WO2009157512A1 - Ultraviolet light sensor - Google Patents

Abstract

Disclosed is an ultraviolet light sensor comprising a photodetector for sensing ultraviolet light, and one or more optical fiber cables for transmitting ultraviolet light to the photodetector.  Each optical fiber cable has a light-receiving part for receiving the ultraviolet light, and the photodetector comprises a β-Ga₂O₃ crystal and electrodes respectively formed on the front surface and the back surface of the β-Ga₂O₃ crystal.

Description

UV sensor

The present invention relates to an ultraviolet sensor, and more particularly to an ultraviolet sensor suitable for continuous monitoring and excellent in durability and electromagnetic noise resistance.
This application claims priority based on Japanese Patent Application No. 2008-167378 for which it applied to Japan on June 26, 2008, and uses the content here.

Ultraviolet emitting tools (for example, ultraviolet lamps) are used in a wide variety of industries such as medical, disinfection of food and equipment, printing, semiconductors, observation, resist exposure, bonding, and molding. Has been. In recent years, ultraviolet light emitting tools that emit ultraviolet light having a short wavelength of 254 nm or less have become important in applications such as water purification, sterilization and sterilization in the food and medical fields. Since this type of ultraviolet emitting tool is a consumable item, it is important to determine the lifetime (time to replace the ultraviolet emitting tool). Conventionally, since the ultraviolet emitting tool cannot be continuously monitored, a life time is set in advance as a guideline for replacing the ultraviolet emitting tool (for example, 2000 hours), and after using the set lifetime, I was trying to replace it. However, since the actual life of the ultraviolet light emitting device is not constant for each ultraviolet light emitting device, it may be shorter or longer than the set life. When the lifetime of the ultraviolet emitting tool becomes shorter than the set lifetime, there is a problem that the ultraviolet emitting tool continues to be used without generating ultraviolet rays. Therefore, if there is an apparatus capable of continuously monitoring the ultraviolet emitting tool, there is no concern that the ultraviolet emitting tool will reach the end of its life before replacement.
Furthermore, when this apparatus is used, when the actual life of the ultraviolet emitting tool becomes longer than the set lifetime, it can be used efficiently until the ultraviolet emitting tool is consumed, resulting in an economic advantage.

UV sensors using semiconductors such as silicon (Si) and aluminum gallium nitride (AlGaN) are known as conventional devices for measuring the power of ultraviolet rays generated from ultraviolet emitting tools. However, in the case of an ultraviolet sensor using a silicon semiconductor, a filter is used to select a measurement wavelength. Therefore, in the short wavelength region of wavelength 254 nm or less, the bandwidth of the received light spectrum is wide, and this filter is easily deteriorated by ultraviolet rays, and the received light wavelength shifts with this deterioration. Calibration of the UV sensor is required. Furthermore, the parts used around the filter have restrictions due to heat resistance (usually a use temperature of 40 ° C. or lower). In other words, it is necessary to frequently adjust the ultraviolet ray measurement location so that the temperature of these components does not become higher than the operating temperature.

As a photodetector material having sensitivity in a short wavelength region of 254 nm or less, there is AlGaN (see, for example, Patent Document 1) other than silicon. However, this AlGaN has a problem that it is deteriorated by oxidation. For this reason, it is difficult to monitor ultraviolet rays continuously and stably for a long period of time.
Phototube-type sensors also have sensitivity in this wavelength range, but also have sensitivity in the wavelength band of ultraviolet rays contained in sunlight (not solar blinds), sensitivity is likely to fluctuate, and heat resistance is not good.

JP 2003-249665 A

In order to manage the life of the ultraviolet emitting tool based on quantitative data, it is essential to measure the ultraviolet power at the local area where the ultraviolet emitting tool is used. However, in reality, it cannot be realized due to problems such as the shape and heat resistance of the light receiving portion of the ultraviolet sensor and the life of the sensing portion. Moreover, if the ultraviolet light receiving part and the sensor head part are integrated as in the case of a conventional ultraviolet sensor, the remote monitoring becomes insufficient, the ultraviolet ray measurement location is restricted, and the monitoring is not always satisfactory. There is a problem that you can not.

The present invention has been made in order to solve such a conventional problem, and by continuously monitoring the life of the ultraviolet emitting tool, it is possible to obtain a predetermined replacement time for the ultraviolet emitting tool. It is an object of the present invention to provide an ultraviolet sensor that enables replacement of the ultraviolet emitting tool in accordance with the actual wear time and enables remote monitoring without restricting the ultraviolet measurement point.

The present invention employs the following means in order to solve the above problems and achieve the object.
(1) An ultraviolet sensor of the present invention includes a photodetector that detects ultraviolet rays and one or a plurality of optical fiber cables that propagate the ultraviolet rays toward the photodetector, and the optical fiber cable receives the ultraviolet rays. The photodetector includes a β-Ga ₂ O ₃ crystal and electrodes formed on the front and back surfaces of the β-Ga ₂ O ₃ crystal, respectively.
According to the ultraviolet sensor as described in said (1), a photodetector can be arrange | positioned away from an ultraviolet-ray emitting tool by using an optical fiber cable. Therefore, the deterioration of the photodetector due to the heat generated by the ultraviolet emitting tool or electromagnetic waves is suppressed, and the heat resistance and durability requirements for the ultraviolet sensor are reduced. In addition, β-Ga ₂ O ₃ crystal is excellent in durability and heat resistance, and is already an oxide, so there is no fear of deterioration due to oxidation. As described above, in the ultraviolet sensor described in the above (1), the shift of the light reception wavelength is difficult to occur. Therefore, it is possible to reduce or eliminate the calibration of the ultraviolet sensor that is performed for the shift of the light receiving wavelength. As a result, the power of the ultraviolet emitting tool can be continuously monitored, and the ultraviolet emitting tool can be replaced before the ultraviolet emitting tool is consumed and the generation of ultraviolet rays is eliminated. In addition, by using the optical fiber cable, the photodetector can be arranged apart from the ultraviolet emitting tool in a state where the light receiving unit is arranged in the vicinity of the ultraviolet emitting tool, so that remote monitoring is possible.
(2) In the ultraviolet sensor according to the above (1), the electrode formed on the surface of the β-Ga ₂ O ₃ crystal is a Schottky electrode, and the ultraviolet light propagated through the optical fiber cable is converted into the shot sensor. It may be introduced into the key electrode.
In the case of (2), ultraviolet rays can be received by the entire surface of the depletion layer of β-Ga ₂ O ₃ crystal extending under the Schottky electrode. Therefore, the utilization efficiency of the β-Ga ₂ O ₃ crystal is increased. Further, the structure of the ultraviolet sensor becomes simple, and the manufacturing process becomes simple.
(3) The ultraviolet sensor according to (1) may continuously monitor the ultraviolet light.
(4) You may use the ultraviolet sensor as described in said (1) for the illumination intensity measurement of the ultraviolet-ray emitting tool which wash | cleans water.
(5) The ultraviolet sensor described in the above (1) may be used for illuminance measurement of an ultraviolet emitting tool for sterilization or sterilization.
(6) In the ultraviolet sensor according to (1), the light receiving unit may have an end surface perpendicular to the optical axis of the ultraviolet light.
In the case of (6), the ultraviolet light emitted from the ultraviolet light emitting tool can be efficiently received by the light receiving unit.
(7) As for the ultraviolet sensor as described in said (1), the said light-receiving part may be formed in cone shape.
In the case of the above (7), the ultraviolet light in the incident direction that is largely shifted laterally from the optical axis of the ultraviolet light emitted from the ultraviolet light emitting tool can be efficiently received by the light receiving unit.
(8) In the ultraviolet sensor according to (1), the light receiving unit may have a slope inclined with respect to the optical axis of the ultraviolet light.
In the case of the above (8), the ultraviolet light incident from the side with respect to the inclined surface of the light receiving unit is reflected by this inclined surface and is incident on the optical fiber cable.
(9) In the ultraviolet sensor according to (1) above, a condensing lens may be disposed in the light receiving unit.
In the case of (9) above, ultraviolet rays can be more effectively incident on the optical fiber cable.
(10) In the ultraviolet sensor according to (1) above, the light receiving unit may be a V-groove formed in the optical fiber cable.
In the case of (10) above, ultraviolet light can be incident on the optical fiber cable from the side of the optical fiber cable.

According to the ultraviolet sensor described in (1) above, the power of the ultraviolet emitting tool can be continuously monitored, and the ultraviolet emitting tool can be replaced before the ultraviolet emitting tool is consumed and the generation of ultraviolet rays is eliminated. Yes. Therefore, continuous generation of ultraviolet rays can be maintained.
In addition, the deterioration of the UV sensor due to the heat generated by the UV emitting tool and electromagnetic waves is suppressed, and the heat resistance and durability requirements for the UV sensor are reduced. Therefore, calibration of the UV sensor due to the shift of the received light wavelength can be reduced or eliminated. .
Further, by using the optical fiber cable, the photodetector can be installed apart from the ultraviolet emitting tool in a state where the light receiving unit is arranged in the vicinity of the ultraviolet emitting tool, so that the ultraviolet emitting tool can be remotely monitored.

It is a schematic diagram which shows the example of schematic structure of the ultraviolet sensor which concerns on one Embodiment of this invention. It is sectional drawing which shows the photodetector of the same embodiment, and the structural example of the vicinity of it in detail. It is sectional drawing which shows the cross-section of the photodetector. It is a top view which shows electrode arrangement | positioning on the surface of the photodetector. It is a top view which shows the electrode arrangement | positioning of the back surface of the photodetector. It is sectional drawing which shows an example of the structure which optically couples an optical fiber cable with respect to the photodetector. It is sectional drawing which shows the modification of the structure which optically couples an optical fiber cable with respect to the photodetector. It is a perspective view which shows the example which processed the front-end | tip of the optical fiber cable of the embodiment, and formed the light-receiving part. It is a perspective view which shows the modification which processed the front-end | tip of the optical fiber cable of the said embodiment, and formed the light-receiving part. It is a perspective view which shows the modification which processed the front-end | tip of the optical fiber cable of the embodiment, and formed the light-receiving part. It is a side view which shows the example which provided the lens in the front-end | tip of the optical fiber cable of the embodiment, and formed the light-receiving part. It is a side view which shows the example which provided the V groove in the side surface of the optical fiber cable of the embodiment, and formed the light-receiving part. The sensitivity of the ultraviolet sensor in an Example is a graph which shows irradiation power dependence. It is a graph which shows the electromotive current and irradiation power of the photodetector in the Example. It is a graph which shows the measurement result of the dark current in the Example.

The present invention will be described below with reference to the drawings based on the best mode.
FIG. 1 is a diagram illustrating a schematic configuration example of an ultraviolet sensor according to an embodiment of the present invention. An ultraviolet sensor 1 shown in FIG. 1 includes a photodetector 2 that detects ultraviolet rays and an optical fiber cable 3 that propagates ultraviolet rays toward the photodetector 2, and the optical fiber cable 3 emits ultraviolet rays emitted from an ultraviolet emitting tool L. It has the light-receiving part 4 which receives light.

FIG. 2 shows an example of the configuration of the photodetector 2 and the vicinity thereof in more detail.
The photodetector 2 includes a β-Ga ₂ O ₃ (β-type gallium oxide) crystal 10 and electrodes formed on the front and back thereof. That is, on the surface of the _β-Ga 2 _{O 3} crystal 10, together with the Schottky electrode 11 of the ultraviolet ray for detection is formed on the back surface of the _β-Ga 2 _{O 3} crystal 10 corresponds to the Schottky electrode 11 The ohmic electrode 12 is formed at the position where the A pad electrode 13 for wiring is formed on the Schottky electrode 11. Further, a test Schottky electrode 14 and an ohmic electrode 15 are formed on the front surface and the back surface of the β-Ga ₂ O ₃ crystal 10, respectively.
Figure 4A is _β-Ga 2 _{O 3} each electrode of the crystal 10 surface shows the arrangement of (the Schottky electrode 11, the Schottky electrode 14 of the pad electrodes 13 and the test), FIG. 4B is _β-Ga 2 _{O 3} crystal 10 back surface The arrangement of each electrode (the ohmic electrode 12 and the test ohmic electrode 15) is shown.

The photodetector 2 is accommodated in the housing 6. The housing 6 is made of a material that does not allow ultraviolet rays to pass through. It is desirable that the ultraviolet rays to be measured be introduced into the housing 6 only by propagation through the optical fiber cable 3.
From the viewpoint of electrostatic shielding of the photodetector 2 housed inside the housing 6, the housing 6 is preferably made of a conductive material. The housing 6 can be formed of a metal such as stainless steel, aluminum, brass, iron, or nickel. The housing 6 may be configured such that a plurality of members are combined and integrated after the photo detector 2 is accommodated.

The photodetector 2 is fixed on a support plate 20 made of sapphire, quartz or the like using a binder 21 such as silver (Ag) paste. The support plate 20 is die bonded to the bottom surface of the housing 6.

An opening 7 through which the optical fiber cable 3 is inserted is formed on the top surface of the housing 6. The optical fiber cable 3 inserted through the opening 7 is arranged such that the emission part 5 faces the Schottky electrode 11 of the photodetector 2.
As the emitting unit 5, for example, an end surface of the optical fiber cable 3 that is polished perpendicularly to the optical axis direction (the vertical direction in FIG. 2) can be used. The upper surface of the Schottky electrode 11 serves as the light receiving surface 11r of the photodetector 2, and the photodetector 2 is disposed so that the light receiving surface 11r faces the light emitting portion 5 of the optical fiber cable 3.

A pair of leads 24 and 25 serving as terminals of the photodetector 2 are drawn out from the bottom surface side of the housing 6 to the outside of the housing 6. In the housing 6, the pad electrode 13 and the ohmic electrode 12 of the photodetector 2 are electrically connected to one end of a pair of leads 24 and 25 via a pair of bonding wires 22 and 23, respectively. For example, a gold (Au) wire having a diameter of 25 μm is used for the pair of bonding wires 22 and 23. A power source 8 such as a battery and an ammeter 9 are connected between the pair of leads 24 and 25. By measuring the current value using this ammeter 9, it is possible to detect ultraviolet rays and measure power.

The β-Ga ₂ O ₃ crystal 10 used in the photodetector 2 has a large sensitivity near a wavelength of 254 nm and is excellent in durability and heat resistance. Since β-Ga ₂ O ₃ is an oxide semiconductor having a high melting point of 1740 ° C. and a wide band gap of 4.7 to 4.9 eV, it becomes a solar blind sensor. Since β-Ga ₂ O ₃ is already an oxide, there is no fear of deterioration due to oxidation. Therefore, it is suitable for measuring the ultraviolet power in the ultraviolet wavelength region, particularly in the wavelength region of 200 to 254 nm. The β-Ga ₂ O ₃ crystal 10 may be a single crystal of β-Ga ₂ O ₃ , a twin crystal or a polycrystal, and in either case, the same effect is obtained.

When single crystal β-Ga ₂ O ₃ is used as the β-Ga ₂ O ₃ crystal 10, for example, the β-Ga ₂ O ₃ single crystal 10 having excellent crystal quality can be manufactured by the following method. In this method, Ga ₂ O ₃ powder having a purity of 4N (99.99% or more) is enclosed in a rubber tube, molded with a rubber press, sintered in an electric furnace at 1500 ° C. for 10 hours, A single crystal is grown by the FZ (Floating Zone) method using the bonded body as a raw material rod. Examples of the single crystal growth conditions include a growth rate of 5 to 10 mm / h, a dry air atmosphere, and a pressure of 1 atm.

The β-Ga ₂ O ₃ single crystal 10 thus produced is sliced with a wire saw or the like in a plane parallel to the (100) plane having the strongest cleaving property, and this (100) plane is then subjected to chemical mechanical polishing (CMP). : Mirror polishing with Chemical Mechanical Polishing) to process into a wafer with a thickness of 0.4 to 0.5 mm.
This β-Ga ₂ O ₃ single crystal 10 has a specific resistance of 0.1 to 0.5 Ωcm and a carrier density of about 10 ¹⁷ to 10 ¹⁸ cm ⁻³ and is electrically conductive. Using this single crystal, the photodetector 2 can be produced without epitaxial growth.

FIG. 3 shows a cross-sectional structure of the photodetector 2. A Schottky electrode 11 and an ohmic electrode 12 are formed on the front surface and the back surface of the β-Ga ₂ O ₃ crystal 10 respectively, so that a vertical Schottky diode is configured in the photodetector 2. At this time, in the β-Ga ₂ O ₃ crystal 10, a depletion layer 10a is formed immediately below the Schottky electrode 11 on the surface, and a conductive layer 10b is formed therebelow.
The Schottky electrode 11 is formed of a thin electrode having a light receiving surface 11r formed on the surface thereof and having translucency with respect to ultraviolet rays to be detected.

In order to detect ultraviolet rays by converting them into electron-hole pairs, it is necessary to form a high resistance layer sandwiched between electrodes. This is because if a low resistance layer is provided between the electrodes, a current easily flows between the electrodes, and the photocurrent cannot be separated. For producing the high resistance layer, there is a method of using a depletion layer by a high resistance thin film, a Schottky contact, or a pn junction. Among these methods, a method using a depletion layer is preferable because it has a current amplification effect and high sensitivity. When a gallium oxide crystal is used for the photodetector 2, oxygen vacancies are generated in the crystal, so that only an n-type semiconductor is obtained. Therefore, as the depletion layer, it is preferable to use a depletion layer by Schottky contact instead of a pn junction. As a result, the structure of the photodetector 2 becomes an MSM (Metal-Semiconductor-Metal) type.

MSM type has horizontal structure and vertical structure. In the case of a horizontal structure, it is necessary to form a comb-shaped electrode by using photolithography or the like. Since it is difficult to increase the area of the comb-shaped electrode, and the depletion layer is formed only directly below the comb-shaped electrode, the utilization efficiency of gallium oxide decreases.

In the present embodiment, a vertical structure MSM type is employed as the structure of the photodetector 2. In the vertical MSM type, as shown in FIG. 3, the photodetector 2 (sensor unit) only forms the Schottky electrode 11 on the surface of the β-Ga ₂ O ₃ crystal 10 and the ohmic electrode 12 on the back surface. It is a simple structure composed. Unlike the horizontal structure, this vertical structure can receive ultraviolet light over the entire surface of the depletion layer 10a extending under the Schottky electrode 11, so that the utilization efficiency of the β-Ga ₂ O ₃ crystal 10 is increased. In addition, since it is not necessary to produce a comb-shaped electrode like a horizontal structure, the structure is simple and the manufacturing process is simple.

Hereinafter, a _β-Ga 2 _{O 3} crystal, _β-Ga 2 _{O 3} an example of production process of the photo detector 2 of vertical structure using a single crystal 10 will be described.

(S1: Annealing of β-Ga ₂ O ₃ single crystal 10)
First, the β-Ga ₂ O ₃ single crystal 10 is washed in the order of hydrofluoric acid, sulfuric acid, acetone, ethanol, and pure water, and heat treatment is performed. The purpose of the heat treatment is to recover defects such as oxygen vacancies remaining in the single crystal after crystal growth. The heat treatment is preferably performed in an oxygen atmosphere at 1100 ° C. for 3 to 24 hours. The reason why the oxygen atmosphere is used is to replenish oxygen vacancies generated when the β-Ga ₂ O ₃ single crystal 10 is grown.

(S2: Formation of protective film on the surface of β-Ga ₂ O ₃ single crystal 10)
Next, a protective film is formed on the surface of the β-Ga ₂ O ₃ single crystal 10. For the formation of the protective film, for example, application of a mounting wax used for fixing the analysis sample is used. Since the mounting wax starts to melt from around 100 ° C., if the melted wax is applied to the slide glass, and the β-Ga ₂ O ₃ single crystal 10 is pressed against the slide glass coated with this wax and then cooled, a protective film Can be easily prepared. Thus, when the back surface of the β-Ga ₂ O ₃ single crystal 10 is irradiated with plasma in the next step, the surface of the β-Ga ₂ O ₃ single crystal 10 is prevented from being irradiated with ions and causing damage. Can do.

(S3: Plasma irradiation on the back surface of β-Ga ₂ O ₃ single crystal 10)
In order to make ohmic contact with the back surface of the β-Ga ₂ O ₃ single crystal 10, plasma irradiation is performed for the purpose of improving conductivity and reducing resistance. This is to forcibly generate defects and improve electrical conductivity due to generation of carrier electrons. As the plasma, low-pressure glow discharge using residual gas can be used. It is preferable that the ion current is several hundred μA, and the current of the entire apparatus is 5 to 10 mA.
The irradiation time is preferably 20 to 40 minutes, more preferably about 30 minutes.

(S4: Removal of protective film on the surface of β-Ga ₂ O ₃ single crystal 10)
After the back surface of the β-Ga ₂ O ₃ single crystal 10 is irradiated with plasma, the protective film on the surface of the β-Ga ₂ O ₃ single crystal 10 is removed. The mounting wax is heated and melted again, and the β-Ga ₂ O ₃ single crystal 10 is peeled off. Further, the β-Ga ₂ O ₃ single crystal 10 is washed with acetone to remove the remaining wax.

(S5: Formation of ohmic electrode on the back surface of β-Ga ₂ O ₃ single crystal 10)
After titanium (Ti) is deposited on the back surface of the β-Ga ₂ O ₃ single crystal 10 to a thickness of 30 to 70 nm (more preferably 30 to 50 nm), gold (Au) is deposited to a thickness of 80 to 150 nm (more preferably 80 to 100 nm), and Au / Ti ohmic electrodes 12 and 15 are formed. The size of the ohmic electrode 12 is preferably 1 to 5 mmφ, and more preferably 3 to 4 mmφ. The larger this size, the smaller the contact resistance.

(S6: Formation of Schottky electrode on the surface of β-Ga ₂ O ₃ single crystal 10)
As the Schottky electrodes 11 and 14, gold (Au), platinum (Pt), or the like, which is a metal having a high work function, is used for an n-type semiconductor. After nickel (Ni) is deposited on the surface of β-Ga ₂ O ₃ single crystal 10 to a thickness of 2 to 5 nm (more preferably 2 nm), Au or Pt is deposited to a thickness of 6 to 10 nm, and Au / Ni or Pt / Ni is deposited. A semitransparent or transparent electrode is prepared. The Schottky electrodes 11 and 14 may be made of Au or Pt alone without inserting a Ni layer.
As a material metal of the Schottky electrodes 11 and 14, in addition to Au and Pt, aluminum (Al), cobalt (Co), germanium (Ge), tin (Sn), indium (In), tungsten (W), molybdenum (Mo ), Chromium (Cr), copper (Cu), and the like.
The reason why the Ni vapor deposition layer is inserted is that the adhesion with the β-Ga ₂ O ₃ single crystal 10 is poor with Au or Pt alone, so that the adhesion is improved. The size of the Schottky electrode 11 is preferably 1 to 5 mmφ, and more preferably 3 to 4 mmφ. As the size of the Schottky electrode 11 is larger, the light receiving surface 11r can be enlarged.

(S7: Formation of pad electrode)
A wiring pad electrode 13 is formed on the Schottky electrode 11. For example, Ni is deposited on the light receiving surface 11r with a thickness of 3 to 10 nm (more preferably 4 to 6 nm), and then Au or Pt is deposited with a thickness of 80 to 150 nm (more preferably 80 to 100 nm). The size of the pad electrode 13 is preferably 0.05 to 1.5 mmφ.

If the photodetector 2 manufactured as described above is connected to the optical fiber cable 3, remote monitoring becomes possible. Specifically, the structure is a pigtail type in which ultraviolet light received by the light receiving unit 4 at the tip of the optical fiber cable 3 is transmitted by the optical fiber cable 3 and detected by the photodetector 2. Since the optical fiber cable 3 is not affected by electromagnetic waves, it is not necessary to shield the surroundings with metal unlike the photodetector 2.
Note that a β-Ga ₂ O ₃ single crystal, instead of a β-Ga ₂ O ₃ twin crystal or a polycrystal, can be similarly used.

For the optical fiber cable 3, it is preferable to use a silica-based optical fiber in order to efficiently transmit ultraviolet rays in the measurement wavelength region. The core diameter is preferably about 200 to 600 μm, and an extremely large one is used as compared with a general communication optical fiber.
The emitting portion 5 of the optical fiber cable 3 and the Schottky electrode 11 of the photodetector 2 can be directly coupled only through the atmosphere in the housing 6. For this reason, it is not necessary to provide the casing 6 with a member made of a material that transmits ultraviolet rays, such as a window material. Note that a window material may be provided depending on the applied ultraviolet sensor from the viewpoint of sealing the photodetector 2 and the emission part 5 of the optical fiber cable 3 in the housing 6.

As shown in FIG. 5B, an optical fiber bundle including a plurality of optical fiber cables 3 can be used as the optical fiber cable 3. There are optical fiber bundles in which a plurality of optical fiber cables 3 are arranged linearly (in a line), or in a planar shape, and any of them can be used. In this case, it is preferable to arrange each optical fiber cable in an annular shape around the pad electrode 13 so that the emitting portion 5 avoids the pad electrode 13 because the incident efficiency to the photodetector 2 is improved. As described above, by using the optical fiber bundle, it is possible to introduce ultraviolet rays into the light receiving surface 11r in a wider range as compared with the case of using one optical fiber cable (see FIG. 5A).

The light receiving portion 4 of the optical fiber cable 3 can be formed by processing the tip of the optical fiber cable 3 as shown in FIGS. 6A to 6C, for example.
FIG. 6A shows the end of the core 31 exposed by removing the protective coating 33 and the clad 32 of the optical fiber cable 3 on an end face 34 perpendicular to the optical axis.
FIG. 6B shows the tip of the core 31 exposed by removing the protective coating 33 and the clad 32 of the optical fiber cable 3 in a conical shape 35. In this case, it is possible to efficiently receive even the ultraviolet rays in the incident direction that are largely shifted laterally from the optical axis.
FIG. 6C shows a case where the tip of the core 31 exposed by removing the protective coating 33 and the clad 32 of the optical fiber cable 3 is a slope. According to this configuration, the ultraviolet light incident from the side with respect to the wedge-shaped portion 36 at the tip is reflected by the inclined surface and incident on the optical fiber cable 3. It is preferable to provide a reflective portion 37 such as an aluminum vapor deposition film on this slope. Thereby, the reflectance of an ultraviolet-ray can be increased and an ultraviolet-ray can be introduce | transduced into the optical fiber cable 30 more appropriately.

7 and 8 show modifications of the light receiving unit 4. The structure of the light receiving unit 4 shown in FIG. 7 is such that a condensing lens 38 is attached to the tip of the optical fiber cable 30. It is preferable to use a cylindrical lens such as a GRIN lens as the condenser lens 38 because it can be directly fixed to the tip of the optical fiber cable 30 by adhesion or fusion.
The structure of the light receiving unit 4 shown in FIG. 8 is such that a V-groove 39 is formed on the side surface of the optical fiber cable 30 so that ultraviolet rays can be incident from the side of the optical fiber cable 30 through the V-groove 39. is there.

When an optical fiber bundle composed of a plurality of optical fiber cables 3 is used as the optical fiber cable 3, a plurality of light receiving portions 4 can be provided by the plurality of optical fiber cables 3. If the optical fiber bundle is integrated in the light receiving unit 4, the number of ultraviolet measurement points by one ultraviolet sensor 1 is one, but the incident sectional area in the light receiving unit 4 can be increased. In this case, the incident directions directed by the respective light receiving units 4 may be aligned in the same direction. Moreover, if each light-receiving part 4 is arrange | positioned radially, for example and it directs each different incident direction, it will become the ultraviolet sensor 1 with low dependence on an incident direction.
Alternatively, a plurality of optical fiber cables 3 are arrayed on the emission unit 5 side, while the optical fiber cable 3 is branched in the middle and separated on the light receiving unit 4 side. You can also. In this case, the total amount of ultraviolet power at a plurality of locations can be measured using one ultraviolet sensor 1.

According to the ultraviolet sensor 1 of the present embodiment, since the distance between the light receiving unit 4 and the photodetector 2 can be secured by the optical fiber cable 3, the ultraviolet sensor 1 (photodetector 2) caused by heat generated by the ultraviolet emitting tool L, electromagnetic waves, or the like. ) Degradation can be suppressed. Furthermore, since the heat resistance and durability requirements for the ultraviolet sensor 1 (photodetector 2) are reduced, the shift of the light receiving wavelength is less likely to occur, and the number of calibrations of the ultraviolet sensor can be reduced or eliminated. . Thereby, continuous monitoring can be realized.

By enabling continuous monitoring, the power of the ultraviolet ray emitting tool L is continuously monitored, so that the ultraviolet ray emitting tool can be replaced before the ultraviolet ray emitting tool L is consumed and no ultraviolet ray is generated. Therefore, continuous generation of ultraviolet rays from the ultraviolet emitting tool L can be maintained.
Furthermore, since the ultraviolet rays propagate through the optical fiber cable 3, the optical fiber is not limited by the positional relationship between the light receiving unit 4 and the ultraviolet ray measurement location (there is no need to provide the photodetector 2 in the immediate vicinity of the ultraviolet ray measurement location). The photodetector 2 can be freely installed via the cable 3. As a result, the ultraviolet emitting tool L can be monitored remotely. That is, for example, the photodetector 2 can be arranged outside the water tank, clean room, or the like where the ultraviolet light emitting tool L is provided. For this reason, deterioration of the ultraviolet sensor 1 (photodetector 2) due to heat generation or electromagnetic waves of the ultraviolet emitting tool L described above does not occur, and the ultraviolet emitting tool L can be monitored stably for a long period of time.
Moreover, since ultraviolet rays are cut according to the wire diameter of the optical fiber cable 3, the illuminance to the photodetector 2 is reduced. Thereby, the deterioration of the photodetector 2 due to ultraviolet irradiation is further reduced, and the durability of the ultraviolet sensor 1 is improved.
Moreover, since the optical fiber cable 3 is used, the ultraviolet illuminance can be measured in a narrow place. Moreover, it becomes possible to make only the optical fiber cable 3 a consumable item. In this case, only the photodetector 2 is sealed, a sealing window cap is provided on the housing 6, and the optical fiber cable 3 is connected to the sealing window cap. Therefore, it is not necessary to perform sealing at the introduction portion (opening portion 7) for introducing the optical fiber cable 3 into the housing 6. As a result, the sealing life in the housing 6 is improved.
The ultraviolet sensor of this embodiment can also be suitably used for illuminance measurement of an ultraviolet emitting tool that cleans water. Moreover, it can be used suitably also for the illumination intensity measurement of the ultraviolet-ray emitting tool which sterilizes or sterilizes in the foodstuffs and the medical field. Moreover, it is applicable not only to these uses but also to illuminance measurement of ultraviolet emitting tools such as printing, semiconductor, observation, resist exposure, adhesion, and molding.

Hereinafter, the present invention will be specifically described with reference to examples.
Gallium oxide powder having a purity of 4N (99.99% or more) was sealed in a rubber tube, subjected to isostatic pressing, and sintered at 1500 ° C. for 10 hours in the atmosphere. Using the obtained sintered body as a raw material rod, a single crystal was grown using an optical FZ apparatus to obtain a β-Ga ₂ O ₃ single crystal. Next, the (100) plane of the obtained β-Ga ₂ O ₃ single crystal was cut out and polished by CMP to obtain a wafer-like substrate. The substrate size is approximately 8 mm × 8 mm.

Using the obtained β-Ga ₂ O ₃ single crystal, electrodes were formed on the front and back of the β-Ga ₂ O ₃ single crystal by the processes of S1 to S7 described above, and a photodetector was manufactured. Each electrode arrangement is as shown in FIG. The Schottky electrode on the surface of the β-Ga ₂ O ₃ single crystal has a diameter of 4 mm and is made of a deposited film of Au (film thickness 8 nm) / Ni (film thickness 2 nm). The ohmic electrode on the back surface of the β-Ga ₂ O ₃ single crystal is disposed at a position corresponding to the Schottky electrode, and has a diameter of 4 mm and is formed of a deposited film of Au (film thickness 100 nm) / Ni (film thickness 50 nm). The pad electrode is disposed in the center of the Schottky electrode, and has a diameter of 1 mm and is formed of a vapor deposition film of Au (film thickness: 100 nm) / Ni (film thickness: 5 nm).

A power source (voltage Vs) and a resistor (resistor R) were connected in series between the electrodes of the photodetector. First, in order to investigate the characteristics of the photodetector, ultraviolet light having a wavelength of 254 nm was directly incident on the photodetector without an optical fiber cable. As the ultraviolet emitting tool, an ultraviolet lamp (ultraviolet generator SLUV-6 manufactured by AS ONE Co., Ltd.) was used. The distance from the ultraviolet lamp to the photodetector was set to 20 cm, and the electromotive current generated in the photodetector at this time was measured. The measurement results are shown in Table 1. Vs is the voltage of the power supply, the resistance value of R is the resistor, P _in ultraviolet power incident on the photodetector, V _R is the voltage between the terminals of the resistor, I _pd is electromotive current, CE sensitivity of the photodetector of the photodetector Represents.

Next, as an example, as shown in FIG. 1, ultraviolet rays were incident on the photodetector through an optical fiber cable. Specifically, the output end of an optical fiber cable having a core diameter of 400 μm is coupled to a Schottky electrode of a photodetector, and the wavelength from an ultraviolet lamp (ultraviolet generator SLUV-6 manufactured by ASONE Corporation) is directed toward the incident end of the optical fiber cable. UV light of 254 nm was continuously irradiated. The distance between the light receiving portion of the optical fiber cable and the ultraviolet lamp is 20 cm as described above. In FIG. 9, the measurement result of the sensitivity and irradiation power of the ultraviolet sensor of a present Example is shown. FIG. 10 shows the measurement results of the electromotive current and irradiation power of the photodetector. From FIG. 9 and FIG. 10, the sensitivity of the ultraviolet sensor of this example and the electromotive current of the photodetector showed dependency on the ultraviolet irradiation power. Moreover, the sensitivity was comparable (several A / W) to that shown in Table 1 without the optical fiber cable.
FIG. 11 shows the measurement result of dark current. From FIG. 10 and FIG. 11, it was confirmed that the dark current was sufficiently small relative to the electromotive current and did not affect the measurement of the ultraviolet power.

L UV emitting tool 1 UV sensor 2 Photo detector 3 Optical fiber cable 4 Light receiving part 10 β-Ga ₂ O ₃ single crystal 11 Schottky electrode 12 Ohmic electrode 13 Pad electrode

Claims (10)

1. A photodetector that detects ultraviolet rays;
   One or a plurality of optical fiber cables that propagate the ultraviolet rays toward the photodetector;
   The optical fiber cable has a light receiving portion that receives the ultraviolet rays,
   The photodetector includes a β-Ga ₂ O ₃ crystal and electrodes formed on the front surface and the back surface of the β-Ga ₂ O ₃ crystal, respectively.
   An ultraviolet sensor characterized by that.
2. The electrode formed on the surface of the β-Ga ₂ O ₃ crystal is a Schottky electrode;
   The ultraviolet sensor according to claim 1, wherein the ultraviolet light propagated through the optical fiber cable is introduced into the Schottky electrode.
3. The ultraviolet sensor according to claim 1, wherein the ultraviolet ray is continuously monitored.
4. The ultraviolet sensor according to claim 1, wherein the ultraviolet sensor is used for illuminance measurement of an ultraviolet emitting tool for washing water.
5. The ultraviolet sensor according to claim 1, wherein the ultraviolet sensor is used for illuminance measurement of an ultraviolet emitting tool for sterilization or sterilization.
6. 2. The ultraviolet sensor according to claim 1, wherein the light receiving section has an end face perpendicular to the optical axis of the ultraviolet light.
7. The ultraviolet sensor according to claim 1, wherein the light receiving portion is formed in a conical shape.
8. 2. The ultraviolet sensor according to claim 1, wherein the light receiving section has a slope inclined with respect to the optical axis of the ultraviolet light.
9. The ultraviolet sensor according to claim 1, wherein a condensing lens is disposed in the light receiving portion.
10. The ultraviolet sensor according to claim 1, wherein the light receiving portion is a V-groove formed in the optical fiber cable.

Images