3 shows one embodiment of the present invention.

Two layers 32.8 layers 33 of the mixed crystal layer of the present invention are formed on a SiC single crystal 31. SiC can be made into a single crystal of 1 inch or more, and the quality of the crystal is good. Therefore, the quality of the mixed crystal layer formed thereon was also good.

Fourth example Another embodiment of the present invention is shown and explained in FIG.

By changing the composition ratio of AQN and SiC in the 2nd layer 41 and the 0th layer 42, the efficiency of current injection into one layer can be greatly improved. In this modification, the ^QN composition on the n-layer side is increased to increase the injection efficiency into the p-layer. By doing so, it has become possible to significantly increase the luminous efficiency. Also, n
It is also possible to lower the AρN composition on the layer side and inject more current into the n-layer side. In this case, by adding an impurity that becomes a luminescent center in addition to the conductivity type determining impurity to the layer into which current is injected, the current can be significantly increased. The luminous efficiency increased.

Fifth example Another embodiment of the present invention is shown and explained in FIG.

A second semiconductor layer 52 having a smaller forbidden band width than the first layer is formed on the first mixed crystal layer 51 exhibiting one conductivity type, and a second semiconductor layer 52 having a larger forbidden band width than the second layer is formed on the second layer. , a third mixed crystal layer 53 having a conductivity type different from that of the first layer is formed. The conductivity type of the second layer can be either p or n. By doing so, current could be efficiently injected into the second layer, and the luminous efficiency could be significantly improved. At this time, even when a pure SiC layer was used as the second layer, the luminous efficiency was improved.

Sixth Embodiment As yet another embodiment of the present invention, a p layer is formed by forming a layer on the outside of the ρn junction layer in contact with one or both of them and having the same conductivity type as the layer in contact with it and containing a higher concentration of impurities. Alternatively, the current in the n layer can be made uniform. In the above embodiments and modified examples, the p-layer and n-layer may be geometrically arranged as desired; for example, the n-layer may be formed first as shown in FIG. Furthermore, the present invention does not rely on the growth method, but uses the molecular beam epitaxial method (M
BE) It is possible to grow by liquid phase epitaxial method (LPE) or the like. In addition, the present invention can be modified and used in various ways as long as it does not depart from the spirit thereof.

Seventh Embodiment Next, an embodiment of the method for growing a 2H type crystal according to the present invention will be described with reference to FIG. FIG. 6 shows a cross-sectional view of an example of a bulk 2H type SiC light emitting diode grown according to the present invention.Metalorganic chemical silver acid method (MOCVD) was used as the growth method. First, the sapphire crystal 61 cut out from (0001) WJ is placed in an MOCVD device and subjected to surface treatment at high temperature.After that, the temperature is lowered to the growth temperature, and nitrogen (N) is used as the AQ raw material trimethylgallium (TMA) diluted with carrier gas. When flowing ammonia gas (NH,) as a raw material to grow AQN62 on the substrate surface, high quality AQN crystals can be grown by flowing the ammonia gas first. After growing AQN, silane and acetylene gas are further introduced to grow AQN and SiC mixed crystal layer 63. After that, only TMA was turned off and the flow rate of ammonia gas was reduced.

The n-type 5iC64 is grown, and the carrier concentration in the n-layer at this time is a high concentration layer of about I x 10''/cm''.

Furthermore, with the flow rate of ammonia gas reduced and a small amount of trimethyl gallium, which is a gallium raw material, flowing, n-type 5
Grow iC65. This n-type layer 65 is a light emitting layer and has a carrier concentration of 5.times.10.times.7/c.sub.3. Next, pour TMA over 65, cut off TMG and ammonia, and form P-type layer 6.
Grow 6. The P-type layer 66 has a carrier concentration of 2×1
0"/cm". After that, using 1 reactive ion etching device (RIE), 2 layers 66.0 layers 65
was etched to expose the first layer 64. Thereafter, AQ: Si alloy 67 was selectively deposited on the second layer and Ni 68 was selectively deposited on the n layer, and heat treatment was performed at a high temperature to create an ohmic contact. The 2H type light emitting device produced in this manner exhibited blue-violet light emission, and the luminous efficiency was more than twice that of the conventional 6H type light emitting device.

The present invention explained in the seventh embodiment is not limited thereto, and can be applied to all elements using the 2H type. Furthermore, a light-emitting element in which AQ instead of Ga is added to the 0 layer 65 can be used as a light-emitting element from near ultraviolet to violet. moreover,
After growing a 2H type crystal, a 2H type crystal substrate can be obtained by etching and removing the sapphire substrate and the AQN crystal, which can be used in many fields. next,
21 (A light-emitting element with higher luminous efficiency can be produced by growing SiC having another crystal structure with a small forbidden band width on a pattern crystal to produce a Peter structure.

Eighth Embodiment FIG. 7 shows a schematic cross-sectional view of the structure of a light emitting device according to an embodiment of the present invention. In the figure, 72 is a 4H type silicon carbide to which lXl0''/cI12 of zinc, a group II element, and lXl0''/cI2#i of selenium, a group II element, are added, which is the main focus of the present invention, and is shown in FIG. In other device structures, it is a light-emitting layer. In addition, 71 in Figure 1 is 4H type silicon carbide doped with lXl0"pieces/cm" of aluminum, and this layer 71
has the function of injecting holes into the layer 72. In the figure, 73 indicates that nitrogen is present at I x 10"/c@"4
This is an H-type silicon carbide substrate, and this layer 73 has the function of injecting electrons into layer 72.

The light emitting device of this example is similar to the conventional 9th light emitting device shown for comparison.
It was several times brighter than the light emitting device shown in the figure.

9th Embodiment Figure 8 shows the structure of a light emitting device used as another example of the present invention. In Figure 0, 82 is lXl0''/Cm2 of tellurium, a group II element, and zinc, a group II element. l
It is 4H type silicon carbide doped with XlolG pieces/cII3, and serves as a light emitting layer in the present light emitting device.

Further, 81 in the figure is 4H type silicon carbide containing 1X10''/cm3 of gallium. This layer 81 functions to inject holes into the layer 82 described above.

Note that the above embodiment is an example showing the structure of a light emitting element, and
Their arrangement does not depend on exchanging geometrical positions. The main focus of the present invention is to use 4H type silicon carbide containing one or more types of atoms of the group (III) and group (III) in the light emitting layer, and the geometrical arrangement of the light emitting device structure and the impurities of the group (III) and (III) It does not specify the method of adding atoms or the method of producing 4H-type silicon carbide. For example, in the LPE method, selenium, a group II atom, may be mixed in solid form into silicon.

These atoms may be added from the gas phase by using a gas such as dimethylzinc or hydrogen selenide in the atmosphere.

[Effects of the Invention] By using the present invention, it has become possible to create a violet or ultraviolet light emitting device, which has been difficult in the past. In addition, commercialization has become possible because crystals of good quality can be obtained over a large area.

Secondly, this has traditionally been difficult. It has become possible to grow a large area 2H type single crystal substrate. Additionally, these materials have made it possible to create violet and ultraviolet light-emitting devices, which was previously difficult.

Furthermore, since a high-brightness blue light-emitting element can be manufactured, by using this element, a large-screen flat display that is easy to see from any angle can be realized.

[Brief explanation of the drawing]

1 to 8 all relate to embodiments of the present invention,
FIG. 1 shows a first embodiment, FIG. 2 shows a second embodiment, FIG. 3 shows a third embodiment, and FIG. 4 shows a fourth embodiment. 5 is a sectional view of each semiconductor device of the fifth embodiment, FIG. 6 is a seventh embodiment, FIG. 7 is an eighth embodiment, and FIG. 8 is a cross-sectional view of each semiconductor device of a ninth embodiment. FIG. 2 is a cross-sectional view of a semiconductor element. 11... Sapphire substrate, 12.23.32... 2 layers (mixed crystal layer), 13.24.
42...n layer (mixed crystal layer). 14.15... Electrode. 31... SiC (single crystal) substrate, 4l-n-AIN: SiC layer, 42... p-AIN S SiC layer, 51... 1st
mixed crystal layer, 52... second mixed crystal layer, 53... third mixed crystal layer, 62... AIN layer, 63... mixed crystal layer, 64- n-SiC layer, 65 - n-5iC layer (light emitting layer), 66...p-5iC layer, 71, 72.73.81.82...4H-5iC layer. Agent Patent Attorney Norihiro Ogo 5//I layer (container) Fig. 1 24% Man (Do & Lu) Fig. 2 32-p)% (Kengoru) 33-1 ( !1 Todoroki layer) 3rd
Figure 41 9-fig)j: Stε4 42-p-AIS
:SrC'J%Figure 4 53...-Recruitment 3 I): LIa & Figure 5 Figure 6 Figure 7 J? l -4H-5iC'(xaJl, 82-14H-
faIe; Te, 1m eyebrow Fig. 8 703... bH-5rC: N base 771. l/2
・-edge Figure 9

Claims (2)

[Claims] (1) A semiconductor device having a multilayer structure including a grown layer of a mixed crystal of aluminum nitride and silicon carbide. (2) In a blue light-emitting element using silicon carbide, group II atoms and impurities are present in the silicon carbide layer of the semiconductor element.
A blue light-emitting semiconductor device containing at least one atom selected from Group VI atoms.