JPH0471278A - Pn junction type light emitting diode using silicon carbide - Google Patents

Abstract

PURPOSE:To manufacture the title light emitting diode in excellent monochromaticity by a method wherein a donor impurities in specific concentration only are added to the vicinity of the pn junction interface of the n type layer comprising the pn junction participating in the light emission. CONSTITUTION:A 6H type n-SiC single crystal substrate 10 as a substrate specimen 25 is mounted on a specimen base 22 so as to be heated by feeding work coils 24 with high-frequency current while feeding hydrogen gas as a carrier gas from a branch pipe 26 into a reaction tube 21. Next, a material gas and an impurity gas are added to the carrier gas so as to successively deposit an n-SiC single crystal layer 11 and a p-Sic single crystal layer 12 for the formation of a pn junction. Then, the substrate specimen 25 is taken out of the reaction tube 21 to selectively etch away the single crystal layers 11 and 12 for the formation of a mesa structure. Next, an n side ohmic electrode 13 comprising Ni is formed on the rear surface of the substrate 10 while a p side ohmic electrode 14 is formed on the surface of the single crystal 12. Through these procedures, the title light emitting diode in excellent monochromaticity and small spectrum half value width can be manufactured.

Description

[Detailed description of the invention]

[0001]

[Industrial application field]

The present invention relates to a pn junction type light emitting diode using silicon carbide, and more particularly to a pn junction type light emitting diode capable of emitting green to purple visible light and near ultraviolet light with high efficiency. [0002]

[Conventional technology]

Light emitting diodes are small, consume little power, and are light emitting sources that can stably emit high-intensity light, so they are widely used as display elements in various display devices. The 9 light emitting diode is also used as a light source for recording and reading information in various information processing devices. Long-wavelength visible light-emitting diodes, which have been widely put into practical use so far, are capable of emitting high-intensity light from red to green. On the other hand, currently developed light-emitting diodes that emit short-wavelength visible light in the blue to violet range still have low brightness and have not yet been put into widespread practical use. [0003] In general, the color of light emitted by a light emitting diode depends on the semiconductor material used. The semiconductor material for short wavelength visible light emitting diodes is silicon carbide (S), which is a group IV-IV compound semiconductor.
iC), gallium nitride (GaN), which is a group II-V compound semiconductor, and zinc sulfide (ZnS) and zinc selenide (ZnS), which are group II-VI compound semiconductors.
nSe). Although research and development of short-wavelength visible light light emitting diodes using these semiconductor materials has been actively conducted, mass production of devices with high brightness and stability that can be widely put into practical use has not yet been achieved. [0004] The most suitable element structure for a light emitting diode is a pn junction type light emitting diode, which can inject electrons and hole carriers into a light emitting region with high efficiency. However, among the semiconductor materials for short wavelength visible light emitting diodes mentioned above, GaN, Zn
It is difficult to obtain p-type crystals of S and Zn5e semiconductors, or even if they are obtained, they have high resistance or are extremely unstable, so it is difficult to fabricate p-n junction type light emitting diodes. Can not. Therefore, MIS (metal-insulating layer-semiconductor) that uses thin insulating layers and high-resistance layers
structure has been adopted. However, this kind of MIS
A light emitting diode having such a structure has drawbacks such as nonuniform device characteristics and unstable two-light emission. [0005] On the other hand, silicon carbide (SiC) can be used to easily obtain p-type crystals and n-type crystals, so that pn junction type light emitting diodes can be manufactured. Until now, many reports have already been made regarding silicon carbide pn junction blue light emitting diodes manufactured by liquid phase epitaxial growth (LPE) (for example, M, Ikeda,
T., Hayakawa, S., Yamagiwa, H.
, Matsunami, and T. Tanaka,
Journal of Applied Physi
cs, Vol, 50. No, 12. pp, 821
5-8225.1979). [0006] However, the pn junction blue light emitting diode fabricated by the LPE method still has low brightness (only a brightness of 15 mcd or less can be obtained when operated at 20 mA. The main reason for this is the growth temperature. is 1,700-1,800
This is thought to be because growth occurs in an active Si melt at a high temperature of .degree. C., so the controllability of growth is poor and unnecessary impurities are likely to be mixed in. Further, the LPE method has a problem of poor mass productivity. [0007] Therefore, recently, the present inventors have developed a chemical vapor deposition method (CV
Using method D), we devised a method for manufacturing a pn junction light emitting diode that can stably emit short wavelength visible light from blue to violet with high brightness, with good controllability and mass production. [0008]

[Problem to be solved by the invention]

However, conventional short wavelength light emitting diodes manufactured using the LPE method or CVD method all give similar emission spectra, and their spectral half-widths are large, so
There was a problem that the monochromaticity of light emission was poor. For example, a typical emission spectrum of a blue light emitting diode using 6H type silicon carbide doped with nitrogen and aluminum as two emission centers is shown in FIG. 8 (reproduced from the above-mentioned paper by Ikeda et al.). The peak wavelength of this emission spectrum is 460~
480 nm, but the spectral half width is 70 to 90
nm (0.4 to 0.5 eV), so it is not pure blue. Only bluish-white luminescence was obtained. [0009] Ikeda et al. conducted a detailed analysis of the emission spectrum in FIG. 8, and as shown in this figure, there are three different emission processes F, E, and M. The luminescence process M is donor-acceptor pair luminescence due to recombination between the nitrogen donor and the aluminum acceptor, and the luminescence process E
Although the details are unknown, it is believed that the light emission is due to recombination involving aluminum impurities, and that the light emission process F is due to the recombination of free excitons. [0010] Conventionally, in order to obtain a light emitting diode with high brightness, LP
Regardless of whether it is manufactured using the E method or the CVD method, a light emission process M based on donor-acceptor pair light emission has been utilized. In this case, by adding both a nitrogen donor and an aluminum acceptor to the n-type layer constituting the pn junction, donor-acceptor pair light emission is caused. However, in donor-acceptor pair emission, the distance between the donor-acceptor involved in one emission is distributed in various ways, and the emission wavelength differs slightly accordingly, so the spectral width is essentially widened. Furthermore, since the peaks due to one emission process F and E coexist, the spectral width is further expanded. [0011] The present invention is intended to solve the above-mentioned conventional problems, and its objectives are as follows. The object of the present invention is to provide a pn junction light emitting diode that has a small spectral half-width and excellent monochromaticity of light emission by utilizing only recombination light emission due to free excitons or recombination light emission involving acceptor impurities. [0012]

[Means to solve the problem]

The present inventors did not use only the recombination emission due to free excitons or the recombination emission involving acceptor impurities.
After conceiving a junction-type light emitting diode,9 After conducting various experiments by applying the manufacturing technology of silicon carbide light emitting diodes using the CVD method that the inventors had devised previously, the following configuration was adopted. By the way. We have completed a pn junction light emitting diode that utilizes only recombination light emission due to free excitons or recombination light emission involving acceptor impurities. [0013] In the pn junction light emitting diode using silicon carbide of the present invention, which utilizes recombination light emission by free excitons, at least p of the n-type layer constituting the pn junction involved in light emission is
Substantially only donor impurities are present near the n-junction interface at 5×1
016cm-3 or less, and in the case of using recombination light emission involving acceptor impurities, the acceptor impurity is added to the p-type layer constituting the pn junction involved in light emission, and the n-type at least pn of layers
Substantially only donor impurities exist near the bonding interface in a 1×1
018 cm-3 or higher, thereby achieving the above objective. [0014] The n-type layer in the pn junction type light emitting diode of the present invention is
Preferably 2 e.g. It is composed of a first n-type layer formed adjacent to the pn junction interface and a second n-type layer formed thereon. In this case, in the case where recombination light emission by free excitons is used, the donor impurity concentration in the first n-type layer is 5
X 1016cm' or less, whereas the donor impurity concentration in the second n-type layer is 5x101
6 cm" or more. Alternatively, the donor impurity concentration in the N5 layer should be set to 5 cm" or more near the p-n junction interface.
X 1016 cm' or less, and may be sloped to gradually increase away from the pn junction. In any case, it is impossible to reduce the donor impurity concentration in the entire n-type layer or a part thereof to 5×10 cm or less using the conventional LPE method. It is necessary to use the CVD method to manufacture the diode. [0015] On the other hand, in a method that utilizes recombination light emission involving acceptor impurities, the donor impurity concentration in the first n-type layer is set to 1×10 18 cm −3 or higher, whereas the second n-type layer The donor impurity concentration in the layer is 1×101
8 cm-3 or less. Alternatively, the donor impurity concentration in the n-type layer may be set to 1.times.10.sup.18 cm.sup.-3 or more in the vicinity of the p-n junction interface, and may be sloped to gradually decrease as it moves away from the p-n junction. [0016] Nitrogen is usually used as the above donor impurity. This nitrogen impurity. When growing an n-type layer by the CVD method, nitrogen gas is added as an impurity gas together with a carrier gas and a source gas to be introduced into the n-type layer. [0017] Aluminum is usually used as the above acceptor impurity. This aluminum impurity makes the p-type layer 2
For example, when growing by CVD method, trimethylaluminum gas is added as an impurity gas together with a carrier gas and a source gas to be introduced into the p-type layer. [0018] Furthermore, it is known that silicon carbide has various crystal polymorphs, and as described below, a desired luminescent color can be obtained by selecting the crystal polymorph. For example, in those that utilize recombination emission due to free excitons, 4H type, 6H type, 15R type, 21R type, or 3C type is preferably used.
By using silicon carbide of the type, ultraviolet, violet, violet, blue, or green light emitting diodes can be produced, respectively. In addition, those using recombination emission involving acceptor impurities are preferably 4H type, 6
By using H-type or 3C-type silicon carbide, purple, blue, or orange light-emitting diodes can be manufactured, respectively. [0019] Furthermore, whether the recombination emission by free excitons or the recombination emission involving acceptor impurities is used, for example, a cubic silicon carbide single crystal substrate may be used. Either use a hexagonal silicon carbide single crystal substrate and grow a p-type layer and an n-type layer on the substantially (111) C plane to form a pn junction, or use a hexagonal silicon carbide single crystal substrate and grow a p-type layer and an n-type layer on the substantially (111) C plane. ) If a p-type layer and an n-type layer are grown on the C-plane to form a pn junction, a pn junction type light emitting diode with better monochromaticity can be obtained. [0020] [Function] The pn junction light emitting diode using silicon carbide of the present invention utilizes recombination light emission due to free excitons or recombination light emission involving acceptor impurities. [0021] The photon energy of light emission due to recombination of free excitons is 7 exciton energy gap'/p, W, J, Ch
(W, J, Choyk
e, Materials Re5earch Bul
letins, Vol. 4. pp, 5141-81
52.1969. Pergamon Press I
nc, ). The exciton energy gap values at room temperature of typical crystal polytypes of silicon carbide are shown in Table 1 below. [0022]

[Table 1] [0023] Since silicon carbide is a semiconductor having an indirect transition type band structure, a light emission process in which phonons are simultaneously emitted is dominant. Therefore, the light emission process F due to the recombination of free excitons shown in FIG. 9 corresponds to light emission in which phonons are emitted at one eccentric position. - In general, phonons have transverse acoustic (TA)
There are four types of modes: longitudinal acoustic (LA) mode, transverse optical (TO) mode, and longitudinal optical (LO) mode. In the case of silicon carbide, the phonon energies of these modes are approximately the same, independent of crystal polymorphism, and are approximately 45 meV, 77 meV, and 94 meV, respectively.
V and 104meV. The emission energy due to the emission process F is the average value of these phonon energies (approximately 8
0 meV), which is smaller than the exciton energy gap. Table 1 above also shows the emission energy, emission wavelength, and emission color of emission process F obtained using various crystal polymorphs. [00241 As is clear from Table 1, when using recombination luminescence due to free excitons, by selecting the crystal polymorphism of silicon carbide, a desired luminescent color can be obtained from visible light from green to purple and ultraviolet light. can be obtained. For example, in the 4H type, wavelength 3
94 nrn ultraviolet light emission, 6H type has a wavelength of 425 nrn
rn violet emission, 15R type emits violet light at a wavelength of 432 nm, 21R type emits blue light at a wavelength of 453 nm, 3C
The mold can emit green light with a wavelength of 544 nm. Note 7
The half-value width of the emission spectrum is approximately 0, which is calculated by adding the approximately 60 meV spread of the four types of phonon energies mentioned above to the approximately 25 meV spread due to the thermal energy of excitons at room temperature.
．． It becomes about 1 eV. This means that in the blue to purple region,
This corresponds to a wavelength spread of about 20 nm. This broadening corresponds to the spectral half-width of 0.4 to 0.5 of the conventional pn junction type light emitting diode that uses donor-acceptor pair emission.
eV (70 to 90 nm), it is about 1/4 to 115, which shows that the pn junction type light emitting diode of the present invention has extremely excellent monochromaticity. [0025] On the other hand, when aluminum is used as the acceptor impurity, light emission due to recombination of acceptor impurities is caused by a light emission process E as shown in FIG. corresponds to the luminescence peak. Therefore, by selecting the crystal polymorphism of silicon carbide, it is possible to obtain a desired emission color from visible light ranging from orange to purple. For example, the 4H type emits violet light with a wavelength of approximately 424 nrn, the 6H type emits blue light with a wavelength of approximately 455 nrn, and the 3C type emits blue light with a wavelength of approximately 584 nrn.
nm orange light emission is obtained. Note that the half width of the 9 emission spectrum is about 01 eV. This corresponds to a wavelength spread of about 20 nm in the blue to violet region. This broadening is due to the spectral half-width of 0.0.
1/4 compared to 4-0.5eV (70-90nm)
~115, indicating that the pn junction type light emitting diode of the present invention has extremely excellent monochromaticity. [0026] In addition, in a pn junction light emitting diode that utilizes recombination light emission involving acceptor impurities, no acceptor impurity is added to the n-type layer, so conventional donor-acceptor pair light emission in the n-type layer does not occur. do not have. However, at least near the pn junction interface of the n-type layer, only the donor impurity is added at a concentration of 1×10 18 cm −3 or more. Therefore, the electron density near the pn junction interface of the n-type layer increases, and when a forward bias voltage is applied, the efficiency of electron injection from the n-type layer to the p-type layer increases. As a result, it is thought that recombination of injected electrons and holes existing in the p-type layer occurs mainly in the p-type layer, and only light emission involving acceptor impurities in the p-type layer is obtained. . [0027]

【Example】

Examples of the present invention will be described below. In Examples 1 to 7, pn junction light emitting diodes were fabricated using recombinant light emission due to free excitons, and in Examples 8 to 12, pn junction light emitting diodes were fabricated using recombination light emission involving acceptor impurities. I made a diode. [0028] (Example 1) In this example, 6H type 5iC (forbidden band width 3.0 eV)
A pn junction type violet light emitting diode was fabricated using this method. [00291] FIG. 1 is a cross-sectional view showing the structure of the pn junction type light emitting diode of this example. The pn junction involved in light emission is an n-3i junction formed sequentially on a 6H type n-3iC single crystal substrate 10.
It is composed of a C single crystal layer 11 and a p-3iC single crystal layer 12. Then, on the back surface of the n-3iC single crystal substrate 10, an n-side ohmic electrode 13 made of Ni is provided,
On the other hand, a p-side ohmic electrode 14 made of Ti is provided on the upper surface of the p-3iC single crystal layer 12. [0030] FIG. 2 is a schematic diagram of the vapor phase growth apparatus used in this example. First, this vapor phase growth apparatus will be explained. [0031] A sample stage 22 is installed with a support rod 23 inside the double-structured quartz reaction tube 21. Both the sample stand 22 and the support rod 23 are made of graphite. The sample stage 22 may be installed horizontally or may be appropriately inclined. Reaction tube 2
A work coil 24 is wound around the outer periphery of the sample 1, and a substrate sample 25 on the sample stage 22 can be heated to a predetermined temperature by passing a high frequency current. A branch pipe 26 is provided on one side of the reaction tube 21 to serve as an inlet for raw material gas, carrier gas, and impurity gas. The nine reaction tubes 21 can be cooled by flowing cooling water through the branch pipes 27 and 28 into the outer tube of the reaction tube 21 having a double structure. The other end of the reaction tube 21 is closed with a stainless steel flange 29, and a stop plate 30 is provided around the periphery of the flange 29.
, bolt 31. Natsu 32. and is sealed by a ○-ring 33. A branch pipe 34 is provided near the center of the flange 29, and the above gas is passed through this branch pipe 34.
is discharged through. [0032] The pn junction type light emitting diode of this example was produced using such a vapor phase growth apparatus. It was made as follows. [0033] First, as shown in FIG. 2, a 6H type n
A -3iC single crystal substrate 10 (dimensions: 1 cm x 1 cm) was placed as a substrate sample 25. As the growth plane of the substrate, a (0001) C plane whose plane orientation was inclined by about 5 degrees from the [0001] direction to the <11-20> direction was used. [0034] Next, using hydrogen gas as a carrier gas,
While flowing from the branch pipe 26 into the reaction tube 21 at a rate of 4 cc, a high frequency current is passed through the work coil 4 to generate n-3iC.
Single crystal substrate 10 was heated to 1,400 to 1,500°C. Then, by adding source gas and impurity gas to the carrier gas, n
-3iC single crystal layer 11 (thickness 5 μm) and p-3i
A C single crystal layer 12 (thickness 5 μm) is grown sequentially to form a pn
A junction was formed. [0035] In this example, monosilane gas and propane gas were used as raw material gases. The flow rate of the raw material gas was approximately 1 cc per minute in both cases. In addition, as an impurity gas,
Trimethylaluminum gas was used for p-type impurities, and nitrogen gas was used for n-type impurities. [0036] When growing the n-3iC single crystal layer 11, nitrogen gas was added at a rate of 0.01 to IOC per minute. However, even if growth is performed without intentionally adding nitrogen gas, residual nitrogen gas in the atmosphere will cause n-3iC to grow.
A single crystal layer 11 was obtained. If nitrogen gas is not intentionally added or if nitrogen gas is added at the above flow rate, nitrogen impurities within the range of 3 x 1015 to 1 x 1018 cm-3 will be added to the n-3iC single crystal layer 11. introduced,
Moreover, a carrier concentration almost the same as the impurity concentration was obtained at room temperature. [0037] On the other hand, when growing the p-3iC single crystal layer 12, trimethylaluminum gas was added at a rate of about 0.2 cc per minute. Due to this addition of impurities, the hole concentration in the p-3iC single crystal layer 12 was approximately 2×10 17 cm −3 . [0038] Then, the substrate sample 25 is taken out from the 9 reaction tube 21, and the n-3iC single crystal layer 11 and p
-3iC single-crystal layer 12 is selectively etched.
A mesa structure as shown in Figure 1 was formed. This etching resulted in a pn junction having a diameter of 1 mm. In addition,
As etching gas, carbon tetrafluoride gas and oxygen gas were used. [0039]Finally, an n-side ohmic electrode 13 made of Ni is formed on the back surface of the n-3iC single crystal substrate 10, and a p-side ohmic electrode 13 made of Ti is formed on the top surface of the p-3iC single crystal layer 12. Electrode 1
By forming 4, a pn junction type light emitting diode as shown in FIG. 1 was obtained. [0040] For comparison, a pn junction light emitting diode was fabricated in the same manner as in the above example except that the nitrogen impurity concentration in the n-SiC single crystal layer 11 was made higher than 5 x 1016 crn''. ] When an operating voltage of approximately 3.5 μ was applied to each of the obtained light emitting diodes, a current of 20 mA flowed, and the color ranged from blue to purple regardless of the nitrogen impurity concentration of the n-SiC single crystal layer 11. However, when the nitrogen impurity concentration is higher than 5 x 101610 l6, a peak due to the emission process F at a wavelength of 425 nm and a peak due to the emission process E at a wavelength of 455 nm, as shown in Figure 8, are obtained. The light emission was mixed and the light emission was inferior to monochromaticity.On the other hand,
When the nitrogen impurity concentration was 5×10 16 cm −3 or lower, the luminescence process F due to recombination of free excitons was dominant, and extremely monochromatic violet luminescence was obtained. A typical emission spectrum is shown in FIG. The half-value width of this emission spectrum was about 20 nm, which was about 1/4 of the half-value width of the emission spectrum of a conventional violet light-emitting diode using silicon carbide. [0042] (Example 2) In this example, as shown in FIG. layer 111 (thickness 4 μm nitrogen impurity concentration approximately 1×10 18 cm −3 ) and a second n-3iC
Single crystal layer 112 (thickness 1 μm, nitrogen impurity concentration 5×10
In the same manner as in Example 1, except that the wavelength 425 with excellent monochromaticity was
A pn junction light emitting diode capable of emitting violet light of nm wavelength was fabricated. [00431] In the pn junction type light emitting diode of this example, only the impurity concentration of the n-3iC single crystal layer 112 adjacent to the pn junction interface is limited to 5 x 1016 cm-3 or less. Therefore, the n-3iC single crystal layer 111 located away from the pn junction has a high impurity concentration, so it has low resistance, and
The operating voltage required to carry a current of A was reduced from about 3.5 volts to about 3.2 volts. [0044] (Example 3) In this example, 4H type 5iC (forbidden band width 3.2 eV)
A pn junction light emitting diode capable of emitting ultraviolet light at a wavelength of 394 nm with a small spectral half width was produced in exactly the same manner as in Example 1 except that a single crystal was used. [0045] (Example 4) In this example, 15R type 5iC (forbidden band width 3°0eV
) A pn junction light emitting diode capable of emitting violet light at a wavelength of 432 nm with a small spectral half width was produced in the same manner as in Example 1 except that a single crystal was used. [0046] (Example 5) In this example, 21R type 5iC (forbidden band width 2.8 eV
) A pn junction light emitting diode capable of emitting blue light at a wavelength of 453 nm with a small spectral half width was produced in the same manner as in Example 1 except that a single crystal was used. [0047] (Example 6) In this example, 3C type 5iC (that is, β-3iC:
A pn junction light emitting diode capable of emitting green light at a wavelength of 544 nm with a small spectral half width was produced in substantially the same manner as in Example 1, except that a single crystal with a forbidden band width of 2.4 eV was used. Note that as the growth surface of the substrate, a (111) C plane whose plane orientation was inclined by about 5 degrees from the [111] direction to the <110> direction was used. [0048] (Example 7) In this example, a 6H type n-3iC single crystal substrate was used,
A pn junction light emitting diode was manufactured in exactly the same manner as in Example 1, except that an n-SiC single crystal layer 11 and a p-3iC single crystal layer 12 were formed on the substantial (0001) Si plane. . [0049] When the light emission characteristics of the obtained light emitting diode were investigated, it was found that the wavelength was 425, as shown in the typical emission spectrum of FIG. 9.
In addition to the emission process F at wavelength 455 nm, a slight emission peak due to emission process E at a wavelength of 455 nm was observed, but the violet emission with excellent monochromaticity was obtained compared to conventional pn junction light emitting diodes using silicon carbide. It was done. [00501 (Example 8) In this example, 6H type 5iC (forbidden band width 3.0 eV)
A pn junction blue light emitting diode was fabricated using the following method. [00511] The pn junction type light emitting diode of this example has the same structure as the pn junction type light emitting diode of example 1 shown in FIG. In other words, the pn junction involved in 9 light emission is the 6H type n-
It is composed of an n-SiC single-crystal layer 11 and a p-3iC single-crystal layer 12 that are sequentially formed on a 5iC single-crystal substrate 10. An n-side ohmic electrode 13 made of Ni is provided on the back surface of the n-SiC single crystal substrate 10, while a p-side ohmic electrode 14 made of Ti is provided on the top surface of the p-5iC single crystal layer 12. is provided. [0052] The pn junction type light emitting diode of this example was manufactured as follows using the vapor phase growth apparatus shown in FIG. [0053] First, as shown in FIG. 2, a 6H type n
-SiC single crystal substrate 10 (dimensions: 1 cm x 1 cm) was placed as substrate sample 25. As the growth plane of the substrate, a (0001) C plane whose plane orientation was inclined by about 5 degrees from the [0001] direction to the <11-20> direction was used. [0054] Then, using hydrogen gas as a carrier gas, the rate of 1×10
A high-frequency current is passed through the work coil 4 while flowing from the branch pipe 26 into the reaction tube 21 at a rate of CC.
C single crystal substrate 10 was heated to 1,400 to 1,500°C. and. By adding raw material gas and impurity gas to the carrier gas, an n-5iC single crystal layer 11 (thickness: 5 μm) and a p-3iC single crystal layer 12 (thickness: 5 μm) are sequentially formed on the n-3iC single crystal substrate 10. was grown to form a pn junction. [0055] In this example, monosilane gas and propane gas were used as raw material gases. The flow rate of the raw material gas was approximately lee per minute in both cases. In addition, as an impurity gas,
Trimethylaluminum gas was used for p-type impurities, and nitrogen gas was used for n-type impurities. [0056] When growing the n-3iC single crystal layer 11, nitrogen gas was added at a rate of 0.05 to 10 cc per minute. By this impurity addition, nitrogen impurities within the range of 5xlO to lx1019 cm-3 are introduced into the n-5iC single crystal layer 11,
Moreover, a carrier concentration almost the same as the impurity concentration was obtained at room temperature. [0057] On the other hand, when growing the p-3iC single crystal layer 12, trimethylaluminum gas was added at a rate of about 0.2 cc per minute. By adding this impurity, the hole concentration of the p-5iC single crystal layer 12 was approximately 2×10 17 cm −3 . [0058] Then, the substrate sample 25 is taken out from the 7 reaction tube 21, and the n-SiC single crystal layer 11 and the p-SiC single crystal layer 11 are etched by dry etching.
-3iC single-crystal layer 12 is selectively etched.
A mesa structure as shown in Figure 1 was formed. This etching resulted in a pn junction having a diameter of 1 mm. In addition,
As etching gas, carbon tetrafluoride gas and oxygen gas were used. [0059] Finally, an n-side ohmic electrode 13 made of Ni is formed on the back surface of the n-5iC single crystal substrate 10, and a p-side ohmic electrode 13 made of Ti is formed on the top surface of the p-3iC single crystal layer 12. Electrode 1
By forming 4, a pn junction type light emitting diode as shown in FIG. 1 was obtained. [00601 For comparison, a pnn junction all-light emitting diode was fabricated in the same manner as in the above example except that the nitrogen impurity concentration in the n-3iC single crystal layer 11 was lower than 1×10 18 cm −3 .

When an operating voltage of about 3.2μ was applied to each of the light emitting diodes obtained in June, a current of 20mA flowed, and no matter what the nitrogen impurity concentration of the n-3iC single crystal layer 11 was, blue light was generated. Violet luminescence was obtained. However, if the nitrogen impurity concentration is lower than 1 x 10180 m-3, a peak due to the emission process F at a wavelength of 425 nrn as shown in Figure 8,
A peak due to emission process E at a wavelength of 455 nrn was mixed, and only light emission with poor monochromaticity was obtained. On the other hand, when the nitrogen impurity concentration is 1×10 18 cm −3 or higher, the luminescence process E involving aluminum impurities is dominant. Extremely monochromatic blue light emission was obtained. A typical emission spectrum is shown in FIG. The half width of this emission spectrum was about 20 nm, which was about 1/4 of the half width of the emission spectrum of a conventional blue light emitting diode using silicon carbide. [0062] (Example 9) In this example, like the pn junction type light emitting diode of Example 2, as shown in FIG. 4, the n-3iC single crystal layer 11 was
The first n
-3iC single crystal layer 111 (thickness 4 μrn, nitrogen impurity concentration 1×1018 cm−3 or less) and a second n-5iC single crystal layer 112 (thickness 1 μm, nitrogen impurity concentration I×1018 cm−3 or less). A pn junction light emitting diode capable of emitting blue light at a wavelength of 455 nm with excellent monochromaticity was fabricated in the same manner as in Example 8, except that it was constructed from the following. [00631] In the pn junction type light emitting diode of this example, only the impurity concentration of the n-3iC single crystal layer 112 adjacent to the pn junction interface is set to 1 x 1018 cm-3 or more. Therefore, the n-5iC single crystal layer 1 away from the pn junction
In No. 11, the impurity concentration is low, so the crystallinity is improved, and the brightness is about 50% compared to the pn junction type light emitting diode of Example 8.
It increased. [0064] (Example 10) In this example, 4H type 5iC (forbidden band width 3.2 eV)
A pn junction light emitting diode capable of emitting violet light at a wavelength of 424 nm with a small spectral half width was produced in exactly the same manner as in Example 8 except that a single crystal was used. [0065] (Example 11) In this example, 3C type 5iC (that is, β-3iC:
A pn junction light emitting diode capable of emitting orange light at a wavelength of 584 nm with a small spectral half width was fabricated in substantially the same manner as in Example 8, except that a single crystal with a forbidden band width of 2.4 eV was used. Note that the growth plane of the substrate has a plane orientation of [111]
(111)C tilted approximately 5 degrees from the direction to the <110> direction
I used a surface. [0066] (Example 12) In this example, a 6H type n-3iC single crystal substrate was used,
A pn junction light emitting diode was produced in exactly the same manner as in Example 8, except that an n-3iC single crystal layer 11 and a p-3iC single crystal layer 12 were formed on the substantial (0001) Si plane. . As the growth surface of the substrate, a surface whose plane orientation was inclined by about 5 degrees from the [0001] direction toward the Raku11-20> direction was used. [0067] When the light emitting characteristics of the obtained light emitting diode were investigated, it was found that the wavelength of 455
In addition to the emission process E at wavelength 425 nm, an emission peak due to emission process F at a wavelength of 425 nm was observed, but blue emission with superior monochromaticity was obtained compared to conventional pn junction light emitting diodes using silicon carbide. . [0068] [Effects of the Invention] According to the present invention, visible light from orange to violet, visible light from green to violet, or near ultraviolet light with a small spectral half-width and excellent monochromaticity, which has not been realized so far, can be produced. A light emitting diode capable of stably emitting light with high efficiency can be manufactured with good controllability and mass production. Such light-emitting diodes make it possible, for example, to make the display parts of various display devices multicolored, and to increase the speed and density of information recording and reading in various information processing devices that use the light-emitting diodes as light sources. Furthermore, since mass production is possible, the field of application of the 9-light emitting diode is dramatically expanded.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing the structure of an embodiment of a pn junction type light emitting diode using silicon carbide of the present invention.

FIG. 2 is a cross-sectional view showing an example of a vapor phase growth apparatus used for manufacturing a pn junction type light emitting diode using silicon carbide of the present invention.

FIG. 3 is a diagram showing a typical emission spectrum of an example of a pn junction light emitting diode using silicon carbide of the present invention, which utilizes recombination light emission due to free excitons.

FIG. 4 is a sectional view showing the structure of another embodiment of a pn junction type light emitting diode using silicon carbide of the present invention.

FIG. 5 is a diagram showing a typical emission spectrum of another example of the pn junction light emitting diode using silicon carbide of the present invention, which utilizes recombination light emission by self-excitons.

FIG. 6 is a diagram showing a typical emission spectrum of an example of a pn junction light emitting diode using silicon carbide of the present invention, which utilizes recombination emission involving acceptor impurities.

FIG. 7 is a diagram showing a typical emission spectrum of another example of the pn junction light emitting diode using silicon carbide of the present invention, which utilizes recombination emission involving acceptor impurities.

FIG. 8 is a conventional pn junction type light emitting diode using silicon carbide.

[Explanation of symbols]

Ion-3iC single crystal substrate 11n-3iC single crystal layer 12p-5iC single crystal layer 13 N-side ohmic electrode 14 P-side ohmic electrode 21 Reaction tube 22 Sample stage 25 Substrate sample 111 1st J) n-3iC single crystal layer 112 Second n-3iC single crystal layer Diagram showing the emission spectrum of

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drawing

[Figure 1]

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[Figure 3]

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[Figure 5]

[Figure 6]

[Figure 7] 1 Figure 8]

Claims (8)

[Claims] 1. A pn junction type light emitting diode using silicon carbide, wherein substantially only donor impurities are added at least in the vicinity of the pn junction interface at 5×10^1 in the n-type layer constituting the pn junction involved in light emission. A pn junction type light emitting diode that substantially utilizes only light emission due to recombination of free excitons by doping at a concentration of ^6cm^-^3 or lower. 2. The n-type layer includes a first n-type layer formed adjacent to a p-n junction interface and a second n-type layer formed thereon.
The donor impurity concentration in the first n-type layer is 5×10^1^6 cm^-^3 or less, while the donor impurity concentration in the second n-type layer is 5. The pn junction type light emitting diode according to claim 1, wherein the pn junction type light emitting diode is x10^1^6 cm^-^3 or more. 3. The silicon carbide is of 4H type, 6H type, 15R type.
2. The pn junction type light emitting diode according to claim 1, wherein the pn junction type light emitting diode is a crystal polymorph selected from the group consisting of type 21R type, and type 3C. 4. The n-type layer or the p-type layer constituting the p-n junction is formed on a substantial (0001) C-plane of a substrate made of a hexagonal silicon carbide single crystal. The pn junction type light emitting diode described in . 5. A pn junction type light emitting diode using silicon carbide, wherein an acceptor impurity is added to the p-type layer constituting the pn junction involved in light emission, and at least the p-type layer of the n-type layer is doped with an acceptor impurity.
In the vicinity of the n-junction interface, substantially only donor impurities are added at 1×
A pn junction light emitting diode which substantially utilizes only recombination light emission involving these acceptor impurities by doping them at a concentration of 10^1^8 cm^-^3 or more. 6. The n-type layer includes a first n-type layer formed adjacent to a p-n junction interface and a second n-type layer formed thereon.
The first n-type layer has a donor impurity concentration of 1×10^1^8cm^-^3 or more, while the second n-type layer has a donor impurity concentration of 1. 6. The pn junction type light emitting diode according to claim 5, which has a size of x10^1^8 cm^-^3 or less. 7. The pn junction type light emitting diode according to claim 5, wherein the silicon carbide is a crystal polymorph selected from the group consisting of 4H type, 6H type, and 3C type. 8. Claim 5, wherein the n-type layer or p-type layer constituting the p-n junction is formed on a substantial (0001) C-plane of a substrate made of a hexagonal silicon carbide single crystal. The pn junction type light emitting diode described in .