WO2012046479A1 - Photodetection element, and method of producing the photodetection element - Google Patents

Photodetection element, and method of producing the photodetection element Download PDF

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WO2012046479A1
WO2012046479A1 PCT/JP2011/065360 JP2011065360W WO2012046479A1 WO 2012046479 A1 WO2012046479 A1 WO 2012046479A1 JP 2011065360 W JP2011065360 W JP 2011065360W WO 2012046479 A1 WO2012046479 A1 WO 2012046479A1
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sensitive layer
layer
substrate
insensitive
zno
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PCT/JP2011/065360
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French (fr)
Japanese (ja)
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弘之 瀬戸
修 中河原
奏子 下藤
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株式会社 村田製作所
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Priority to CN201180048331.7A priority Critical patent/CN103180963B/en
Priority to JP2012537599A priority patent/JP5294162B2/en
Publication of WO2012046479A1 publication Critical patent/WO2012046479A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/08—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors
    • H01L31/09—Devices sensitive to infrared, visible or ultraviolet radiation
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/02—Details
    • H01L31/0224—Electrodes

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  • the present invention relates to a photodetection element and a method for manufacturing the photodetection element, and more particularly to a photoconductive photodetection element whose resistance value changes by irradiation with ultraviolet light and a method for manufacturing the photodetection element.
  • Photodetectors represented by ultraviolet sensors are widely used as flame sensors for fire alarms, burner combustion monitoring devices, etc., as well as for detecting the amount of UV irradiation outdoors, and for UV detection devices such as UV irradiation devices. In recent years, it is expected to be applied to optical communication devices.
  • photodetection elements of this type include a photoconductive type in which a resistance value is changed by ultraviolet irradiation and a photovoltaic type in which a photovoltaic force is generated by ultraviolet irradiation.
  • ZnO As a material for a light detection element, ZnO having a large band gap energy of 3.3 eV (wavelength: 375 nm) and having a good photoconductivity with respect to ultraviolet rays has attracted attention. Moreover, this ZnO is promising because it is inexpensive, excellent in safety, and easy to process.
  • Patent Document 1 proposes a photoconductive ultraviolet sensor in which a ZnO thin film and an electrode for extracting a change in resistance value due to ultraviolet irradiation of the thin film are formed on a substrate.
  • Patent Document 1 As shown in FIG. 15, patterning is performed on one main surface of a substrate 101 to form a pair of electrodes 102 a and 102 b facing each other, and the central portions of the electrodes 102 a and 102 b are masked. Sputtering is performed using ZnO as a target in this state, thereby forming a sensitive layer 103 made of a ZnO thin film.
  • an optical filter such as a bandpass filter.
  • JP-A-3-241777 (Claim 1, FIG. 1, second column, line 44 to column 47)
  • the conventional ultraviolet sensor as shown in Patent Document 1 has a large dark current because the sensitive layer 103 is exposed on the surface, has a large transient characteristic, lacks a sharp fall characteristic, and has a poor sensor performance. There was a problem of being inferior.
  • the sensitive layer 103 is in direct contact with the atmosphere as shown in FIG.
  • the above-mentioned case is inferior in spectral characteristics, and has a large response characteristic peak particularly in the UV-A region on the long wavelength side, particularly 370 nm. Therefore, flat characteristics in the entire UV-A and UV-B regions are obtained. There was a problem that it could not be obtained.
  • the insulating protective film 104 is formed on the surface of the sensitive layer 103 so that the sensitive layer 103 is not in contact with the atmosphere, the sensitive layer 103 and the insulating protective film 104 As a result, the dark current may increase. That is, in this case, the insulating protective film 104 is more stable as a compound than the sensitive layer 103, and therefore oxygen deficiency occurs on the sensitive layer 103 side, and a conductive layer is formed on the surface layer. When a voltage is applied in such a state, a current leaks through the conductive layer, leading to an increase in dark current. As a result, there is a possibility that the ultraviolet intensity cannot be detected accurately.
  • the conventional ultraviolet sensor has a large dark current and is inferior in excessive characteristics and falling characteristics, and inferior in sensor performance.
  • the present invention has been made in view of such circumstances, a high-performance photodetector capable of suppressing dark current, having good transient characteristics and falling characteristics, and excellent in spectral characteristics, and its manufacture. It aims to provide a method.
  • the inventors of the present invention have conducted extensive research using a ZnO-based material as a material for a light detection element. As a result, the insensitive layer formed of ZnO as a main component is formed on the surface of the sensitive layer. It was found that transient characteristics and falling characteristics can be improved, dark current can be suppressed, and spectral characteristics can be improved.
  • the light detection element according to the present invention includes a sensitive layer having a main component formed of ZnO, and a pair of layers arranged in an opposing manner with a predetermined interval therebetween.
  • a non-sensitive layer whose main component is made of the same material as the sensitive layer is It is characterized by being provided in contact.
  • the sensitive layer is formed on the surface of the one main surface of the substrate, the pair of electrodes is formed on the surface of the sensitive layer, and
  • the sensitive layer is preferably provided at least between the electrodes and bonded to the sensitive layer.
  • the pair of electrodes are formed on the surface of the one main surface of the substrate, and the sensitive layer covers the end of the electrode. It is also preferred that the insensitive layer is formed on the surface of one of the main surfaces, and the insensitive layer is formed on the surface of the sensitive layer.
  • the substrate is made of a translucent material that transmits the incident light.
  • the incident light is applied to at least one of the principal surface side and the other principal surface side of the substrate.
  • an insulating protective film is formed on the surface of the insensitive layer.
  • the insulating protective film is formed of a silicon compound.
  • a metal thin film having a high reflectance is formed on the surface of the insulating protective film.
  • the insensitive layer has a film thickness of 3 nm or more and less than 140 nm.
  • the sensitive layer has a thickness of 10 nm to 100 nm.
  • the method for manufacturing a photodetecting element of the present invention includes a sensitive layer formed of ZnO as a main component and a pair of electrodes arranged in a facing manner with a predetermined interval on one main surface side of the substrate.
  • a sensitive layer formed of ZnO as a main component and a pair of electrodes arranged in a facing manner with a predetermined interval on one main surface side of the substrate.
  • Forming a ZnO-based material and an insulating material whose main component is the same as that of the sensitive layer using the ZnO-based material, and applying a first film-forming process to the sensitive layer on which the electrode is formed under vacuum.
  • the second film-forming process is performed continuously following the first film-forming process, the insensitive layer made of a ZnO material on the surface of the sensitive layer, and the insulation protection It is characterized by sequentially forming films.
  • the pair of electrodes is formed on the surface of the sensitive layer, the pair of electrodes is formed on the surface of the sensitive layer,
  • the insensitive layer is preferably formed so as to be bonded to at least the sensitive layer between the electrodes.
  • the sensitive layer is covered with one of the substrates so as to cover an end portion of the electrode. It is also preferable that the insensitive layer is formed on the surface of the sensitive layer, and then the insensitive layer is formed on the surface of the sensitive layer.
  • the sensitive layer whose main component is made of ZnO and the pair of electrodes arranged opposite to each other at a predetermined interval are formed on one main surface side of the substrate
  • the insensitive layer the main component of which is made of the same material as the sensitive layer, is provided so as to be in contact with the sensitive layer. It has a —ZnO homojunction surface, which suppresses the presence of oxygen vacancies and adsorbed molecules and stabilizes the surface properties of the interface.
  • a photocurrent having a small transient characteristic corresponding to the photoexcitation intensity can be obtained, and the transient characteristic can be improved.
  • the fall characteristic is improved, and the dark current can be suppressed.
  • the insensitive layer has the same or substantially the same light absorption characteristics as the ZnO thin film, the non-uniformity of sensitivity that has a large response characteristic peak in the UV-A region on the long wavelength side, particularly around 370 nm is improved.
  • the flatness of the spectral characteristics in the wavelength band of 280 to 380 nm can be improved, and the amount of ultraviolet rays can be detected with high accuracy in the UV-A and UV-B regions.
  • the predetermined interval is used.
  • the part of the sensitive layer is joined to the insensitive layer, and the above effect can be obtained.
  • the pair of electrodes and the sensitive layer are formed on the surface of one main surface of the substrate, and the insensitive layer is also insensitive even when formed on the surface of the sensitive layer. It will join with a layer and there can exist the said effect.
  • the substrate is formed of a light-transmitting material that transmits the incident light, thereby detecting incident light from the other main surface of the substrate opposite to the sensitive layer forming surface. Can do.
  • the incident light intensity can be detected even when the incident light is applied to at least one main surface of the one main surface side and the other main surface side of the substrate.
  • an insulating protective film made of a silicon compound or the like on the surface of the insensitive layer, dark current can be reduced.
  • the sensitive layer and the insulating protective film are not in contact with each other, so that the formation of a conductive layer on the surface layer of the sensitive layer can be avoided, thereby increasing the dark current. The reduction can be achieved without doing so.
  • the metal thin film having a high reflectance is formed on the surface of the insulating protective film, when light is irradiated from the other main surface side of the substrate, the light transmitted through the sensitive layer is the metal thin film. Reflecting and contributing to carrier generation, it is possible to improve the sensor sensitivity.
  • the film thickness of the insensitive layer is set to 3 nm or more and less than 140 nm, it is possible to ensure good spectral characteristics without causing an increase in dark current.
  • the thickness of the sensitive layer is 10 nm or more and 100 nm or less, the ratio of the output current to the dark current can be sufficiently increased, and an ultraviolet sensor suitable for a specific application such as a sunshine monitor application can be obtained. Is possible.
  • a sensitive layer whose main component is made of ZnO and a pair of electrodes arranged in a facing manner with a predetermined interval are provided on one main surface of the substrate.
  • FIG. 3 is a diagram showing dark current of each sample produced in Example 1. It is a figure which shows the transient characteristic and fall characteristic of the photoresponse current of the sample numbers 1 and 5 produced in Example 1.
  • FIG. 6 is a diagram illustrating spectral characteristics of samples prepared in Example 2.
  • FIG. FIG. 6 is a diagram showing the spectral characteristics of each sample produced in Example 3.
  • FIG. 10 is a diagram showing output current characteristics of each sample produced in Example 5. It is a figure which shows ratio of the output current of sample number 21 produced in Example 5, and sample number 23, and a dark current. It is a figure which shows the optical response characteristic of the sample number 21 produced in Example 5. FIG. It is a figure which shows the optical response characteristic of the sample number 23 produced in Example 5.
  • FIG. 1 is a cross-sectional view schematically showing an embodiment of an ultraviolet sensor as a light detection element according to the present invention.
  • the ultraviolet sensor includes a sensitive layer 1 whose main component is made of ZnO, and a pair of electrodes 2a and 2b arranged opposite to each other at a predetermined interval t (for example, 5 to 10 ⁇ m).
  • a non-sensitive layer 4 formed on the main surface side and made of the same material as the sensitive layer 1 is provided so as to be in contact with the sensitive layer 1.
  • the sensitive layer 1 is formed on the surface of the substrate 3, and a pair of electrodes 2 a and 2 b are arranged on the surface of the sensitive layer 1 with a predetermined interval t facing each other. It has a planar structure.
  • the insensitive layer 4 whose main component is made of ZnO is formed at the end of the predetermined interval portion (hereinafter referred to as “bearing portion”) 5 where the sensitive layer 1 is exposed and the electrodes 2a and 2b.
  • An insulating protective film 6 is formed on the surface of the insensitive layer 4.
  • the sensitive layer 1 only needs to be formed of ZnO as a main component, and may contain a small amount of impurities (for example, Al, Ga, In, etc.) as necessary.
  • the insensitive layer 4 may not be completely the same as the sensitive layer 1 and may contain a small amount of impurities different from the sensitive layer 1 as long as the main component is formed of ZnO.
  • the material for forming the substrate 3 is not particularly limited.
  • a ferroelectric crystal such as LiTaO 3 (LT) or LiNbO 3 (LN), preferably a translucent material that transmits ultraviolet light.
  • a transparent material such as sapphire having a light transmittance of 50% or more in the ultraviolet region (for example, a region in the vicinity of 310 nm) or heat-resistant tempered glass, or a light-transmitting material having good transparency is used.
  • the insulating protective film 6 may be formed of an insulating material that can protect the ultraviolet sensor from external damage.
  • a silicon compound such as SiO 2 or SiN X can be preferably used. .
  • the electrode material for forming the electrodes 2a and 2b is not particularly limited as long as it has good conductivity and is not damaged in a series of film forming steps, and Ti, Au, Pt, Pd, etc. should be used. Can do.
  • the electrodes 2a and 2b are formed in a single layer structure or a laminated structure.
  • the lower metal layer in contact with ZnO has good adhesion to ZnO, and it is preferable to use Ti or Al that forms ohmic bonding.
  • the upper metal layer formed on the lower metal layer may be any material as long as it has good conductivity and is not damaged in a series of film forming steps. For example, Au, Pt, Pd, or the like can be used.
  • the electrodes 2a and 2b may have any shape as long as they are arranged to face each other with a predetermined interval t. For example, an interdigital type is preferable because sensitivity can be improved.
  • the insensitive layer 4 containing ZnO as a main component is interposed between the sensitive layer 1 and the insulating protective film 6, dark current does not increase and light is irradiated.
  • Various characteristics such as a transient characteristic at the rise of the light, a fall characteristic when the light irradiation is stopped, and a spectral characteristic can be improved, and a high-performance ultraviolet sensor can be obtained.
  • the bare part 5 of the sensitive layer 1 has a photoresponse current that varies greatly depending on the measurement atmosphere and the like, it is difficult to ensure reliability.
  • the bare part 5 is preferably covered with an insulating protective film 6.
  • SiO 2 when SiO 2 is used as the insulating protective film 6, the standard free energy of formation ⁇ G ° of ZnO is ⁇ 318.3 kcal / mol, whereas the standard free energy of formation ⁇ G ° of SiO 2 is ⁇ 856 kcal / mol. mol and lower, SiO 2 has a high stability as a compound in comparison with the ZnO.
  • oxygen on the ZnO surface is separated from the crystal lattice to cause oxygen vacancies, and oxygen moves to the insulating protective film 6 side to form a conductive layer on the surface of the bare part 5.
  • a voltage is applied between the electrodes 2a and 2b, a current leaks through the conductive layer, resulting in an increase in dark current during non-irradiation and a highly accurate photoresponse current during light irradiation. There is a risk that it will not be possible.
  • the insensitive layer 4 whose main component is made of ZnO is interposed between the insulating protective film 6 and the bare portion 5, and the interface of the bare portion 5 is made a ZnO-ZnO homojunction. Therefore, the formation of a conductive layer on the surface of the bare portion 5 is avoided, and the dark current is reduced.
  • FIG. 2 is an enlarged view of the main part of FIG.
  • the above-described insensitive layer 4 is formed on the surface of the bare part 5, and the insulating protective film 6 is formed on the surface of the insensitive layer 4. Since the insulating protective film 6 is more stable as a compound than the insensitive layer 4 as described above, oxygen deficiency occurs on the surface layer of the insensitive layer 4 in contact with the insulating protective film 6, and the insensitive layer Thus, the conductive layer 7 is formed on the surface layer 4. That is, the bare portion 5 does not come into contact with the insulating protective film 6, so that it is possible to avoid the formation of a conductive layer on the surface of the bare portion 5, thereby suppressing current leakage from the sensitive layer 1 and dark current. Can be avoided.
  • the moisture-resistant protective film can be formed while avoiding an increase in dark current due to the provision of the insulating protective film 6, it is possible to improve the reliability and suppress air discharge and the like. It is possible to obtain an ultraviolet sensor having good environmental resistance.
  • the insensitive layer 4 is formed on the surface of the bare part 5, the bare part 5 is joined to the insensitive layer 4 having a ZnO—ZnO homojunction surface, and dangling. Without being influenced by ring bonds (molecular orbitals in which unpaired electrons having no binding partner exist), it is possible to obtain a photoresponse current having a small transient characteristic according to the photoexcitation intensity.
  • the surface of the bare part 5 is bonded to the insensitive layer 4 through the ZnO—ZnO homojunction surface in this way, the photoresponse current is sharp even at the fall when the light irradiation is stopped. The falling characteristic can be improved.
  • the insensitive layer 4 mainly composed of ZnO having the same or substantially the same light absorption characteristics as that of the sensitive layer 1 is inserted on the surface of the bare part 5 of the sensitive layer 1, The peak can be suppressed by absorbing light in the peak wavelength band.
  • the thickness of the insensitive layer 4 is not particularly limited, but is preferably 3 nm or more and less than 140 nm. That is, when the thickness of the insensitive layer 4 is less than 3 nm, it is difficult to sufficiently reduce the dark current because the thickness of the insensitive layer 4 is too thin. On the other hand, if the film thickness of the insensitive layer 4 exceeds 140 nm, it is convenient for reducing the dark current because the film thickness is thick. However, for example, when ultraviolet rays are incident from the direction of arrow A, light absorption increases. This may cause a decrease in spectral sensitivity.
  • the current ratio I / I 0 decreases.
  • the current ratio I / I 0 becomes excessively small, which is not preferable when used for a sunshine monitor or the like. That is, when this ultraviolet sensor is used for a sunshine monitor or the like, it is the ultraviolet intensity (about 1 mW / cm 2 ) outdoors on a cloudy day, and the ratio I / I 0 is 50 in order to obtain a desired sensor sensitivity.
  • the film thickness of the sensitive layer 1 exceeds 100 nm, it falls to less than 50.
  • the thickness of the sensitive layer 1 is not limited, it is preferably 100 nm or less depending on the application.
  • the thickness of the sensitive layer 1 needs to be at least 10 nm.
  • the sensitive layer 1 is formed on the surface of one main surface of the substrate 3, and the pair of electrodes 2a and 2b are formed on the surface of the sensitive layer 1.
  • the interface of the sensitive layer 1 is a ZnO-ZnO homojunction.
  • the presence of oxygen deficiency and adsorbed molecules is suppressed, and the surface properties of the interface are stabilized.
  • a photocurrent having a small transient characteristic corresponding to the photoexcitation intensity can be obtained, and the transient characteristic can be improved.
  • the fall characteristic is improved, and the dark current can be suppressed.
  • the sensitive layer 1 is formed on the substrate 3 by using a high frequency magnetron sputtering method with a ZnO-based material as a target.
  • the substrate 3 and the target are arranged facing each other, the substrate 3 is heated, and a predetermined flow rate of argon gas and oxygen gas is introduced into the sputtering apparatus under a predetermined vacuum, and a high frequency power source is applied to perform sputtering for a predetermined time. Processing is performed to produce the sensitive layer 1 having a predetermined film thickness on the substrate 3.
  • electrodes 2a and 2b are formed on the sensitive layer 1 by a lift-off method. That is, a photoresist is applied to the surface of the sensitive layer 1 and then pre-baked, and then exposed and developed through a photomask. Thereafter, one or more electrode layers are formed by using a thin film forming method such as a vacuum evaporation method, an electron beam evaporation method, or a sputtering method. Next, unnecessary electrode layers are removed by etching using an organic solvent, thereby forming electrodes 2a and 2b arranged in a confronting manner with a predetermined interval t (for example, 5 to 10 ⁇ m).
  • a predetermined interval t for example, 5 to 10 ⁇ m
  • the insensitive layer 4 and the insulating protective film 6 are continuously formed in a vacuum using, for example, a sputtering apparatus capable of revolving.
  • the insensitive layer 4 when the insensitive layer 4 is formed, a ZnO-based material is used as a target, and when the insulating protective film 6 is formed, an insulating protective material such as a silicon compound is used as a target, and the central portions of the electrodes 2a and 2b are maintained while maintaining a vacuum state.
  • the insensitive layer 4 and the insulating protective film 6 are formed by continuously sputtering using a mask.
  • the insensitive layer 4 and the insulating protective film 6 are continuously formed in a vacuum, the interface between the insensitive layer 4 and the insulating protective film 6 can be formed uniformly. Thus, it is possible to manufacture an ultraviolet sensor that can suppress an increase in dark current even with a thinner insensitive layer 4.
  • FIG. 3 is a cross-sectional view showing a modification of the first embodiment.
  • a metal thin film 8 having a high reflectivity is formed on the surface of the insulating protective film 6.
  • the metal thin film 8 is not particularly limited as long as it has a high reflectance in the ultraviolet region, and for example, Pt, Ag, Al, Mg, Mo, or the like can be used.
  • the thickness of the metal thin film 8 is not particularly limited as long as it reflects ultraviolet light, and for example, it may be formed to about 200 nm.
  • FIG. 4 is a cross-sectional view schematically showing a second embodiment of the ultraviolet sensor according to the present invention.
  • the second embodiment includes a sensitive layer 11 whose main component is formed of ZnO.
  • a pair of electrodes 12a and 12b arranged opposite to each other at a predetermined interval t is formed on one main surface side of the substrate 13 and the main component is formed of the same material as the sensitive layer 11.
  • the sensitive layer 14 is formed over the entire surface of the sensitive layer 11.
  • a pair of electrodes 12a and 12b are arranged in a planar manner on the surface of the substrate 13 with a predetermined interval t, and the ends of the electrodes 12a and 12b are covered.
  • the sensitive layer 11 is formed on the surface of one main surface of the substrate 13 including the bare portion 15.
  • a non-sensitive layer 14 whose main component is made of ZnO is formed on the surface of the sensitive layer 11, and an insulating protective film 16 is formed on the surface of the non-sensitive layer 14.
  • the dark current is the same as in the first embodiment. Without causing an increase in the light level, it is possible to improve various characteristics such as transient characteristics at the start of light irradiation, falling characteristics when light irradiation is stopped, and spectral characteristics. Can be obtained.
  • the ultraviolet sensor according to the second embodiment can be manufactured as follows.
  • the central portions of the electrodes 12a and 12b are masked, and a high-frequency magnetron sputtering is performed using a ZnO-based material as a target.
  • the sensitive layer 11 is produced by the method, and then the insensitive layer 14 and the insulating protective film 16 are formed by the same method as in the first embodiment, whereby the ultraviolet sensor can be produced.
  • a metal thin film having a high reflectance is formed on the surface of the insulating protective film 16, and the direction opposite to the formation surface of the electrodes 12a and 12b. It is also preferable to irradiate with ultraviolet light and reflect it with a metal thin film, thereby improving the detection accuracy of ultraviolet light.
  • the electrodes 2a, 2b, 12a, and 12b it is also preferable to perform electrolytic plating on the surfaces of the electrodes 2a, 2b, 12a, and 12b to form a plating film made of Ni, Au, or the like. In this way, the plating film is formed on the electrode surface. By doing so, even if surface mounting is performed with the electrode surface facing downward, sufficient mechanical strength is imparted to the electrode surface, so that an ultraviolet sensor suitable for surface mounting can be obtained.
  • the sensitive layers 1 and 11 are produced by the high frequency magnetron sputtering method, but the film forming method is not particularly limited, and other film forming methods may be used.
  • the insensitive layer 5 and the insulating protective films 6 and 16 are continuously formed under vacuum using a sputtering apparatus capable of revolving, but the same effect can be obtained. If it is, it will not specifically limit.
  • the present invention can also be applied to other light detection elements other than the ultraviolet sensor.
  • LT substrate LiTaO 3 substrate with a thickness of about 350 ⁇ m is prepared as a substrate, and a high-frequency magnetron sputtering method is used to produce a sensitive layer with a thickness of 500 nm on the LT substrate as follows. did.
  • a non-doped ZnO sintered body was cut to a thickness of 5 mm and a diameter of 100 mm, and adhered to a copper backing plate.
  • the inside of the sputtering apparatus is evacuated to a back pressure of about 10 ⁇ 5 Pa, and then argon gas (flow rate: 5.57 ⁇ 10 ⁇ 2 Pa ⁇ m 3 / s). ) (33 sccm) and oxygen gas (flow rate: 4.90 ⁇ 10 ⁇ 3 Pa ⁇ m 3 / s) (2.9 sccm) were introduced into the sputtering apparatus, pressure: 0.35 to 0.7 Pa, high frequency output : 300 W, substrate temperature: 420 ° C., and the substrate holder was rotated for 15 minutes to perform film formation.
  • a pair of electrodes was formed on the sensitive layer by the lift-off method. That is, first, a photoresist was applied to the surface of the sensitive layer, then pre-baked, and further exposed and developed through a photomask. Next, using an electron beam evaporation method, a Ti film having a thickness of about 20 nm and an Au film having a thickness of 400 nm were sequentially formed. Then, an unnecessary electrode layer was removed using an organic solvent to form a pair of electrodes arranged opposite to each other. The interelectrode distance (predetermined interval) was 10 ⁇ m.
  • the insensitive layer and the insulating protective film were continuously formed under the following conditions.
  • Target High purity ZnO Gas flow rate: Argon 8.44 ⁇ 10 ⁇ 2 Pa ⁇ m 3 / s (50 sccm) Oxygen 1.69 ⁇ 10 ⁇ 2 Pa ⁇ m 3 / s (10 sccm) Gas pressure; 0.21 Pa High frequency output: 250W Deposition time: 5 minutes Substrate temperature: normal temperature (no heating) [Insulating protective film] Target; high-purity SiO 2 Gas flow rate: Argon 5.07 ⁇ 10 ⁇ 2 Pa ⁇ m 3 / s (30 sccm) Oxygen 2.19 ⁇ 10 ⁇ 2 Pa ⁇ m 3 / s (13 sccm) High frequency output: 600W Film formation time: 63 minutes Thereafter, an etching pattern is formed using a photoresist, the insulating protective film and the insensitive layer are selectively removed with buffered hydrofluoric acid (BHF), and a part of the electrode is exposed on the surface. In this way
  • sample numbers 3 and 4 were prepared by the same method and procedure as sample numbers 1 and 2, except that the insensitive layer was not provided and the film configuration was substrate / sensitive layer / (electrode + insulating protective film). A comparative sample was obtained.
  • FIG. 5 shows the measurement results of sample numbers 1 to 6, and the vertical axis represents dark current (A).
  • Sample Nos. 1, 2, 5, and 6 as the example samples all had a non-sensitive layer formed on the surface of the sensitive layer, so that the dark current could be suppressed to 10 ⁇ 11 A or less.
  • FIG. 6 shows the measurement results.
  • Sample No. 5 has a large transient characteristic at the time of rising, and the photoresponse current tends to increase slightly even after rising.
  • Sample No. 1 had a small transient characteristic, and after the photoresponse current rose, it became a substantially linear state, and a photoresponse current close to the photoexcitation intensity could be obtained.
  • Sample No. 1 having the insensitive layer has a smaller time change of the photoresponse current than Sample No. 5 having no insensitive layer, and can improve the transient characteristics and the falling characteristics at the time of rising.
  • the current average value of the photoresponse current for 1 to 3 seconds after light irradiation (hereinafter referred to as “initial average value”) and the current average value of the photoresponse current for 25 to 27 seconds after light irradiation (hereinafter referred to as “steady state”).
  • the average value was measured, and the ratio of the steady average value to the initial average value was determined with the initial average value set to 100, thereby measuring the rate of change of the photoresponsive current.
  • the sample number 5 is 31.7%, whereas the sample number 1 is 3.1%, and the sample number 1 has less fluctuation in the photo-response current after the start-up than the sample number 5. confirmed.
  • the inventors of the present invention used a c-cut sapphire substrate having a thickness of 350 nm on both sides and fabricated a sensitive layer having a thickness of 40 nm under a film forming condition in a high-frequency magnetron sputtering method for 15 minutes.
  • a sample was prepared by the same method and procedure as in Sample No. 1 except that the film thickness was 40 nm, and the various characteristics described above were measured. As in Sample No. 1, good results were obtained.
  • Samples Nos. 7 and 8 were prepared in the same manner and procedure as Sample No. 1, except that the thickness of the insensitive layer was 2.8 nm and 140 nm.
  • each sample was irradiated with ultraviolet light in the wavelength range of 280 to 430 nm from an ultraviolet light source equipped with a spectroscope, and the spectral characteristics were examined. It was.
  • Fig. 7 shows the measurement results.
  • the horizontal axis indicates the wavelength (nm), and the vertical axis indicates the spectral sensitivity (a.u.).
  • the spectral sensitivity improves as the thickness of the insensitive layer decreases.
  • the thickness of the insensitive layer was as thin as 2.8 nm and the flatness was good, but when dark current was measured separately, it was confirmed that the dark current was reduced.
  • Sample No. 1 has flatness that does not cause a problem in practical use, although unevenness is generated according to the irradiation wavelength of ultraviolet rays.
  • the preferable film thickness of the insensitive layer was 3 nm or more and less than 140 nm.
  • Sample numbers 11 and 12 were prepared by the same method and procedure as sample number 1 except that the distance between electrodes of the bare part (predetermined interval) was 5 ⁇ m.
  • the film structure in which the sensitive layer is formed on the bare portion and the insensitive layer and the insulating protective film are not formed is the same as the sample numbers 11 and 12 in the sample numbers 13 and 14 of the substrate / (electrode + sensitive layer). It was produced by the method / procedure.
  • Fig. 8 shows the measurement results.
  • the horizontal axis indicates the wavelength (nm), and the vertical axis indicates the spectral sensitivity (a.u.).
  • Sample Nos. 13 and 14 do not have a non-sensitive layer, and therefore do not have a ZnO—ZnO homojunction surface, the spectral characteristics have a mountain shape with a peak at a wavelength of about 370 nm and are flat. It was found that the spectral characteristics were inferior.
  • the wavelength is a wavelength band having a peak near 370 nm. It was found that this response can be effectively suppressed, and flat spectral characteristics can be realized in the UV-A and UV-B regions of 280 nm to 380 nm.
  • Samples Nos. 15 to 18 were prepared in the same manner as Sample No. 1 except that the thickness of the sensitive layer was variously changed to 10 nm, 20 nm, 40 nm, and 160 nm.
  • Figure 9 shows the relationship between the film thickness and the output current I and the dark current I 0.
  • the horizontal axis represents the film thickness (nm)
  • the vertical axis represents the current I (A)
  • the ⁇ mark represents the output current I
  • the ⁇ mark represents the dark current I 0 .
  • FIG. 10 shows the relationship between each film thickness, the current ratio I / I 0 between the output current I and the dark current I 0 .
  • the horizontal axis is the film thickness (nm), and the vertical axis is the current ratio I / I 0 .
  • the current ratio I / I 0 decreases as the thickness of the sensitive layer increases. That is, when the film thickness is 40 nm or less, the current ratio I / I 0 is 100 or more, but when the film thickness is 160 nm, the current ratio I / I 0 decreases to about 10 to 20. Assuming a sunshine UV monitor, the UV intensity outdoors on a cloudy day is about 1 mW / cm 2. Even in this case, in order to secure a current ratio I / I 0 of 50 or more, the sensitive layer It has been found that the film thickness is preferably 100 nm or less.
  • a c-cut sapphire substrate (hereinafter referred to as “sapphire substrate”) having a thickness of about 350 ⁇ m and polished on both sides was prepared, and a pair of electrodes was formed on the sapphire substrate by a lift-off method.
  • a photoresist was applied to the surface of the sapphire substrate, then pre-baked, and further exposed and developed through a photomask.
  • a Ti film having a thickness of about 40 nm and an Au film having a thickness of 400 nm were sequentially formed.
  • an unnecessary electrode layer was removed using an organic solvent to form a pair of electrodes arranged opposite to each other.
  • the interelectrode distance (predetermined interval) was 10 ⁇ m.
  • a sensitive layer having a thickness of 40 nm was formed on a sapphire substrate including electrodes.
  • a non-doped ZnO sintered body was cut to a thickness of 5 mm and a diameter of 100 mm, and adhered to a copper backing plate.
  • the sapphire substrate and the target are arranged opposite to each other, the inside of the sputtering apparatus is evacuated to a back pressure of about 10 ⁇ 5 Pa, and then argon gas (flow rate: 5.57 ⁇ 10 ⁇ 2 Pa ⁇ m 3 / s). ) and oxygen gas (flow rate: 4.90 to ⁇ 10 -3 Pa ⁇ m 3 / s) was introduced into the sputtering apparatus, the pressure: 0.35 ⁇ 0.7 Pa, a high frequency output: 300 W, substrate temperature: 300 ° C. A film formation process was performed by rotating the substrate holder for 14 minutes under the above conditions to produce a sensitive layer having a thickness of 40 nm.
  • the insensitive layer and the insulating protective film were the same as the sample number 1 except that a self-revolving high frequency magnetron sputtering apparatus was used and the insensitive layer was formed for 6.5 minutes. Was formed continuously.
  • Example samples were prepared.
  • the insensitive layer had a thickness of 28 nm, and the insulating protective film had a thickness of 290 nm.
  • a sample No. 22 was prepared by the same method and procedure as Sample No. 21 except that the insensitive layer was not provided and the film configuration was substrate / (electrode + sensitive layer) / insulating protective film. A sample was used.
  • sample number 23 was prepared in the same method and procedure as sample number 1 except that the film configuration was substrate / (electrode + sensitive layer) and was in a bare state. It was.
  • FIG. 11 shows the change over time of the photoresponse current.
  • the horizontal axis represents time (seconds), and the vertical axis represents photoresponse current (A).
  • the solid line indicates the sample number 21 and the broken line indicates the sample number 23.
  • the dark current before ultraviolet irradiation is 1.0 ⁇ 10 ⁇ 7 A in the sample number 23, whereas the dark current before the UV irradiation is 1.0 ⁇ 10 ⁇ 10 A in the sample number 21. It was found that there was a reduction effect of 3 digits or more.
  • sample No. 23 has a slow rise as shown in part A. This is because the bare surface is a discontinuous crystal cut surface in contact with air, so there are many oxygen vacancies and adsorbed molecules in the air. Therefore, electrons in the ZnO conduction band excited by ultraviolet light are This is probably due to the oxygen deficiency and interaction with the molecules with a long relaxation time.
  • Sample No. 21 can obtain a transient characteristic with a steep rise corresponding to the photoexcitation intensity because a good junction of ZnO—ZnO is formed at the interface between the sensitive layer and the insensitive layer.
  • FIG. 12 shows the measurement results.
  • the sample number 22 which is a comparative sample has a current ratio I / I 0 of about 10 to 20. This is because when the insulating protective film is formed directly on the sensitive layer, there are many unstable factors that cannot be controlled due to excessively low resistance depending on the surface state of the sensitive layer, and therefore the current ratio I / I 0 is 10 to 10 It seems to have become as small as about 20.
  • Sample No. 21 which is an example sample, has a stable and low dark current I 0 due to the ZnO—ZnO junction.
  • the current ratio I / I 0 is as large as 150 to 350, and the detection accuracy of the UV sensor is high. Was found to be good.
  • ultraviolet irradiation was repeated at intervals of 5 seconds to evaluate the photoresponse characteristics.
  • the ultraviolet irradiation was performed at a wavelength of 365 nm and an ultraviolet intensity of 1 mW / cm 2 .
  • FIG. 13 shows the measurement result of sample number 21
  • FIG. 14 shows the measurement result of sample number 22.
  • the horizontal axis represents time (seconds), and the vertical axis represents detected current (A).
  • the detection current of sample number 22 is increased every time the measurement is repeated. This is because the dark current is large and the dark current that has not been reduced is superimposed on the output current, and as a result, the detection current seems to increase each time the measurement is repeated.
  • sample No. 21 has a non-sensitive layer formed on the surface of the sensitive layer, so the dark current is low, and the dark current is sufficiently reduced 5 seconds after the ultraviolet irradiation is stopped. Since the ultraviolet rays were re-irradiated, as shown in FIG. 13, it was found that the current value became substantially constant and a good photoresponse characteristic was obtained.
  • a photodetection element such as a photoconductive ultraviolet sensor that can suppress dark current, has good transient characteristics and falling characteristics, and good spectral characteristics.

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Abstract

A sensitive layer (1) comprising a main component of ZnO is formed on the surface of a substrate (3), and a pair of electrodes (2a,2b) are arranged on the surface of the sensitive layer (1) in an opposing formation across a predetermined interval (t) (e.g. 5 to 10µm) so that a so-called planar structure is formed. An insensitive layer (4) comprising a main component of ZnO is formed on a predetermined interval portion (5) where the surface of the sensitive layer (1) is exposed and end portions of the electrodes (2a,2b), and an insulating protective film (6) comprising substances such as SiO2 is formed on the surface of the insensitive layer (4). Accordingly, a photodetection element such as a high-performance UV light sensor is achieved that is capable of suppressing dark current, has good transient and falling properties, and also has excellent spectral properties. A similar effect can be obtained even when the electrodes and the sensitive layer are formed on the surface of the substrate, and the insensitive layer and the insulating protective film are sequentially formed on the surface of the sensitive layer.

Description

光検出素子、及び該光検出素子の製造方法Photodetection element and method for manufacturing the same
　本発明は、光検出素子、及び該光検出素子の製造方法に関し、より詳しくは、紫外光の光照射により抵抗値が変化する光導電型の光検出素子とその製造方法に関する。 The present invention relates to a photodetection element and a method for manufacturing the photodetection element, and more particularly to a photoconductive photodetection element whose resistance value changes by irradiation with ultraviolet light and a method for manufacturing the photodetection element.
　紫外線センサに代表される光検出素子は、火災報知器、バーナーの燃焼監視装置等の火炎センサや屋外での紫外線照射量を検出したり、紫外線照射装置等の紫外線検出デバイスとして広く使用されており、近年では光通信デバイスへの応用にも期待されている。 Photodetectors represented by ultraviolet sensors are widely used as flame sensors for fire alarms, burner combustion monitoring devices, etc., as well as for detecting the amount of UV irradiation outdoors, and for UV detection devices such as UV irradiation devices. In recent years, it is expected to be applied to optical communication devices.
　この種の光検出素子としては、従来より、紫外線照射により抵抗値が変化する光導電型と、紫外線照射により光起電力が発生する光起電力型が知られている。 Conventionally known photodetection elements of this type include a photoconductive type in which a resistance value is changed by ultraviolet irradiation and a photovoltaic type in which a photovoltaic force is generated by ultraviolet irradiation.
　また、光検出素子用材料としては、バンドギャップエネルギーが３．３ｅＶ（波長：３７５ｎｍ）と大きく、紫外線に対して良好な光導電性を有するＺｎＯが注目されている。しかも、このＺｎＯは安価で安全性にも優れ、加工が容易であることから有望視されている。 Further, as a material for a light detection element, ZnO having a large band gap energy of 3.3 eV (wavelength: 375 nm) and having a good photoconductivity with respect to ultraviolet rays has attracted attention. Moreover, this ZnO is promising because it is inexpensive, excellent in safety, and easy to process.
　そして、例えば、特許文献１には、基板上にＺｎＯ薄膜と該薄膜の紫外線照射による抵抗値の変化を抽出する電極を形成した光導電型紫外線センサが提案されている。 For example, Patent Document 1 proposes a photoconductive ultraviolet sensor in which a ZnO thin film and an electrode for extracting a change in resistance value due to ultraviolet irradiation of the thin film are formed on a substrate.
　この特許文献１では、図１５に示すように、基板１０１の一方の主面上にパターンニングを行って一対の電極１０２ａ、１０２ｂを対向状に形成し、電極１０２ａ、１０２ｂの中央部をマスクした状態でＺｎＯをターゲットにスパッタリングを行い、これによりＺｎＯ薄膜からなる感応層１０３を形成している。そして、紫外線センサを上述のように構成することにより、バンドパスフィルタ等の光学フィルターを要することなく、照射量に対し直線的な光電流を得ている。 In Patent Document 1, as shown in FIG. 15, patterning is performed on one main surface of a substrate 101 to form a pair of electrodes 102 a and 102 b facing each other, and the central portions of the electrodes 102 a and 102 b are masked. Sputtering is performed using ZnO as a target in this state, thereby forming a sensitive layer 103 made of a ZnO thin film. By configuring the ultraviolet sensor as described above, a linear photocurrent is obtained with respect to the dose without requiring an optical filter such as a bandpass filter.
　また、この特許文献１では、基板の一方の主面にＺｎＯ薄膜からなる感応層を予め形成した後、マスク法やエッチング法などにより所定の電極パターンを形成した構造であっても、上述と同様の効果が得られ、保護層を設けることにより、電極損傷のない紫外線センサを得ることができるとされている。 Moreover, in this patent document 1, even if it has a structure in which a sensitive layer made of a ZnO thin film is formed in advance on one main surface of a substrate and then a predetermined electrode pattern is formed by a mask method or an etching method, the same as described above. It is said that an ultraviolet sensor free from electrode damage can be obtained by providing a protective layer.
特開平３－２４１７７７号公報（請求項１、図１、第２欄第４４行目～同欄第４７行目）JP-A-3-241777 (Claim 1, FIG. 1, second column, line 44 to column 47)
　しかしながら、特許文献１に示すような従来の紫外線センサは、感応層１０３が表面露出していることから暗電流が大きい上に、過渡特性が大きく、立ち下がり特性も鋭敏性に欠け、センサ性能に劣るという問題があった。 However, the conventional ultraviolet sensor as shown in Patent Document 1 has a large dark current because the sensitive layer 103 is exposed on the surface, has a large transient characteristic, lacks a sharp fall characteristic, and has a poor sensor performance. There was a problem of being inferior.
　すなわち、この場合、図１５に示すように感応層１０３が大気に直接接触することになる。しかしながら、該感応層１０３の表面には酸素欠陥や大気中の吸着分子が多く存在し、このため紫外光により励起されたＺｎＯ伝導帯の電子がこれら酸素欠陥や吸着分子と緩和時間の長い相互作用を生じ、その結果、立ち上がり時の過渡特性が大きくなる。また、紫外光の照射を停止した場合も、同様の理由から立ち下がり特性は緩やかに低下して鋭敏性に欠けるおそれがある。さらに、感応層１０３が大気中の水分と反応するため、感応層１０３の表面性状が安定せず、このため抵抗が極端に低い部分が生じ、紫外光を精度良く検知できなくなるおそれがある。 That is, in this case, the sensitive layer 103 is in direct contact with the atmosphere as shown in FIG. However, there are many oxygen vacancies and adsorbed molecules in the atmosphere on the surface of the sensitive layer 103. Therefore, electrons in the ZnO conduction band excited by ultraviolet light interact with these oxygen vacancies and adsorbed molecules for a long relaxation time. As a result, the transient characteristics at the time of rising increase. Further, even when the irradiation with ultraviolet light is stopped, the falling characteristic is gradually lowered for the same reason, and there is a possibility that the sharpness is lacking. Furthermore, since the sensitive layer 103 reacts with moisture in the atmosphere, the surface properties of the sensitive layer 103 are not stable, and thus there is a possibility that a part having extremely low resistance is generated, and ultraviolet light cannot be detected with high accuracy.
　しかも、上述の場合は、分光特性にも劣り、特に長波長側のＵＶ－Ａ領域、特に３７０ｎｍに大きな応答特性のピークをもち、このためＵＶ－Ａ、ＵＶ－Ｂ領域全般で平坦な特性が得られないという問題があった。 In addition, the above-mentioned case is inferior in spectral characteristics, and has a large response characteristic peak particularly in the UV-A region on the long wavelength side, particularly 370 nm. Therefore, flat characteristics in the entire UV-A and UV-B regions are obtained. There was a problem that it could not be obtained.
　また、図１６に示すように、感応層１０３の表面に絶縁保護膜１０４を形成し、感応層１０３を大気と接しないようにした場合であっても、該感応層１０３と絶縁保護膜１０４とが接合されることから、暗電流の増大を招くおそれがある。すなわち、この場合、絶縁保護膜１０４は感応層１０３に比べ化合物としての安定性が高く、このため感応層１０３側に酸素欠損が生じて表層面に導電層が形成される。そして、このような状態で電圧を印加すると、導電層を介して電流がリークし、このため暗電流の増大を招き、その結果、紫外線強度を精度良く検知できなくなるおそれがある。 Further, as shown in FIG. 16, even when the insulating protective film 104 is formed on the surface of the sensitive layer 103 so that the sensitive layer 103 is not in contact with the atmosphere, the sensitive layer 103 and the insulating protective film 104 As a result, the dark current may increase. That is, in this case, the insulating protective film 104 is more stable as a compound than the sensitive layer 103, and therefore oxygen deficiency occurs on the sensitive layer 103 side, and a conductive layer is formed on the surface layer. When a voltage is applied in such a state, a current leaks through the conductive layer, leading to an increase in dark current. As a result, there is a possibility that the ultraviolet intensity cannot be detected accurately.
　このように従来の紫外線センサでは、暗電流が大きい上に、過度特性や立下り特性に劣り、センサ性能に劣っていた。 As described above, the conventional ultraviolet sensor has a large dark current and is inferior in excessive characteristics and falling characteristics, and inferior in sensor performance.
　本発明はこのような事情に鑑みなされたものであって、暗電流を抑制でき、良好な過渡特性と立ち下がり特性を有し、かつ分光特性にも優れた高性能の光検出素子とその製造方法を提供することを目的とする。 The present invention has been made in view of such circumstances, a high-performance photodetector capable of suppressing dark current, having good transient characteristics and falling characteristics, and excellent in spectral characteristics, and its manufacture. It aims to provide a method.
　本発明者らは、光検出素子用材料としてＺｎＯ系材料を使用し、鋭意研究を行ったところ、主成分がＺｎＯで形成された不感応層を前記感応層の表面に形成することにより、立ち上がり時の過渡特性や立ち下がり特性を向上させることができ、かつ暗電流を抑制でき、分光特性も改善できるという知見を得た。 The inventors of the present invention have conducted extensive research using a ZnO-based material as a material for a light detection element. As a result, the insensitive layer formed of ZnO as a main component is formed on the surface of the sensitive layer. It was found that transient characteristics and falling characteristics can be improved, dark current can be suppressed, and spectral characteristics can be improved.
　本発明はこのような知見に基づきなされたものであって、本発明に係る光検出素子は、主成分がＺｎＯで形成された感応層と、所定間隔を介して対向状に配された一対の電極とが、基板の一方の主面側に形成され、前記感応層で入射光を検知する光検出素子において、主成分を前記感応層と同一材料で形成した不感応層が、前記感応層と接するように設けられていることを特徴としている。 The present invention has been made on the basis of such knowledge, and the light detection element according to the present invention includes a sensitive layer having a main component formed of ZnO, and a pair of layers arranged in an opposing manner with a predetermined interval therebetween. In the photodetecting element in which an electrode is formed on one main surface side of the substrate and detects incident light with the sensitive layer, a non-sensitive layer whose main component is made of the same material as the sensitive layer is It is characterized by being provided in contact.
　また、本発明の光検出素子は、前記感応層が、前記基板の前記一方の主面の表面に形成されると共に、前記一対の電極は、前記感応層の表面に形成され、かつ、前記不感応層は、少なくとも前記電極間に前記感応層に接合して設けられているのが好ましい。 In the photodetector of the present invention, the sensitive layer is formed on the surface of the one main surface of the substrate, the pair of electrodes is formed on the surface of the sensitive layer, and The sensitive layer is preferably provided at least between the electrodes and bonded to the sensitive layer.
　さらに、本発明の光検出素子は、前記一対の電極が、前記基板の前記一方の主面の表面に形成されると共に、前記感応層は、前記電極の端部を覆うように前記基板の前記一方の主面の表面に形成され、かつ、前記不感応層は、前記感応層の表面に形成されているのも好ましい。 Further, in the photodetecting element of the present invention, the pair of electrodes are formed on the surface of the one main surface of the substrate, and the sensitive layer covers the end of the electrode. It is also preferred that the insensitive layer is formed on the surface of one of the main surfaces, and the insensitive layer is formed on the surface of the sensitive layer.
　また、本発明の光検出素子は、前記基板が、前記入射光を透過する透光性材料で形成されているのが好ましい。 In the photodetecting element of the present invention, it is preferable that the substrate is made of a translucent material that transmits the incident light.
　また、本発明の光検出素子は、前記入射光が、前記基板の前記一方の主面側及び他方の主面側のうちの少なくともいずれかの主面に照射されるのが好ましい。 In the light detection element of the present invention, it is preferable that the incident light is applied to at least one of the principal surface side and the other principal surface side of the substrate.
　また、本発明の光検出素子は、前記不感応層の表面に絶縁保護膜が形成されているのが好ましい。 In the photodetecting element of the present invention, it is preferable that an insulating protective film is formed on the surface of the insensitive layer.
　また、本発明の光検出素子は、前記絶縁保護膜が、ケイ素化合物で形成されているのが好ましい。 In the photodetecting element of the present invention, it is preferable that the insulating protective film is formed of a silicon compound.
　さらに、本発明の光検出素子は、高反射率を有する金属薄膜が、前記絶縁保護膜の表面に形成されているのが好ましい。 Furthermore, in the light detection element of the present invention, it is preferable that a metal thin film having a high reflectance is formed on the surface of the insulating protective film.
　また、本発明の光検出素子は、前記不感応層が、膜厚が３ｎｍ以上１４０ｎｍ未満であるのが好ましい。 In the photodetector of the present invention, it is preferable that the insensitive layer has a film thickness of 3 nm or more and less than 140 nm.
　また、本発明の光検出素子は、前記感応層は、膜厚が１０ｎｍ以上１００ｎｍ以下であるのが好ましい。 In the photodetecting element of the present invention, it is preferable that the sensitive layer has a thickness of 10 nm to 100 nm.
　また、本発明の光検出素子の製造方法は、主成分がＺｎＯで形成された感応層と、所定間隔を有して対向状に配された一対の電極とを基板の一方の主面側に形成し、主成分が前記感応層と同一のＺｎＯ系材料及び絶縁性材料を用意し、前記ＺｎＯ系材料を使用し、前記電極が形成された感応層に、真空下、第１の成膜処理を行い、さらに前記絶縁性材料を使用し、前記第１の成膜処理に引き続き連続的に第２の成膜処理を行い、前記感応層の表面にＺｎＯ材料からなる不感応層、及び絶縁保護膜を順次形成することを特徴としている。 In addition, the method for manufacturing a photodetecting element of the present invention includes a sensitive layer formed of ZnO as a main component and a pair of electrodes arranged in a facing manner with a predetermined interval on one main surface side of the substrate. Forming a ZnO-based material and an insulating material whose main component is the same as that of the sensitive layer, using the ZnO-based material, and applying a first film-forming process to the sensitive layer on which the electrode is formed under vacuum. In addition, using the insulating material, the second film-forming process is performed continuously following the first film-forming process, the insensitive layer made of a ZnO material on the surface of the sensitive layer, and the insulation protection It is characterized by sequentially forming films.
　また、本発明の光検出素子の製造方法は、前記感応層を、前記基板の前記一方の主面の表面に形成した後、前記一対の電極を前記感応層の表面に形成し、その後、前記不感応層を、少なくとも前記電極間に前記感応層と接合するように形成するのが好ましい。 Further, in the method for producing a photodetecting element of the present invention, after the sensitive layer is formed on the surface of the one main surface of the substrate, the pair of electrodes is formed on the surface of the sensitive layer, The insensitive layer is preferably formed so as to be bonded to at least the sensitive layer between the electrodes.
　また、本発明の光検出素子の製造方法は、前記一対の電極を前記基板の前記一方の主面の表面に形成した後、前記感応層を前記電極の端部を覆うように前記基板の一方の主面の表面に形成し、その後前記不感応層を前記感応層の表面に形成するのも好ましい。 In the method for manufacturing a photodetecting element according to the present invention, after the pair of electrodes is formed on the surface of the one main surface of the substrate, the sensitive layer is covered with one of the substrates so as to cover an end portion of the electrode. It is also preferable that the insensitive layer is formed on the surface of the sensitive layer, and then the insensitive layer is formed on the surface of the sensitive layer.
　本発明の光検出素子によれば、主成分がＺｎＯで形成された感応層と、所定間隔を介して対向状に配された一対の電極とが、基板の一方の主面側に形成され、前記感応層で入射光を検知する光検出素子において、主成分を前記感応層と同一材料で形成した不感応層が、前記感応層と接するように設けられているので、感応層の界面はＺｎＯ－ＺｎＯのホモ接合面を有することとなり、酸素欠損や吸着分子の存在が抑制され、界面の表面性状も安定化する。そしてこれにより光励起強度に応じた過渡特性の小さい光電流を得ることができ、過渡特性を向上させることができる。また、光照射を停止した場合も、過渡特性の場合と同様の理由から鋭敏に立ち下がり、立ち下がり特性が向上し、暗電流も抑制することができる。 According to the light detection element of the present invention, the sensitive layer whose main component is made of ZnO and the pair of electrodes arranged opposite to each other at a predetermined interval are formed on one main surface side of the substrate, In the photodetector for detecting incident light with the sensitive layer, the insensitive layer, the main component of which is made of the same material as the sensitive layer, is provided so as to be in contact with the sensitive layer. It has a —ZnO homojunction surface, which suppresses the presence of oxygen vacancies and adsorbed molecules and stabilizes the surface properties of the interface. As a result, a photocurrent having a small transient characteristic corresponding to the photoexcitation intensity can be obtained, and the transient characteristic can be improved. In addition, even when the light irradiation is stopped, it falls sharply for the same reason as in the case of the transient characteristic, the fall characteristic is improved, and the dark current can be suppressed.
　しかも、不感応層はＺｎＯ薄膜と同一乃至略同一の光吸収特性を有することから、長波長側のＵＶ－Ａ領域、特に３７０ｎｍ付近に大きな応答特性のピークをもつという感度の不均一性も改善され、２８０～３８０ｎｍの波長帯域での分光特性の平坦性を向上させることができ、ＵＶ－Ａ、ＵＶ－Ｂ領域で高精度に紫外線量を検出することが可能となる。 In addition, since the insensitive layer has the same or substantially the same light absorption characteristics as the ZnO thin film, the non-uniformity of sensitivity that has a large response characteristic peak in the UV-A region on the long wavelength side, particularly around 370 nm is improved. In addition, the flatness of the spectral characteristics in the wavelength band of 280 to 380 nm can be improved, and the amount of ultraviolet rays can be detected with high accuracy in the UV-A and UV-B regions.
　また、前記感応層が、前記基板の前記一方の主面の表面に形成されると共に、前記不感応層は、少なくとも前記電極間に前記感応層に接合して設けられた場合は、上記所定間隔部分の感応層が不感応層と接合されることとなり、上記効果を奏することができる。 Further, when the sensitive layer is formed on the surface of the one main surface of the substrate and the insensitive layer is provided to be bonded to the sensitive layer at least between the electrodes, the predetermined interval is used. The part of the sensitive layer is joined to the insensitive layer, and the above effect can be obtained.
　さらに、前記一対の電極及び前記感応層は、前記基板の一方の主面の表面に形成されると共に、前記不感応層は、前記感応層の表面に形成された場合も、感応層が不感応層と接合されることとなり、上記効果を奏することができる。 Furthermore, the pair of electrodes and the sensitive layer are formed on the surface of one main surface of the substrate, and the insensitive layer is also insensitive even when formed on the surface of the sensitive layer. It will join with a layer and there can exist the said effect.
　また、前記基板は、前記入射光を透過する透光性材料で形成されることにより、前記基板の感応層形成面とは反対側の他方の主面からの入射光に対しても検知することができる。 In addition, the substrate is formed of a light-transmitting material that transmits the incident light, thereby detecting incident light from the other main surface of the substrate opposite to the sensitive layer forming surface. Can do.
　また、前記入射光は、前記基板の前記一方の主面側及び他方の主面側のうちの少なくともいずれかの主面に照射された場合であっても、入射光強度を検知することができる。 Further, the incident light intensity can be detected even when the incident light is applied to at least one main surface of the one main surface side and the other main surface side of the substrate. .
　また、不感応層の表面にケイ素化合物等からなる絶縁保護膜を形成することにより、暗電流を低減することが可能となる。すなわち、不感応層を設けることにより感応層と絶縁保護膜とが接することがなくなることから、感応層の表層面に導電層が形成されるのを回避することができ、これにより暗電流は増大することなく、低減化を図ることができる。 Further, by forming an insulating protective film made of a silicon compound or the like on the surface of the insensitive layer, dark current can be reduced. In other words, by providing the insensitive layer, the sensitive layer and the insulating protective film are not in contact with each other, so that the formation of a conductive layer on the surface layer of the sensitive layer can be avoided, thereby increasing the dark current. The reduction can be achieved without doing so.
　また、高反射率を有する金属薄膜が、前記絶縁保護膜の表面に形成されることにより、基板の他方の主面側から光が照射された場合、感応層を透過した光が前記金属薄膜で反射し、キャリア発生に寄与することから、センサ感度の向上を図ることが可能となる。 In addition, since a metal thin film having a high reflectance is formed on the surface of the insulating protective film, when light is irradiated from the other main surface side of the substrate, the light transmitted through the sensitive layer is the metal thin film. Reflecting and contributing to carrier generation, it is possible to improve the sensor sensitivity.
　また、前記不感応層の膜厚を３ｎｍ以上１４０ｎｍ未満とすることにより、暗電流の増大を招くことなく、良好な分光特性を確保することができる。 Also, by setting the film thickness of the insensitive layer to 3 nm or more and less than 140 nm, it is possible to ensure good spectral characteristics without causing an increase in dark current.
　また、前記感応層は、膜厚を１０ｎｍ以上１００ｎｍ以下とすることにより、暗電流に対する出力電流の比率を十分に大きくすることができ、日照モニタ用途等の特定用途に適した紫外線センサを得ることが可能となる。 In addition, by setting the thickness of the sensitive layer to 10 nm or more and 100 nm or less, the ratio of the output current to the dark current can be sufficiently increased, and an ultraviolet sensor suitable for a specific application such as a sunshine monitor application can be obtained. Is possible.
　また、本発明の光検出素子の製造方法によれば、主成分がＺｎＯで形成された感応層と、所定間隔を有して対向状に配された一対の電極とを基板の一方の主面側に形成し、主成分が前記感応層と同一のＺｎＯ系材料及び絶縁性材料を用意し、前記ＺｎＯ系材料を使用して前記電極が形成された感応層に、真空下、第１の成膜処理を行い、さらに前記絶縁性材料を使用し、前記第１の成膜処理に引き続き連続的に第２の成膜処理を行い、前記感応層の表面にＺｎＯ材料からなる不感応層、及び絶縁保護膜を順次形成するので、不感応層と絶縁保護膜との界面を均質に形成することができ、より薄い不感応層でも暗電流の増大を抑制した高性能の光検出素子を得ることができる。 In addition, according to the method for manufacturing a photodetecting element of the present invention, a sensitive layer whose main component is made of ZnO and a pair of electrodes arranged in a facing manner with a predetermined interval are provided on one main surface of the substrate. A ZnO-based material and an insulating material, the main components of which are the same as those of the sensitive layer, are prepared, and the first component is formed under vacuum on the sensitive layer on which the electrodes are formed using the ZnO-based material. Performing a film treatment, further using the insulating material, performing a second film-forming process continuously following the first film-forming process, and forming a non-sensitive layer made of a ZnO material on the surface of the sensitive layer; and Insulating protective films are formed in sequence, so that the interface between the insensitive layer and the insulating protective film can be formed uniformly, and a high-performance photodetector that suppresses the increase in dark current even with a thinner insensitive layer can be obtained. Can do.
本発明に係る光検出素子としての紫外線センサの一実施の形態（第１実施の形態）を模式的に示す断面図である。It is sectional drawing which shows typically one Embodiment (1st Embodiment) of the ultraviolet sensor as a photon detection element which concerns on this invention. 図１の要部断面図である。It is principal part sectional drawing of FIG. 前記第１の実施の形態の変形例を模式的に示す断面図である。It is sectional drawing which shows typically the modification of the said 1st Embodiment. 本発明に係る第２の実施の形態を模式的に示す断面図である。It is sectional drawing which shows typically 2nd Embodiment which concerns on this invention. 実施例１で作製された各試料の暗電流を示す図である。FIG. 3 is a diagram showing dark current of each sample produced in Example 1. 実施例１で作製された試料番号１及び５の光応答電流の過渡特性及び立ち下がり特性を示す図である。It is a figure which shows the transient characteristic and fall characteristic of the photoresponse current of the sample numbers 1 and 5 produced in Example 1. FIG. 実施例２で作製された各試料の分光特性を示す図である。6 is a diagram illustrating spectral characteristics of samples prepared in Example 2. FIG. 実施例３で作製された各試料の分光特性を示す図である。FIG. 6 is a diagram showing the spectral characteristics of each sample produced in Example 3. 実施例４で作製された各試料の膜厚と出力電流及び暗電流との関係を示す図である。It is a figure which shows the relationship between the film thickness of each sample produced in Example 4, an output current, and a dark current. 実施例４で作製された各試料の膜厚と出力電流と暗電流との比を示す図である。It is a figure which shows the ratio of the film thickness of each sample produced in Example 4, an output current, and a dark current. 実施例５で作製された各試料の出力電流特性を示す図である。FIG. 10 is a diagram showing output current characteristics of each sample produced in Example 5. 実施例５で作製された試料番号２１及び試料番号２３の出力電流と暗電流との比を示す図である。It is a figure which shows ratio of the output current of sample number 21 produced in Example 5, and sample number 23, and a dark current. 実施例５で作製された試料番号２１の光応答特性を示す図である。It is a figure which shows the optical response characteristic of the sample number 21 produced in Example 5. FIG. 実施例５で作製された試料番号２３の光応答特性を示す図である。It is a figure which shows the optical response characteristic of the sample number 23 produced in Example 5. FIG. 特許文献１に記載された従来の紫外線センサを示す断面図である。It is sectional drawing which shows the conventional ultraviolet sensor described in patent document 1. 従来の紫外線センサに絶縁保護膜を形成した状態を示す断面図である。It is sectional drawing which shows the state which formed the insulating protective film in the conventional ultraviolet sensor.
　次に、本発明の実施の形態を添付図面を参照しながら詳説する。 Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
　図１は、本発明に係る光検出素子としての紫外線センサの一実施の形態を模式的に示す断面図である。 FIG. 1 is a cross-sectional view schematically showing an embodiment of an ultraviolet sensor as a light detection element according to the present invention.
　この紫外線センサは、主成分がＺｎＯで形成された感応層１と、所定間隔ｔ（例えば、５～１０μｍ）を介して対向状に配された一対の電極２ａ、２ｂとが、基板３の一方の主面側に形成され、かつ、主成分を前記感応層１と同一材料で形成した不感応層４が、感応層１と接するように設けられている。 The ultraviolet sensor includes a sensitive layer 1 whose main component is made of ZnO, and a pair of electrodes 2a and 2b arranged opposite to each other at a predetermined interval t (for example, 5 to 10 μm). A non-sensitive layer 4 formed on the main surface side and made of the same material as the sensitive layer 1 is provided so as to be in contact with the sensitive layer 1.
　すなわち、この紫外線センサは、感応層１が、基板３の表面に形成されると共に、該感応層１の表面には所定間隔ｔを介して一対の電極２ａ、２ｂが対向状に配され、所謂プレーナ型構造とされている。そして、感応層１が表面露出した所定間隔部分（以下、この所定間隔部分を「ベア部」という。）５及び電極２ａ、２ｂの端部には、主成分がＺｎＯからなる不感応層４が形成され、該不感応層４の表面に絶縁保護膜６が形成されている。 That is, in this ultraviolet sensor, the sensitive layer 1 is formed on the surface of the substrate 3, and a pair of electrodes 2 a and 2 b are arranged on the surface of the sensitive layer 1 with a predetermined interval t facing each other. It has a planar structure. The insensitive layer 4 whose main component is made of ZnO is formed at the end of the predetermined interval portion (hereinafter referred to as “bearing portion”) 5 where the sensitive layer 1 is exposed and the electrodes 2a and 2b. An insulating protective film 6 is formed on the surface of the insensitive layer 4.
　感応層１は、主成分がＺｎＯで形成されていればよく、必要に応じて微量の不純物（例えば、Ａｌ、Ｇａ、Ｉｎ等）を含んでいてもよい。 The sensitive layer 1 only needs to be formed of ZnO as a main component, and may contain a small amount of impurities (for example, Al, Ga, In, etc.) as necessary.
　また、不感応層４は、感応層１と完全同一でなくてもよく、主成分がＺｎＯで形成されていれば感応層１とは異なる不純物を微量に含んでいてもよい。 Further, the insensitive layer 4 may not be completely the same as the sensitive layer 1 and may contain a small amount of impurities different from the sensitive layer 1 as long as the main component is formed of ZnO.
　また、基板３を形成する材料としては、特に限定されるものではないが、例えば、ＬｉＴａＯ３（ＬＴ）やＬｉＮｂＯ３（ＬＮ）等の強誘電体結晶、好ましくは、紫外光を透過する透光性材料、例えば、紫外線領域（例えば、波長が３１０ｎｍ近傍領域）での光透過率が５０％以上のサファイア、耐熱強化ガラス等の透明材料又は透明性の良好な透光性材料が使用される。そしてこのような透光性材料を使用することにより、基板２の一方の主面側である矢印Ａ方向から紫外光が照射された場合のみならず、基板２の他方の主面側である矢印Ｂ方向から紫外光が照射された場合であっても、紫外線を検知することができる。 The material for forming the substrate 3 is not particularly limited. For example, a ferroelectric crystal such as LiTaO 3 (LT) or LiNbO 3 (LN), preferably a translucent material that transmits ultraviolet light. For example, a transparent material such as sapphire having a light transmittance of 50% or more in the ultraviolet region (for example, a region in the vicinity of 310 nm) or heat-resistant tempered glass, or a light-transmitting material having good transparency is used. And by using such a translucent material, not only when the ultraviolet light is irradiated from the direction of the arrow A which is one main surface side of the substrate 2, but also the arrow which is the other main surface side of the substrate 2 Even when ultraviolet light is irradiated from the B direction, the ultraviolet light can be detected.
　特に、矢印Ｂ方向から紫外光が照射された場合には、感応層１によって紫外線強度が検知されるので、不感応層４や絶縁保護膜６の膜厚、更には光透過特性に対する制約もなくなり、材料選択の自由度を拡げることができる。また、電極２ａ、２ｂを下方にして基板実装することが可能となり、表面実装に適した紫外線センサを得ることができる。 In particular, when ultraviolet light is irradiated from the direction of arrow B, since the ultraviolet intensity is detected by the sensitive layer 1, there are no restrictions on the film thickness of the insensitive layer 4 and the insulating protective film 6, and further on the light transmission characteristics. The degree of freedom of material selection can be expanded. Moreover, it becomes possible to mount on a board with the electrodes 2a and 2b facing downward, and an ultraviolet sensor suitable for surface mounting can be obtained.
　また、絶縁保護膜６としては、紫外線センサを外的な損傷から保護し得る絶縁性材料で形成されていればよく、例えば、ＳｉＯ２やＳｉＮＸ等のケイ素化合物を好んで使用することができる。 The insulating protective film 6 may be formed of an insulating material that can protect the ultraviolet sensor from external damage. For example, a silicon compound such as SiO 2 or SiN X can be preferably used. .
　電極２ａ、２ｂを形成する電極材料は、良導電性を有し、一連の成膜工程で損傷しないものであれば特に限定されるものではなく、Ｔｉ、Ａｕ、Ｐｔ、Ｐｄ等を使用することができる。 The electrode material for forming the electrodes 2a and 2b is not particularly limited as long as it has good conductivity and is not damaged in a series of film forming steps, and Ti, Au, Pt, Pd, etc. should be used. Can do.
　尚、電極２ａ、２ｂは、一層構造又は積層構造に形成されている。電極２ａ、２ｂを積層構造にする場合は、ＺｎＯと接する下部金属層はＺｎＯに対して良好な密着性があり、オーム性接合となるＴｉやＡｌを使用することが好ましい。さらに、下部金属層の上に形成される上部金属層は良導電性を有し、一連の成膜工程で損傷しないものであればよく、例えば、Ａｕ、Ｐｔ、Ｐｄ等を使用することができる。また、電極２ａ、２ｂは、所定間隔ｔを介して対向状に配されていれば、どのような形状でもよく、例えば、インターデジタル型にすれば感度を向上させることができるので好ましい。 The electrodes 2a and 2b are formed in a single layer structure or a laminated structure. When the electrodes 2a and 2b have a laminated structure, the lower metal layer in contact with ZnO has good adhesion to ZnO, and it is preferable to use Ti or Al that forms ohmic bonding. Furthermore, the upper metal layer formed on the lower metal layer may be any material as long as it has good conductivity and is not damaged in a series of film forming steps. For example, Au, Pt, Pd, or the like can be used. . Further, the electrodes 2a and 2b may have any shape as long as they are arranged to face each other with a predetermined interval t. For example, an interdigital type is preferable because sensitivity can be improved.
　上記紫外線センサによれば、感応層１と絶縁保護膜６との間にＺｎＯを主成分とする不感応層４が介装されているので、暗電流の増大を招くこともなく、光照射時の立ち上がり時における過渡特性や光照射を停止したときの立ち下がり特性、更には分光特性等の諸特性を向上させることができ、高性能の紫外線センサを得ることが可能となる。 According to the ultraviolet sensor, since the insensitive layer 4 containing ZnO as a main component is interposed between the sensitive layer 1 and the insulating protective film 6, dark current does not increase and light is irradiated. Various characteristics such as a transient characteristic at the rise of the light, a fall characteristic when the light irradiation is stopped, and a spectral characteristic can be improved, and a high-performance ultraviolet sensor can be obtained.
　以下、その理由を詳述する。 The reason for this will be described in detail below.
（１）暗電流
　感応層１のベア部５表面は、測定雰囲気等によって光応答電流が大きく変動し、信頼性を確保するのが困難であることから、耐環境特性を確保するためには、ベア部５を絶縁保護膜６で被覆するのが好ましい。 (1) Dark current Since the surface of the bare portion 5 of the sensitive layer 1 has a photoresponse current that varies greatly depending on the measurement atmosphere and the like, it is difficult to ensure reliability. The bare part 5 is preferably covered with an insulating protective film 6.
　しかしながら、〔発明が解決しようとする課題〕の項でも述べたように、絶縁保護膜６をベア部５の表面に直接形成すると、感応層１のベア部５に導電層が形成され、このため光照射を停止したときに導電層を介して電流がリークし、その結果，暗電流の増大を招き、光照射時における光応答電流（＝出力電流－暗電流）を高精度に検知することが困難となる。 However, as described in the section of [Problems to be Solved by the Invention], when the insulating protective film 6 is directly formed on the surface of the bare part 5, a conductive layer is formed on the bare part 5 of the sensitive layer 1. When light irradiation is stopped, current leaks through the conductive layer. As a result, dark current increases, and photoresponse current (= output current-dark current) during light irradiation can be detected with high accuracy. It becomes difficult.
　すなわち、例えば、絶縁保護膜６としてＳｉＯ２を使用した場合、ＺｎＯの標準生成自由エネルギーΔＧ°は－３１８．３ｋcal／molであるのに対し、ＳｉＯ２の標準生成自由エネルギーΔＧ°は－８５６ｋcal／molと低く、ＳｉＯ２はＺｎＯに比べて化合物としての安定性が高い。 That is, for example, when SiO 2 is used as the insulating protective film 6, the standard free energy of formation ΔG ° of ZnO is −318.3 kcal / mol, whereas the standard free energy of formation ΔG ° of SiO 2 is −856 kcal / mol. mol and lower, SiO 2 has a high stability as a compound in comparison with the ZnO.
　したがって、絶縁保護膜６が接するベア部５ではＺｎＯ表面の酸素が結晶格子から離脱して酸素欠損を生じ、絶縁保護膜６側に酸素が移動してベア部５の表層面に導電層が形成されることになる。このため、電極２ａ、２ｂ間に電圧を印加すると、前記導電層を介して電流がリークし、その結果、非照射時における暗電流の増大を招き、光照射時に高精度な光応答電流を得ることができなくなるおそれがある。 Therefore, in the bare part 5 in contact with the insulating protective film 6, oxygen on the ZnO surface is separated from the crystal lattice to cause oxygen vacancies, and oxygen moves to the insulating protective film 6 side to form a conductive layer on the surface of the bare part 5. Will be. For this reason, when a voltage is applied between the electrodes 2a and 2b, a current leaks through the conductive layer, resulting in an increase in dark current during non-irradiation and a highly accurate photoresponse current during light irradiation. There is a risk that it will not be possible.
　そこで、本実施の形態では、主成分がＺｎＯで形成された不感応層４を絶縁保護膜６とベア部５との間に介在させてベア部５の界面をＺｎＯ－ＺｎＯホモ接合とし、これによりベア部５の表層面に導電層が形成されるのを回避し、暗電流の低減化を図っている。 Therefore, in the present embodiment, the insensitive layer 4 whose main component is made of ZnO is interposed between the insulating protective film 6 and the bare portion 5, and the interface of the bare portion 5 is made a ZnO-ZnO homojunction. Therefore, the formation of a conductive layer on the surface of the bare portion 5 is avoided, and the dark current is reduced.
　図２は図１の要部拡大図である。 FIG. 2 is an enlarged view of the main part of FIG.
　ベア部５の表面には上述した不感応層４が形成され、該不感応層４の表面に絶縁保護膜６が形成されている。そして、上述したように絶縁保護膜６は不感応層４よりも化合物としての安定性が高いことから、絶縁保護膜６が接する不感応層４の表層面に酸素欠損が生じ、該不感応層４の表層面には導電層７が形成されることになる。すなわち、ベア部５は絶縁保護膜６と接することはなく、したがってベア部５の表層面に導電層が形成されるのを回避でき、これにより感応層１からの電流リークが抑制され、暗電流が増大するのを回避することができる。 The above-described insensitive layer 4 is formed on the surface of the bare part 5, and the insulating protective film 6 is formed on the surface of the insensitive layer 4. Since the insulating protective film 6 is more stable as a compound than the insensitive layer 4 as described above, oxygen deficiency occurs on the surface layer of the insensitive layer 4 in contact with the insulating protective film 6, and the insensitive layer Thus, the conductive layer 7 is formed on the surface layer 4. That is, the bare portion 5 does not come into contact with the insulating protective film 6, so that it is possible to avoid the formation of a conductive layer on the surface of the bare portion 5, thereby suppressing current leakage from the sensitive layer 1 and dark current. Can be avoided.
　このように本実施の形態では、絶縁保護膜６を設けることによる暗電流の増大を回避しつつ耐湿性保護膜を形成できるので、信頼性の向上と共に気中放電なども抑制することが可能となり、良好な耐環境性を有する紫外線センサを得ることが可能となる。 As described above, in this embodiment, since the moisture-resistant protective film can be formed while avoiding an increase in dark current due to the provision of the insulating protective film 6, it is possible to improve the reliability and suppress air discharge and the like. It is possible to obtain an ultraviolet sensor having good environmental resistance.
（２）過渡特性及び立ち下がり特性
　感応層１のベア部５は、不連続な結晶切断面であるため、酸素欠損や吸着分子などが多く存在する。したがって、ベア表面が表面露出して大気に接触すると、紫外光により励起されたＺｎＯ伝導帯の電子は、これらの酸素欠損や吸着分子と緩和時間の長い相互作用を生じる、このため光照射の際に光応答電流が増大し、立ち上がり時の過渡特性が大きくなる。 (2) Transient characteristics and falling characteristics Since the bare portion 5 of the sensitive layer 1 is a discontinuous crystal cut surface, there are many oxygen vacancies and adsorbed molecules. Therefore, when the bare surface is exposed to the atmosphere and exposed to the atmosphere, electrons in the ZnO conduction band excited by ultraviolet light cause interaction with these oxygen vacancies and adsorbed molecules with a long relaxation time. In addition, the optical response current increases, and the transient characteristics at the time of startup increase.
　しかるに、本実施の形態では、ベア部５の表面に不感応層４を形成しているので、ベア部５はＺｎＯ－ＺｎＯのホモ接合面を有する不感応層４と接合されることとなり、ダングリングボンド（結合相手のいない不対電子が存在する分子軌道）の影響を受けることもなく、光励起強度に応じた過渡特性の小さい光応答電流を得ることが可能となる。 However, in this embodiment, since the insensitive layer 4 is formed on the surface of the bare part 5, the bare part 5 is joined to the insensitive layer 4 having a ZnO—ZnO homojunction surface, and dangling. Without being influenced by ring bonds (molecular orbitals in which unpaired electrons having no binding partner exist), it is possible to obtain a photoresponse current having a small transient characteristic according to the photoexcitation intensity.
　また、このようにベア部５の表面はＺｎＯ－ＺｎＯのホモ接合面を介して不感応層４に接合されることから、光照射を停止した場合の立ち下がり時も、光応答電流は鋭敏に低下し、立ち下がり特性の向上を図ることができる。 Further, since the surface of the bare part 5 is bonded to the insensitive layer 4 through the ZnO—ZnO homojunction surface in this way, the photoresponse current is sharp even at the fall when the light irradiation is stopped. The falling characteristic can be improved.
（３）分光特性
　感応層１のベア部５の表面に該感応層１と同一乃至略同一の光吸収特性を有するＺｎＯを主成分とする不感応層４を挿入しているので、光応答のピーク部分の波長帯の光を吸収して、ピークを抑えることができる。 (3) Spectral characteristics Since the insensitive layer 4 mainly composed of ZnO having the same or substantially the same light absorption characteristics as that of the sensitive layer 1 is inserted on the surface of the bare part 5 of the sensitive layer 1, The peak can be suppressed by absorbing light in the peak wavelength band.
　したがって、感応層１上に不感応層４を形成していないベア状態の紫外線センサに比べ、２８０ｎｍ～３８０ｎｍの波長帯域、すなわちＵＶ－Ａ及びＵＶ－Ｂの各紫外領域で、より一層平坦な分光特性を有する紫外線センサを実現することが可能となる。 Therefore, compared with a bare ultraviolet sensor in which the insensitive layer 4 is not formed on the sensitive layer 1, a more flat spectroscopic spectrum is obtained in the wavelength band of 280 nm to 380 nm, that is, in each ultraviolet region of UV-A and UV-B. An ultraviolet sensor having characteristics can be realized.
　尚、不感応層４の膜厚は、特に限定されるものではないが、３ｎｍ以上１４０ｎｍ未満が好ましい。すなわち、不感応層４の膜厚が３ｎｍ未満になると、不感応層４の膜厚が薄すぎるため暗電流を十分に低減するのが困難である。一方、不感応層４の膜厚が１４０ｎｍを超えると、膜厚が厚いため暗電流の低減化には好都合であるが、例えば、矢印Ａ方向から紫外線を入射する場合は、光吸収が大きくなりすぎて分光感度の低下を招くおそれがある。 The thickness of the insensitive layer 4 is not particularly limited, but is preferably 3 nm or more and less than 140 nm. That is, when the thickness of the insensitive layer 4 is less than 3 nm, it is difficult to sufficiently reduce the dark current because the thickness of the insensitive layer 4 is too thin. On the other hand, if the film thickness of the insensitive layer 4 exceeds 140 nm, it is convenient for reducing the dark current because the film thickness is thick. However, for example, when ultraviolet rays are incident from the direction of arrow A, light absorption increases. This may cause a decrease in spectral sensitivity.
　また、感応層１の膜厚も、特に限定されるものではないが、例えば、日照モニタ等に使用する場合は、１０ｎｍ以上１００ｎｍ以下が好ましい。すなわち、紫外線センサでは、紫外線を検知したときの出力電流Ｉと紫外線照射を停止したときに流れる暗電流Ｉ０との電流比Ｉ／Ｉ０が大きいのが好ましく、この電流比Ｉ／Ｉ０が十分に大きくなると、光応答電流（＝出力電流Ｉ－暗電流Ｉ０）も大きくなることから、紫外線強度を高精度に検知することが可能となる。 Further, the thickness of the sensitive layer 1 is not particularly limited, but is preferably 10 nm or more and 100 nm or less when used for, for example, a sunshine monitor. That is, in the ultraviolet sensor, the output current I and is preferably a large current ratio I / I 0 of the ultraviolet irradiation and the dark current I 0 flowing when stopped, the current ratio I / I 0 when the detected ultraviolet If it becomes sufficiently large, the photoresponse current (= output current I−dark current I 0 ) also increases, so that the ultraviolet intensity can be detected with high accuracy.
　しかしながら、感応層１の膜厚が厚くなるに伴い、電流比Ｉ／Ｉ０は低下する。そして、膜厚が１００ｎｍを超えると、電流比Ｉ／Ｉ０が過度に小さくなって日照モニタ等に使用する場合は好ましくない。すなわち、本紫外線センサを日照モニタ等に使用する場合、曇りの日の屋外での紫外線強度（約１ｍＷ／ｃｍ２）であり、所望のセンサ感度を得るためには上記比Ｉ／Ｉ０は５０以上が好ましいが、感応層１の膜厚が１００ｎｍを超えると、５０未満に低下する。 However, as the thickness of the sensitive layer 1 increases, the current ratio I / I 0 decreases. When the film thickness exceeds 100 nm, the current ratio I / I 0 becomes excessively small, which is not preferable when used for a sunshine monitor or the like. That is, when this ultraviolet sensor is used for a sunshine monitor or the like, it is the ultraviolet intensity (about 1 mW / cm 2 ) outdoors on a cloudy day, and the ratio I / I 0 is 50 in order to obtain a desired sensor sensitivity. Although the above is preferable, when the film thickness of the sensitive layer 1 exceeds 100 nm, it falls to less than 50.
　したがって、感応層１の膜厚は限定されないものの、用途によっては１００ｎｍ以下が好ましい。 Therefore, although the thickness of the sensitive layer 1 is not limited, it is preferably 100 nm or less depending on the application.
　ただし、感応層１で紫外線強度を検知するためには、感応層１の膜厚は少なくとも１０ｎｍ以上が必要である。 However, in order for the sensitive layer 1 to detect the ultraviolet intensity, the thickness of the sensitive layer 1 needs to be at least 10 nm.
　このように本第１の実施の形態によれば、感応層１が、基板３の一方の主面の表面に形成されると共に、一対の電極２ａ、２ｂが、前記感応層１の表面に形成され、かつ、不感応層４は、電極２ａ、２ｂの端部を覆うようにベア部５を含む感応層１の表面に形成されているので、感応層１の界面はＺｎＯ－ＺｎＯのホモ接合面を有することとなり、酸素欠損や吸着分子の存在が抑制され、界面の表面性状も安定化する。そしてこれにより光励起強度に応じた過渡特性の小さい光電流を得ることができ、過渡特性を向上させることができる。また、光照射を停止した場合も、過渡特性の場合と同様の理由から鋭敏に立ち下がり、立ち下がり特性が向上し、暗電流も抑制することができる。 Thus, according to the first embodiment, the sensitive layer 1 is formed on the surface of one main surface of the substrate 3, and the pair of electrodes 2a and 2b are formed on the surface of the sensitive layer 1. In addition, since the insensitive layer 4 is formed on the surface of the sensitive layer 1 including the bare portion 5 so as to cover the ends of the electrodes 2a and 2b, the interface of the sensitive layer 1 is a ZnO-ZnO homojunction. As a result, the presence of oxygen deficiency and adsorbed molecules is suppressed, and the surface properties of the interface are stabilized. As a result, a photocurrent having a small transient characteristic corresponding to the photoexcitation intensity can be obtained, and the transient characteristic can be improved. In addition, even when the light irradiation is stopped, it falls sharply for the same reason as in the case of the transient characteristic, the fall characteristic is improved, and the dark current can be suppressed.
　次に、上記紫外線センサの製造方法を詳述する。 Next, the manufacturing method of the ultraviolet sensor will be described in detail.
　まず、高周波マグネトロンスパッタ法を使用し、ＺｎＯ系材料をターゲットとして基板３上に感応層１を形成する。 First, the sensitive layer 1 is formed on the substrate 3 by using a high frequency magnetron sputtering method with a ZnO-based material as a target.
　すなわち、基板３とターゲットとを対向させて配し、基板３を加熱すると共に、所定の真空下、所定流量のアルゴンガス及び酸素ガスをスパッタ装置に導入し、高周波電源を印加して所定時間スパッタリング処理を行い、基板３上に所定膜厚の感応層１を作製する。 That is, the substrate 3 and the target are arranged facing each other, the substrate 3 is heated, and a predetermined flow rate of argon gas and oxygen gas is introduced into the sputtering apparatus under a predetermined vacuum, and a high frequency power source is applied to perform sputtering for a predetermined time. Processing is performed to produce the sensitive layer 1 having a predetermined film thickness on the substrate 3.
　次に、リフトオフ法により、感応層１上に電極２ａ、２ｂを形成する。すなわち、感応層１の表面にフォトレジストを塗布した後、プリベークし、次いでフォトマスクを介して露光・現像を行う。そしてこの後、真空蒸着法、電子ビーム蒸着法、スパッタリング法等の薄膜形成法を使用して一層又は二層以上の電極層を形成する。次いで、不要な電極層を有機溶剤を使用してエッチング除去し、これにより所定間隔ｔ（例えば、５～１０μｍ）を介して対向状に配された電極２ａ、２ｂを形成する。 Next, electrodes 2a and 2b are formed on the sensitive layer 1 by a lift-off method. That is, a photoresist is applied to the surface of the sensitive layer 1 and then pre-baked, and then exposed and developed through a photomask. Thereafter, one or more electrode layers are formed by using a thin film forming method such as a vacuum evaporation method, an electron beam evaporation method, or a sputtering method. Next, unnecessary electrode layers are removed by etching using an organic solvent, thereby forming electrodes 2a and 2b arranged in a confronting manner with a predetermined interval t (for example, 5 to 10 μm).
　次に、不感応層４及び絶縁保護膜６を、例えば、自公転できるスパッタ装置を使用し、真空中で連続的に形成する。 Next, the insensitive layer 4 and the insulating protective film 6 are continuously formed in a vacuum using, for example, a sputtering apparatus capable of revolving.
　すなわち、不感応層４の形成に際してはＺｎＯ系材料をターゲットとし、絶縁保護膜６の形成に際してはケイ素化合物等の絶縁保護材をターゲットとし、真空状態を維持しつつ、電極２ａ、２ｂの中央部をマスクして連続的にスパッタリングし、不感応層４及び絶縁保護膜６を形成する。 That is, when the insensitive layer 4 is formed, a ZnO-based material is used as a target, and when the insulating protective film 6 is formed, an insulating protective material such as a silicon compound is used as a target, and the central portions of the electrodes 2a and 2b are maintained while maintaining a vacuum state. The insensitive layer 4 and the insulating protective film 6 are formed by continuously sputtering using a mask.
　このように本実施の形態では、真空中で連続的に不感応層４及び絶縁保護膜６を形成しているので、不感応層４と絶縁保護膜６との界面を均質に形成することができ、より薄い不感応層４でも暗電流の増大を抑制することができる紫外線センサを製造することができる。 Thus, in this embodiment, since the insensitive layer 4 and the insulating protective film 6 are continuously formed in a vacuum, the interface between the insensitive layer 4 and the insulating protective film 6 can be formed uniformly. Thus, it is possible to manufacture an ultraviolet sensor that can suppress an increase in dark current even with a thinner insensitive layer 4.
　図３は、第１の実施の形態の変形例を示す断面図であって、この変形例では絶縁保護膜６の表面に高反射率を有する金属薄膜８が形成されている。 FIG. 3 is a cross-sectional view showing a modification of the first embodiment. In this modification, a metal thin film 8 having a high reflectivity is formed on the surface of the insulating protective film 6.
　この変形例では、矢印Ｂ方向から紫外線を照射させた場合に、感応層１を透過した入射光が金属薄膜８で反射し、これによりキャリア発生に寄与することができることから、センサ感度のより一層の向上を図ることができる。 In this modified example, when ultraviolet rays are irradiated from the direction of arrow B, incident light transmitted through the sensitive layer 1 is reflected by the metal thin film 8 and can thereby contribute to carrier generation. Can be improved.
　そして、このような金属薄膜８としては、紫外線領域で高反射率を有するものであれば特に限定されるものではなく、例えば、Ｐｔ、Ａｇ、Ａｌ、Ｍｇ、Ｍｏ等を使用することができる。 The metal thin film 8 is not particularly limited as long as it has a high reflectance in the ultraviolet region, and for example, Pt, Ag, Al, Mg, Mo, or the like can be used.
　また、金属薄膜８の膜厚も、紫外光が反射するのであれば、特に限定されるものではなく、例えば、２００ｎｍ程度に形成すればよい。 Also, the thickness of the metal thin film 8 is not particularly limited as long as it reflects ultraviolet light, and for example, it may be formed to about 200 nm.
　図４は、本発明に係る紫外線センサの第２の実施の形態を模式的に示した断面図であって、本第２の実施の形態は、主成分がＺｎＯで形成された感応層１１と、所定間隔ｔを介して対向状に配された一対の電極１２ａ、１２ｂとが、基板１３の一方の主面側に形成され、かつ、主成分を前記感応層１１と同一材料で形成した不感応層１４が、感応層１１の表面全域に形成されている。 FIG. 4 is a cross-sectional view schematically showing a second embodiment of the ultraviolet sensor according to the present invention. The second embodiment includes a sensitive layer 11 whose main component is formed of ZnO. A pair of electrodes 12a and 12b arranged opposite to each other at a predetermined interval t is formed on one main surface side of the substrate 13 and the main component is formed of the same material as the sensitive layer 11. The sensitive layer 14 is formed over the entire surface of the sensitive layer 11.
　すなわち、この第２の実施の形態では、所定間隔ｔを介して一対の電極１２ａ、１２ｂが基板１３の表面に対向状に配されたプレーナ型構造とされ、電極１２ａ、１２ｂの端部を覆うようにベア部１５を含む基板１３の一方の主面の表面に感応層１１が形成されている。また、感応層１１の表面には主成分がＺｎＯからなる不感応層１４が形成され、さらに該不感応層１４の表面には絶縁保護膜１６が形成されている。 That is, in the second embodiment, a pair of electrodes 12a and 12b are arranged in a planar manner on the surface of the substrate 13 with a predetermined interval t, and the ends of the electrodes 12a and 12b are covered. As described above, the sensitive layer 11 is formed on the surface of one main surface of the substrate 13 including the bare portion 15. A non-sensitive layer 14 whose main component is made of ZnO is formed on the surface of the sensitive layer 11, and an insulating protective film 16 is formed on the surface of the non-sensitive layer 14.
　本第２の実施の形態でも、感応層１１と絶縁保護膜１６との間にＺｎＯを主成分とする不感応層１４が介装されているので、第１の実施の形態と同様、暗電流の増大を招くこともなく、光照射時の立ち上がり時における過渡特性や光照射を停止したときの立ち下がり特性、更には分光特性等の諸特性を向上させることができ、高性能の紫外線センサを得ることが可能となる。 Also in the second embodiment, since the insensitive layer 14 mainly composed of ZnO is interposed between the sensitive layer 11 and the insulating protective film 16, the dark current is the same as in the first embodiment. Without causing an increase in the light level, it is possible to improve various characteristics such as transient characteristics at the start of light irradiation, falling characteristics when light irradiation is stopped, and spectral characteristics. Can be obtained.
　本第２の実施の形態の紫外線センサは、以下のようにして作製することができる。 The ultraviolet sensor according to the second embodiment can be manufactured as follows.
　すなわち、第１の実施の形態で述べたリフトオフ法を使用して基板１３上に電極１２ａ、１２ｂを作製した後、電極１２ａ、１２ｂの中央部をマスクし、ＺｎＯ系材料をターゲットとして高周波マグネトロンスパッタ法により感応層１１を作製し、その後、第１の実施の形態と同様の方法で不感応層１４及び絶縁保護膜１６を形成し、これにより紫外線センサを作製することができる。 That is, after the electrodes 12a and 12b are formed on the substrate 13 by using the lift-off method described in the first embodiment, the central portions of the electrodes 12a and 12b are masked, and a high-frequency magnetron sputtering is performed using a ZnO-based material as a target. The sensitive layer 11 is produced by the method, and then the insensitive layer 14 and the insulating protective film 16 are formed by the same method as in the first embodiment, whereby the ultraviolet sensor can be produced.
　尚、本発明は上記実施の形態に限定されるものではない。上記第２の実施の形態においても、第１の実施の形態の変形例と同様、絶縁保護膜１６の表面に高反射率を有する金属薄膜を形成し、電極１２ａ、１２ｂの形成面と反対方向から紫外光を照射させて金属薄膜で反射させ、これにより紫外線の検知精度を向上させるのも好ましい。 The present invention is not limited to the above embodiment. Also in the second embodiment, as in the modification of the first embodiment, a metal thin film having a high reflectance is formed on the surface of the insulating protective film 16, and the direction opposite to the formation surface of the electrodes 12a and 12b. It is also preferable to irradiate with ultraviolet light and reflect it with a metal thin film, thereby improving the detection accuracy of ultraviolet light.
　また、上記各実施の形態で、電極２ａ、２ｂ、１２ａ、１２ｂの表面に電解めっきを行なってＮｉやＡｕ等からなるめっき皮膜を形成するのも好ましく、このように電極表面にめっき皮膜を形成することにより、電極面を下方にして表面実装しても電極面には十分な機械的強度が付与されることから、表面実装に適した紫外線センサを得ることが可能となる。 In each of the above embodiments, it is also preferable to perform electrolytic plating on the surfaces of the electrodes 2a, 2b, 12a, and 12b to form a plating film made of Ni, Au, or the like. In this way, the plating film is formed on the electrode surface. By doing so, even if surface mounting is performed with the electrode surface facing downward, sufficient mechanical strength is imparted to the electrode surface, so that an ultraviolet sensor suitable for surface mounting can be obtained.
　また、上記各実施の形態では、感応層１、１１を高周波マグネトロンスパッタ法で作製しているが、成膜方法は特に限定されるものではなく、他の成膜方法を使用してもよい。また、上記実施の形態では、自公転できるスパッタ装置を使用して不感応層５及び絶縁保護膜６、１６を真空下、連続的に成膜しているが、同様の効果を得ることができるのであれば、特に限定されるものではない。また、本発明は、紫外線センサ以外の他の光検出素子にも適用可能である。 In each of the above embodiments, the sensitive layers 1 and 11 are produced by the high frequency magnetron sputtering method, but the film forming method is not particularly limited, and other film forming methods may be used. In the above embodiment, the insensitive layer 5 and the insulating protective films 6 and 16 are continuously formed under vacuum using a sputtering apparatus capable of revolving, but the same effect can be obtained. If it is, it will not specifically limit. The present invention can also be applied to other light detection elements other than the ultraviolet sensor.
　次に、本発明の実施例を具体的に説明する。 Next, specific examples of the present invention will be described.
（試料の作製）
　基板として、厚さ約３５０μｍのＬｉＴａＯ３基板（以下、「ＬＴ基板」という。）を用意し、高周波マグネトロンスパッタ法を使用し、以下のようにしてＬＴ基板上に膜厚５００ｎｍの感応層を作製した。 (Sample preparation)
A LiTaO 3 substrate (hereinafter referred to as “LT substrate”) with a thickness of about 350 μm is prepared as a substrate, and a high-frequency magnetron sputtering method is used to produce a sensitive layer with a thickness of 500 nm on the LT substrate as follows. did.
　すなわち、ターゲットとして、ノンドープのＺｎＯ焼結体を厚さ５ｍｍ、直径１００ｍｍに切断し、銅製バッキングプレートに貼着したものを用意した。 That is, as a target, a non-doped ZnO sintered body was cut to a thickness of 5 mm and a diameter of 100 mm, and adhered to a copper backing plate.
　そして、ＬＴ基板とターゲットとを対向状に配し、背圧約１０-5Ｐａ程度にスパッタ装置内を真空状態にした後、アルゴンガス（流量：５．５７×１０-2Ｐａ・ｍ３／ｓ）（３３sccm）及び酸素ガス（流量：４．９０×１０-3Ｐａ・ｍ３／ｓ）（２．９sccm）を前記スパッタ装置内に導入し、圧力：０．３５～０．７Ｐａ、高周波出力：３００Ｗ、基板温度：４２０℃の条件下で１５分間基板ホルダを回転させて成膜処理を行った。 Then, the LT substrate and the target are arranged facing each other, the inside of the sputtering apparatus is evacuated to a back pressure of about 10 −5 Pa, and then argon gas (flow rate: 5.57 × 10 −2 Pa · m 3 / s). ) (33 sccm) and oxygen gas (flow rate: 4.90 × 10 −3 Pa · m 3 / s) (2.9 sccm) were introduced into the sputtering apparatus, pressure: 0.35 to 0.7 Pa, high frequency output : 300 W, substrate temperature: 420 ° C., and the substrate holder was rotated for 15 minutes to perform film formation.
　次に、リフトオフ法により感応層上に一対の電極を形成した。すなわち、まず、感応層の表面にフォトレジストを塗布した後、プリベークし、さらにフォトマスクを介して露光・現像を行った。次いで、電子ビーム蒸着法を使用し、膜厚が約２０ｎｍのＴｉ膜及び膜厚が４００ｎｍのＡｕ膜を順次成膜した。そしてその後、有機溶剤を使用して不要な電極層を除去し、互いに対向状に配された一対の電極を形成した。尚、電極間距離（所定間隔）は１０μｍとした。 Next, a pair of electrodes was formed on the sensitive layer by the lift-off method. That is, first, a photoresist was applied to the surface of the sensitive layer, then pre-baked, and further exposed and developed through a photomask. Next, using an electron beam evaporation method, a Ti film having a thickness of about 20 nm and an Au film having a thickness of 400 nm were sequentially formed. Then, an unnecessary electrode layer was removed using an organic solvent to form a pair of electrodes arranged opposite to each other. The interelectrode distance (predetermined interval) was 10 μm.
　次に、自公転可能な高周波マグネトロンスパッタ装置を使用し、以下の条件で不感応層及び絶縁保護膜を連続的に形成した。 Next, using a high-frequency magnetron sputtering apparatus capable of revolving, the insensitive layer and the insulating protective film were continuously formed under the following conditions.
　〔不感応層〕
　ターゲット：高純度ＺｎＯ
　ガス流量：アルゴン　８．４４×１０-2Ｐａ・ｍ３／ｓ（５０sccm）
　　　　　　酸素　１．６９×１０-2Ｐａ・ｍ３／ｓ（１０sccm）
　ガス圧力；０．２１Ｐａ
　高周波出力：２５０Ｗ
　成膜時間：５分
　基板温度：常温（加熱なし）
〔絶縁保護膜〕
　ターゲット；高純度ＳｉＯ２
　ガス流量：アルゴン　５．０７×１０-2Ｐａ・ｍ３／ｓ（３０sccm）
　　　　　　酸素　２．１９×１０-2Ｐａ・ｍ３／ｓ（１３sccm）
　高周波出力：６００Ｗ
　成膜時間：６３分
　この後、フォトレジストを使用してエッチングパターンを形成し、バッファード弗酸（ＢＨＦ）で絶縁保護膜及び不感応層を選択除去し、電極の一部を表面露出させ、これにより試料番号１及び２の実施例試料を作製した。尚、不感応層の膜厚は２８ｎｍ、絶縁保護膜の膜厚は２９０ｎｍであった。 [Insensitive layer]
Target: High purity ZnO
Gas flow rate: Argon 8.44 × 10 −2 Pa · m 3 / s (50 sccm)
Oxygen 1.69 × 10 −2 Pa · m 3 / s (10 sccm)
Gas pressure; 0.21 Pa
High frequency output: 250W
Deposition time: 5 minutes Substrate temperature: normal temperature (no heating)
[Insulating protective film]
Target; high-purity SiO 2
Gas flow rate: Argon 5.07 × 10 −2 Pa · m 3 / s (30 sccm)
Oxygen 2.19 × 10 −2 Pa · m 3 / s (13 sccm)
High frequency output: 600W
Film formation time: 63 minutes Thereafter, an etching pattern is formed using a photoresist, the insulating protective film and the insensitive layer are selectively removed with buffered hydrofluoric acid (BHF), and a part of the electrode is exposed on the surface. In this way, sample samples of sample numbers 1 and 2 were produced. The insensitive layer had a thickness of 28 nm, and the insulating protective film had a thickness of 290 nm.
　また、不感応層を設けず、膜構成を基板／感応層／（電極＋絶縁保護膜）とした以外は、試料番号１及び２と同様の方法・手順で試料番号３及び４を作製し、比較例試料とした。 In addition, sample numbers 3 and 4 were prepared by the same method and procedure as sample numbers 1 and 2, except that the insensitive layer was not provided and the film configuration was substrate / sensitive layer / (electrode + insulating protective film). A comparative sample was obtained.
　また、別の比較例試料として、不感応層及び絶縁保護膜を設けず、膜構成を基板／（感応層＋電極）とした以外は、試料番号１及び２と同様の方法・手順で、ベア状態の試料番号５及び６を作製し、比較例試料とした。 In addition, as another comparative example sample, a bare layer and an insulating protective film are not provided, and the film configuration is substrate / (sensitive layer + electrode). Sample Nos. 5 and 6 in the state were prepared and used as comparative example samples.
〔暗電流の評価〕
　試料番号１～６の各試料について、デジタル・エレクトロメータ（アドバンテスト社製ＴＲ８６５２）を使用し、紫外線を照射することなく電極間に３．０Ｖの電圧を印加し、これにより暗電流を測定した。 [Evaluation of dark current]
For each of the samples Nos. 1 to 6, a digital electrometer (TR8652 manufactured by Advantest Co., Ltd.) was used, and a voltage of 3.0 V was applied between the electrodes without irradiating ultraviolet rays, thereby measuring the dark current.
　図５は試料番号１～６の測定結果を示し、縦軸が暗電流（Ａ）を示している。 FIG. 5 shows the measurement results of sample numbers 1 to 6, and the vertical axis represents dark current (A).
　この図５から明らかなように、試料番号３、４は、感応層が絶縁保護膜と接しているため、暗電流が１．２×１０-7～５×１０-9Ａとなり、暗電流が増大することが分かった。 As is apparent from FIG. 5, in Sample Nos. 3 and 4, since the sensitive layer is in contact with the insulating protective film, the dark current is 1.2 × 10 −7 to 5 × 10 −9 A, and the dark current is It was found to increase.
　これに対し実施例試料である試料番号１、２、５、６は、いずれも感応層の表面に不感応層が形成されているため、暗電流が１０-11Ａ以下に抑制できた。 In contrast, Sample Nos. 1, 2, 5, and 6 as the example samples all had a non-sensitive layer formed on the surface of the sensitive layer, so that the dark current could be suppressed to 10 −11 A or less.
〔過渡特性及び立ち下がり特性の評価〕
　試料番号１及び５について、ＬＥＤ紫外線光源から３６５ｎｍの波長の紫外光を、約４０秒間試料に照射し、３．０Ｖの電圧を印加して出力電流を測定し、立ち上がり時の過渡特性及び立ち下がり特性を調べた。 [Evaluation of transient characteristics and falling characteristics]
For sample numbers 1 and 5, the sample was irradiated with UV light with a wavelength of 365 nm from an LED UV light source for about 40 seconds, a voltage of 3.0 V was applied, and the output current was measured. The characteristics were investigated.
　図６はその測定結果を示している。横軸は時間（秒）、縦軸は光応答電流（＝出力電流－暗電流）（Ａ）を示している。 FIG. 6 shows the measurement results. The horizontal axis represents time (seconds), and the vertical axis represents photoresponse current (= output current−dark current) (A).
　この図６から明らかなように試料番号５は、立ち上がり時の過渡特性が大きく、しかも光応答電流は立ち上がった後も若干増加傾向にあることが分かった。 As can be seen from FIG. 6, Sample No. 5 has a large transient characteristic at the time of rising, and the photoresponse current tends to increase slightly even after rising.
　これに対し試料番号１は、過渡特性が小さく、光応答電流は立ち上がった後、略直線状態となり、光励起強度に近い光応答電流を得ることができた。 On the other hand, Sample No. 1 had a small transient characteristic, and after the photoresponse current rose, it became a substantially linear state, and a photoresponse current close to the photoexcitation intensity could be obtained.
　また、光照射の停止時についても、試料番号５では、光応答電流は緩やかな曲線を描きながら徐々に低下し、立ち下がりの鋭敏性に欠けることが分かった。 Also, when the light irradiation was stopped, it was found that in Sample No. 5, the photoresponse current gradually decreased while drawing a gentle curve and lacked the sharpness of the fall.
　これに対し試料番号１は、光照射の停止時に瞬時に低下し、立ち下がり特性が向上することが確認された。 In contrast, it was confirmed that Sample No. 1 was instantaneously lowered when the light irradiation was stopped, and the falling characteristics were improved.
　すなわち、不感応層を有する試料番号１は、不感応層を有さない試料番号５に比べ、光応答電流の時間変化が小さく、立ち上がり時の過渡特性や立ち下がり特性を改善できることが分かった。 That is, it was found that Sample No. 1 having the insensitive layer has a smaller time change of the photoresponse current than Sample No. 5 having no insensitive layer, and can improve the transient characteristics and the falling characteristics at the time of rising.
　また、試料番号１及び５について、光応答電流の変化率を測定した。 Moreover, the change rate of the photoresponsive current was measured for sample numbers 1 and 5.
　すなわち、光照射後１～３秒の光応答電流の電流平均値（以下、「初期平均値」という。）と、光照射後２５～２７秒の光応答電流の電流平均値（以下、「定常平均値」という。）を測定し、初期平均値を１００として初期平均値に対する定常平均値の比率を求め、これにより光応答電流の変化率を測定した。 That is, the current average value of the photoresponse current for 1 to 3 seconds after light irradiation (hereinafter referred to as “initial average value”) and the current average value of the photoresponse current for 25 to 27 seconds after light irradiation (hereinafter referred to as “steady state”). The average value ”) was measured, and the ratio of the steady average value to the initial average value was determined with the initial average value set to 100, thereby measuring the rate of change of the photoresponsive current.
　その結果、試料番号５が３１．７％であるのに対し、試料番号１は３．１％であり、試料番号１は試料番号５に比べ、立ち上がり後も光応答電流の変動が少ないことが確認された。 As a result, the sample number 5 is 31.7%, whereas the sample number 1 is 3.1%, and the sample number 1 has less fluctuation in the photo-response current after the start-up than the sample number 5. confirmed.
　尚、本発明者らは、厚さ３５０ｎｍの両面研磨したｃカットサファイア基板を使用し、高周波マグネトロンスパッタ法における成膜条件を１５分として膜厚４０ｎｍの感応層を作製し、電極を構成するＴｉ膜の膜厚を４０ｎｍとした以外は、試料番号１と同様の方法・手順で試料を作製し、上述した各種特性を測定したところ、試料番号１と同様、良好な結果が得られた。 The inventors of the present invention used a c-cut sapphire substrate having a thickness of 350 nm on both sides and fabricated a sensitive layer having a thickness of 40 nm under a film forming condition in a high-frequency magnetron sputtering method for 15 minutes. A sample was prepared by the same method and procedure as in Sample No. 1 except that the film thickness was 40 nm, and the various characteristics described above were measured. As in Sample No. 1, good results were obtained.
　不感応層の膜厚を２．８ｎｍ及び１４０ｎｍとした以外は、試料番号１と同様の方法・手順で試料番号７及び８の試料をそれぞれ作製した。 Samples Nos. 7 and 8 were prepared in the same manner and procedure as Sample No. 1, except that the thickness of the insensitive layer was 2.8 nm and 140 nm.
　次いで、試料番号１（不感応層の膜厚：２８ｎｍ）、７及び８について、分光器を備えた紫外線光源から２８０～４３０ｎｍの波長範囲の紫外光を、各試料に照射し、分光特性を調べた。 Next, for sample No. 1 (thickness of insensitive layer: 28 nm), 7 and 8, each sample was irradiated with ultraviolet light in the wavelength range of 280 to 430 nm from an ultraviolet light source equipped with a spectroscope, and the spectral characteristics were examined. It was.
　図７はその測定結果である。横軸は波長（ｎｍ）を示し、縦軸は分光感度（a.u.）を示している。 Fig. 7 shows the measurement results. The horizontal axis indicates the wavelength (nm), and the vertical axis indicates the spectral sensitivity (a.u.).
　この図７から明らかなように不感応層の膜厚が薄くなるに伴い、分光感度は向上することが分かる。 As can be seen from FIG. 7, the spectral sensitivity improves as the thickness of the insensitive layer decreases.
　すなわち、試料番号８は不感応層の膜厚が１４０ｎｍと厚いため、不感応層での光吸収が大きく応答特性が小さくなることが分かった。 That is, in Sample No. 8, since the thickness of the insensitive layer was as thick as 140 nm, it was found that the light absorption in the insensitive layer was large and the response characteristic was small.
　尚、試料番号７は、不感応層の膜厚が２．８ｎｍと薄く、平坦性は良好であるが、別途暗電流を測定したところ、暗電流の低下を招くことが確認された。 In Sample No. 7, the thickness of the insensitive layer was as thin as 2.8 nm and the flatness was good, but when dark current was measured separately, it was confirmed that the dark current was reduced.
　これに対し試料番号１は、紫外線の照射波長に応じて凹凸は生じているものの、実用性に問題が生じない程度の平坦性を有することが確認された。 On the other hand, it was confirmed that Sample No. 1 has flatness that does not cause a problem in practical use, although unevenness is generated according to the irradiation wavelength of ultraviolet rays.
　以上の結果より、不感応層の好ましい膜厚は、３ｎｍ以上１４０ｎｍ未満であることが分かった。 From the above results, it was found that the preferable film thickness of the insensitive layer was 3 nm or more and less than 140 nm.
　ベア部の電極間距離（所定間隔）を５μｍとした以外は、試料番号１と同様の方法・手順で試料番号１１、１２を作製した。 Sample numbers 11 and 12 were prepared by the same method and procedure as sample number 1 except that the distance between electrodes of the bare part (predetermined interval) was 5 μm.
　また、ベア部上に感応層を形成し、不感応層及び絶縁保護膜を形成しなかった膜構成が基板／（電極＋感応層）の試料番号１３、１４を試料番号１１、１２と同様の方法・手順で作製した。 In addition, the film structure in which the sensitive layer is formed on the bare portion and the insensitive layer and the insulating protective film are not formed is the same as the sample numbers 11 and 12 in the sample numbers 13 and 14 of the substrate / (electrode + sensitive layer). It was produced by the method / procedure.
　そして、試料番号１１～１４の各試料について、実施例２と同様の方法・手順で分光特性を測定した。 Then, the spectral characteristics of the samples Nos. 11 to 14 were measured by the same method and procedure as in Example 2.
　図８はその測定結果である。横軸は波長（ｎｍ）を示し、縦軸は分光感度（a.u.）を示している。 Fig. 8 shows the measurement results. The horizontal axis indicates the wavelength (nm), and the vertical axis indicates the spectral sensitivity (a.u.).
　試料番号１３、１４は、不感応層を有しておらず、したがってＺｎＯ－ＺｎＯホモ接合面を有していないことから、分光特性は波長：３７０ｎｍ付近をピークとする山形形状となって平坦性に欠け、分光特性に劣ることが分かった。 Since Sample Nos. 13 and 14 do not have a non-sensitive layer, and therefore do not have a ZnO—ZnO homojunction surface, the spectral characteristics have a mountain shape with a peak at a wavelength of about 370 nm and are flat. It was found that the spectral characteristics were inferior.
　これに対し試料番号１１、１２は、感応層と同一の光吸収特性を有する不感応層が感応層と絶縁保護膜との間に介在しているので、波長：３７０ｎｍ付近のピークとなる波長帯の応答を効果的に抑えることができ、２８０ｎｍ～３８０ｎｍのＵＶ－Ａ、ＵＶ－Ｂ領域で平坦な分光特性を実現できることが分かった。 On the other hand, in Sample Nos. 11 and 12, since the insensitive layer having the same light absorption characteristics as the sensitive layer is interposed between the sensitive layer and the insulating protective film, the wavelength is a wavelength band having a peak near 370 nm. It was found that this response can be effectively suppressed, and flat spectral characteristics can be realized in the UV-A and UV-B regions of 280 nm to 380 nm.
　感応層の厚みを１０ｎｍ、２０ｎｍ、４０ｎｍ、１６０ｎｍと種々異ならせた以外は試料番号１と同様にして試料番号１５～１８の各試料を作製した。 Samples Nos. 15 to 18 were prepared in the same manner as Sample No. 1 except that the thickness of the sensitive layer was variously changed to 10 nm, 20 nm, 40 nm, and 160 nm.
　次いで、試料番号１５～１８の各試料について、試料番号１と同様の方法・手順で、紫外光照射時の出力電流Ｉ、及び紫外光照射が停止してから５秒後の暗電流Ｉ０を測定した。 Next, for each of the samples Nos. 15 to 18, the output current I at the time of ultraviolet light irradiation and the dark current I 0 after 5 seconds after the ultraviolet light irradiation was stopped by the same method and procedure as the sample number 1. It was measured.
　図９は各膜厚と出力電流Ｉ及び暗電流Ｉ０の関係を示している。横軸が膜厚（ｎｍ）、縦軸が電流Ｉ（Ａ）であり、図中、◆印が出力電流Ｉ、●印が暗電流Ｉ０を示している。 Figure 9 shows the relationship between the film thickness and the output current I and the dark current I 0. The horizontal axis represents the film thickness (nm), the vertical axis represents the current I (A), and in the figure, the ♦ mark represents the output current I, and the ● mark represents the dark current I 0 .
　この図９から明らかなように、感応層の膜厚が厚くなるのに伴い、出力電流の上昇曲線が暗電流の上昇曲線に比べて緩やかになり、両者が近づく傾向にあることが分かる。 As can be seen from FIG. 9, as the thickness of the sensitive layer increases, the output current rise curve becomes gentler than the dark current rise curve, and both tend to approach each other.
　図１０は各膜厚と出力電流Ｉと暗電流Ｉ０との電流比Ｉ／Ｉ０との関係を示している。横軸が膜厚（ｎｍ）、縦軸が電流比Ｉ／Ｉ０である。 FIG. 10 shows the relationship between each film thickness, the current ratio I / I 0 between the output current I and the dark current I 0 . The horizontal axis is the film thickness (nm), and the vertical axis is the current ratio I / I 0 .
　この図１０から明らかなように、感応層の膜厚が厚くなるのに伴い、電流比Ｉ／Ｉ０が減少している。すなわち、膜厚が４０ｎｍ以下では電流比Ｉ／Ｉ０は１００以上となるが、膜厚が１６０ｎｍになると、電流比Ｉ／Ｉ０は１０～２０程度に減少する。そして、日照の紫外線モニタを想定した場合、曇りの日の屋外での紫外線強度は約１ｍＷ／ｃｍ２であり、この場合でも５０以上の電流比Ｉ／Ｉ０を確保するためには、感応層の膜厚は１００ｎｍ以下とするのが好ましいことが分かった。 As is apparent from FIG. 10, the current ratio I / I 0 decreases as the thickness of the sensitive layer increases. That is, when the film thickness is 40 nm or less, the current ratio I / I 0 is 100 or more, but when the film thickness is 160 nm, the current ratio I / I 0 decreases to about 10 to 20. Assuming a sunshine UV monitor, the UV intensity outdoors on a cloudy day is about 1 mW / cm 2. Even in this case, in order to secure a current ratio I / I 0 of 50 or more, the sensitive layer It has been found that the film thickness is preferably 100 nm or less.
（試料の作製）
　基板として、厚さ約３５０μｍの両面研磨したｃカットサファイア基板（以下、「サファイア基板」という。）を用意し、リフトオフ法によりサファイア基板上に一対の電極を形成した。 (Sample preparation)
As a substrate, a c-cut sapphire substrate (hereinafter referred to as “sapphire substrate”) having a thickness of about 350 μm and polished on both sides was prepared, and a pair of electrodes was formed on the sapphire substrate by a lift-off method.
　すなわち、まず、サファイア基板の表面にフォトレジストを塗布した後、プリベークし、さらにフォトマスクを介して露光・現像を行った。次いで、電子ビーム蒸着法を使用し、膜厚が約４０ｎｍのＴｉ膜及び膜厚が４００ｎｍのＡｕ膜を順次成膜した。そしてその後、有機溶剤を使用して不要な電極層を除去し、互いに対向状に配された一対の電極を形成した。尚、電極間距離（所定間隔）は１０μｍとした。 That is, first, a photoresist was applied to the surface of the sapphire substrate, then pre-baked, and further exposed and developed through a photomask. Next, using an electron beam evaporation method, a Ti film having a thickness of about 40 nm and an Au film having a thickness of 400 nm were sequentially formed. Then, an unnecessary electrode layer was removed using an organic solvent to form a pair of electrodes arranged opposite to each other. The interelectrode distance (predetermined interval) was 10 μm.
　次に、高周波マグネトロンスパッタ法を使用し、電極を含むサファイア基板上に膜厚４０ｎｍの感応層を作製した。 Next, using a high frequency magnetron sputtering method, a sensitive layer having a thickness of 40 nm was formed on a sapphire substrate including electrodes.
　すなわち、ターゲットとして、ノンドープのＺｎＯ焼結体を厚さ５ｍｍ、直径１００ｍｍに切断し、銅製バッキングプレートに貼着したものを用意した。 That is, as a target, a non-doped ZnO sintered body was cut to a thickness of 5 mm and a diameter of 100 mm, and adhered to a copper backing plate.
　そして、サファイア基板とターゲットとを対向状に配し、背圧約１０-5Ｐａ程度にスパッタ装置内を真空状態にした後、アルゴンガス（流量：５．５７×１０-2Ｐａ・ｍ３／ｓ）及び酸素ガス（流量：４．９０×１０-３Ｐａ・ｍ３／ｓ）を前記スパッタ装置内に導入し、圧力：０．３５～０．７Ｐａ、高周波出力：３００Ｗ、基板温度：３００℃の条件下で１４分間基板ホルダを回転させて成膜処理を行い、膜厚４０ｎｍの感応層を作製した。 Then, the sapphire substrate and the target are arranged opposite to each other, the inside of the sputtering apparatus is evacuated to a back pressure of about 10 −5 Pa, and then argon gas (flow rate: 5.57 × 10 −2 Pa · m 3 / s). ) and oxygen gas (flow rate: 4.90 to × 10 -3 Pa · m 3 / s) was introduced into the sputtering apparatus, the pressure: 0.35 ~ 0.7 Pa, a high frequency output: 300 W, substrate temperature: 300 ° C. A film formation process was performed by rotating the substrate holder for 14 minutes under the above conditions to produce a sensitive layer having a thickness of 40 nm.
　次に、自公転可能な高周波マグネトロンスパッタ装置を使用し、不感応層は成膜時間を６．５分間とした以外は、試料番号１と同様の方法・手順で、不感応層及び絶縁保護膜を連続的に形成した。 Next, the insensitive layer and the insulating protective film were the same as the sample number 1 except that a self-revolving high frequency magnetron sputtering apparatus was used and the insensitive layer was formed for 6.5 minutes. Was formed continuously.
　この後、フォトレジストを使用してエッチングパターンを形成し、バッファード弗酸（ＢＨＦ）で絶縁保護膜及び不感応層を選択除去し、電極の一部を表面露出させ、これにより試料番号２１の実施例試料を作製した。尚、不感応層の膜厚は２８ｎｍ、絶縁保護膜の膜厚は２９０ｎｍであった。 Thereafter, an etching pattern is formed using a photoresist, the insulating protective film and the insensitive layer are selectively removed with buffered hydrofluoric acid (BHF), and a part of the electrode is exposed to the surface. Example samples were prepared. The insensitive layer had a thickness of 28 nm, and the insulating protective film had a thickness of 290 nm.
　また、不感応層を設けず、膜構成を基板／（電極＋感応層）／絶縁保護膜とした以外は、試料番号２１と同様の方法・手順で試料番号２２の試料を作製し、比較例試料とした。 A sample No. 22 was prepared by the same method and procedure as Sample No. 21 except that the insensitive layer was not provided and the film configuration was substrate / (electrode + sensitive layer) / insulating protective film. A sample was used.
　また、別の比較例試料として、膜構成を基板／（電極＋感応層）とし、ベア状態とした以外は、試料番号１と同様の方法・手順で、試料番号２３を作製し、比較例試料とした。 In addition, as another comparative example sample, sample number 23 was prepared in the same method and procedure as sample number 1 except that the film configuration was substrate / (electrode + sensitive layer) and was in a bare state. It was.
〔光応答電流の経時変化〕
　実施例試料である試料番号２１とベア状態の試料番号２３の各試料について、デジタル・エレクトロメータ（アドバンテスト社製ＴＲ８６５２）を使用し、１．２５ｍＷ／ｃｍ２の紫外線を照射し、３０秒後に紫外線照射を停止し、照射時から照射停止後１０秒間の光応答電流を計測した。 [Time-dependent change in photoresponse current]
For each sample of sample number 21 which is an example sample and sample number 23 in a bare state, a digital electrometer (TR8652 manufactured by Advantest) was used and irradiated with 1.25 mW / cm 2 of ultraviolet light, and after 30 seconds, ultraviolet light was irradiated. Irradiation was stopped, and photoresponse current was measured for 10 seconds after irradiation was stopped.
　図１１は光応答電流の経時変化を示している。横軸が時間（秒）、縦軸は光応答電流（Ａ）である。また、図中、実線が試料番号２１を示し、破線が試料番号２３を示している。 FIG. 11 shows the change over time of the photoresponse current. The horizontal axis represents time (seconds), and the vertical axis represents photoresponse current (A). In the figure, the solid line indicates the sample number 21 and the broken line indicates the sample number 23.
　この図１１から明らかなように、紫外線照射前の暗電流は、試料番号２３は、１．０×１０-7Ａ台であるのに対し、試料番号２１は１．０×１０-10Ａ台であり、３桁以上の低減効果があることが分かった。 As is clear from FIG. 11, the dark current before ultraviolet irradiation is 1.0 × 10 −7 A in the sample number 23, whereas the dark current before the UV irradiation is 1.0 × 10 −10 A in the sample number 21. It was found that there was a reduction effect of 3 digits or more.
　過渡特性も、試料番号２３は、Ａ部に示すように立ち上がりが緩やかになっている。これはベア表面が、空気と接触する不連続な結晶切断面であるため、酸素欠損や空気中の吸着分子などが多く存在し、このため紫外光により励起されたＺｎＯ伝導帯の電子が、これらの酸素欠損や分子と緩和時間の長い相互作用が生じたためと思われる。 Also in the transient characteristics, sample No. 23 has a slow rise as shown in part A. This is because the bare surface is a discontinuous crystal cut surface in contact with air, so there are many oxygen vacancies and adsorbed molecules in the air. Therefore, electrons in the ZnO conduction band excited by ultraviolet light are This is probably due to the oxygen deficiency and interaction with the molecules with a long relaxation time.
　これに対し試料番号２１は、感応層と不感応層との界面がＺｎＯ－ＺｎＯの良好な接合が形成されるので、光励起強度に対応した立ち上がりの急峻な過渡特性を得ることができることが分かる。 On the other hand, it can be seen that Sample No. 21 can obtain a transient characteristic with a steep rise corresponding to the photoexcitation intensity because a good junction of ZnO—ZnO is formed at the interface between the sensitive layer and the insensitive layer.
　しかも、試料番号２３は、光照射時の光応答電流も時間の経過と共に若干の低下傾向になっているのに対し、試料番号２１は光照射時の電流変動も殆ど生じないことが分かる。 In addition, it can be seen that in Sample No. 23, the photoresponse current at the time of light irradiation tends to slightly decrease with the passage of time, whereas Sample No. 21 hardly causes current fluctuation at the time of light irradiation.
　また、立下り特性についても、試料番号２３は、出力電流は緩やかに低下しているのに対し、試料番号２１は、急峻に低下しており、したがって、短時間で繰り返し測定を行なっても、常に一定の入力に対しては、一定の出力特性を示すことが分かった。 As for the falling characteristics, the output current of Sample No. 23 is gradually decreased, whereas that of Sample No. 21 is sharply decreased. Therefore, even if repeated measurement is performed in a short time, It has been found that a constant output characteristic is exhibited for a constant input.
〔電流比Ｉ／Ｉ０〕
　実施例試料の試料番号２１と不感応層を有さない試料番号２２の各々８個について、紫外線照射時の出力電流Ｉと紫外線照射を停止してから５秒後の暗電流Ｉ０を測定し、電流比Ｉ／Ｉ０を求めた。尚、紫外線照射は、波長３６５ｎｍで紫外線強度１ｍＷ／ｃｍ２で行なった。 [Current ratio I / I 0 ]
For the sample number 21 of the example sample and the sample number 22 each having no insensitive layer, the output current I at the time of UV irradiation and the dark current I 0 after 5 seconds from the UV irradiation stop were measured. to determine the current ratio I / I 0. The ultraviolet irradiation was performed at a wavelength of 365 nm and an ultraviolet intensity of 1 mW / cm 2 .
　図１２はその測定結果を示している。 FIG. 12 shows the measurement results.
　この図１２から明らかなように、比較例試料である試料番号２２は、電流比Ｉ／Ｉ０が１０～２０程度であった。これは感応層上に絶縁保護膜を直接形成すると、感応層の表面状態によっては抵抗が過度に低くなったりして制御できない不安定な要因が多く、このため電流比Ｉ／Ｉ０が１０～２０程度と小さくなったものと思われる。 As is apparent from FIG. 12, the sample number 22 which is a comparative sample has a current ratio I / I 0 of about 10 to 20. This is because when the insulating protective film is formed directly on the sensitive layer, there are many unstable factors that cannot be controlled due to excessively low resistance depending on the surface state of the sensitive layer, and therefore the current ratio I / I 0 is 10 to 10 It seems to have become as small as about 20.
　これに対し実施例試料である試料番号２１は、ＺｎＯ－ＺｎＯ接合により、暗電流Ｉ０が安定して低く、その結果、電流比Ｉ／Ｉ０が１５０～３５０と大きく、紫外線センサの感知精度が良好であることが分かった。 In contrast, Sample No. 21, which is an example sample, has a stable and low dark current I 0 due to the ZnO—ZnO junction. As a result, the current ratio I / I 0 is as large as 150 to 350, and the detection accuracy of the UV sensor is high. Was found to be good.
〔光応答特性〕
　試料番号２１及び試料番号２２の各試料について、５秒間隔で紫外線照射を繰り返し、光応答特性を評価した。尚、紫外線照射は、波長３６５ｎｍ、紫外線強度１ｍＷ／ｃｍ２で行なった。 (Optical response characteristics)
For each sample of sample number 21 and sample number 22, ultraviolet irradiation was repeated at intervals of 5 seconds to evaluate the photoresponse characteristics. The ultraviolet irradiation was performed at a wavelength of 365 nm and an ultraviolet intensity of 1 mW / cm 2 .
　図１３は、試料番号２１の測定結果を示し、図１４は、試料番号２２の測定結果を示している。横軸は時間（秒）、縦軸は検出電流（Ａ）である。 FIG. 13 shows the measurement result of sample number 21, and FIG. 14 shows the measurement result of sample number 22. The horizontal axis represents time (seconds), and the vertical axis represents detected current (A).
　試料番号２２は、図１４に示すように、測定を繰り返す毎に検出電流が大きくなっている。これは暗電流が大きく、減少し切っていない暗電流が出力電流に重畳され、その結果、測定を繰り返す毎に検出電流が大きくなってしまったものと思われる。 As shown in FIG. 14, the detection current of sample number 22 is increased every time the measurement is repeated. This is because the dark current is large and the dark current that has not been reduced is superimposed on the output current, and as a result, the detection current seems to increase each time the measurement is repeated.
　これに対し試料番号２１は感応層の表面に不感応層が形成されていることから、暗電流も低く、紫外線照射を停止してから５秒後には暗電流は十分に減少し、この状態で紫外線を再照射しているので、図１３に示すように、略一定の安定した電流値となり、良好な光応答特性が得られることが分かった。 On the other hand, sample No. 21 has a non-sensitive layer formed on the surface of the sensitive layer, so the dark current is low, and the dark current is sufficiently reduced 5 seconds after the ultraviolet irradiation is stopped. Since the ultraviolet rays were re-irradiated, as shown in FIG. 13, it was found that the current value became substantially constant and a good photoresponse characteristic was obtained.
　暗電流を抑制でき、過渡特性及び立ち下がり特性が良好で、分光特性も良好な光導電型紫外線センサ等の光検出素子を実現する。 Realizes a photodetection element such as a photoconductive ultraviolet sensor that can suppress dark current, has good transient characteristics and falling characteristics, and good spectral characteristics.
１、１１　感応層
２ａ、２ｂ、１２ａ、１２ｂ　電極
３、１３　基板
４、１４　不感応層
６、１６　絶縁保護膜 1, 11 Sensitive layer 2a, 2b, 12a, 12b Electrode 3, 13 Substrate 4, 14 Insensitive layer 6, 16 Insulating protective film

Claims (13)

  1. 　主成分がＺｎＯで形成された感応層と、所定間隔を介して対向状に配された一対の電極とが、基板の一方の主面側に形成され、前記感応層で入射光を検知する光検出素子において、
    　主成分が前記感応層と同一材料で形成された不感応層が、前記感応層と接するように設けられていることを特徴とする光検出素子。     A sensitive layer in which the main component is made of ZnO and a pair of electrodes arranged opposite to each other at a predetermined interval are formed on one main surface side of the substrate, and the sensitive layer detects the incident light. In the detection element,
    An insensitive layer, the main component of which is made of the same material as the sensitive layer, is provided so as to be in contact with the sensitive layer.
  2. 　前記感応層は、前記基板の前記一方の主面の表面に形成されると共に、前記一対の電極は、前記感応層の表面に形成され、
    　かつ、前記不感応層は、少なくとも前記電極間に前記感応層に接合して設けられていることを特徴とする請求項１記載の光検出素子。     The sensitive layer is formed on the surface of the one main surface of the substrate, and the pair of electrodes is formed on the surface of the sensitive layer,
    The light-sensitive element according to claim 1, wherein the insensitive layer is provided between at least the electrodes and bonded to the sensitive layer.
  3. 　前記一対の電極が、前記基板の前記一方の主面の表面に形成されると共に、前記感応層は、前記電極の端部を覆うように前記基板の前記一方の主面の表面に形成され、
    　かつ、前記不感応層は、前記感応層の表面に形成されていることを特徴とする請求項１記載の光検出素子。     The pair of electrodes are formed on the surface of the one main surface of the substrate, and the sensitive layer is formed on the surface of the one main surface of the substrate so as to cover an end of the electrode,
    2. The light detecting element according to claim 1, wherein the insensitive layer is formed on a surface of the sensitive layer.
  4. 　前記基板は、前記入射光を透過する透光性材料で形成されていることを特徴とする請求項１乃至請求項３のいずれかに記載の光検出素子。 4. The photodetecting element according to claim 1, wherein the substrate is made of a translucent material that transmits the incident light.
  5. 　前記入射光は、前記基板の前記一方の主面側及び他方の主面側のうちの少なくともいずれかの主面に照射されることを特徴とする請求項１乃至請求項４のいずれかに記載の光検出素子。 The incident light is applied to at least one main surface of the one main surface side and the other main surface side of the substrate. Photodetector element.
  6. 　前記不感応層の表面に絶縁保護膜が形成されていることを特徴とする請求項１乃至請求項５のいずれかに記載の光検出素子。 6. The light detecting element according to claim 1, wherein an insulating protective film is formed on a surface of the insensitive layer.
  7. 　前記絶縁保護膜は、ケイ素化合物で形成されていることを特徴とする請求項６記載の光検出素子。 The light detection element according to claim 6, wherein the insulating protective film is formed of a silicon compound.
  8. 　高反射率を有する金属薄膜が、前記絶縁保護膜の表面に形成されていることを特徴とする請求項６又は請求項７記載の光検出素子。 8. The light detecting element according to claim 6, wherein a metal thin film having a high reflectance is formed on a surface of the insulating protective film.
  9. 　前記不感応層は、膜厚が３ｎｍ以上１４０ｎｍ未満であることを特徴とする請求項１乃至請求項８のいずれかに記載の光検出素子。 9. The photodetector according to claim 1, wherein the insensitive layer has a thickness of 3 nm or more and less than 140 nm.
  10. 　前記感応層は、膜厚が１０ｎｍ以上１００ｎｍ以下であることを特徴とする請求項１乃至請求項９のいずれかに記載の光検出素子。 The light-sensitive element according to claim 1, wherein the sensitive layer has a thickness of 10 nm to 100 nm.
  11. 　主成分がＺｎＯで形成された感応層と、所定間隔を有して対向状に配された一対の電極とを基板の一方の主面側に形成し、
    　主成分が前記感応層と同一のＺｎＯ系材料及び絶縁性材料を用意し、
    　前記ＺｎＯ系材料を使用し、前記電極が形成された感応層に、真空下、第１の成膜処理を行い、さらに前記絶縁性材料を使用し、前記第１の成膜処理に引き続き連続的に第２の成膜処理を行い、前記感応層の表面にＺｎＯ材料からなる不感応層、及び絶縁保護膜を順次形成することを特徴とする光検出素子の製造方法。     Forming a sensitive layer made of ZnO as a main component and a pair of electrodes arranged opposite to each other at a predetermined interval on one main surface side of the substrate;
    Prepare a ZnO-based material and an insulating material whose main component is the same as the sensitive layer,
    Using the ZnO-based material, a first film forming process is performed under vacuum on the sensitive layer on which the electrode is formed, and further using the insulating material, the first film forming process is continuously performed. A method of manufacturing a photodetecting element, comprising: performing a second film forming process to sequentially form a non-sensitive layer made of a ZnO material and an insulating protective film on the surface of the sensitive layer.
  12. 　前記感応層を、前記基板の前記一方の主面の表面に形成した後、前記一対の電極を前記感応層の表面に形成し、その後、前記不感応層を、少なくとも前記電極間に前記感応層と接合するように形成することを特徴とする請求項１１記載の光検出素子の製造方法。 After forming the sensitive layer on the surface of the one main surface of the substrate, the pair of electrodes is formed on the surface of the sensitive layer, and then the insensitive layer is formed at least between the sensitive layers. 12. The method for manufacturing a photodetecting element according to claim 11, wherein the photodetecting element is formed so as to be bonded to the light detecting element.
  13. 　前記一対の電極を前記基板の前記一方の主面の表面に形成した後、前記感応層を前記電極の端部を覆うように前記基板の一方の主面の表面に形成し、その後前記不感応層を前記感応層の表面に形成することを特徴とする請求項１１記載の光検出素子の製造方法。 After the pair of electrodes is formed on the surface of the one main surface of the substrate, the sensitive layer is formed on the surface of the one main surface of the substrate so as to cover an end of the electrode, and then the insensitive 12. The method of manufacturing a light detecting element according to claim 11, wherein a layer is formed on the surface of the sensitive layer.
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