JP2001007385A - Ultraviolet ray emitting device and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultraviolet ray emitting device capable of emitting ultraviolet rays from a semiconductor p-n junction, and a manufacturing method thereof. SOLUTION: An n-type diamond semiconductor crystal layer 4, doped with S which are to become donor atoms, is grown, e.g. by a plasma CVD on a p-type diamond semiconductor crystal 2 made of a B-doped high-pressure synthesized diamond or natural (IIb) type diamond, thereby forming a p-n junction 6. A forward voltage is applied from the p-n junction 6 to emit ultraviolet rays.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultraviolet light emitting device which emits ultraviolet light, emits ultraviolet light, erases with ultraviolet light, and emits ultraviolet light through pn junction of diamond, and a method of manufacturing the same.

[0002]

2. Description of the Related Art A diamond semiconductor is a very special semiconductor crystal having a wide band gap of 5.5 eV. Since the band gap is wide, a change in semiconductor characteristics due to heat as seen in a silicon device is small. It is possible to make devices that operate at very high temperatures.

With respect to p-type diamond semiconductors, very high quality diamond semiconductor thin films have been obtained. Its typical characteristic, hole mobility, is 1500 cm ² V ⁻¹ s.
^{Approximately -1} is obtained with good reproducibility, which is sufficient for fabricating high-speed, large-current devices.

On the other hand, it has been difficult to obtain a high-quality n-type diamond semiconductor because an appropriate donor atom has not been found in the past, and therefore its application is limited. , Especially p
A practical device using an n-junction could not be manufactured up to the present.

Recently, the present inventors have proposed the synthesis of an n-type diamond semiconductor, which has been the biggest problem to be solved for the application of the diamond semiconductor (Japanese Patent Application No. Hei 11-1999).
124682). In this proposal, a high-quality n-type diamond semiconductor is obtained by introducing a sulfur atom as a donor into a diamond semiconductor crystal by adding a sulfur compound, typically hydrogen sulfide, in microwave plasma CVD. The electron mobility, which is a typical characteristic, is about 600 cm ² V ⁻¹ s ⁻¹ , and the activation energy (impurity level) is about 0.38 eV. At present, it is inferior to that of a p-type diamond semiconductor, but it can still be expected to be sufficiently applied to devices.

[0006]

However, a diamond semiconductor device having a good pn junction has not yet been obtained, and there is no semiconductor light emitting device utilizing a pn junction of a diamond semiconductor. On the other hand, as a semiconductor light emitting device, efforts have been made to manufacture a light emitting diode (hereinafter, referred to as “LED”) and a semiconductor laser (hereinafter, referred to as “LD”) over a wide wavelength range from ultraviolet to infrared. However, there are still no semiconductor light emitting devices that emit ultraviolet light.

Accordingly, an object of the present invention is to provide an ultraviolet light emitting device capable of emitting ultraviolet light from a pn junction of a semiconductor and a method of manufacturing the same.

[0008]

According to another aspect of the present invention, there is provided an ultraviolet light emitting device according to the present invention, which is a semiconductor crystal having a band gap energy corresponding to an ultraviolet region. A pn junction formed of a p-type semiconductor crystal having atoms and an n-type semiconductor crystal having donor atoms is provided, and ultraviolet light is emitted by applying a forward voltage to the pn junction.
The invention according to claim 2 is an n-type diamond semiconductor crystal in which the semiconductor crystal is diamond, the p-type semiconductor crystal is a p-type diamond semiconductor crystal, and the n-type semiconductor crystal is doped with sulfur as a donor atom. It is characterized by being. According to a third aspect of the present invention, in the p-type semiconductor crystal, p-type semiconductor crystal is doped with boron as an acceptor atom.
It is a diamond semiconductor crystal.

The invention according to claim 4 has, in addition to the above arrangement, p
The diamond semiconductor crystal is a high-pressure synthetic diamond doped with boron. The invention according to claim 5 is characterized in that the p-type diamond semiconductor crystal is a natural IIb
It is a shaped diamond. The invention according to claim 6 is characterized in that it has a structure in which a p-type diamond semiconductor crystal and a p-type diamond semiconductor crystal are laminated on an insulating diamond substrate. According to a seventh aspect of the present invention, the donor atom concentration is 10 ¹³ / cm ³ to 10 ²¹ / cm ^3.
It is characterized by being in the range. An eighth aspect of the present invention is characterized in that the pn junction has a structure in which the pn junction is formed with a steepness of an atomic order.

With such a configuration, the ultraviolet light emitting device of the present invention has a high-quality and steep pn junction, and emits ultraviolet light when a forward voltage is applied.

Further, in the method of manufacturing a diamond semiconductor device according to the present invention, a first step of forming a p-type diamond semiconductor crystal layer in a vapor phase synthesis method in which a thin film is grown based on activation of a source gas, A second step of forming an n-type diamond semiconductor crystal layer in which donor atoms are sulfur, wherein a pn junction is formed with a steepness on the order of atoms. In a tenth aspect of the present invention, in addition to the above-described configuration, in the first step, the dopant of the p-type diamond semiconductor crystal is boron, and boron and carbon of a hydrocarbon serving as a source of constituent atoms of the p-type diamond semiconductor crystal. Is 20 to 20,000 ppm. The invention according to claim 11 is
In the second step, the ratio of sulfur to carbon of hydrocarbon which is a source of constituent atoms of the diamond semiconductor crystal is 100
It is characterized by being 0 to 10000 ppm. Further, the twelfth aspect of the present invention is characterized in that, in the vapor phase synthesis method, at least one of electricity, heat and light is used for activating the source gas.

With such a configuration, the method for manufacturing an ultraviolet light emitting device of the present invention can manufacture an ultraviolet light emitting device having good quality and a steep pn junction.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to FIGS. The band gap of diamond is 5.5 eV (225 nm), which is the energy width in the ultraviolet region. Further, as shown in FIGS. 1 and 2, the cathodoluminescence and photoluminescence of an n-type diamond semiconductor doped with sulfur as a donor atom indicate 5.22 eV (237.7 n).
m) has an emission peak. It can also be seen that a good quality p-type diamond semiconductor also has a similar emission peak. Therefore, a diamond semiconductor is most suitable as the ultraviolet light emitting material.

FIGS. 3A to 3C are schematic cross-sectional views of an ultraviolet light emitting device that emits ultraviolet light using a pn junction of a diamond semiconductor according to the present invention. In the figure,
Arrows indicate ultraviolet light emission from the pn junction. Referring to FIG. 3 (a), the ultraviolet light emitting device 10 of the present invention is a high pressure synthetic diamond or natural II doped with boron.
An n-type diamond semiconductor crystal layer 4 doped with sulfur serving as a donor atom is grown on a p-type diamond semiconductor crystal 2 formed of b-type diamond by, for example, a plasma CVD method to form a pn junction 6.

The boron-doped high-pressure synthetic diamond can be produced by, for example, an ultra-high-pressure high-temperature method of 50 kbar or 1500 ° C. or more. The naturally produced diamond crystal called IIb type is a p-type diamond semiconductor containing boron. .

The ultraviolet light emitting device 20 shown in FIG.
Is a p-type diamond semiconductor crystal layer 5 doped with boron, for example, formed by a plasma CVD method on an insulating diamond substrate 3 formed of ordinary synthetic diamond or natural diamond, and a plasma CVD method, for example.
A pn junction 8 is formed by growing an n-type diamond semiconductor crystal layer 7 doped with sulfur by a method. The ultraviolet light emitting device 30 shown in FIG.
It is formed by inverting the conductivity type of the ultraviolet light emitting device 20 shown in FIG.

The thickness of the p-type diamond semiconductor crystal layer 5 is about 1 μm, but may be about 1 nm or more. Further, the concentration of the doped boron may be 10 ¹³ cm ⁻³ or more, and the upper limit is about 10 ²¹ cm ⁻³ . The thickness of a p-type diamond semiconductor crystal formed of boron-doped high-pressure synthetic diamond or natural IIb type diamond is about 500 μm, but may be any thickness that can be formed.
The boron concentration may be a p-type diamond semiconductor, and may be 10 ¹³ cm ⁻³ or more.

The n-type diamond semiconductor crystal layer 4,
7 has a thickness of about 1 μm, but may have a thickness of about 1 nm or more. The concentration of sulfur doped as a donor is 1
0 ¹³ cm ⁻³ or more, and the upper limit is about 10 ²¹ cm ⁻³ .

In FIGS. 3A to 3C, 11, 13, and 2
Reference numerals 1, 23, 31, and 33 indicate electrodes. These electrodes are obtained by depositing titanium (Ti) on diamond, and further depositing gold (Au) thereon to prevent oxidation of the titanium. The electrodes 23 and 33 in FIGS. 3B and 3C may be formed on the back side (exposed side) of the insulating diamond substrate.

Next, the characteristics of the ultraviolet light emitting device of the present invention will be described. FIG. 4 is a diagram showing the results of analysis of impurities in the depth direction in the diamond semiconductor device shown in FIG. The ultraviolet light emitting device 20 is analyzed by secondary ion mass spectrometry (hereinafter, referred to as “SIMS”), and the profile in the depth direction includes the n-type diamond semiconductor crystal layer 7 doped with sulfur from the surface of the first layer;
FIG. 4 shows the boron-doped p-type diamond semiconductor crystal layer 5 of the second layer and the insulator diamond substrate 3 in the range indicated by the arrow in the figure. In FIG. 4, the profiles indicated by a and b are backgrounds.

In the case of diamond, different atoms, such as boron (B) and sulfur (S), are very difficult to diffuse in the crystal, and this is advantageous for the formation of a pn junction. As shown in FIG. 4, the change in the impurity concentration at the interface is extremely steep. That is, the p-type diamond semiconductor crystal layer and the n-type diamond semiconductor crystal layer are switched in the atomic order to form a pn junction. Therefore, the pn junction formed by the ultraviolet light emitting device of the present invention is very good and steep in atomic order.

FIG. 5 is a diagram showing an emission spectrum when a current is applied in the forward direction to the diamond semiconductor pn junction according to the present invention. At room temperature, 237 nm (5.
At 23 eV), strong emission was observed, and at the same time, broad emission occurred in the visible region, but the intensity was considerably weaker than the peak at 237 nm. Therefore, ultraviolet light is emitted from the pn junction interface of the diamond semiconductor.

The ultraviolet light emitting device of the present invention has a good rectifying characteristic in which a current flows in the forward direction but no current flows in the reverse direction. It also has good rectification characteristics at high temperatures of 400 ° C. and 500 ° C.

Next, a method of manufacturing the ultraviolet light emitting device of the present invention will be described. The ultraviolet light emitting device of the present invention can be manufactured by a gas phase synthesis method. As the gas phase synthesis method, at least one of electricity, heat, and light energy may be used depending on the method of activating the source gas. In the present embodiment, microwave plasma CVD using electric energy and heat energy is used. Here is an example by the method.
The sulfur-doped n-type diamond semiconductor is manufactured by the manufacturing method disclosed in Japanese Patent Application No. 11-124682 by the present inventors.

FIG. 6 is a schematic configuration diagram of a microwave plasma CVD apparatus used in this embodiment. As shown in FIG. 6, the microwave plasma CVD apparatus 40 includes, for example, a microwave generator 41 of 2.45 GHz, an isolator and a power monitor 43, and a tuner 45, and a reaction tube 47 irradiated with microwaves. A vacuum pump (not shown) for evacuating the reaction tube 47, a gas supply line 49 for selectively supplying a mixed gas or a purge gas to the reaction tube 47, and a plurality of optical windows 51, 51. And a substrate holder 53 provided in the reaction tube.
And a temperature control system 5 for heating or cooling the insulator diamond substrate 55 installed on the substrate holder 53.
And a gas is supplied onto the substrate to generate microwave plasma 59. The substrate temperature is monitored by an optical pyrometer.

Next, an example of the growth conditions for the n-type diamond semiconductor crystal is shown in FIG. Referring to FIG. 7, in the present embodiment, a mixed gas of volatile hydrocarbon / sulfur compound / hydrogen such as alkane and alkene is used as a source gas. Hydrocarbons are used as a source of carbon which is a constituent element of diamond, sulfur compounds are used as a source of donor atoms, and hydrogen is used as a carrier gas.

Examples of the sulfur compound include inorganic sulfur compounds such as hydrogen sulfide (H ₂ S) and carbon disulfide (CS ₂ ), and organic sulfur compounds such as lower alkyl mercaptan. Hydrogen sulfide is most preferred. Therefore,
As the mixed gas, it is preferable to use methane / hydrogen sulfide / hydrogen.

The concentration of volatile hydrocarbons in the mixed gas is 0.1.
It is good to use 1% to 5%, preferably 0.5% to 3.0%. The concentration of sulfur compounds in the mixed gas is 1 ppm
~ 2000ppm, preferably 5ppm ~ 200ppm
Good to use in.

In this embodiment, the methane concentration is 1% and the hydrogen sulfide is 10 to 100 ppm. As the concentration of hydrogen sulfide increases, the carrier concentration increases. In this range, the mobility is 5 from the point where the addition amount of hydrogen sulfide becomes maximum at 50 ppm.
0 ppm is most preferred.

The total gas flow rate depends on the scale of the apparatus, for example, the volume of the reaction tube, the supply gas flow rate, the exhaust volume, and the like. In this embodiment, it is 200 ml / min. The gas flow rate is controlled by a mass flow controller corresponding to each gas type. The addition amount of hydrogen sulfide is determined by diluting with a carrier hydrogen using a mixed gas cylinder of 100 ppm hydrogen sulfide / hydrogen and controlling the flow rate by a mass flow controller to a predetermined amount. It is controlled to the ratio of the amount added.

In this embodiment, a mixed gas cylinder of 100 ppm hydrogen sulfide / hydrogen is used. Hydrogen sulfide concentration 50p
pm, the total flow rate is 200 ml / min
In the case of (1), the carrier hydrogen gas was set to 100 ml / min, and 10
Flowing 0 ml / min results in a total hydrogen sulfide concentration of 50 pp
m.

In the case of microwave plasma CVD, the atmospheric pressure is within a range of about 30 to 60 Torr.
Torr. The microwave discharge maintains the glow discharge at a relatively high pressure. The temperature of the substrate on which diamond is deposited is 700 ° C. to 1100 ° C., but is 830 ° C. in the present embodiment. Insulating diamond substrate (10
The diamond semiconductor layer is homoepitaxially grown on the (0) plane, but is not limited to the (100) plane.
Plane or (110) plane.

Next, an example of the growth conditions for the p-type diamond semiconductor crystal is shown in FIG. Referring to FIG. 8, in the present embodiment, it is preferable to use CH ₄ / B ₂ H ₆ / H ₂ as a mixed gas. The boron compound diborane (B ₂ H ₆ ) is used as the source of the acceptor atom. CH ₄ 1.0% of the mixed gas, B ₂ H ₆ is 0.1~100p
pm, B / C ratio is 20 to 20000 ppm.

In this embodiment, 100 ppm diborane (B
Using a mixed gas cylinder of ₂ H ₆ ) / hydrogen, the concentration of diborane introduced into the reaction tube is set to 50 ppm. The total gas flow rate is 200 to 500 ml / min, but in this embodiment, the total gas flow rate is 200 ml / min in order to continue the process with the n-type diamond semiconductor.

The growth pressure is 40 to 50 Torr,
The pressure is set to 40 Torr at the same pressure in order to continue the process with the n-type diamond semiconductor. Substrate temperature is 700 ° C
950 ° C., but the same temperature of 830 ° C. in order to continue the process with the n-type diamond semiconductor.

Next, a method of manufacturing the ultraviolet light emitting device having the structure shown in FIG. 3B will be described. First, a (100) insulative diamond substrate whose surface has been cleaned is placed on a substrate holder, and hydrogen purge is repeated several times from a gas supply line to remove nitrogen and oxygen from the vacuum vessel. The surface temperature is controlled to be 830 ° C. and the pressure is controlled to 40 Torr. The substrate surface temperature is measured by, for example, an optical pyrometer.

Next, while performing microwave discharge under a pressure control of 40 Torr, the gas supply line was switched between a hydrogen gas for purging and a mixed gas, and methane 1 was supplied to the reaction tube.
% / Diborane 50 ppm / hydrogen mixed gas 200 ml /
min, plasma is generated above the substrate, and this plasma flow is supplied to the insulating diamond substrate, and p
The epitaxial diamond semiconductor crystal layer grows epitaxially.

When the film thickness reaches a predetermined value, the gas supply line is switched, and a mixed gas of methane 1% / hydrogen sulfide 50 ppm / hydrogen 200 ml / min is introduced into the reaction tube. The n-type diamond semiconductor layer is supplied on the layer and epitaxially grows.

When the film thickness reaches a predetermined value, the gas supply line is switched to hydrogen purge, the microwave discharge is stopped, and the heating of the substrate is stopped or cooled. Finally, when the temperature returns to room temperature, the p-type diamond semiconductor crystal layer and the n-type
The ultraviolet light emitting device having the stacked diamond semiconductor crystal layer is taken out, and electrodes are deposited.

In the ultraviolet light emitting device manufactured in this manner, a pn junction is formed by a high-quality p-type diamond semiconductor and a high-quality n-type diamond semiconductor doped with sulfur, which is an optimum donor. When a forward current is applied, ultraviolet light is emitted from the pn junction interface. Therefore, a very good ultraviolet light emitting device that emits ultraviolet light from the pn junction interface can be manufactured.

[0041]

As described above, the ultraviolet light emitting device of the present invention has a high-quality and steep pn junction, and has an effect that ultraviolet light is emitted from the pn junction when a forward voltage is applied. Further, the method for manufacturing an ultraviolet light emitting device of the present invention has an effect that an ultraviolet light emitting device having good quality and a steep pn junction can be manufactured.

[Brief description of the drawings]

FIG. 1 is a diagram showing a cathodoluminescence spectrum of a sulfur-doped n-type diamond semiconductor according to the present invention. The temperature was 112 K, the sample was sulfur-doped (100) diamond, and the hole mobility was 580 cm ^2.
V ⁻¹ s ⁻¹ . The excitation energy is 25k
V.

FIGS. 2A and 2B are diagrams showing a photoluminescence spectrum of an n-type diamond semiconductor doped with sulfur according to the present invention, wherein FIG.
Shows the spectrum of an n-type diamond semiconductor to which 100 ppm of hydrogen sulfide is added. The temperature was 77 K and the excitation laser was 211.3 nm.

FIG. 3 is a schematic sectional view of an ultraviolet light emitting device having a pn junction according to the present invention, wherein (a) shows an ultraviolet light emitting device formed by growing an n-type diamond semiconductor crystal layer on a p-type diamond semiconductor crystal; (B) shows a p-type diamond semiconductor crystal layer and an n-type
FIG. 3C is a diagram showing an ultraviolet light emitting device formed by laminating a diamond semiconductor crystal layer, and FIG. 3C is a diagram showing an ultraviolet light emitting device formed to have a conductivity type opposite to that of FIG.

FIG. 4 is a diagram showing a result of an analysis of impurities in a depth direction in the ultraviolet light emitting device shown in FIG. 3 (b).

FIG. 5 is a diagram showing an emission spectrum when a current flows in a forward direction through a diamond semiconductor pn junction according to the present invention.

FIG. 6 shows a microwave plasma CV used in the present embodiment.
It is a schematic structure figure of D apparatus.

FIG. 7 is a diagram showing an example of conditions for growing an n-type diamond semiconductor crystal according to the present invention.

FIG. 8 is a diagram showing an example of a growth condition of a p-type diamond semiconductor crystal according to the present invention.

[Explanation of symbols]

 2 p-type diamond semiconductor crystal 4,7 n-type diamond semiconductor crystal layer 6,8,12 pn junction 5 p-type diamond semiconductor crystal layer 10,20,30 ultraviolet light emitting device 11,13,21,23,31,33 electrode 40 Microwave plasma CVD device 41 Microwave generator 45 Tuner 47 Reaction tube 49 Gas supply line 51 Optical window 53 Substrate holder 55 Insulator diamond substrate 57 Temperature control system 59 Microwave plasma

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoichiro Sato 1-1 Namiki, Tsukuba, Ibaraki Pref. Inorganic Materials Research Laboratory (72) Inventor Mika Gamo 1-2-25-13, Ninomiya, Tsukuba, Ibaraki Pref. 4G077 AA03 AB02 BA03 DB16 EB01 EB04 ED06 EF04 EH05 HA01 HA06 5F041 AA11 CA02 CA14 CA33 CA49 CA57 CA64 CA82 CA92 5F045 AA09 AB07 AC19 AD12 AE23 BB05 BB16 CA09 DA60 DA63 DP04 EB02 EB09 CB07 E03 CB09 E03 CB09

Claims (12)

[Claims] 1. A semiconductor crystal having a band gap energy corresponding to an ultraviolet region, comprising a pn junction formed of a p-type semiconductor crystal having an acceptor atom and an n-type semiconductor crystal having a donor atom. An ultraviolet light emitting device that emits ultraviolet light by applying a forward voltage to the device. 2. The semiconductor crystal is diamond,
The ultraviolet light emitting device according to claim 1, wherein the p-type semiconductor crystal is a p-type diamond semiconductor crystal, and the n-type semiconductor crystal is an n-type diamond semiconductor crystal doped with sulfur as a donor atom. 3. The ultraviolet light emitting device according to claim 2, wherein the p-type semiconductor crystal is a p-type diamond semiconductor crystal doped with boron as an acceptor atom. 4. The ultraviolet light emitting device according to claim 2, wherein the p-type diamond semiconductor crystal is a high-pressure synthetic diamond doped with boron. 5. The ultraviolet light emitting device according to claim 2, wherein the p-type diamond semiconductor crystal is a natural IIb type diamond. 6. The ultraviolet light emitting device according to claim 2, wherein the ultraviolet light emitting device has a structure in which the p-type diamond semiconductor crystal and the p-type diamond semiconductor crystal are laminated on an insulating diamond substrate. 7. The method according to claim 1, wherein the donor atom concentration is 10 ¹³ / cm ^{3 or} less.
The ultraviolet light emitting device according to claim 1, wherein the ultraviolet light emitting device has a range of 10 ²¹ / cm ³ . 8. The ultraviolet light emitting device according to claim 1, wherein said pn junction has a structure in which said pn junction is joined at a steepness of an atomic order. 9. A vapor phase synthesis method in which a thin film is grown based on activation of a source gas, a first step of forming a p-type diamond semiconductor crystal layer;
A second step of forming an n-type diamond semiconductor crystal layer in which donor atoms are sulfur, and forming a pn junction structure with a steepness of an atomic order. 10. The p-type diamond semiconductor crystal according to claim 1, wherein the dopant of the p-type diamond semiconductor crystal is boron, and the ratio of boron to the carbon of a hydrocarbon serving as a source of constituent atoms of the p-type diamond semiconductor crystal is 20 to 20,000 ppm.
The method for manufacturing an ultraviolet light emitting device according to claim 9, wherein: 11. The ultraviolet ray according to claim 9, wherein in the second step, a ratio of the sulfur to carbon of a hydrocarbon which is a source of a constituent atom of the diamond semiconductor crystal is 1,000 to 10,000 ppm. Light emitting device manufacturing method. 12. The method according to claim 9, wherein at least one of electricity, heat and light is used to activate the source gas in the vapor phase synthesis method.