JP4766363B2 - Diamond ultraviolet light sensor element and manufacturing method thereof - Google Patents

Description

The present invention relates to a diamond ultraviolet light sensor element and a manufacturing method thereof .

A diamond semiconductor has a considerably large band gap of about 5.5 eV (corresponding to about 225 nm at an optical wavelength) at room temperature, and exhibits electrical conductivity as an insulator in an intrinsic state to which no dopant (impurity) is added. As a method of growing a single crystal thin film, a microwave-excited plasma vapor phase growth method using an atmosphere substantially containing carbon and hydrogen, for example, CH ₄ (methane) and H ₂ (hydrogen) gas has been developed (Patent Document 1). Has been widely spread. In addition, it is also widely used to control p-type conductivity by adding boron as a dopant in microwave-excited plasma vapor deposition.

Since the microwave-excited plasma vapor deposition method is a vapor deposition method using an atmosphere containing hydrogen, it is known that the surface of the grown diamond single crystal film is substantially covered with hydrogen. ing. That is, there is a CH molecular structure in which dangling bonds of carbon atoms (C) are terminated by hydrogen atoms (H) on the surface (hereinafter referred to as “hydrogenation”). It is known that a surface conductive layer in which holes of main carriers are localized near the surface (within 2 nm) is generated in the diamond near the surface. This surface electrical conductive layer is also known to exist in undoped and boron doped (100), (111) plane single crystal thin films, and polycrystalline thin films as well.

The generation mechanism of this surface conductive layer is in a state of great debate worldwide, but at least experimentally, this surface conductive layer exists stably (1) up to about 200 ° C. and (2) is hydrogenated. It is known that it only occurs on the diamond surface. By applying a solution treatment (oxidation treatment) to remove surface-bonded hydrogen, for example, immersion in a boiled sulfuric acid / nitric acid mixture,
This surface conductive layer is also known to disappear, and the present inventors have also confirmed.

As a so-called photoconductive sensor element that detects ultraviolet light irradiated to the light receiving portion by a change in the electrical resistance of the light receiving portion or a change in the amount of photoinduced current, the detection sensitivity is also applicable to visible light in the wavelength range of 400 nm to 650 nm. As well as Al _x Ga _1-x N (0 ≦ x ≦ 1) semiconductors and diamond semiconductors that do not have any detection sensitivity to the visible light or the noise light in the infrared region, etc. What has been considered is conventionally considered.

The photodetection principle of these photoconductive sensor elements is to generate electron-hole pairs in the semiconductor by irradiating the semiconductor of the light receiving part with light having energy greater than the band gap, and the electric resistance of this carrier is reduced. A change or a change in the amount of photoinduced current is detected. Therefore, an element structure can be constructed with a two-terminal element in which two electrodes are bonded to a semiconductor material, and an extremely simplified ultraviolet sensor element can be manufactured.

As an example of applying a diamond semiconductor to an ultraviolet light sensor element, for example, Non-Patent Document 1
Describes a photoconductive sensor element using a surface conductive layer of a polycrystalline diamond thin film as a light receiving part and achieving a detection sensitivity of 0.03 A / W with respect to 200 nm ultraviolet light irradiation. Yes. The principle of light detection is explained by the conventional principle of detecting a change in current applied between two electrodes by generating electron-hole pairs in diamond when diamond semiconductor is irradiated with light with energy above the band gap. Detection sensitivity. Non-Patent Document 2 discloses that in a photoconductive sensor element using a polycrystalline diamond film from which a surface conductive layer has been removed by an oxidation treatment as a light receiving portion, 0.02 A / W
However, the detection sensitivity is insufficient for practical use.

As an example of the prior art, Patent Document 2 discloses a diamond ultraviolet light sensor using, as a light receiving portion, a diamond-mond polycrystalline thin film having a thickness of 40 μm or a (100) and (111) -oriented thin film and a surface from which bound hydrogen is removed from the surface. This is a technology related to elements, and its detection sensitivity is insufficient for practical use. Patent Document 3 is a diamond ultraviolet light sensor element using a surface conductive layer of diamond as a light receiving part, and its detection sensitivity wavelength has characteristics over the entire visible light range,
This is a photoconductive sensor element that utilizes defect levels in the band gap of diamond.
It is not possible to selectively detect 30 nm ultraviolet rays.
HJ Looi, MD Whitfield, and RB Jackman, Appl. Phys. Letts. 74, 3332 (1999) RD McKeag and RB Jackman, Diamond Relat. Mater. 7, 513 (1998) Japanese Examined Patent Publication No. 59-027754 (Patent No. 1272929) Japanese Patent Laid-Open No. 11-248531 Japanese Patent Application Laid-Open No. 11-097721

In a conventional photoconductive light receiving element using Si, Al _x Ga _1-x N (0 ≦ x ≦ 1), and a diamond semiconductor as a light receiving portion, irradiated ultraviolet light is absorbed inside the semiconductor of the light receiving portion. Therefore, the ratio of the magnitude of the photocurrent to the power of the irradiated ultraviolet light, that is, the quantum efficiency is 100.
% Of ideal elements, for example, the limit values of light receiving sensitivity are 0.18 A / W and 0.19 A / W for ultraviolet light with a wavelength of 220 nm and 230 nm, respectively, and light for extremely weak light The change in the amount of induced current was extremely small.

The present invention provides a diamond ultraviolet light sensor element in which the light receiving sensitivity to ultraviolet light having a wavelength of 230 nm or less is increased by at least about 15000 times the above limit value while avoiding the complexity of the element structure and taking advantage of the characteristics of the photoconductive sensor element. It is to provide.

Specifically, ultraviolet light with a wavelength of 230 nm or less irradiated to the light receiving unit is detected by a change in the electrical resistance of the light receiving unit or a change in the amount of photo-induced current, and visible light with a wavelength of 400 nm or more has no detection sensitivity. A conductive sensor element, a flame sensor and an ultraviolet light sensor using the photoconductive sensor element. As the structure of the photosensor element, a photoconductive type, a pn type, a pin type, and a Schottky diode type have already been industrialized. In particular, the present invention relates to a photoconductive sensor element having a two-terminal electrode.

The present invention also provides: (1) a photoconductive sensor element that detects light irradiated to the light receiving portion by a change in electrical resistance of the light receiving portion material or a change in photoinduced current, and substantially comprises carbon and hydrogen. in an atmosphere containing, deposited by plasma vapor deposition or vapor deposition, the diamond ultraviolet light sensor element having a light receiving portion of the treated single-crystal diamond king aqueous solution was boiled after film formation, It is.

The present invention is also (2) the diamond ultraviolet light sensor element according to (1), wherein two electrodes are bonded to the hydrogenated surface of the diamond single crystal .

The present invention also relates to (3) mainly serving photoinduced current component flows through the table Menden conductive layer of hydrogenated near the surface of the diamond single crystal (1) or (2) diamond ultraviolet light sensor device according to .
The present invention also relates to (4) a method of manufacturing a photoconductive sensor element for detecting light irradiated to a light receiving part by a change in electrical resistance of a light receiving part material or a change in a photo-induced current. A step of forming a diamond single crystal on a substrate using a plasma vapor deposition method or a vapor deposition method, and a step of treating the diamond single crystal in an aqueous solution boiled after the film formation. And a step of forming two electrodes on the hydrogenated surface of the diamond single crystal, and a method for producing a diamond ultraviolet light sensor element.

The ultraviolet light sensor element of the present invention is an ultraviolet light sensing mechanism resulting from a fundamentally different mechanism from a sensor element based on electrical conduction of carriers generated by a light absorption process in a conventional semiconductor, and the conventional Overcoming the limit of detection sensitivity, it is improved by about 4 digits. Although it is expected to be put to practical use as an ultraviolet light sensor element, technical improvement is required for improving its stability for industrialization. Generally, high-quality electrical and optical diamond semiconductors are CH ₄ (methane).
And by epitaxial growth on a diamond (100) or (111) plane single crystal substrate synthesized at high pressure by a microwave-excited plasma vapor phase growth method using H ₂ (hydrogen) as a source gas.

Although this method is also used in the embodiments of the present invention, since it is a vapor phase growth method using an atmosphere containing hydrogen, a hydrogenated diamond surface conductive layer is used for the light receiving portion.

In the photoconductive sensor element in which the two-terminal electrode shown in FIGS. 1 and 2 is formed on the hydrogenated surface conductive layer, the present invention has a light receiving sensitivity by irradiating the surface conductive layer with ultraviolet light having a wavelength of 220 nm. 0 which is a theoretical limit value based on photoconductivity of photoexcited carriers in a conventional semiconductor
. Realize 3100 A / W which is at least 15000 times 18 A / W. It has also been confirmed that such a high light receiving sensitivity cannot be realized when the surface of the diamond single crystal film or the surface of the high pressure synthetic diamond substrate subjected to the oxidizing solution treatment in the element structure is used as a light receiving portion.

Conducted by carriers (electrons or holes) generated by absorption of ultraviolet light (energy 5.6 eV) having a energy larger than the energy gap of 5.5 eV of diamond semiconductor at a wavelength of 220 nm inside the diamond semiconductor. In the electric conduction mechanism, the light receiving sensitivity of about 0.2 A / W is the limit. On the other hand, if the molecular excitation mechanism of ultraviolet light to the hydrogenated surface structure responsible for the generation of holes in the surface conductive layer and the lattice relaxation phenomenon based on photoexcitation are utilized, a substantial increase in the surface conductive layer will occur. It is considered that the positive hole concentration can be dramatically increased, and it is assumed that the light receiving sensitivity of 3100 A / W is actually related to the molecular excitation mechanism.

The photoconductive sensor element shown in FIGS. 1 and 2 was manufactured by the process described below, and the light receiving sensitivity characteristic with respect to ultraviolet light was measured.

As shown in FIG. 1, diamond and B (boron), which is a p-type dopant element, are added.
Epitaxial single crystal film 2 includes CH ₄ (methane) as a source gas, H ₂ (hydrogen) as a carrier gas for dilution, and 1 Vol (0.01)% hydrogen diluted B (CH ₃ ) ₃ (trimethylboron) as a dopant. By microwave-excited plasma vapor phase epitaxy used as a source gas for B,
A thickness of 0.5 μm was grown on an Ib diamond (100) single crystal substrate 3 having a length of 2.5 × width of 2.5 × thickness of 0.5 mm produced by a high pressure synthesis method. The growth conditions at this time were as follows. Substrate temperature 930 ° C., growth pressure 80 Torr, and microwave power 400
W, CH ₄ flow rate 500 sccm, CH ₄ / H ₂ concentration ratio 0.06% (vol), and B (
The CH ₃ ) ₃ / CH ₄ concentration ratio was 0.01 (vol)%, and the growth time was 2 hours.

The grown diamond (100) plane single crystal film 2 was immersed in boiling aqua regia for 10 minutes and then overflow washed with ultrapure water. Thereafter, ultrasonic cleaning was performed in a solution of each of acetone and isopropyl alcohol, and resist patterning for producing the electrode 1 shown in FIGS. 1 and 2 was performed by photolithography. Thereafter, Ti (thickness 15 nm) and Au (thickness 150 nm) are stacked and deposited by electron beam evaporation.
The comb-shaped two-terminal TiAu electrode 1 pattern shown in FIGS. 1 and 2 was formed by the lift-off method. The electrode width (corresponding to 1L in FIGS. 1 and 2) of the TiAu electrode 1 was 10 μm, and the electrode interval (corresponding to 2L in FIGS. 1 and 2) was 10 μm. Of the two terminal electrodes,
The area of one electrode is 8.1 × 10 ⁻⁴ cm ² , and the light receiving area is 5.3 × 10 ⁻⁴ c.
It was m ^2.

The photoconductive sensor element thus produced was set in a vacuum chamber equipped with a two-short prober, and the inside of the chamber was maintained at a vacuum degree of 0.05 Pa by a turbo molecular pump. The emitted light from the xenon mercury lamp was monochromatized in the range of 215 to 420 nm through the spectroscope, and the photoconductive light-receiving element was irradiated through the quartz window under the condition that the light quantity 6 μW / cm ² was constant.

FIG. 3a shows current-voltage (IV) characteristics measured in a dark room where no light is irradiated.
b shows the IV characteristics measured during irradiation with ultraviolet light having a wavelength of 220 nm. Here, the IV characteristic was measured by the two-terminal method. As shown in FIG. 3a, the dark current not irradiated with ultraviolet light of this element is 2 pA or less at ± 15 V, and it can be seen that an extremely weak dark current is realized.

On the other hand, as shown in FIG. 3b, by irradiating with ultraviolet light having a wavelength of 220 nm, a photoinduced current as much as 10 ⁷ times that of the dark current is obtained, and reaches a high level of 1 μA at ± 2 V or more. Such a photoinduced current of 10 ⁷ times was not obtained even when irradiated with light having a wavelength of 230 nm or more. When the detection sensitivity defined by the photocurrent value with respect to the incident light power of ultraviolet light is calculated, it reaches 3100 A / W. The value of the detection sensitivity reaches 15000 times the limit value 0.2 A / W of the photocurrent caused by the photoexcited carriers in the conventional semiconductor.

Until now detectable semiconductor sensor elements 10 ^{-15 W} stuff wavelength 230nm following ultraweak ultraviolet light did not exist until now, even weak ultraviolet light femto watt class by the present invention, sufficient detectable The device is realized for the first time. The optical element of the present invention is used in combustion control monitors for industrial combustion furnaces, gas turbine engines, jet engines, etc., flame sensors for flame detectors linked to fire alarms, and silicon large-scale integrated circuit fabrication processes. It is applied to the stepper exposure device and the ultraviolet sensor in the ultraviolet irradiation device, which opens up a new market for semiconductor sensor elements.

It is sectional drawing of the diamond ultraviolet light sensor element of this invention. It is a top view which shows the electrode pattern of the diamond ultraviolet light sensor element of this invention. It is a graph which shows the (a) dark current IV characteristic of the diamond ultraviolet light sensor element of this invention, and the (IV) IV characteristic measured during irradiation of the ultraviolet light of wavelength 220nm.

Explanation of symbols

1: TiAu electrode 2: Diamond single crystal film 3: Diamond (100) single crystal substrate

Claims (4)

A photoconductive sensor element that detects light irradiated to the light receiving part by a change in electrical resistance of the light receiving part material or a change in photoinduced current,
The light-receiving part has a diamond single crystal formed in a plasma or vapor phase growth method in an atmosphere substantially containing carbon and hydrogen and treated in an aqua regia solution boiled after the film formation. Diamond ultraviolet light sensor element. Diamond ultraviolet light sensor device according to claim 1 in which the two electrodes are joined to the hydrogenated surface of diamond single crystal. Diamond ultraviolet light sensor device according to claim 1 or 2 main serving photoinduced current component flows through the table Menden conductive layer near the surface that is hydrogenation of the diamond monocrystal. A method of manufacturing a photoconductive sensor element that detects light irradiated to a light receiving part by a change in electrical resistance of a light receiving part material or a change in a light-induced current,
Forming a diamond single crystal on a substrate using a plasma vapor deposition method or a vapor deposition method in an atmosphere containing carbon and hydrogen; and
Treating the diamond single crystal in an aqueous solution boiled after film formation;
And a step of forming two electrodes on the hydrogenated surface of the diamond single crystal.

Images