JP4294170B2 - Diamond UV light emitting element - Google Patents

Description

【００７５】
表１から明らかなように、絶縁層合成時のプラズマ中の窒素濃度が、２０００ｐｐｍ以上となる比較例１および比較例２の試料では、電流流入による自由励起子再結合発光を得ることができない。その一方で、窒素濃度２００ｐｐｍ以下の実施例１および実施例３の試料では、電流注入による自由励起子再結合発光が得られている。
したがって、本発明にかかる自由励起子再結合発光ダイヤモンド紫外線発光素子を得るには、合成時のプラズマ中の窒素濃度の上限が２００ｐｐｍであることが理解できる。
【００７６】
また、実施例３の自由励起子再結合発光ダイヤモンド紫外線発光素子におけるダイヤモンド絶縁層中の窒素濃度を２次イオン質量分析法（ＳＩＭＳ）で分析したところ、約９０ｐｐｍという値を得た。
この結果から、本発明にかかる自由励起子再結合発光ダイヤモンド紫外線発光素子を得るには、ダイヤモンド絶縁層中の窒素濃度の上限が９０ｐｐｍであることが理解できる。
【００７７】
【発明の効果】
上記の説明のように、本発明にかかる気相合成ダイヤモンド結晶を用いた自由励起子再結合発光ＭＩＳダイヤモンド紫外線発光素子は、短い波長の紫外線を電流注入により発生することができる。
【図面の簡単な説明】
【図１】本発明にかかるダイヤモンド紫外線発光素子の構成を示す概念図。
【図２】本発明にかかるダイヤモンド紫外線発光素子のダイオード特性図。
【図３】本発明にかかるダイヤモンド紫外線発光素子の電流注入による自由励起子再結合発光（紫外線発光）の特性図。
【図４】本発明にかかるダイヤモンド紫外線発光素子と従来のダイヤモンド紫外線発光素子の紫外線発光特性図。
【図５】本発明にかかるホウ素添加半導体ダイヤモンドと同一の条件下で作製した試料からの、電流注入発光スペクトル図。
【図６】本発明の第２の実施の形態にかかるダイヤモンド紫外線発光素子の構成を示す概念図。
【符号の説明】
１ ホウ素添加ダイヤモンド結晶層（半導体層）
３ 無添加ダイヤモンド層（絶縁層）
５ 第１の電極（Ｗ）
７ 第２の電極（Ｗ）
１０，２０ ダイヤモンド紫外線発光素子
２１ 無添加ダイヤモンド結晶基板層
２２ ホウ素添加ダイヤモンド結晶層（半導体層）
２３ 気相合成無添加ダイヤモンド結晶層（絶縁層）
２４ 第１の電極（Ｗ）
２５ 第２の電極（Ｗ）
２６，２７ ワイヤ
５１，７１ ワイヤ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a free exciton recombination luminescent diamond using vapor-phase synthetic diamond that emits ultraviolet rays that can be used in the fields of optical information recording / reading processing, photolithography, optical processing, phosphor excitation light source, etc. The present invention relates to an ultraviolet light emitting element.
[0002]
[Prior art]
Ultraviolet light has a short wavelength and can be used for microfabrication. For example, there are various demands such as increasing recording density using optical recording / reading processing and increasing mounting density using semiconductor microprocessing equipment. is there.
[0003]
Examples of the ultraviolet light source include a deuterium lamp and an excimer laser. However, the deuterium lamp has low efficiency and low brightness in ultraviolet emission. In addition, since excimer lasers use gas, they are large, require water cooling, are inconvenient to handle, and some use halogen or the like. As described above, the conventional ultraviolet light source has various inconveniences in use.
[0004]
Diamond has also been known as a material that emits ultraviolet rays. This diamond ultraviolet light emitting device is small, highly efficient, high in luminance, and excellent in safety.
In particular, when a MIS (Metal-Insulator-Semiconductor) diode structure is employed, the light emission efficiency can be further improved. This is because the energy barrier generated at the semiconductor / insulator interface has an effect of confining carriers contributing to light emission. In the MIS light emitting element, the light emitting portion is near the boundary between the insulating layer and the insulating layer of the semiconductor layer.
[0005]
Conventional MIS diamond light emitting devices using diamond as an insulating layer include, for example, (1) JP-A-4-240784, (2) JP-A-7-307487, (3) JP-A-8-330624, and the like. It is described in.
[0006]
In the ultraviolet light emission of these conventional MIS diamond light emitting elements, boron is added to diamond constituting the semiconductor layer, and additive-free diamond is used for the insulating layer. However, the ultraviolet light emission of these conventional diamond light emitting elements is dominated by ultraviolet light emission due to impurities or lattice defects, and free exciton recombination light emission having a short wavelength inherent to diamond is not dominant.
In addition, these publications describe free exciton recombination emission, which is a cathodoluminescence (CL) method in which an electron beam is emitted from the outside in order to confirm the characteristics of diamond. It only explains the results measured by.
[0007]
That is, the ultraviolet light-emitting device disclosed in Japanese Patent Laid-Open No. 4-240784 is based on boron band light emission having a peak of ultraviolet light emission at 260 nm, and free exciton recombination light emission is not dominant.
Further, the short wavelength light emitting element disclosed in Japanese Patent Laid-Open No. 7-307487 is based on boron-bound exciton recombination light emission having a peak of ultraviolet light emission at 238 nm, and is free exciton recombination light emission having good light emission efficiency. The UV emission by is not dominant.
[0008]
When considering the MIS diamond ultraviolet light emitting element, the light emission caused by such impurities and defects has a longer wavelength than the intrinsic light emission, which is disadvantageous as the mechanism of the short wavelength light emitting element. In order to improve the emission intensity, high-density defects or high-concentration impurities must be introduced into the crystal. As a result, the crystal quality is lowered and the intensity of ultraviolet light emission is reduced. Furthermore, emission peaks with different wavelengths induced by the introduction of impurities / defects consume a part of the implantation energy, and the useful ultraviolet emission efficiency is also lowered. For these reasons, light emission due to impurities and defects is not practical as a mechanism of a current injection type light emitting device.
[0009]
On the other hand, free exciton recombination light emission is intrinsic light emission in each material, and generally has the shortest wavelength and the highest density of states among the light emission obtained from the material. It is most desirable to realize In diamond, an intrinsic spectrum related to free exciton recombination emission is examined by an analytical method such as cathodoluminescence. The energy of free excitons of diamond at room temperature corresponds to a wavelength of 229 nm, but actually light emission called a phonon sideband group appearing in the vicinity of 235 nm, 242 nm, 249 nm, and 257 nm is mainly observed. In general, all of these are referred to as “free exciton recombination emission”, and particularly suitable as an ultraviolet light emitting element is emission having an energy of around 235 nm. Here, this emission is referred to as “free exciton recombination”. This is called “coupled emission”.
[0010]
[Problems to be solved by the invention]
As described above, the conventional MIS diamond ultraviolet light emitting elements have insufficient quality of diamond crystals forming the light emitting layer, and contain many impurities and defects. For this reason, when configured as a current injection type light emitting device, sufficient emission intensity could not be obtained for free exciton recombination light emission which is most advantageous in practical use.
[0011]
For example, in the spectrum of a light-emitting element described in JP-A-7-307487, the intensity of free exciton recombination emission (235 nm), which is the original emission of diamond, is an example of constrained excitation due to impurities and defects. It is clearly small with respect to the intensity of the child light emission (238 nm), which is less than a fraction. That is, although this light emitting element employs a structure in which the insulating layer is a light emitting layer, light emission (238 nm) due to impurities that cannot be present in the insulating layer is obtained. This means that it does not function as the main light emitting layer. This leads to low practical device light emission efficiency, which is inferior in practical use.
[0012]
On the other hand, in the case of the MIS diamond light-emitting device of the present invention, free exciton recombination light emission is larger than the emission intensity of bound excitons, which are an example of impurities and defects, and the intensity ratio is several times or more. This is characterized by the fact that it is defined as ultraviolet light emission in which free exciton recombination light emission is dominant.
[0013]
An object of the present invention is to provide a light emitting element by current injection excitation in which free exciton recombination light emission having a short wavelength intrinsic to diamond is dominant, using a diamond MIS structure.
[0014]
This will be described with reference to FIG.
FIG. 4 is a characteristic diagram showing the light emission state by current injection in the ultraviolet region of the MIS diamond ultraviolet light emitting device according to the present invention and the conventional MIS diamond ultraviolet light emitting device disclosed in Japanese Patent Laid-Open No. 7-307487. The solid line shows the characteristics of the diamond light emitting device according to the present invention, and the broken line shows the characteristics of the conventional diamond light emitting device. In FIG. 4, the scales of the vertical axis of the solid line and the broken line are normalized by the maximum light emission peak intensity for comparison.
[0015]
As is clear from the figure, the diamond light-emitting device according to the present invention has a peak at 235 nm, which is emission due to free exciton recombination emission, and is 238 nm, which is emission of bound exciton, which is an example of impurities and defects. It is extremely large and dominant in comparison with the strength of.
However, the conventional diamond light-emitting element has a peak at 238 nm, which is a bound exciton emission, which is an example of impurities and defects, and has a low intensity at 235 nm, which is emission by free exciton recombination emission.
That is, in the present invention, ultraviolet light emission in which free exciton recombination light emission is dominant can be obtained.
[0016]
[Means for Solving the Problems]
In order to achieve the above object, the invention of claim 1 is provided with a semiconductor layer made of a diamond crystal and one surface of the semiconductor layer. Additive-free An insulating layer made of diamond crystals, The semiconductor layer is composed of diamond crystals added with boron obtained by a high temperature and high pressure method in the presence of a nitrogen removing agent, and the insulating layer is composed of diamond crystals obtained by vapor phase synthesis with a nitrogen concentration of 90 ppm or less. , Emits light when excited by current injection 235nm Free exciton recombination emission Do not observe light emission due to impurities and lattice defects in the region with a peak and a wavelength of 300 nm or less A diamond ultraviolet light emitting element was obtained.
[0017]
A second aspect of the present invention is the diamond ultraviolet light emitting element according to the first aspect, wherein the diamond insulating layer functions as a light emitting layer.
[0020]
Claim 3 The invention of claim 1 or claim 2 In the diamond ultraviolet light-emitting device, the number of nitrogen atoms in the plasma at the time of crystal synthesis of the gas phase synthetic diamond insulating layer is 200 ppm or less as a ratio to the number of carbon atoms. Crystals synthesized in a gas phase under various atmospheres It was.
[0021]
Claim 4 The invention of claim 1 to claim 1 3 In the diamond ultraviolet light-emitting device according to any one of the above, the diamond insulating layer is a diamond crystal obtained by a microwave plasma vapor phase synthesis method (MW-CVD method).
[0022]
Claim 5 The invention of claim 1 to claim 1 4 In the diamond ultraviolet light-emitting device according to any one of the above, the diamond insulating layer is a diamond crystal obtained by homoepitaxial growth.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
The structure of a free exciton recombination luminescence MIS diamond ultraviolet light emitting device using the vapor phase synthetic diamond crystal according to the first embodiment of the present invention will be described in detail with reference to FIG. Hereinafter, a free exciton recombination light-emitting MIS diamond ultraviolet light-emitting device obtained in this embodiment is referred to as Example 1.
FIG. 1 is a cross-sectional view schematically showing a configuration of a diamond ultraviolet light emitting element 10 that emits free exciton recombination using a vapor phase synthetic diamond crystal provided on a diamond crystal substrate.
[0027]
A free exciton recombination light-emitting diamond ultraviolet light-emitting device 10 includes a boron-added high-pressure diamond crystal layer (semiconductor layer) 1 and a diamond crystal layer grown by vapor-phase synthesis on the first surface of the boron-added high-pressure diamond crystal layer ( Insulating layer) 3, first electrode 5 made of tungsten (W) provided on the growth surface of vapor-phase synthetic diamond crystal layer 3, and tungsten (W) provided on the second surface of high-pressure synthetic diamond crystal layer 1. And the second electrode 7.
[0028]
A wire 51 is connected to the first electrode 5, and a wire 71 is connected to the second electrode 7.
[0029]
The semiconductor layer 1 and the insulating layer 3 are made of high-quality diamond that contains only trace amounts of impurities other than lattice defects and dopants.
[0030]
The diamond crystal layer 1 constituting the free exciton recombination light emitting diamond ultraviolet light emitting element 10 is made of a high pressure synthetic diamond crystal obtained by a high temperature high pressure method described below.
Here, the high-temperature and high-pressure method is a so-called temperature difference method, in which a carbon raw material is dissolved in a flux metal in a temperature and pressure region where diamond can stably exist, and the carbon is seed crystal (diamond fine crystal). This is a method for producing diamond deposited on a crystal.
Diamond manufacturing methods using the temperature difference method are disclosed in, for example, Japanese Patent Application Laid-Open Nos. 4-108532 and 5-200271.
[0031]
As the flux metal, a material capable of sufficiently dissolving carbon and functioning as a catalyst for promoting the crystal growth of diamond is used. As the flux metal, as described in the literature (for example, Kanda et al., Journal of Chemical Society of Japan 1981, vol. 9, p. 1349 to 1355), specifically, iron (Fe) and / or cobalt (Co) and / or An alloy containing nickel (Ni) is used.
[0032]
The high-pressure diamond crystal layer (semiconductor layer) 1 is manufactured under the following growth conditions using a temperature difference method (high-temperature high-pressure method).
[0033]
[Growth conditions]
Carbon raw material: pyrolytic carbon; boron (B) added as a dopant at 1000 ppm
Flux metal: Iron (Fe) -Cobalt (Co) alloy
Nitrogen remover: Aluminum (Al), Titanium (Ti), Zirconium (Zr)
Growth temperature: 1450 ° C
Synthesis pressure: 6.5 GPa
Growth time: 61.5 hours
Here, the nitrogen removing agent refers to a metal that has a higher affinity for nitrogen than carbon and can be added to the flux metal to reduce the nitrogen concentration in the diamond crystal. Specific examples include Al, Ti, Zr and the like as described in the literature (H. Sumiya and S. Satoh, Diam. Related Matter., Vol. 5, p. 1359 (1996), etc.).
[0034]
A seed crystal was arranged and synthesized so that the growth direction was [001] under the above conditions. As a result of the synthesis, a light blue single crystal having {100} and {111} facets weighing 64.0 mg was obtained.
This crystal was polished into a plate having a thickness of 0.5 mm, 2 mm × 2 mm by Skyf disk polishing.
When this crystal was measured using infrared absorption spectroscopy, the effective acceptor concentration in the crystal was 9 ppm. Further, when the nitrogen concentration in the crystal was similarly quantified by infrared spectroscopy, a value of 0.1 ppm or less was obtained.
[0035]
On this boron-added diamond semiconductor layer 1, an additive-free diamond insulating layer 3 that is homoepitaxially grown by the MW-CVD method is grown.
[0036]
The diamond insulating layer 3 was formed by homoepitaxial growth using a MW-CVD apparatus using high-purity methane gas and high-purity hydrogen gas under the following conditions.
In the synthesis, in order to clean the substrate surface, H ₂ Plasma treatment was applied for 10 minutes.
[0037]
[Growth conditions]
Substrate: Boron-added high-pressure diamond crystal
MW output: 500W
Gas: CH _Four ; 0.2%, H ₂ 99.8%
Gas purity: CH _Four 99.9999%, H ₂ ; 99.9999%
Flow rate: 500ml / min
Composite pressure: 40 Torr
Synthesis time: 20min
[0038]
The film thickness of the diamond insulating layer obtained under the above conditions was approximately 20 nm. Since a hydrogen-terminated conductive layer is formed on the surface of a diamond film usually produced by a gas phase synthesis method, the sample was treated with a mixed chrome acid for 10 minutes to insulate the surface.
[0039]
A first electrode 5 made of tungsten was formed on the additive-free insulating vapor-phase synthetic diamond film (insulating layer) 3 by sputtering as follows.
[0040]
[Sputtering conditions]
Target metal: Tungsten (W)
Gas: Ar; 30 ml / min, pressure: 5 mTorr
Substrate temperature: 200 ° C
Voltage: 700V
Current: 1A
Deposition time: 2 min
Film thickness: 360mm
[0041]
Next, a positive photoresist layer is formed on the tungsten layer (first electrode) 5 by, for example, spin coating (photoresist viscosity: 15 Cp, rotation speed: 3,500 rpm, time: 30 seconds), and then 80 in the atmosphere. After drying at a temperature of 30 ° C. for 30 minutes, a mask aligner is used to expose unnecessary portions with ultraviolet rays (ultraviolet light exposure: 350 mJ / cm ² The exposed portion is removed with a photoresist developer, and the resist film is formed by drying in the atmosphere at a temperature of 130 ° C. for 30 minutes.
[0042]
Using this resist film, the tungsten layer is etched with aqua regia (hydrochloric acid: nitric acid = 3: 1) for 3 minutes.
Thereafter, ultrasonic cleaning is performed using acetone for 3 minutes, the resist is removed, and the electrode 5 is formed.
[0043]
Subsequently, a second electrode 7 was also formed on the lower surface of the sample in the same manner as the first electrode 5 was formed.
[0044]
The current-voltage characteristics of the free exciton recombination luminescence MIS diamond ultraviolet light emitting element 10 using the vapor phase synthetic diamond crystal thus obtained will be described with reference to FIG. FIG. 2 shows the voltage (V) applied between the first electrode 5 and the second electrode 7 on the horizontal axis, and the current (mA) flowing from the first electrode 5 to the second electrode 7 on the vertical axis. .
[0045]
As is apparent from the figure, when a reverse bias voltage is applied so that the first electrode 5 has a positive potential, the leakage current is 0.1 mA or less until 200 V is applied. At the time of forward bias in which a voltage is applied so that the first electrode 5 becomes negative, the current suddenly increases from about −120V. This result means that diode characteristics are obtained by the MIS structure.
[0046]
The result of measuring the current injection emission spectrum will be described with reference to FIG.
In the figure, light emission was measured when a voltage of 140 V was applied between the electrodes and a current of 4 mA was applied. The horizontal axis represents wavelength (nm) and the vertical axis represents light emission intensity (arbitrary scale). .
[0047]
As is clear from the figure, extremely strong free exciton recombination emission (main peak wavelength 235 nm and sub peak (phonon sideband) wavelength 242 nm) can be obtained in the ultraviolet region, and impurities are emitted in the region of wavelength 300 nm or less. In addition, light emission caused by lattice defects cannot be observed. This result shows that a diamond light-emitting device in which free exciton recombination light emission is dominant is obtained which is most practically advantageous in the device of the present invention.
[0048]
On the other hand, FIG. 5 shows an emission spectrum when a light-emitting element in which a tungsten electrode is manufactured in the same manner as in Example 1 is subjected to a current injection operation in a boron-added diamond semiconductor manufactured by a high-temperature and high-pressure method under the same conditions. In this case, boron-bound exciton recombination emission (wavelength: 238 nm) caused by impurities appears. From the comparison with this result, in the device of the present invention, the contribution of light emission from the boron-added diamond semiconductor layer is relatively small, which means that the diamond insulating layer functions as a main light emitting layer.
[0049]
That is, according to the present invention, the ultraviolet light emission generated by current injection is mostly free exciton recombination light emission with high efficiency, and light emission due to inefficient impurities / lattice defects hardly occurs. A diamond ultraviolet light emitting element having a MIS structure that emits free exciton recombination efficiently can be obtained.
Furthermore, according to the present invention, it is possible to obtain a diamond ultraviolet light emitting element having a MIS structure with high luminous efficiency, in which the diamond insulating layer can function as a main light emitting layer.
[0050]
As described above, according to the present invention, it is possible to provide a MIS structure diamond ultraviolet light emitting element that operates by current injection and in which free exciton recombination light emission is dominant.
[0051]
In the above description, the insulating diamond crystal film 1 may be single crystal or polycrystalline.
[0052]
Another embodiment of a free exciton recombination luminescence MIS diamond ultraviolet light emitting device by current injection according to the present invention will be described with reference to FIG.
FIG. 6 is a cross-sectional view schematically showing a configuration of a MIS structure diamond ultraviolet light emitting element 20 in which free exciton recombination light emission using a gas phase synthetic diamond crystal provided on a diamond crystal substrate is dominant. Hereinafter, this MIS structure diamond ultraviolet light emitting element 20 is referred to as Example 2.
[0053]
A free exciton recombination luminescent diamond ultraviolet light emitting device 20 includes a high-pressure diamond crystal substrate 21 made of an additive-free diamond crystal obtained by a high-temperature and high-pressure method, and boron-added grown on the surface of the high-pressure diamond crystal substrate 21 by vapor phase synthesis. Gas phase synthesized diamond crystal layer (semiconductor layer) 22 and boron-added gas phase synthesized diamond crystal layer 22 are grown on a part of the growth surface by gas phase synthesis, and an additive-free high quality gas phase synthesized diamond crystal layer (insulating) Layer) 23, a first electrode 24 made of tungsten (W) provided on the surface of the high-quality vapor-phase synthetic diamond crystal layer (insulating layer) 23, and the boron-added vapor-phase synthetic diamond crystal layer (semiconductor layer) ) 22 and a second electrode 25 made of tungsten (W) provided on a part of the surface of 22.
[0054]
A wire 26 is connected to the first electrode 24, and a wire 27 is connected to the second electrode 25.
[0055]
A diamond crystal substrate 21 serving as a substrate of the free exciton recombination luminescent diamond ultraviolet light emitting element 20 is made of a high-pressure synthetic diamond crystal obtained by a high-temperature high-pressure method in the same manner as the diamond crystal layer shown in the first embodiment.
[0056]
Similar to the first embodiment, the high-pressure synthetic diamond crystal substrate 21 is manufactured under the following growth conditions using a temperature difference method (high-temperature high-pressure method).
[0057]
[Growth conditions]
Raw material carbon: pyrolytic carbon
Flux metal: Iron (Fe) -Cobalt (Co) alloy
Nitrogen remover: Aluminum (Al), Titanium (Ti), Zirconium (Zr)
Growth temperature: 1450 ° C
Synthesis pressure: 6.5 GPa
Growth time: 90 hours
[0058]
A seed crystal was arranged and synthesized so that the growth direction was [001] under the above conditions. As a result of synthesis, a colorless single crystal having a facet of {100} and {111} weighing 70.5 mg was obtained.
This crystal was polished into a plate having a thickness of 0.5 mm, 2 mm × 2 mm by Skyf disk polishing.
[0059]
On this additive-free high-pressure synthetic diamond crystal substrate 21, a boron-added diamond semiconductor layer 22 that is homoepitaxially grown by the MW-CVD method is grown.
[0060]
The boron-added vapor phase synthetic diamond semiconductor layer 22 was formed by homoepitaxial growth using a high-purity methane gas and a high-purity hydrogen gas by a MW-CVD apparatus under the following conditions.
In the synthesis, in order to clean the substrate surface, H ₂ Plasma treatment was applied for 10 minutes.
[0061]
[Growth conditions]
Substrate: IIa (100) high-pressure diamond crystal
MW output: 600W
Gas: CH _Four ; 0.1%, H ₂ 99.9%
Gas purity: CH _Four 99.9999%, H ₂ ; 99.9999%
Boron source: Trimethylboron (B (CH _Three ) _Three )
Ratio of the number of nitrogen atoms and the number of carbon atoms in the plasma during vapor phase synthesis (B / C): 100 ppm
Flow rate: 500ml / min
Composite pressure: 40 Torr
Temperature: 850-900 ° C
Synthesis time: 30 hours
Film thickness: 5μm
[0062]
On the boron-added diamond semiconductor layer 22, an additive-free diamond insulating layer 23 that is homoepitaxially grown by the MW-CVD method is grown.
[0063]
The additive-free high-quality diamond insulating layer 23 was formed by homoepitaxial growth using a MW-CVD apparatus using high-purity methane gas and high-purity hydrogen gas under the following conditions.
[0064]
[Growth conditions]
MW output: 600W
Gas: CH _Four ; 0.2%, H ₂ 99.8%
Gas purity: CH _Four 99.9999%, H ₂ ; 99.9999%
Flow rate: 500ml / min
Composite pressure: 40 Torr
Temperature: 850-900 ° C
Synthesis time: 2 hours
Film thickness: 0.2 μm
[0065]
An aluminum mask was formed on the additive-free gas phase synthetic diamond insulating layer 23 by photolithography.
[0066]
A part of the additive-free gas phase synthetic diamond crystal layer (insulating layer) 23 is removed by reactive ion etching (RIE). The mask was made of aluminum and etched under the following conditions.
[Etching conditions]
Gas: O ₂ ; 20 ml / min, CF _Four 2.5 ml / min, pressure; 50 mTorr
RF power: 200W
Etching time: 12 min
[0067]
The surface of the boron-added gas phase synthetic diamond crystal layer (semiconductor layer) 22 exposed by the etching process and the surface of the additive-free gas phase synthetic diamond crystal layer (insulating layer) 23 left by the etching process are the same as in Example 1. Then, tungsten electrodes 24 and 25 are produced by photolithography.
The conditions for forming the tungsten electrode were as follows.
[0068]
[Sputtering conditions]
Gas: Ar; 30 ml / min, pressure: 5 mTorr
Substrate temperature: 200 ° C
Voltage: 700V
Current: 1A
Deposition time: 2 min
Film thickness: 360mm
[0069]
Thus, the MIS diamond ultraviolet light emitting element 20 using the vapor phase synthetic diamond crystal is formed.
[0070]
When current was injected into the MIS diamond ultraviolet light emitting element 20 having the above structure, free exciton recombination light emission having a 235 nm peak similar to FIG. 5 was obtained.
[0071]
Hereinafter, the dependence of the free exciton recombination emission on the nitrogen concentration in the insulating layer 3 during the current injection operation of the MIS structure diamond ultraviolet light emitting device of Example 1 shown in FIG. 1 will be described.
Nitrogen is an impurity that is easily incorporated into diamond crystals and inhibits free exciton recombination luminescence. Therefore, control of the nitrogen concentration in the diamond insulating layer, which is the main light emitting layer, is very important for obtaining a MIS structure diamond ultraviolet light emitting device in which free exciton recombination light emission is dominant according to the present invention.
[0072]
When the diamond insulating layer was produced by the MW-CVD synthesis method, the following samples were produced by changing the nitrogen concentration in the plasma. Other conditions are the same as those in Example 1.
[0073]
The ratio N / C between the number of nitrogen atoms N and the number of carbon atoms C in the plasma during synthesis of each sample was 100 ppm or less in Example 1, 200 ppm in Example 3, 2000 ppm in Comparative Example 1, and 20000 ppm in Comparative Example 2. there were. In addition, in Example 1, although intentional nitrogen addition was not performed, the result of the component analysis of the hydrogen and methane gas used for the synthesis, and the nitrogen concentration calculated from the leak amount of the synthesizer are described.
Table 1 shows the results of examining these samples for the presence or absence of free exciton recombination (FE) emission during the current injection operation.
[0074]
[Table 1]

[0075]
As is clear from Table 1, in the samples of Comparative Example 1 and Comparative Example 2 in which the nitrogen concentration in the plasma at the time of synthesizing the insulating layer is 2000 ppm or more, free exciton recombination emission due to current inflow cannot be obtained. On the other hand, in the samples of Example 1 and Example 3 having a nitrogen concentration of 200 ppm or less, free exciton recombination emission by current injection was obtained.
Therefore, in order to obtain the free exciton recombination luminescent diamond ultraviolet light emitting device according to the present invention, it can be understood that the upper limit of the nitrogen concentration in the plasma during synthesis is 200 ppm.
[0076]
Moreover, when the nitrogen concentration in the diamond insulating layer in the free exciton recombination luminescent diamond ultraviolet light emitting device of Example 3 was analyzed by secondary ion mass spectrometry (SIMS), a value of about 90 ppm was obtained.
From this result, it can be understood that the upper limit of the nitrogen concentration in the diamond insulating layer is 90 ppm in order to obtain the free exciton recombination light emitting diamond ultraviolet light emitting device according to the present invention.
[0077]
【The invention's effect】
As described above, the free exciton recombination luminescence MIS diamond ultraviolet light emitting element using the vapor phase synthetic diamond crystal according to the present invention can generate ultraviolet light having a short wavelength by current injection.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram showing the configuration of a diamond ultraviolet light emitting device according to the present invention.
FIG. 2 is a diode characteristic diagram of the diamond ultraviolet light emitting element according to the present invention.
FIG. 3 is a characteristic diagram of free exciton recombination light emission (ultraviolet light emission) by current injection in the diamond ultraviolet light emitting element according to the present invention.
FIG. 4 is an ultraviolet light emission characteristic diagram of a diamond ultraviolet light emitting device according to the present invention and a conventional diamond ultraviolet light emitting device.
FIG. 5 is a current injection emission spectrum diagram of a sample manufactured under the same conditions as the boron-added semiconductor diamond according to the present invention.
FIG. 6 is a conceptual diagram showing a configuration of a diamond ultraviolet light emitting element according to a second embodiment of the present invention.
[Explanation of symbols]
1 Boron-added diamond crystal layer (semiconductor layer)
3 Additive-free diamond layer (insulating layer)
5 First electrode (W)
7 Second electrode (W)
10,20 Diamond UV light emitting device
21 Additive-free diamond crystal substrate layer
22 Boron-added diamond crystal layer (semiconductor layer)
23 Gas phase synthesis additive-free diamond crystal layer (insulating layer)
24 1st electrode (W)
25 Second electrode (W)
26, 27 wires
51, 71 wire

Claims (5)

A semiconductor layer made of a diamond crystal and an insulating layer made of an additive-free diamond crystal provided on one surface of the semiconductor layer;
The semiconductor layer is composed of diamond crystals added with boron obtained by a high temperature and high pressure method in the presence of a nitrogen removing agent,
The insulating layer is composed of diamond crystals having a nitrogen concentration of 90 ppm or less obtained by a vapor phase synthesis method,
A diamond ultraviolet light emitting element that emits light by excitation by current injection , has a peak in recombination light emission at 235 nm, and does not observe light emission due to impurities or lattice defects in a wavelength region of 300 nm or less .   The diamond ultraviolet light emitting element according to claim 1, wherein the diamond insulating layer functions as a light emitting layer. Nitrogen atoms in the plasma during the CVD diamond insulating layer crystal synthesis according to claim 1 or claim 2 is a gas phase synthesized diamond crystals under the following atmosphere 200ppm the ratio to the number of carbon atoms Diamond ultraviolet light emitting element. The diamond ultraviolet light emitting element according to any one of claims 1 to 3, wherein the diamond insulating layer is a diamond crystal obtained by a microwave plasma vapor phase synthesis method. The diamond ultraviolet light emitting element according to any one of claims 1 to 4 , wherein the vapor phase synthetic diamond insulating layer is a diamond crystal obtained by homoepitaxial growth .

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