JP2529001B2 - Method for manufacturing pn junction type light emitting diode using silicon carbide - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a pn junction type light emitting diode using silicon carbide, and particularly to a short wavelength visible light emitting diode capable of emitting blue to violet high brightness light.

(Prior Art) Light emitting diodes are widely used as display elements in various display devices because they are small in size, consume little power, and are a light emitting source capable of stably emitting high brightness light. Also,
The light emitting diode is also used as a light source for reading and recording information in various information processing devices. The long-wavelength visible light emitting diodes that have been widely put into practical use so far can emit high-luminance red to green light. On the other hand, the currently developed light emitting diodes that emit short-wavelength blue to violet visible light still have low brightness and have not been widely put into practical use.

Generally, the emission color of a light emitting diode depends on the semiconductor material used. Semiconductor materials for short wavelength visible light emitting diodes are silicon carbide (SiC), which is a IV-IV group compound semiconductor.
It is limited to II-V compound semiconductor gallium nitride (GaN), and II-VI compound semiconductors zinc sulfide (ZnS) and zinc selenide (ZnSe). Although short-wavelength visible light emitting diodes have been actively researched and developed using these semiconductor materials, mass production of devices having high brightness and stability to the extent that they can be widely put into practical use has not been achieved.

For the device structure of a light emitting diode, a pn junction type light emitting diode that can inject electrons and hole carriers into the light emitting region with high efficiency is most suitable. However, among the above semiconductor materials for short-wavelength visible light emitting diodes, it is difficult to obtain p-type crystals for GaN, ZnS, and ZnSe semiconductors, or is it high resistance even if obtained? Or, because it is extremely unstable, it is not possible to fabricate a pn junction type light emitting diode. Therefore, a MIS (metal-insulating layer-semiconductor) structure using a thin insulating layer or a high resistance layer is adopted. However, the light emitting diode having such a MIS structure has drawbacks such as nonuniform device characteristics and unstable light emission.

On the other hand, silicon carbide (SiC) contains p-type crystals and n-type crystals.
Since a type crystal can be easily obtained, a pn junction type light emitting diode can be manufactured. So far, many reports have been made on the pn junction type blue light emitting diode of silicon carbide manufactured by the liquid phase epitaxial growth method (LPE method) (eg, M. Ikeda, T. Hayakawa, S. Yamagi).
wa, H.Matsunami.and T.Tanaka, Journal of Applied Phy
sics, Vol. 50, No. 12, pp. 8215-8225, 1979).

However, the brightness of the pn junction type blue light-emitting diode made by the LPE method is still low, and the brightness of less than 15 mcd is obtained when operated at 20 mA. It is thought that the main reason for this is that the growth temperature is as high as 1,700 to 1,800 ° C and the growth occurs in the active Si melt, so that the growth controllability is poor and unnecessary impurities are easily mixed. In addition, the LPE method has a problem of poor mass productivity.

(Problems to be Solved by the Invention) Since the chemical vapor deposition method (CVD method) can precisely control the supply amounts of the source gas and the impurity gas for doping, the growth of the SiC single crystal can be performed. It can be controlled accurately. However, there are very few examples of making blue light emitting diodes by the CVD method (for example, S, Nishino, A. Ibaraki, H. Mat.
sunami, and T.Tanaka, Japanese Journal of Applied Ph
ysics, Vol. 19, p. L353, 1980). In this conventional example, since the growth temperature is as high as about 1,800 ° C, the brightness of the obtained light emitting diode is still low.

In recent years, in the CVD method, if monosilane (SiH ₄ ) gas and propane (C ₃ H ₈ ) gas are used as the source gas and the growth plane orientation of the SiC single crystal substrate is appropriately selected, the growth is relatively low below 1,600 ° C. It has been reported that SiC single crystals can be obtained at temperature (for example, N. Kuroda, K. Shibahara, W. Yoo,
S. Nishino, and H. Matsunami, Extended Abstracts of th
e 19th Conference on Solid State Devices and Mater
ials, Tokyo, 1987, pp.227-230). However, at such a low temperature, the decomposition of propane is insufficient, and it is necessary to supply excessively with respect to monosilane, resulting in poor controllability of growth. In addition, unnecessary impurities may be mixed in the growth layer. Therefore, the Si obtained by such a method
Even if C single crystal is used, it is not possible to obtain a pn junction type light emitting diode that can emit light with high brightness and stability.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a pn junction type light emitting diode capable of stably emitting blue to violet short wavelength visible light with high brightness in a stable manner.
It is to provide a method excellent in controllability and mass productivity manufactured by the method.

(Means for Solving the Problems) The present inventors comprehensively studied various conditions in the CVD method, such as a raw material gas, an impurity gas, a growth temperature, a growth plane orientation of a substrate, and a growth rate, and described below. We have completed a manufacturing method with excellent controllability and mass productivity.

A method for manufacturing a pn junction type light emitting diode using silicon carbide according to the present invention is a pn junction type light emitting diode using silicon carbide by a chemical vapor deposition method using a silane compound and a hydrocarbon compound as source gases. And a step of growing a first silicon carbide single crystal layer having a first conductivity type on a silicon carbide single crystal substrate having a growth plane orientation inclined from a [0001] direction to a <110> direction. A step of growing a second silicon carbide single crystal layer having a second conductivity type on the first silicon carbide single crystal layer. Further, in this manufacturing method, monosilane or disilane is used as the silane compound, and acetylene is used as the hydrocarbon compound, and the growth step is performed within a temperature range of 1,300 to 1,500 ° C. Thereby, the above object is achieved.

According to the present invention, in the above manufacturing method, the impurity acting as the emission center is doped only in the surface region of the first silicon carbide single crystal layer forming a pn junction with the second silicon carbide single crystal layer. It was done.

(Operation) In the present invention, since the silicon carbide single crystal layer is grown on the silicon carbide substrate whose growth plane orientation is tilted from the [0001] direction to the <110> direction, a decrease in crystallinity of the growth layer is avoided. can do. Moreover, since the growth temperature of the silicon carbide single crystal layer is set in the range of 1,300 to 1,500 ° C., it is possible to prevent both the quality deterioration of the SiC single crystal in the growth layer and the incorporation of unnecessary impurities into the growth layer.

(Example) The basic principle of the present invention will be described below.

In the manufacturing method of the present invention, the growth plane orientation of the substrate is [00
It is necessary to incline from the [01] direction to the <110> direction. If it is tilted in the other direction, the crystallinity of the growth layer will decrease. The inclination angle of the growth plane orientation is preferably within the range of 2 to 15 degrees. If the tilt angle is less than 2 degrees, different crystal polymorphs grow together. Moreover, when the inclination angle is larger than 15 degrees, the surface flatness of the growth layer deteriorates. The <110> direction, which is the tilt direction, includes not only the [110] direction but also all directions crystallographically equivalent to this direction.

The growth temperature is preferably in the range of 1,300-1,500 ° C. If the growth temperature is lower than 1,300 ℃, S in the growth layer
The quality of iC single crystal is inferior. Further, if the growth temperature is higher than 1,500 ° C, unnecessary impurities are mixed in the growth layer.

In the manufacturing method of the present invention, the SiC single crystal layer is grown on the SiC single crystal substrate by the CVD method. At this time, the source gas and the impurity gas are supplied together with the carrier gas to the substrate heated to the above growth temperature.

As the raw material gas, a silane compound (for example, monosilane or disilane (Si ₂ H ₆ )) and a hydrocarbon compound (for example, acetylene (C ₂ H ₂ )) are used. As described above, when conventional propane is used as the source gas, propane is not sufficiently decomposed in the above growth temperature range, and it is necessary to supply excessively to monosilane and disilane. Controllability of. If acetylene, which decomposes substantially completely in the above growth temperature range, is used, by supplying acetylene at half the flow rate when monosilane is used, or at the same flow rate when disilane is used. By supplying acetylene, high-quality SiC crystals can be grown with extremely good controllability. Therefore, a combination of monosilane or disilane and acetylene is particularly preferable as the source gas.

As the impurity gas, for example, nitrogen (N ₂ ) gas and trimethylaluminum ((CH ₃ ) ₃ Al) gas are used. Nitrogen (N) is used as an n-type dopant (donor impurity), and aluminum (Al) is used as a p-type dopant (acceptor impurity) and an emission center.

Hydrogen (H ₂ ) gas or argon (Ar) gas is usually used as the carrier gas, but hydrogen gas is preferably used.

In the manufacturing method of the present invention, when the n-SiC single crystal layer is grown, preferably, for example, trimethylaluminum gas is added to the impurity gas so that the aluminum impurity acting as a luminescence center is generated in the n-SiC single crystal layer. To be doped. More preferably, this aluminum impurity is doped only in the surface region of the n-SiC single crystal layer that forms a pn junction with the subsequently grown p-SiC single crystal layer. When such doping is performed, the quality of the n-SiC single crystal layer is improved, so that a light emitting diode with high emission brightness can be obtained. Moreover, the operating voltage is lowered.

The growth rate of the SiC single crystal layer is preferably 1 to 10 μm per hour. If the growth rate is less than 1 μm / hr, unnecessary impurities are mixed in the growth layer. Also, the growth rate is 10 μm
If it is larger, the crystallinity and surface flatness of the growth layer are reduced.

 Examples of the present invention will be described below.

Example 1 In this example, p using 6H type SiC (forbidden band width 3.0 eV) was used.
An n-junction type blue light emitting diode was produced.

FIG. 1 is a schematic diagram of the vapor phase growth apparatus used in this example. First, this vapor phase growth apparatus will be described.

A sample stage 2 is installed by a support rod 3 inside a double-structured quartz reaction tube 1. Sample base 2 and support rod 3
Are made of graphite. The sample stage 2 may be installed horizontally or may be appropriately inclined. A work coil 4 is wound around the outer periphery of the reaction tube 1 and a high-frequency current is passed to heat the substrate sample 5 on the sample table 2 to a predetermined temperature. On one side of the reaction tube 1, a branch tube 6 serving as an inlet for the raw material gas, the carrier gas, and the impurity gas is provided. Branch tube inside the outer tube of the reaction tube 1 having a double structure
The reaction tube 1 can be cooled by flowing cooling water through 7,8. The other end of the reaction tube 1 is closed by a flange 9 made of stainless steel, and is sealed by a stop plate 10, a bolt 11, a nut 12 and an O-ring 13 arranged on the peripheral edge of the flange 9. Branch pipe near the center of the flange 9
14 is provided, and the above-mentioned gas is discharged through this branch pipe 14.

FIG. 2 is a sectional view showing the structure of the light emitting diode of this embodiment. This light emitting diode was manufactured as follows using the vapor phase growth apparatus of FIG.

First, as shown in FIG. 1, a 6H type n was placed on the sample table 2.
A -SiC single crystal substrate 20 (size: about 1 cm x 1 cm) was mounted as a substrate sample 5. As the growth surface of the substrate, a surface whose plane orientation was tilted in the range of 0 to 25 degrees from the [0001] direction to the <110> direction was used.

Then, while using hydrogen gas as a carrier gas at a rate of 10 per minute, a high-frequency current is caused to flow through the work coil 4 while flowing from the branch pipe 6 into the reaction tube 1 to produce the n-SiC single crystal substrate 20.
Was heated to 1200-1700 ° C. Then, by adding the source gas and the impurity gas to the carrier gas, n-SiC
An n-SiC single crystal layer 21 (thickness 5 μm) and a p-SiC single crystal layer 22 (thickness 5 μm) were sequentially grown on the single crystal substrate 20 to form a pn junction.

In this example, disilane gas and acetylene gas were used as the source gas at the same flow rate. By setting the flow rate of each source gas to 0.1 to 10 cc / min, 0.2 to 20 μ / h
A growth rate of m was obtained. When monosilane was used as the source gas, exactly the same result was obtained by using the double flow rate of acetylene. As the impurity gas, nitrogen gas with a flow rate of 1/2 of the source gas and trimethylaluminum gas with a flow rate of 1/20 were used for the n-SiC single crystal layer 21, and for the p-SiC single crystal layer 22, , Trimethylaluminum gas at 1/5 flow rate of the source gas was used.

Then, the substrate sample 5 is taken out from the reaction tube 1 and the n-SiC single crystal layer 21 and the p-SiC single crystal layer 22 are selectively etched by a dry etching method to form a mesa structure as shown in FIG. Formed. By this etching, the dimension of the pn junction became about 1 mm in diameter. As the etching gas, carbon tetrafluoride (CF ₄ ) gas and oxygen (O ₂ ) were used.
Gas was used.

Finally, on the back surface of the n-SiC single crystal substrate 20, n
A side ohmic electrode 23 is formed, and a p-side ohmic electrode 24 made of an Al-Si alloy is formed on the upper surface of the p-SiC single crystal layer 22 to form a pn junction type light emission as shown in FIG. I got a diode. When a forward current was applied to the obtained pn junction type light emitting diode, blue light emission with a peak wavelength of 470 nm was observed.

In this example, various pn junction type light emitting diodes were manufactured by changing various conditions such as the growth temperature, the inclination angle of the growth plane direction, and the growth rate, and the brightness thereof was measured. The obtained results are shown in FIGS. 3 to 5. FIG. 3 shows the relationship between the brightness and the growth temperature, FIG. 4 shows the relationship between the brightness and the inclination angle of the growth plane direction, and FIG. 5 shows the relationship between the brightness and the growth rate.
As is clear from these figures, the growth temperature is 1,300-1,500.
℃, growth plane orientation inclination angle 2 to 15 degrees, growth rate 1 to hour
The light-emitting diode manufactured under the condition of 10 μm showed a brightness of 15 mcd or more, which was higher than that of the conventional blue light-emitting diode when operated at 20 mA, and the maximum brightness reached 80 mcd.
In addition, the variation in the maximum brightness of light-emitting diodes manufactured under the same conditions was within 20% for 20 wafers.

For comparison, conventional propane was used in place of acetylene as the raw material gas, and the flow rate was optimized, except that
A pn junction type light emitting diode was produced in the same manner as in the above example. When the brightness of the obtained light emitting diode was measured, it was found that the brightness was higher than that when acetylene was used as the source gas.
Only a few to one tenth of the brightness was obtained.
For reference, an example of the relationship between the brightness and the growth temperature is
It is shown in FIG. 3 (dotted line). In addition, the variation in the maximum brightness of light-emitting diodes manufactured under the same conditions was about 50% for 20 wafers.

Example 2 In this example, a pn junction capable of emitting violet light with a peak wavelength of 430 nm was performed in the same manner as in Example 1 except that a 4H type n-SiC (forbidden band width 3.2 eV) single crystal substrate was used. Type light emitting diode was produced. A light-emitting diode manufactured under the conditions of a growth temperature of 1,300 to 1,500 ℃, a growth plane orientation inclination angle of 2 to 15 degrees, and a growth rate of 1 to 10 μm per hour shows a brightness of at least 2 mcd when operated at 20 mA, The maximum brightness reached 8 mcd.

Example 3 In this example, pn capable of emitting blue-green light with a peak wavelength of 490 nm was performed in the same manner as in Example 1 except that a 15R type n-SiC (forbidden band width 2.9 eV) single crystal substrate was used. A junction type light emitting diode was produced. The light emitting diode manufactured under the conditions of the growth temperature of 1,300 to 1,500 ℃, the inclination angle of the growth plane direction of 2 to 15 degrees, and the growth rate of 1 to 10 μm / hour showed the brightness of at least 15 mcd when operated at 20 mA, Maximum brightness is 90 mcd
Reached

Example 4 In this example, as shown in FIG. 6, an n-SiC single crystal layer 2
1 is an n-SiC single crystal layer 21 containing no acceptor impurities.
1 (thickness 4 μm) and n-SiC containing acceptor impurities
A pn junction type light emitting diode capable of emitting blue light with a peak wavelength of 470 nm was produced in the same manner as in Example 1 except that the pn junction type light emitting diode was composed of the single crystal layer 212 (thickness 1 μm).

When the n-SiC single crystal layer 211 was formed, the growth was performed by adding only nitrogen gas at a half flow rate of the source gas as an impurity gas. In addition, when forming the n-SiC single crystal layer 212, nitrogen gas having a flow rate of 1/2 of the source gas and trimethylaluminum gas having a flow rate of 1/20 were added as impurity gases for growth.

Growth temperature 1,300-1,500 ℃, growth plane orientation inclination angle 2-
The light-emitting diode manufactured under the conditions of 15 ° C. and a growth rate of 1 to 10 μm / h has an improved quality because the n-SiC single crystal layer 211 does not contain acceptor impurities and its quality is improved. , And emitted blue light with a maximum brightness of 90 mcd. Moreover, the operating voltage has been reduced from 3.6V to 3.3V.

(Effects of the Invention) According to the present invention, it is possible to prevent both the deterioration of the quality of the SiC single crystal in the growth layer and the mixing of unnecessary impurities into the growth layer. As a result, it is possible to manufacture a light emitting diode capable of stably emitting blue to purple short wavelength visible light with high brightness, which has not been realized so far, by a method excellent in controllability and mass productivity. Such a light emitting diode enables, for example, multicoloring of a display portion in various display devices, and speeding up and high density of information recording / reading in various information processing devices using the light emitting diode as a light source. Moreover, since it can be mass-produced, the application field of the light emitting diode is dramatically expanded.

[Brief description of drawings]

FIG. 1 is a sectional view showing the structure of an example of a vapor phase growth apparatus used in the manufacturing method of the present invention, and FIG. 2 is a sectional view of a pn junction type light emitting diode using silicon carbide, which is an embodiment of the present invention.
3, 4, and 5 are the pn of FIG. 2, respectively.
A diagram showing the dependence of the brightness of the junction type light emitting diode on the growth temperature, the inclination angle of the growth plane orientation, and the growth rate,
FIG. 6 shows a pn using silicon carbide which is another embodiment of the present invention.
It is sectional drawing of a junction type light emitting diode. 1 …… Reaction tube, 2 …… Sample stage, 5 …… Substrate sample, 20 …… n−S
iC single crystal substrate, 21,211,212 …… n-SiC single crystal layer, 22 ……
p-SiC single crystal layer, 23 ... n side ohmic electrode, 24 ... p side ohmic electrode.

Continuation of the front page (56) Reference JP-A-2-46779 (JP, A) JP-A-63-179516 (JP, A) JP-A-49-34786 (JP, A)

Claims (2)

(57) [Claims] 1. A method for producing a pn junction type light emitting diode using silicon carbide by a chemical vapor deposition method using a silane-based compound and a hydrocarbon compound as source gases, wherein the growth plane direction is [0001]. From the [] direction to the <110> direction, and a step of growing a first silicon carbide single crystal layer having a first conductivity type on the silicon carbide single crystal substrate; and, on the first silicon carbide single crystal layer, A step of growing a second silicon carbide single crystal layer having a second conductivity type, wherein monosilane or disilane is used as the silane-based compound, acetylene is used as the hydrocarbon compound, and the growth step is 1,300 to 1,500. Conduct within the temperature range of ℃,
A method for manufacturing a pn junction type light emitting diode using silicon carbide. 2. The impurity acting as an emission center is doped only in the surface region of the first silicon carbide single crystal layer forming a pn junction with the second silicon carbide single crystal layer.
4. A method for manufacturing a pn junction type light emitting diode using silicon carbide according to item 1.