JP2011176090A - Ultraviolet sensor and method for manufacturing same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultraviolet sensor and a method for manufacturing the same, using low-cost inexpensive gallium oxide single-crystal substrate. <P>SOLUTION: The ultraviolet sensor includes the gallium oxide single-crystal substrate 11 which uses an orthogonal plane 41, orthogonal with respect to the growing direction of gallium oxide single crystal or a surface tilted from the orthogonal plane 41 by a prescribed angle as a light receiving surface 12r; an ohmic electrode 13 formed on a first surface of the gallium oxide single crystal substrate 11; and a Schottky electrode 12, formed on a second surface of the gallium oxide single crystal substrate 11 including the light-receiving surface 12r. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an ultraviolet sensor that detects ultraviolet rays emitted from an ultraviolet lamp or the like and a method for manufacturing the same.

  Ultraviolet lamps that irradiate ultraviolet rays are used in a wide variety of industries such as sterilization of water and air, cleaning of semiconductors and food containers, and surface modification of semiconductors. This ultraviolet lamp is a consumable item, and its lifetime is an important point. However, since the ultraviolet lamp cannot be continuously monitored, the lifetime is determined in advance as a standard. However, the lifetime of each lamp is not constant, and there may be a deviation from the set time. If the actual life is shorter than the set time, it will be used without generating UV light, so the desired purification and sterilization effects cannot be obtained, and if the actual life is longer than the set time, it can still be used. Nevertheless, it will be a waste of exchange.

  In order to solve such a problem, there is a conventional sensor that continuously monitors the ultraviolet lamp by detecting the ultraviolet ray irradiated by the ultraviolet lamp. As this sensor, there is one using silicon. However, since the selection of the measurement wavelength is performed using a filter, the bandwidth of the light reception spectrum is wide in the short wavelength region near 254 nm, the filter is deteriorated by ultraviolet light, and the light reception wavelength is shifted accordingly. Calibration for adjustment is required. Furthermore, due to the heat resistance problem of filter peripheral parts and the like, there is a restriction that the filter is normally used at 40 ° C. or lower, so that the measurement location must be frequently adjusted.

  A photoelectric tube is known as a sensor for detecting ultraviolet rays having a wavelength of 280 nm or less. This photoelectric tube has already been put into practical use as a sensor for detecting flickering of a flame, and is mainly used for a flame sensor for automatic control of a large-scale combustion apparatus such as an industrial furnace, but a sensor using a photoelectric tube is not a solar blind sensor. Therefore, there is a problem that the sensitivity is likely to fluctuate and the heat resistance is low.

  In contrast, there are solar blind ultraviolet sensors and ultraviolet photodetectors that use a gallium oxide single crystal substrate and are excellent in heat resistance and durability (see, for example, Patent Documents 1 and 2).

JP 2009-130012 A JP 2009-200222 PR

  In the gallium oxide single crystal substrate described above, a single crystal ingot is sliced with a wire saw in a plane parallel to the (100) plane (hereinafter referred to as a plane), and this a plane is subjected to chemical mechanical polishing (CMP). It is manufactured by mirror polishing with mechanical polishing and processing into a wafer. However, when slicing the a-plane of a single crystal of the gallium oxide single crystal substrate, a step of cutting the single crystal as a previous step is performed. That is, the step of slicing the a-plane in the single crystal is a step of slicing a plane parallel to the a-plane of the single crystal in a cut state with a wire saw. Since the gallium oxide single crystal substrate is manufactured by the above-described ring cutting and slicing processes, there is a problem that the manufacturing process takes time and cost.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide an ultraviolet sensor using a low-cost gallium oxide single crystal substrate and a manufacturing method thereof.

  In order to solve the above-described problems, an ultraviolet sensor according to the present invention includes a gallium oxide single crystal having a light-receiving surface that is an orthogonal plane orthogonal to the growth direction of the gallium oxide single crystal or a plane inclined by a predetermined angle from the orthogonal plane. A crystal substrate; a first electrode formed on a first surface of the gallium oxide single crystal substrate; and a second electrode formed on a second surface of the gallium oxide single crystal substrate including the light receiving surface.

  In addition, the method for manufacturing an ultraviolet sensor according to the present invention provides the gallium oxide single crystal so that an orthogonal plane orthogonal to the growth direction of the gallium oxide single crystal or a plane inclined by a predetermined angle from the orthogonal plane becomes a cut plane. The first electrode is formed on the first surface of the gallium oxide single crystal substrate, and the second surface of the gallium oxide single crystal substrate including the light reception surface is formed. A second electrode is formed.

  According to the present invention, a low-cost gallium oxide single crystal substrate can be used for an ultraviolet sensor.

2 is a cross-sectional view showing a configuration of an ultraviolet sensor according to Embodiment 1. FIG. It is a top view which shows the sensor chip in a package. 6 is a schematic diagram for explaining a method A. FIG. 6 is a schematic diagram for explaining a manufacturing process of the ultraviolet sensor according to Embodiment 1. FIG. 3 is a graph showing sensor sensitivity and capacitance of the ultraviolet sensor according to Example 1. FIG. 6 is a cross-sectional view showing a configuration of the ultraviolet sensor according to the second embodiment. It is a figure which shows the surface state of a Schottky electrode. 6 is a schematic diagram for explaining a manufacturing process of the ultraviolet sensor according to Embodiment 2. FIG. 6 is a graph showing the impurity concentration of an ultraviolet sensor according to Example 2. 6 is a table showing impurity concentration, specific resistance and carrier density of an ultraviolet sensor according to Example 2. It is a graph which shows the correlation of the specific resistance of the ultraviolet sensor which concerns on Example 2, a carrier density, and Si density | concentration. It is a graph which shows the correlation of the sensor sensitivity of the ultraviolet sensor which concerns on Example 3, the lifetime of a sensor, and the number of the abrasion cracks. 6 is a graph showing resistance between ohmic electrodes in an ultraviolet sensor according to Example 4. It is a graph which shows the sensor sensitivity in the ultraviolet sensor which concerns on Example 4. 10 is a graph showing sensor sensitivity in an ultraviolet sensor according to Example 5.

  Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1)
First, the ultraviolet sensor according to Embodiment 1 will be described with reference to FIGS. 1 and 2. FIG. 1 is a cross-sectional view showing the configuration of the ultraviolet sensor according to the first embodiment. FIG. 2 is a top view showing the sensor chip in the package. As shown in FIG. 1, in the ultraviolet sensor 1, a sensor chip 10 for detecting ultraviolet rays is accommodated in a package 2 and sealed from an external atmosphere.

The package 2 includes a flat plate-shaped stem 22, a cap 23 that is installed on the stem 22 and is a cylindrical member having an opening 20 in the center, and a window member 21 that covers the opening 20 from the inside of the cap 23. The interior is filled with an inert gas such as nitrogen or argon, or is maintained in a vacuum state.
The stem 22 and the cap 23 are preferably conductive from the viewpoint of electrostatic shielding of the sensor chip 10 accommodated therein, and are formed of, for example, a metal such as stainless steel, aluminum, brass, iron, or nickel.
The window member 21 can be made of sapphire or quartz (quartz), which is made of a material that is transparent to ultraviolet rays to be detected and has a large transmittance with respect to ultraviolet rays having a wavelength of around 254 nm. The window member 21 is bonded to the inside of the cap 23 using an epoxy adhesive 24 so as to cover the opening 20 from the inside of the package 2.

The sensor chip 10 includes a gallium oxide (Ga ₂ O ₃ ) single crystal substrate (hereinafter referred to as a single crystal substrate) 11, and the single crystal substrate 11 is formed on the upper surface (first surface) of the single crystal substrate 11. The Schottky electrode 12 for detecting ultraviolet rays is formed. In addition, an ohmic electrode 13 that makes ohmic contact with the single crystal substrate 11 is formed on the lower surface (second surface) of the single crystal substrate 11 corresponding to the Schottky electrode 12.

  The single crystal substrate 11 has an insulating layer 11a formed on the surface thereof, and a conductive layer 11b formed under the insulating layer 11a. The single crystal substrate 11 can separate electron-hole pairs generated by ultraviolet excitation by forming the insulating layer 11a on the surface. The Schottky electrode 12 is in contact with the insulating layer 11a, and the ohmic electrode 13 is formed in contact with the conductive layer 11b. A pad electrode 14 for wiring is formed on the single crystal substrate 11.

  The first surface of the single crystal substrate 11 and the upper surface of the Schottky electrode 12 are a light receiving surface 12r that receives light such as ultraviolet rays, and the sensor chip 10 is stemmed so that the light receiving surface 12r faces the window member 21 of the package 2. 22 is installed.

  The gallium oxide single crystal used for the single crystal substrate 11 has a selective sensitivity in a wavelength region of a wavelength of 280 nm or less, and particularly has a large sensitivity in the vicinity of a wavelength of 254 nm. Since the gallium oxide single crystal is an oxide semiconductor having a wide band gap of 4.7 to 4.9 eV, it becomes a sensor for a solar blind. Furthermore, since the gallium oxide single crystal has a high melting point of 1740 ° C. and is already an oxide, there is no fear of deterioration due to oxidation, and it has excellent heat resistance, stability and durability.

  Leads 31 and 32 serving as terminals of the ultraviolet sensor 1 are drawn from the stem 22 to the outside of the package 2 and are electrically connected to the current / voltage source 3, respectively. One end 31a of the lead 31 is electrically connected to the pad electrode 14 via an Au bonding wire 25 having a diameter of 25 μm. Further, the lead 31 is fixed to the stem 22 through the glass 26. The lead 32 is electrically connected to the ohmic electrode 13 of the sensor chip 10 by being connected to the stem 22. Although the diameter of the bonding wire 25 is 25 μm, it is not limited to this.

  Further, as shown in FIG. 2, the single crystal substrate 11 is installed at the center of the stem 22, and the Schottky electrode 12 is formed at the center thereof. Note that the Schottky electrode 12 is formed from the single crystal substrate 11 to the semicircular portion of the pad electrode 14. In Embodiment 1, the single crystal substrate 11 and the Schottky electrode 14 are formed in a circular shape, but may be in the shape of an ellipse or the like.

  In the first embodiment, an orthogonal surface orthogonal to the growth direction of the gallium oxide single crystal is used as the light receiving surface 12r (hereinafter, this method is referred to as method A). Hereinafter, the method A will be described in detail with reference to FIG.

FIG. 3 is a schematic diagram for explaining the method A. The arrows a, b, and c shown in FIG. 3 indicate the crystal orientation of the gallium oxide single crystal.
As shown in FIG. 3, the orthogonal plane 41 is a plane orthogonal to the growth direction of the ingot 4 of the gallium oxide single crystal, that is, the c-axis direction. By using this orthogonal surface 41 as the light receiving surface 12r, the single crystal substrate 11 can be cut out only by the step of cutting the ingot 4 in a circle. When the a-surface 42 is the light-receiving surface 12r, the gallium oxide single crystal substrate is cut out by performing a two-step process of cutting the ingot 4 and slicing it. Therefore, the working time can be shortened and the yield can be improved by using the orthogonal surface 41 as the light receiving surface 12r as compared with the case where the a surface 42 is used as the light receiving surface 12r. Further, when the light receiving surface 12r is mirror-polished, the surface a may be cleaved because the a-side 42 is a cleaved surface. However, the surface may not be scaled off by the cleavage, and the working time can be reduced. .

  Here, in Embodiment 1, the orthogonal surface 41 is the light receiving surface 12r, but a surface inclined by a predetermined angle from the orthogonal surface 41 may be the light receiving surface 12r. For example, when the (001) plane (hereinafter referred to as c-plane) having a cleavage property inclined by about 14 ° from the growth direction is used as the light-receiving surface 12r, the single crystal substrate 11 is formed from the ingot 4 by using cleavage. Can be easily cut out. The inclination from the cleavage plane does not greatly affect the sensor performance. Therefore, in consideration of the workability of cutting the single crystal substrate 11 from the ingot 4, the light receiving surface 12r is preferably a surface inclined in the range of −20 ° to 20 ° from the orthogonal surface 41, and the angle formed by the orthogonal surface 41 and the c surface. A plane inclined in a range of −15 ° to 15 ° in the direction is more preferable, and a plane parallel to the orthogonal plane 41 and the c plane is particularly preferable.

  Hereinafter, a method for manufacturing the ultraviolet sensor using the method A will be described step by step with reference to FIG. FIG. 4 is a schematic diagram for explaining a manufacturing process of the ultraviolet sensor according to the first embodiment.

(S1: Growth of gallium oxide single crystal and cutting of single crystal substrate)
A gallium oxide powder having a purity of 4N is enclosed in a rubber tube as a raw material, and compression molded by an isostatic press. After compression molding, it is fired in an air atmosphere at 1400-1600 ° C. for 10-40 hours using an electric furnace, and the resulting gallium oxide sintered body is used as a raw material rod. Using this raw material rod, a gallium oxide single crystal is grown by FZ (Floating Zone) method. As single crystal growth conditions, the growth rate is 5 to 30 mm / h, the atmosphere is dry air, and the pressure is 1 atm.
The grown gallium oxide single crystal ingot 4 is attached to a slide glass and cut so that a plane perpendicular to the growth direction of the gallium oxide single crystal becomes a cut surface, whereby a single crystal substrate 11 is obtained. The thickness of the single crystal substrate 11 is preferably 0.6 to 0.7 mm.

(S2: Polishing of gallium oxide single crystal substrate)
The cut out single crystal substrate 11 is affixed to a polishing jig and ground by performing grinding for 10 to 30 minutes using a # 1000 polishing machine. Subsequently, a mirror surface is obtained by polishing each with a 1 μm diamond and CMP for 20 to 60 minutes, preferably 20 to 30 minutes.

(S3: Annealing of single crystal substrate)
The polished single crystal substrate 11 is washed with acetone and ethanol and subjected to heat treatment. This heat treatment is performed for the purpose of forming an insulating layer 11a necessary for separating carriers generated by photoexcitation on the single crystal substrate 11 and recovering defects remaining in the gallium oxide single crystal after crystal growth. The heat treatment is performed in an oxygen atmosphere at 1100 ° C. for 3 to 24 hours. When the time is shorter than 3 hours, the crystallinity is not sufficiently recovered, and even when the treatment time is longer than 24 hours, the properties are almost saturated and the characteristics are not changed. The reason for using oxygen is to supplement oxygen vacancies generated during the growth of gallium oxide single crystals.

  After the single crystal substrate 11 is annealed, electrodes are formed on the single crystal substrate 11 by the following steps S4 to S6 (not shown).

(S4: Formation of ohmic electrode)
After depositing Ti for 30 to 100 nm, preferably 50 to 80 nm, Al is deposited for 100 to 300 nm, preferably 150 to 300 nm, to form an Al / Ti ohmic electrode 13. The electrode size is 1 to 5 mmφ, preferably 3 to 4 mmφ. The contact resistance decreases as the size increases. For the vapor deposition, for example, an electron beam vapor deposition method (EB vapor deposition method) is used.

(S5: Formation of pad electrode)
A pad electrode 14 for wiring is formed on the single crystal substrate 11. The size of the pad electrode 14 is 0.05 to 1.5 mmφ, Cr (13a) is 10 to 50 nm, preferably 30 to 50 nm, Au or Pt is 30 to 100 nm, preferably 50 to 100 nm, and is deposited on the single crystal substrate 11. To do.

(S6: Formation of Schottky electrode)
As a material for the Schottky electrode 12, Au, Pt, or the like, which is a metal having a large work function because of an n-type semiconductor, is used. After vapor-depositing Ni 2 to 5 nm, preferably 2 nm, Au or Pt is vapor-deposited 6 to 10 nm to produce a metal thin-film electrode having translucency or transparency of Au / Ni or Pt / Ti. In addition, Au, Pt without inserting an Ni layer, Au, Pt, Al, Co, Ge, Sn, In, W, Mo, Cr, Cu, etc. can be used for the metal. For vapor deposition, for example, EB vapor deposition is used.

  Ni is vapor-deposited because Au or Pt alone has poor adhesion to the substrate, so a thin Ni layer is inserted to improve adhesion. This is the light receiving surface 12r, and the electrode size in this case is 1 to 5 mmφ, preferably 1 to 2 mmφ. The larger the size, the larger the light receiving surface.

Example 1
The ultraviolet sensor 1 was produced according to the process of S1-6 mentioned above.
A gallium oxide powder having a purity of 4N was enclosed in a rubber tube and compression molded by an isostatic press. After the compression molding, firing was performed in an air atmosphere at 1500 ° C. for 40 hours using an electric furnace, and a gallium oxide single crystal was grown by the FZ method using the obtained gallium oxide sintered body. As single crystal growth conditions, the growth rate was 20 mm / h, the atmosphere was dry air, and the pressure was 1 atm.
The obtained gallium oxide single crystal ingot 4 was attached to a slide glass and cut so that a plane perpendicular to the growth direction of the gallium oxide single crystal was a cut surface. The thickness of the single crystal substrate 11 was 0.65 mm.

  The cut out single crystal substrate 11 was affixed to a polishing jig, and was ground by grinding with a # 1000 polishing machine for 20 minutes. As the polishing jig, MA-200D manufactured by Musashino Electronics Co., Ltd. was used. Subsequently, a mirror surface was obtained by polishing each with a 1 μm diamond and CMP for 30 minutes.

  The polished single crystal substrate 11 was washed with acetone and ethanol, and heat-treated at 1100 ° C. for 4 hours in an oxygen atmosphere.

  Next, an electrode was manufactured according to the above-described steps S4 to S6. The ohmic electrode 13 on the second surface of the single crystal substrate 11 was deposited with Ti by 75 nm and then with Al by 300 nm. On the other hand, the Schottky electrode 12 on the first surface of the single crystal substrate 11 was formed by depositing 2 nm of Ni and then depositing 8 nm of Au. The pad electrode 14 for wiring was 1 mmφ, and after depositing 50 nm of Cr, deposit 100 nm of Au. At this time, the substantial light receiving portion is a portion obtained by removing the pad electrode 1 mmφ from the Schottky electrode portion.

In order to protect the single crystal substrate 11 on which the Schottky electrode 12 was formed, packaging was performed using the package 2 in which the window member 21 was previously bonded to the cap 23 with an epoxy adhesive and the leads 31 to 32 were provided. At this time, the package 2 was filled with an inert gas.
Ultraviolet rays can be detected by connecting the current / voltage source 3 to the leads 31 to 32 of the packaged ultraviolet sensor 1 and measuring the current value as shown in FIG.

  A plurality of ultraviolet sensors 1 prepared in this way are prepared, and a plurality of ultraviolet sensors 1 are continuously irradiated with ultraviolet rays having a wavelength of 254 nm using a low pressure mercury lamp QGL200U-21 manufactured by Iwasaki Electric Co., Ltd. Was measured. Moreover, the electrostatic capacitance [F] of the some ultraviolet sensor 1 was measured by CV measurement. For the CV measurement, M1-490K manufactured by Sanwa Denki Keiki Co., Ltd. was used. The measurement results are shown in FIG.

FIG. 5 is a graph illustrating sensor sensitivity and capacitance of the ultraviolet sensor according to the first embodiment. The shaded area shown in FIG. 5 indicates the characteristic range of the ultraviolet sensor using the a-surface as the light receiving surface.
The ultraviolet sensor using the a-surface as the light-receiving surface changes the sensor sensitivity to 1.0 × 10 ^{−2 to} 1.0 × 10 ⁻⁴ [A / W] and electrostatic capacity by changing the production conditions of the ultraviolet sensor. Can be changed from 1.0 × 10 ^{−12 to} 1.0 × 10 ⁻⁹ [F]. As shown in FIG. 5, it was confirmed that the ultraviolet sensor 1 has the same sensor characteristics (sensor sensitivity, capacitance, etc.) as the ultraviolet sensor using the a-surface as the light receiving surface.
In addition, the single crystal substrate used for the ultraviolet sensor using the a-surface as the light receiving surface 12r can be cut out from about 25 to 30 sheets from the ingot. On the other hand, about 50 to 60 single crystal substrates 11 could be cut out from the ingot 4.

(Embodiment 2)
In the first embodiment, the ultraviolet sensor is manufactured by using the above-described method A. However, in addition to the method A, the following methods B to E are appropriately combined to reduce the cost and provide an ultraviolet sensor having good sensor characteristics. Can be made.
Method B: A method of growing a gallium oxide single crystal by adjusting the amount of impurities in the raw material powder used when growing the gallium oxide single crystal.
Method C: A method of adjusting the surface state of the single crystal substrate.
Method D: A method in which an ohmic electrode is formed on a single crystal substrate using an ultrasonic soldering device (ultrasonic soldering iron) and die bonding is performed between the single crystal substrate and a stem.
Method E: A method of forming a Schottky electrode using the IBS method.

The configuration of an ultraviolet sensor that combines all of the above-described methods A to E will be described with reference to FIG.
FIG. 6 is a cross-sectional view showing a configuration of the ultraviolet sensor according to the second embodiment. In FIG. 6, the same reference numerals as those in FIG. 1 denote the same elements as those shown in FIG.

  The ultraviolet sensor 100 includes a sensor chip 110 instead of the sensor chip 10 illustrated in FIG. 1, and includes a package 102 instead of the package 2. The sensor chip 110 has a single crystal substrate 111 instead of the single crystal substrate 11 shown in FIG. The sensor chip 110 has a Schottky electrode 112 instead of the Schottky electrode 12 and an ohmic electrode 113 instead of the ohmic electrode 13.

  The package 102 is different from the package 2 in that the window member 21 is bonded to the cap 23 by a low-melting-point glass 124, and the single crystal substrate 111 is adjusted in Si concentration and Fe concentration in the raw material powder and polishing scratches. This is different from the single crystal substrate 11 in that respect. The Schottky electrode 112 is different from the Schottky electrode 12 in that the Schottky electrode 112 is formed on the single crystal substrate 111 by using the IBS method. The ohmic electrode 113 is formed on the single crystal substrate 11 by a low melting point metal using an ultrasonic solderer. It differs from the ohmic electrode 13 in that it is formed.

Next, the details of the methods B to E will be described using the configuration of the ultraviolet sensor 100 described above. First, method B will be described.
Method B is a method for growing a gallium oxide single crystal having a low carrier density by adjusting the amount of impurities in the raw material powder. Impurities to be adjusted include Si and Fe.

The carrier density in the crystal and sensor sensitivity are closely related, and the carrier density range is preferably 1 × 10 ¹⁷ to 1 × 10 ^18, more preferably 1.47 × 10 ^{17 to} 2.51 × 10 ¹⁸ , 2-5 * 10 < ¹⁷ > cm <^-3> is especially preferable. When the carrier density is too high, the gallium oxide single crystal has high conductivity but the crystallinity is lowered, and when applied to the sensor chip 110, not only high sensor sensitivity but also dark current increases. . On the other hand, when the carrier density is too low, the gallium oxide single crystal has a high resistance in the crystal and the photocurrent hardly flows.

  Si is closely related to the carrier density of the grown gallium oxide single crystal, and the Si concentration in the raw material powder is preferably 1 to 50 ppm, more preferably 5 to 30 ppm, and particularly preferably 6 to 29 ppm. . The carrier density tends to increase in proportion to the Si concentration, and if the Si concentration is too high, the crystallinity of the gallium oxide single crystal is lowered, which is not suitable for application to the sensor chip 110. On the other hand, when the Si concentration is too low, the resistance in the gallium oxide single crystal becomes high, and the photocurrent flowing when applied to the sensor chip 110 becomes small.

  Fe affects the conductivity of the gallium oxide single crystal, and the Fe concentration in the raw material powder is preferably 3 ppm or less, and particularly preferably 1 ppm or less. This is because, when the sensor chip 110 is made from a gallium oxide single crystal using a raw material powder containing a lot of Fe, the conductivity is remarkably reduced by incorporating Fe into the gallium oxide single crystal, and ultraviolet rays This is because it becomes difficult to react.

Next, method C will be described with reference to FIG.
FIG. 7 is a diagram illustrating the surface state of the Schottky electrode. In FIG. 7, the same reference numerals as those in FIG. 6 denote the same elements as those shown in FIG.
In the method C, when the single crystal substrate 111 is mirror-polished, the first surface of the single crystal substrate 111 is provided with a predetermined polishing scratch as shown in FIG. In this method, the Schottky electrode 112 is formed in a mesh shape. This technique C relieves stress caused by the difference in thermal expansion coefficient between the Schottky electrode 112 and the single crystal substrate 111, suppresses a decrease in sensor sensitivity due to disconnection of the Schottky electrode 112, and the durability of the sensor chip 110. Has the effect of improving the performance.

The polishing scratches are preferably 0.1 to 0.5 mm in length and 0.02 to 0.1 mm in width. Moreover, 10-100 pieces are preferable within the range of 1 mm < ² >, and 30-60 pieces are especially preferable for an abrasion crack. If the polishing scratches exceed this size, or if the number of polishing scratches exceeds this range, the Schottky electrode 113 may be disconnected. On the other hand, when the polishing scratches are less than this size, or when the number of polishing scratches is less than this range, the above-described stress relaxation is significantly reduced.

  The role of the Schottky electrode 112 formed on the first surface of the single crystal substrate 111 is to collect carriers generated by ultraviolet excitation and to extract them as a photocurrent. If the location where the carrier is generated directly under the Schottky electrode 112 and the pad electrode 14 and the bonding wire 25 are electrically connected by the Schottky electrode 112, the carrier can be taken out as a photocurrent. Therefore, even when the first surface of the single crystal substrate 111 has irregularities due to polishing flaws, and the Schottky electrode 112 is formed in a mesh shape along with the irregularities, the function as the Schottky electrode 112 is as long as it is not disconnected. There is no significant damage. Note that the polishing scratches are not limited to the first surface of the single crystal substrate 111 but may be uniformly provided on the surface of the single crystal substrate 111 such as the second surface of the single crystal substrate 111.

Next, method D will be described.
Method D is a method of forming the ohmic electrode 113 on the single crystal substrate 111 with a low melting point metal using an ultrasonic soldering machine.

  The ultraviolet sensor operates by receiving light such as ultraviolet light and taking out the generated photocurrent as a signal. In order to efficiently extract this photocurrent to the outside, it is necessary to reduce the resistance of the ohmic electrode. The ohmic electrode formed by vapor deposition has a resistance between the ohmic electrodes of about 1 to 10 [kΩ]. By subjecting the gallium oxide single crystal substrate on which this electrode is deposited to a sintering process, the resistance between the ohmic electrodes can be improved.

  However, according to the method D, the ohmic electrode 113 having the same resistance as that obtained by the above-described sintering process can be formed by using an ultrasonic solderer and a low melting point metal when the ohmic electrode 113 is formed. it can. Furthermore, since the ohmic electrode 113 can be formed on the single crystal substrate 111 in a short time without performing a method that requires a vacuum process such as vapor deposition, an effect of cost reduction can be achieved. For example, ultrasonic solder, In, Sn, or the like is used for the low melting point metal.

Further, together with the formation of the ohmic electrode 113, die bonding of the single crystal substrate 111 and the stem 22 is performed using a low melting point metal. Since the die bonding material does not contain an organic substance, it is possible to suppress the decomposition of the organic substance and the absorption of the ultraviolet ray by the decomposed substance by the ultraviolet irradiation, and it is possible to detect ultraviolet rays having a shorter wavelength.
Further, by bonding the window member 21 and the cap 23 with the low-melting glass 124, the effect of suppressing the ultraviolet absorption by the organic substance can be obtained as in the case of die bonding using the low-melting metal.

Next, method E will be described.
The technique E is a technique for forming the Schottky electrode 112 by evaporating Au or Pt on the single crystal substrate 111 using the IBS method.

  The higher the density of the metal thin film deposited on the gallium oxide single crystal substrate, the higher the durability against ultraviolet rays. However, Au or Pt alone has poor adhesion to the gallium oxide single crystal substrate. In this method, in order to supply Au or Pt to the substrate with a stronger force, an IBS method is used in which film formation is performed at a high vacuum of two orders of magnitude or more compared to a normal sputtering method. By performing sputtering under high vacuum by the IBS method, the kinetic energy imparted to the particles can be deposited on a predetermined substrate with almost no loss, so that a thin film with high adhesion and density can be obtained. Therefore, by forming a dense Schottky electrode 112 as a metal thin film on the single crystal substrate 111 using the IBS method, an electrode having a higher density and adhesion than an electrode formed using, for example, the EB vapor deposition method can be obtained. As a result, durability can be improved.

  In the second embodiment, an ultraviolet sensor is manufactured by appropriately combining B to E with the above-described method A, but two methods such as method B and C, method B and D, method C and E are added to method A. Even if it is an ultraviolet sensor, there exist effects, such as a cost reduction and the improvement of a sensor sensitivity. In addition, the ultraviolet sensor which added the three methods such as the methods B to D, the methods C to E, the methods B, C, and E to the method A is lower in cost than the ultraviolet sensor obtained by adding the two methods to the method A, and the sensor sensitivity. It is more preferable in terms of improvement, and an ultraviolet sensor obtained by adding all methods B to E to method A is particularly preferable.

Next, a manufacturing method of the ultraviolet sensor 100 will be described for each manufacturing process with reference to FIGS.
FIG. 8 is a schematic diagram for explaining a manufacturing process of the ultraviolet sensor according to the second embodiment.

(S11: Growth of gallium oxide single crystal and cutting of crystal substrate)
A gallium oxide powder having a purity of 4N with an Si concentration of 30 ppm or less and an Fe concentration of 1 ppm or less is enclosed in a rubber tube as a raw material, and compression molded by an isostatic press. After compression molding, it is fired in an air atmosphere at 1400-1600 ° C. for 10-40 hours using an electric furnace, and the resulting gallium oxide sintered body is used as a raw material rod. Using this raw material rod, a gallium oxide single crystal is grown by FZ (Floating Zone) method. As single crystal growth conditions, the growth rate is 5 to 30 mm / h, the atmosphere is dry air, and the pressure is 1 atm.
The grown gallium oxide single crystal ingot 104 is attached to a slide glass and cut so that a plane perpendicular to the growth direction of the gallium oxide single crystal becomes a cut surface. This is used as a single crystal substrate 111. The thickness of the single crystal substrate 111 is preferably 0.6 to 0.7 mm.

(S12: Polishing of gallium oxide single crystal substrate)
The cut out single crystal substrate 111 is affixed to a polishing jig and ground by performing grinding for 10 to 30 minutes using a # 1000 polishing machine. Subsequently, a mirror surface is obtained by polishing each with a 1 μm diamond and CMP for 20 to 60 minutes, preferably 20 to 30 minutes. At this time, polishing scratches having a length of 0.1 to 0.5 mm and a width of 0.02 to 0.1 mm are provided, and 30 to 60 polishing scratches are provided within a range of 1 mm ² .

(S13: Single crystal annealing)
The polished single crystal substrate 111 is washed with acetone and ethanol and subjected to heat treatment. This heat treatment forms the insulating layer 111a necessary for the separation of carriers generated by photoexcitation on the single crystal substrate 111 as in the first embodiment, and recovers defects remaining in the gallium oxide single crystal after crystal growth. Do it for the purpose. The heat treatment is performed in an oxygen atmosphere at 1100 ° C. for 3 to 24 hours. In addition, in the case of a single crystal substrate having a low carrier density prepared by using raw material powder having a low Si concentration, this step can be omitted because an insulating layer for carrier separation is not required. is there.

(S14: Formation of ohmic electrode)
The low melting point metal 5 is attached to the second surface of the single crystal substrate 111 with an ultrasonic solderer heated to 200 to 250 ° C. Thereafter, the surface oxide film of the low-melting-point metal 5 is broken preferably by applying vibration with ultrasonic waves for about 1 to 5 seconds, and the low-melting-point metal 5 diffuses into the single-crystal substrate 111 so that the ohmic electrode 113 is single crystal It is formed on the whole or part of the second surface of the substrate 111. The contact resistance decreases as the size increases.

(S15: Mount on stem)
A metal block 6a is placed on a hot plate heated to 300 to 350 degrees, and a stem 22 provided with leads 31 to 32 is placed on the block 6a and heated. The single crystal substrate 111 on which the ohmic electrode 113 is formed is placed on the stem 22 so that the ohmic electrode 113 and the stem 22 are in contact with each other. Uniform pressure is applied from above the single crystal substrate 111 with tweezers, slide glass or the like, the low melting point metal 5 on the second surface of the single crystal substrate 111 is spread uniformly, and die bonding of the single crystal substrate 111 and the stem 22 is performed. . By removing the stem 22 from the block 6a and cooling, the mounting of the single crystal substrate 111 to the stem 22 is completed.

(S16: Formation of pad electrode)
A pad electrode 14 for wire bonding is produced. The upper surface of the single crystal substrate 111 is covered with a pad electrode mask 6b, and a pad electrode 14 is formed by EB vapor deposition. The size of the pad electrode 14 is 0.05 to 1.5 mmφ, Cr14a is 10 to 100 nm, preferably 30 to 50 nm, Au or Pt14b is 80 to 150 nm, preferably 90 to 100 nm, and is deposited on the first surface of the single crystal substrate 111. To do.

(S17: Formation of Schottky electrode)
As a material for the Schottky electrode 112, as in the first embodiment, Au, Pt, or the like, which is a metal having a high work function, is used. In order to deposit the Schottky electrode 112 with high adhesion and durability on the single crystal substrate 111, the upper portion of the single crystal substrate 111 is covered with the Schottky electrode mask 6c, and Au or Pt is deposited by 6 to 10 nm by the IBS method. Then, the Schottky electrode 112 which is a translucent or transparent light-transmitting metal thin film is manufactured. In addition to Au and Pt, Al, Co, Ge, Sn, In, W, Mo, Cr, Cu, etc. can be used as the metal.
In the formation of a Schottky electrode by the IBS method, ion energy, ion current density, ion species, operating vacuum during sputtering, deposition rate, and the like are listed as formation conditions. The conditions used for forming the Schottky electrode 112 are as follows: ion energy is 500 to 1200 eV, ion current density is 1 to 10 mA / cm 2, ion species is Ar ion, operating vacuum is 4 to 5 × 10 ⁻³ Pa, and deposition rate is 0.1-0.2 nm / sec is preferable. For example, a 10 nm thick Au thin film formed under these conditions has an ultraviolet transmittance of about 60% at a wavelength of 200 nm. This is the light receiving surface 12r, and the electrode size in this case is 1 to 5 mmφ, preferably 1 to 2 mmφ. Note that the larger the electrode size, the larger the light receiving surface, but the damage when receiving ultraviolet rays with a constant illuminance also increases.

(Example 2)
A plurality of ultraviolet sensors having different Si concentrations and Fe concentrations were produced according to the steps S11 to S17 shown in FIG.
A gallium oxide powder having a Si concentration of 6 ppm and an Fe concentration of 1 ppm and having a purity of 4N was sealed in a rubber tube and compression molded by an isostatic press. After the compression molding, firing was performed in an air atmosphere at 1500 ° C. for 40 hours using an electric furnace, and a gallium oxide single crystal was grown by the FZ method using the obtained gallium oxide sintered body. As single crystal growth conditions, the growth rate was 20 mm / h, the atmosphere was dry air, and the pressure was 1 atm.
The obtained gallium oxide single crystal ingot 104 was affixed to a slide glass and cut so that the orthogonal plane 41 was a cut plane. This was used as a single crystal substrate 111. The thickness of the single crystal substrate 111 was 0.65 mm.

  The cut out single crystal substrate 111 was affixed to a polishing jig and grounded by grinding with a # 1000 polishing machine for 20 minutes. MA-200D manufactured by Musashino Electronics Co., Ltd. was used as the polishing jig. Subsequently, a mirror surface was obtained by polishing each with a 1 μm diamond and CMP for 30 minutes.

  The polished single crystal substrate 111 was washed with acetone and ethanol, and heat-treated at 1100 ° C. for 4 hours in an oxygen atmosphere.

  The low melting point metal 5 is applied to the second surface of the single crystal substrate 111 with an ultrasonic solderer heated to 225 degrees, and the ohmic electrode 113 is attached to the second surface of the single crystal substrate 111 by applying vibration with ultrasonic waves for about 3 seconds. Formed in part.

  A metal block 6 a was placed on a hot plate heated to 325 degrees, the stem 22 was placed on the block 6 a and heated, and the single crystal substrate 111 on which the ohmic electrode 113 was formed was placed on the stem 22. The single crystal substrate 111 was pressed uniformly with a slide glass, and die bonding of the single crystal substrate 111 and the stem 22 was performed. After die bonding, the stem 22 was removed from the block 6a and cooled.

  After cooling, the upper surface of the single crystal substrate 111 was covered with a pad electrode mask 6b, and a pad electrode 14 was formed by EB vapor deposition. The size of the pad electrode 14 was 0.775 mmφ, Cr 14 a was 50 nm, Au 14 b was 100 nm, and vapor deposition was performed on the first surface of the single crystal substrate 111.

Au was vapor-deposited to a thickness of 10 nm on the first surface of the single crystal substrate 111 including the light receiving surface 12r by the IBS method to form the Schottky electrode 112. As conditions for the IBS method, ion energy is 850 eV, ion current density is 5.5 mA / cm ² , ion species is Ar ion, operating vacuum is 4.5 × 10 ⁻³ Pa, and deposition rate is 0.15 nm / sec. It was. The electrode size was 2 mmφ. At this time, a substantial light receiving portion is a portion obtained by excluding 0.775 mmφ of the pad electrode 14 from 2 mmφ of the Schottky electrode 112.

In order to protect the single crystal substrate 111 on which the Schottky electrode 112 is formed, packaging was performed using the package 102 in which the window member 21 was previously bonded to the cap 23 with the low melting point glass 124 and the leads 31 to 32 were provided. . At this time, the package 102 was filled with an inert gas to produce the ultraviolet sensor 100A.
Next, using a plurality of raw material powders having different Si concentrations and Fe concentrations, ultraviolet sensors B to G were produced in the same manner as the ultraviolet sensor 100A.

  The UV sensors 100A-G were continuously irradiated with UV light having a wavelength of 254 nm using a low-pressure mercury lamp QGL200U-21 manufactured by Iwasaki Electric Co., Ltd., and it was confirmed whether or not to operate as an UV sensor. As a result, the ultraviolet sensors 100F and G did not operate as ultraviolet sensors.

  FIG. 9 is a graph showing the impurity concentration of the ultraviolet sensor according to Example 2. Each of A to G shown in FIG. 9 represents each of the ultraviolet sensors 100A to G. The hatched area indicates the Fe concentration range that operates as an ultraviolet sensor. As shown in FIG. 9, the ultraviolet sensors 100F and G that do not operate as the ultraviolet sensor have Fe concentrations of 14 and 18 ppm. From this, it was confirmed that those having an Fe concentration of 14 or more outside the hatched range do not operate as an ultraviolet sensor. Moreover, it was confirmed that the Fe concentration of 3 or less operates as an ultraviolet sensor.

Next, the specific resistance [Ωcm] and the carrier density [cm ⁻³ ] of the sensor chips of the ultraviolet sensors 100A to 100C were measured using a Hall effect measuring device manufactured by Bio-Rad Laboratories. The measurement results are shown in FIGS.

FIG. 10 is a table showing the impurity concentration, specific resistance, and carrier density of the ultraviolet sensor according to Example 2. FIG. 11 is a graph showing the correlation of the specific resistance, carrier density, and Si concentration of the ultraviolet sensor according to Example 2.
As shown in FIGS. 10 and 11, since the carrier density and specific resistance decrease as the Si concentration increases, and the carrier concentration and specific resistance increase as the Si concentration decreases, they are included in the raw material powder. It has been confirmed that the Si concentration is closely related to the carrier density of the grown gallium oxide single crystal.

(Example 3)
In accordance with steps S11 to S17 shown in FIG. 8, a plurality of ultraviolet sensors having different states on the surface of the single crystal substrate were produced.
A plurality of ultraviolet sensors were produced under the same conditions as in Example 2 except that raw material powder having an Si concentration of 4 ppm and an Fe concentration of 1 ppm was used. In manufacturing the plurality of ultraviolet sensors, each of the plurality of ultraviolet sensors has a different number of polishing scratches per unit area on the single crystal substrate 111 in the step of polishing the gallium oxide single crystal substrate shown in S12 of FIG. The polishing scratches were adjusted.
Using a low-pressure mercury lamp QGL200U-21 manufactured by Iwasaki Electric Co., Ltd., a plurality of ultraviolet sensors having different numbers of polishing scratches are continuously irradiated with ultraviolet light having a wavelength of 254 nm. % Time to decrease was measured. The measurement results are shown in FIG.

FIG. 12 is a graph showing the correlation among the sensor sensitivity, the sensor life, and the number of polishing flaws of the ultraviolet sensor according to Example 3.
As shown in FIG. 12, the sensor sensitivity slightly decreases as the number of polishing flaws increases, but no significant decrease is observed. From this, it was confirmed that the influence of the number of polishing scratches on the sensor sensitivity was not great. On the other hand, it was confirmed that the time until the sensor sensitivity decreased by 10% became longer as the number of polishing scratches increased. This is because when the Schottky electrode 112 is formed in a mesh shape in accordance with the unevenness of the first surface of the single crystal substrate 111 due to polishing scratches, the influence of heat accompanying ultraviolet irradiation can be alleviated. Note that when the Schottky electrode 112 is uniformly formed on a flat single crystal substrate 111 that is not provided with polishing scratches, the sensor sensitivity is high, but a metal thin film such as Au aggregates due to heat, which may lead to a decrease in sensitivity. .

Example 4
In accordance with the steps S11 to S17 shown in FIG. 8, a plurality of ultraviolet sensors having different ohmic electrode forming methods were produced.
An ultraviolet sensor 100H was manufactured under the same conditions as in Example 2 except that raw material powder having an Si concentration of 4 ppm and an Fe concentration of 1 ppm was used. When the ultraviolet sensor 100H is manufactured, an ohmic electrode is formed on the single crystal substrate 111 using Cerasolzer (registered trademark) manufactured by Kuroda Techno Co., Ltd. as a low melting point metal in the ohmic electrode forming step shown in S14 of FIG. 113 was formed.

Further, an ultraviolet sensor 100I and an ultraviolet sensor 100J using the ohmic electrode forming step shown in S4 of the first embodiment instead of the ohmic electrode forming step shown in S14 of FIG. 8 were manufactured.
The ultraviolet sensor 100I includes a gallium oxide single crystal substrate on which an ohmic electrode is formed by Ti / Al vapor deposition in the ohmic electrode forming step. In the ultraviolet sensor 100I, the gallium oxide single crystal substrate is mounted on the stem 22 using an In junction.
The ultraviolet sensor 100J includes a gallium oxide single crystal substrate on which an ohmic electrode is formed by vapor deposition of Ti / Al and subjected to sintering (800 ° C., 2 minutes) in the ohmic electrode formation process. In the ultraviolet sensor 100J, the gallium oxide single crystal substrate is mounted on the stem 22 using a silver paste.

  The resistance between the ohmic electrodes of these ultraviolet sensors 100H to J was measured using a diode curve tracer manufactured by Kikusui Electronics Corporation. In addition, the ultraviolet ray sensors 100H to J were continuously irradiated with ultraviolet rays having a wavelength of 254 nm using the above-described SLUV-6, and the sensor sensitivity was measured. The measurement results are shown in FIGS.

  FIG. 13 is a graph illustrating resistance between ohmic electrodes in the ultraviolet sensor according to Example 4. FIG. 14 is a graph illustrating sensor sensitivity in the ultraviolet sensor according to Example 4. Each of HJ shown in FIGS. 13 and 14 represents the ultraviolet sensors 100H-J, respectively.

  As shown in FIG. 13, the ohmic electrode of the ultraviolet sensor 100I formed by vapor deposition has a resistance of 1 to 10 kΩ, and the ohmic electrode of the ultraviolet sensor 100J subjected to the sintering process is 10 to 1000Ω. Therefore, although the improvement of resistance can be confirmed by the sinter process, it leads to a cost increase since the process is increasing. On the other hand, it was confirmed that the ohmic electrode 113 of the ultraviolet sensor 100H has a resistance equivalent to that of the ultraviolet sensor 100J.

  Further, as shown in FIG. 14, it was confirmed that the ultraviolet sensor 100J had better sensor sensitivity than the ultraviolet sensor 100I, and the ultraviolet sensor 100H had better sensor sensitivity than the ultraviolet sensor 100J. From this, it can be seen that the use of ultrasonic solder improves the ohmic characteristics and, as a result, increases the photocurrent that can be extracted as an ultraviolet sensor.

(Example 5)
In accordance with the steps S11 to S17 shown in FIG. 8, a plurality of ultraviolet sensors having different Schottky electrode forming methods were produced.
An ultraviolet sensor 100K was produced under the same conditions as in Example 2 except that raw material powder having an Si concentration of 24 ppm and an Fe concentration of 1 ppm was used.
Further, an ultraviolet sensor 100L using the Schottky electrode formation step shown in S6 of the first embodiment instead of the Schottky electrode formation step shown in S17 of FIG. 8 was manufactured.

  The ultraviolet ray sensors 100K and L were continuously irradiated with ultraviolet rays having a wavelength of 254 nm using the above-described QGL200U-21, and the sensor sensitivity was measured. The measurement results are shown in FIG.

FIG. 15 is a graph illustrating sensor sensitivity in the ultraviolet sensor according to Example 5. K and L shown in FIG. 15 indicate the ultraviolet sensors 100K and L, respectively.
As shown in FIG. 15, the ultraviolet sensor 100L has a sensor sensitivity of 3 × 10 ^{−3 to} 6 × 10 ⁻⁴ [A / W], while the ultraviolet sensor 100K has a sensor sensitivity of 1 × 10 ^{−3 to} 6 × 10 ^−3. [A / W]. Therefore, it was confirmed that the sensor sensitivity is improved when the Schottky electrode 112 is formed by using the IBS method.

  The present invention can be implemented in various other forms without departing from the gist or main features thereof. Therefore, the above-described first and second embodiments are merely examples in all respects and should not be interpreted in a limited manner. The scope of the present invention is shown by the scope of claims, and is not restricted by the text of the specification. Moreover, all modifications, various improvements, substitutions and modifications belonging to the equivalent scope of the claims are all within the scope of the present invention.

  The orthogonal surface described in the claims is, for example, the orthogonal surface 41 in the first and second embodiments, and the light receiving surface is, for example, the light receiving surface 12r. The gallium oxide single crystal substrates are, for example, gallium oxide single crystal substrates 11 and 111, and the packages are, for example, package 2 and package 102. The first surface is, for example, the first surface of the gallium oxide single crystal substrates 11 and 111, and the second surface is, for example, the second surface of the gallium oxide single crystal substrates 11 and 111. The low melting point metal is, for example, the low melting point metal 5, and the low melting point glass is, for example, the low melting point glass 124. The window member is, for example, a window member 21, and the first and second terminals are, for example, leads 31 and 32.

1,100 UV sensor,
2,102 packages,
3 Current / voltage source,
4,104 ingots,
5 low melting point metal,
10,110 sensor chip,
11,111 Gallium oxide single crystal substrate,
12,112 Schottky electrodes,
13,113 ohmic electrodes,
14 pad electrodes,
20 opening,
21 window members,
22 stem,
23 cap,
24 adhesives,
25 Bonding wire,
26 Glass,
31, 32 leads,
31a One end of the lead 31,
41 orthogonal plane,
124 Low melting glass.

Claims (18)

A gallium oxide single crystal substrate having a light-receiving surface with an orthogonal plane orthogonal to the growth direction of the gallium oxide single crystal or a plane inclined at a predetermined angle from the orthogonal plane;
A first electrode formed on a first surface of the gallium oxide single crystal substrate;
A second electrode formed on a second surface of the gallium oxide single crystal substrate including the light receiving surface;
An ultraviolet sensor comprising:   The predetermined angle is an angle formed by the orthogonal plane and a (001) plane of the gallium oxide single crystal, and is an angle of −20 ° or more and 20 ° or less from the orthogonal plane in the direction of the angle. Item 6. The ultraviolet sensor according to Item 1.   The first electrode is an ohmic electrode that is in ohmic contact with the gallium oxide single crystal substrate, and is formed by diffusing a low-melting-point metal into a part of the gallium oxide single crystal substrate. Item 3. The ultraviolet sensor according to Item 2.   The second electrode is a light-transmitting metal thin film formed on the light receiving surface, making a Schottky contact with the gallium oxide single crystal substrate and deposited on the gallium oxide single crystal substrate by an IBS method. The ultraviolet sensor according to claim 1. A package in which the gallium oxide single crystal substrate is housed and sealed from an external atmosphere, and a window member having a light-transmitting property with respect to ultraviolet rays is provided at least in part;
The ultraviolet sensor according to claim 1, further comprising: first and second terminals that are electrically connected to the first electrode and the second electrode and are drawn out of the package. . The window member is bonded to the package with a low-melting glass,
6. The ultraviolet sensor according to claim 5, wherein the gallium oxide single crystal substrate is die-bonded inside the package with a low melting point metal. The light receiving surface has 10 or more and 100 or less scratches of 1 mm ^{2 to} a length of 0.1 mm or more and 0.5 mm or less and a width of 0.02 mm or more and 0.1 mm or less. The ultraviolet sensor according to claim 1.   The ultraviolet sensor according to claim 1, wherein the gallium oxide single crystal has an Si concentration of 1 ppm or more and 50 ppm or less and an Fe concentration of 3 ppm or less. 9. The ultraviolet sensor according to claim 1, wherein the gallium oxide single crystal has an electric conductivity of a carrier density of 1 × 10 ¹⁷ cm ⁻³ or more and 1 × 10 ¹⁸ cm ⁻³ or less. The gallium oxide single crystal is cut at a predetermined thickness so as to receive a cut surface so that a plane orthogonal to the growth direction of the gallium oxide single crystal or a plane inclined at a predetermined angle from the plane is a cut plane. Face and
Forming a first electrode on a first surface of the gallium oxide single crystal substrate;
A method of manufacturing an ultraviolet sensor, comprising: forming a second electrode on a second surface of the gallium oxide single crystal substrate including the light receiving surface.   The predetermined angle is an angle formed by the orthogonal plane and a (001) plane of the gallium oxide single crystal, and is an angle of −20 ° or more and 20 ° or less from the orthogonal plane in the direction of the angle. Item 11. A method for producing an ultraviolet sensor according to Item 10. The first electrode is an ohmic electrode that is in ohmic contact with the surface of the gallium oxide single crystal substrate;
The ultraviolet sensor according to claim 10 or 11, wherein the first electrode is formed by diffusing a low melting point metal into a part of the gallium oxide single crystal substrate by a predetermined ultrasonic wave by an ultrasonic soldering device. Method. The second electrode is a Schottky electrode that makes Schottky contact with the surface of the gallium oxide single crystal substrate,
The method for manufacturing an ultraviolet sensor according to claim 10, wherein the second electrode is formed by depositing a light-transmitting metal thin film on the gallium oxide single crystal substrate by an IBS method. The gallium oxide single crystal substrate on which the first electrode and the second electrode are formed is housed in a package in which a window member having a light-transmitting property to ultraviolet rays is provided at least partially, and sealed from an external atmosphere And
The method for manufacturing an ultraviolet sensor according to claim 10, wherein first and second terminals electrically connected to the first electrode and the second electrode are drawn out of the package. The window member is bonded to the package with a low-melting glass,
15. The method of manufacturing an ultraviolet sensor according to claim 14, wherein the gallium oxide single crystal substrate is die-bonded inside the package with a low melting point metal. The cut surface was polished so as to have 10 or more and 100 or less scratches having a length of 0.1 mm or more and 0.5 mm or less and a width of 0.02 mm or more and 0.1 mm or less per 1 mm ² . The method for manufacturing an ultraviolet sensor according to claim 10, wherein the cut surface is a light receiving surface.   The gallium oxide single crystal is obtained by compressing and molding a gallium oxide powder having a Si concentration of 1 ppm or more and 50 ppm or less and an Fe concentration of 3 ppm or less, and firing it under predetermined conditions. The method for producing an ultraviolet sensor according to any one of claims 10 to 16, wherein the gallium oxide single crystal is grown by an FZ method. 18. The ultraviolet sensor according to claim 10, wherein the gallium oxide single crystal has an electric conductivity of a carrier density of 1 × 10 ¹⁷ cm ⁻³ or more and 1 × 10 ¹⁸ cm ⁻³ or less. Production method.

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