WO2004047187A1 - Optical sensor - Google Patents

Optical sensor Download PDF

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Publication number
WO2004047187A1
WO2004047187A1 PCT/JP2003/014522 JP0314522W WO2004047187A1 WO 2004047187 A1 WO2004047187 A1 WO 2004047187A1 JP 0314522 W JP0314522 W JP 0314522W WO 2004047187 A1 WO2004047187 A1 WO 2004047187A1
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Prior art keywords
optical sensor
dioxide
transition metal
oxide
light
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PCT/JP2003/014522
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French (fr)
Japanese (ja)
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Zenji Hiroi
Yuji Muraoka
Tohru Yamauchi
Yutaka Ueda
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Zenji Hiroi
Yuji Muraoka
Tohru Yamauchi
Yutaka Ueda
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Application filed by Zenji Hiroi, Yuji Muraoka, Tohru Yamauchi, Yutaka Ueda filed Critical Zenji Hiroi
Priority to AU2003280803A priority Critical patent/AU2003280803A1/en
Publication of WO2004047187A1 publication Critical patent/WO2004047187A1/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
    • H01L31/10—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 characterised by potential barriers, e.g. phototransistors
    • H01L31/101—Devices sensitive to infrared, visible or ultraviolet radiation
    • H01L31/102—Devices sensitive to infrared, visible or ultraviolet radiation characterised by only one potential barrier
    • H01L31/109—Devices sensitive to infrared, visible or ultraviolet radiation characterised by only one potential barrier the potential barrier being of the PN heterojunction type

Definitions

  • the present invention relates to an optical sensor using a transition metal oxide.
  • a semiconductor-based optical sensor that uses photoconduction or photovoltaic power is used.
  • the former is a photoconductive cell using cadmium sulfide or lead sulfide, and the latter is a photodiode using a Pn junction such as silicon. Since these semiconductor materials have a band gap energy of 2 eV or less, they have high sensitivity to light in the visible to near infrared region, but have high sensitivity to ultraviolet light having energy of 3 eV or more. Low.
  • materials for conventional photoconductive cells materials that are environmentally problematic such as cadmium and lead are used, which is not preferable.
  • highly toxic materials are not used, which is preferable from the viewpoint of environmental health.
  • U V tron ultraviolet detector tube
  • Oxides containing titanium and transition metal oxides are generally chemically stable at high temperatures and have no toxicity.
  • oxides containing titanium are used as various materials because of their high chemical stability and catalytic action. Due to its particularly high optical activity, many practical studies have been made on materials for photocatalysts and solar cells. Its electrical properties are large band gaps (for example, 3.0 eV for titanium dioxide, Strontium titanate is a semiconductor having 3.2 eV). Therefore, it does not show absorption in the visible-infrared region and absorbs ultraviolet light with a wavelength of 400 nm or less well.
  • the present invention provides a simple and highly sensitive ultraviolet light sensor using a transition metal oxide heterojunction.
  • titanium oxide obtained a high-quality single crystals with large (T i 0 2 or S rT I_ ⁇ 3) used. These are doped with a small amount of Nb, Ta, As, Sb, W or La to have n-type semiconductor characteristics.
  • a transition metal oxide is epitaxially grown on the n-type substrate for the purpose of forming a pn junction or a junction having similar characteristics.
  • the crystal structure of the junction it is necessary that the crystal structure of the junction be the same or similar, and this allows electrons or holes to pass through the junction interface to the other side. Move to the member.
  • a x CuO y A is L a, Y, B i, T 1, Pb, P r, Nd, B a, S r , Strontium titanate
  • a major feature of the transition metal oxide / n-type titanium oxide heterojunction in the optical sensor according to the present invention lies in its junction band structure. Titanium oxide has a large band gap of about 3 eV, while transition metal oxide has a small band gap of about 1 eV. When the two junctions were fabricated, the top of the valence band and the conduction band Both Toms are higher on the transition metal oxide side. However, since the band gap value is greatly different and the Fermi level of titanium oxide is directly below the conduction band, a large potential gradient is generated near the junction, especially in the valence band. From the characteristic band structure described above, it can be seen that the present junction device exhibits the same rectification characteristics as a normal semiconductor pn junction.
  • FIG. 1 is a diagram showing a basic part of a photoconductive cell using an optical sensor according to the present invention.
  • FIG. 2 is a diagram showing a basic part of a photovoltaic cell using the optical sensor 1 according to the present invention.
  • FIG. 3 is a diagram showing a basic band structure of the optical sensor according to the present invention.
  • FIG. 4 is a schematic view of a laser ablation apparatus for forming a transition metal thin film.
  • Fig. 5 the optical sensor according to the present invention V0 2 / T i 0 2: is a diagram showing an ultraviolet intensity dependence of the photo-induced current that put the Nb heterojunction.
  • FIG. 6 is, V0 2 / T i 0 2 : is a view showing a change in band structure due to UV irradiation in Nb heterojunction.
  • Figure 7 is, V0 2 / T i 0 2 : is a diagram showing the light intensity dependence of the photovoltaic in Nb heterojunction.
  • Figure 8 is, V0 2 / T i 0 2 : is a graph showing a temporal change in the photovoltaic when turned 'off light in Nb heterojunction.
  • L a Ti0 2
  • strontium titanate S
  • the thickness of the substrate is from 1 mm to 1 m.
  • the thickness of the thin film is several nm to several hundred nm.
  • the concentration of Nb in the substrate is preferably 0.1 wt% or less.
  • Fig. 1 shows the basic structure of the photoconductive cell.
  • a pair of electrodes A and B are fabricated on a transition metal oxide thin film grown on a titanium oxide substrate.
  • a voltage of several millivolts to several volts is applied between the electrodes, and a change in the flowing current value due to irradiation with ultraviolet light is extracted as an output.
  • Fig. 2 shows the basic structure of the photovoltaic cell. The voltage between the electrodes A and B formed on the surface of the transition metal oxide thin film and the bottom of the titanium oxide substrate is measured. The change in voltage due to UV irradiation is extracted as sensor output.
  • Figure 3 shows a schematic band structure of a heterojunction consisting of titanium oxide and transition metal oxide, which is the basis of this device. Titanium oxide has a large band gap of about 3 eV, while transition metal oxide has a small band gap of about 1 eV. When both junctions are fabricated, the top of the valence band and the potion of the conduction band are both higher on the transition metal oxide side as shown in Fig. 3. However, the large difference in band gap value and the fact that the Fermi level of titanium oxide is directly below the conduction band causes a large potential gradient, especially in the valence band.
  • FIG. 4 is a schematic view of a laser ablation apparatus for forming a transition metal oxide thin film.
  • the laser ablation device that forms the transition metal oxide thin film is composed of a heating device 2, a KrF excimer laser irradiation device 3, and a pulse motor around the processing chamber 1.
  • One night 4 and O 2 / ⁇ 3 supply pipe 5 are provided.
  • the heating device 2 holds the substrate W at the tip facing the processing chamber 1, and arranges a thickness monitor 6 in the vicinity thereof, and the pulse monitor 4 advances and retreats the rod 7 facing the processing chamber 11.
  • the rod 7 has a holder 8 for the target T at the end.
  • the ablation device Nb-doped S r T i 0 3 of the substrate under the following conditions (001) surface L a 0. 9 S r 0 .
  • a thin film was formed.
  • the film formation conditions were a temperature of 700 ° C, an oxygen partial pressure of 10 Pa, a film formation rate of 1 nm / min, and a film thickness of 30 nm.
  • the film formation conditions were a temperature of 600 ° C, an oxygen partial pressure of 10 Pa, a film formation rate of 1 nm / min, and a film thickness of 50 nm.
  • Figure 5 of the above V0 2 / T I_ ⁇ 2 shows the ultraviolet intensity dependence of V0 2 photoinduced current in Nb junction.
  • the photoinduced current changes linearly for weak ultraviolet light with a wavelength of 365 nm, and tends to gradually deviate from the straight line for strong ultraviolet light with a wavelength of 300-400 nm. This is because the electric resistance is reduced by a sixth order holes generated has moved to V0 2 thin film in the titanium oxide by light irradiation as shown in the illustration V_ ⁇ 2 film p-type. Since the amount of injected holes is proportional to the intensity of the incident light, the photo-induced current is almost proportional to the amount of incident light at low light amounts.
  • FIG. 7 by UV irradiation in FIG V0 2 / T i 0 2 shows the amount dependency of photovoltaic occurring Nb junction. For light with a wavelength of 365 nm, it changes linearly when the light amount is small, and the increase tends to be saturated when the light amount is large. It can be seen that a maximum of 0.5 V photoelectromotive force is generated by ultraviolet irradiation. This hole only V0 2 thin film of electrons and holes generated in the titanium oxide by light irradiation as FIG. 6 Since it moved to, because the electromotive force is generated between the V_ ⁇ 2 film and a titanium oxide substrate.
  • FIG. 8 shows the time change of photovoltaic power when light is switched at room temperature.
  • the rise at the time of light irradiation is as fast as a few microseconds, and the decay when off is several hundreds of microseconds. This value is more than a few microseconds for the relaxation time of a typical silicon photodiode and less than 30 to 100 milliseconds for the decay time of cadmium sulfide used as a photoconductive device. This on / off operation was extremely high with no regression even after repeated thousands of times.
  • the optical sensor according to the present invention exhibits photodiode characteristics, it functions as a highly sensitive optical sensor. In particular, it has high sensitivity to ultraviolet light, and is useful in fields such as lithography and communications that use ultraviolet light, which is expected to grow in the future. Furthermore, it has been confirmed that it has sensitivity to radiation such as X-rays. It can also be used for high energy particles such as neutron beams by introducing an appropriate absorbent. On the other hand, it has sufficient sensitivity to visible light. Industrial applicability
  • the optical sensor according to the present invention can be applied as a simple optical sensor that is made of only an oxide and has high sensitivity particularly to ultraviolet light.

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  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • Electromagnetism (AREA)
  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Computer Hardware Design (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Power Engineering (AREA)
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Abstract

A simple and highly sensitive optical sensor having a transition metal oxide heterojunction is disclosed. A fundamental portion of the sensor comprises titanium dioxide (TiO2) or strontium titanate (SrTiO3) doped with a small amount of Nb, Ta, As, Sb, W or La so as to have n-type semiconductor characteristics, on which vanadium dioxide (VO2), divanadium trioxide (V2O3), chromium dioxide (CrO2), a perovskite oxide containing manganese, iron, cobalt, or nickel (ABO3: wherein A is a simple substance or a solid solution of Y, a rare earth element, Tl, Pb, Bi, Ba, Sr, Ca; and B is Mn, Fe, Co, or Ni), a copper oxide (AxCuOy: wherein A is a simple substance or a solid solution of La, Y, Bi, Tl, Pb, Pr, Nd, Ba, Sr, Ca) or ruthenium dioxide (RuO2) is epitaxially grown as the transition water oxide. The sensor serves as a photoconductive cell or a photodiode under ultraviolet light irradiation.

Description

明細書 光センサー 技術分野  Description Optical sensor Technical field
本発明は、 遷移金属酸化物を用いた光センサーに関する。 背景技術  The present invention relates to an optical sensor using a transition metal oxide. Background art
現在、 半導体を用いた光センサ一には光伝導または光起電力を利用したものが 使われている。 前者には硫化カドミウム、 硫化鉛等を用いた光伝導セルがあり、 後者にはシリコンなどの P n接合を用いたフォトダイオードがある。 これらの半 導体材料はバンドギャップエネルギーが 2 e V以下であるため、 可視から近赤外 領域の光に対して高い感度を有するが、 3 e V以上のエネルギーを有する紫外線 に対しては感度が低い。  At present, a semiconductor-based optical sensor that uses photoconduction or photovoltaic power is used. The former is a photoconductive cell using cadmium sulfide or lead sulfide, and the latter is a photodiode using a Pn junction such as silicon. Since these semiconductor materials have a band gap energy of 2 eV or less, they have high sensitivity to light in the visible to near infrared region, but have high sensitivity to ultraviolet light having energy of 3 eV or more. Low.
従来の光伝導セルの材料としては、 いずれもカドミウム、 鉛といった環境衛生 上問題となる材料を用いており好ましくない。 これに対し本発明にあっては毒性 の強い材料を使用せず、 環境衛生上も好ましい。  As materials for conventional photoconductive cells, materials that are environmentally problematic such as cadmium and lead are used, which is not preferable. On the other hand, in the present invention, highly toxic materials are not used, which is preferable from the viewpoint of environmental health.
現在広く使われている紫外線センサ一として紫外線検出管 （U V t r o n ) が ある。 これはガス入り光電管の一種であり、 波長 1 8 5— 2 6 0 n mの紫外線に 対して感度を有する。その主な用途はボイラーや火災報知器用の炎検出器であり、 外光に影響されず炎中の微弱な紫外線を検出する。 しかし、 光電管であるため 3 0 0 V前後の高い動作電圧を必要とすることから複雑な回路を必要とし、 また、 寿命にも問題がある。 さらに高温環境下では使用できない。  One of the widely used ultraviolet sensors at present is an ultraviolet detector tube (U V tron). This is a type of gas-filled phototube, and has sensitivity to ultraviolet light with a wavelength of 185-2600 nm. Its main use is as a flame detector for boilers and fire alarms, which detects weak ultraviolet rays in flames without being affected by external light. However, since it is a phototube, it requires a high operating voltage of about 300 V, so a complicated circuit is required, and there is also a problem with the life. Furthermore, it cannot be used in a high temperature environment.
チタンを含む酸化物や遷移金属酸化物は一般に高温でも化学的に安定であり、 毒性を持たない。 特にチタンを含む酸化物についてはその高い化学的安定性や触 媒作用のためにせくから様々な材料として用いられている。 特に高い光学活性を 有するため、 光触媒や太陽電池用の材料として多くの実用研究がなされている。 その電気的性質は大きなバンドギャップ（例えば、二酸化チタンでは 3 . 0 e V、 チタン酸ストロンチウムでは 3. 2 e V) を有する半導体である。 よって可視 - 赤外領域に対しては吸収を示さず、 400 nm以下の波長の紫外線をよく吸収す る。 また不純物として Nb， T a, As， S b, W、 または、 L aを少量ドープ して n型半導体特性を持たせたものでは弱い光伝導現象を示すことが知られてい る。しかしながら、その光伝導性は小さく、センサーなどへの応用は困難である。 近年、 酸化物を利用して従来の半導体エレクトロニクスデバイスを置き換えよ うという研究が盛んに行われている。特にバンドギャップの大きな酸化物を用い、 これにドーピングを行って p n接合を形成することで透明なダイオードゃトラン ジス夕を作成する試みが行われている。 また、 酸化物デバイスは従来の半導体が 苦手とする高温や放射線環境下において使用可能なデバイスとして期待されてい る。 しかしながら、 これまでに得られた特性は従来の半導体デバイスのそれには 程遠く、 実際のデバイス応用には及んでいない。 その主な原因を以下に挙げる。 Oxides containing titanium and transition metal oxides are generally chemically stable at high temperatures and have no toxicity. In particular, oxides containing titanium are used as various materials because of their high chemical stability and catalytic action. Due to its particularly high optical activity, many practical studies have been made on materials for photocatalysts and solar cells. Its electrical properties are large band gaps (for example, 3.0 eV for titanium dioxide, Strontium titanate is a semiconductor having 3.2 eV). Therefore, it does not show absorption in the visible-infrared region and absorbs ultraviolet light with a wavelength of 400 nm or less well. It is also known that those that dope a small amount of Nb, Ta, As, Sb, W, or La as impurities and have n-type semiconductor characteristics exhibit weak photoconductive phenomena. However, its photoconductivity is small, and application to sensors and the like is difficult. In recent years, there has been much research into using oxides to replace conventional semiconductor electronics devices. In particular, attempts have been made to create a transparent diode-to-transistor transistor by using a large band gap oxide and doping it to form a pn junction. In addition, oxide devices are expected to be devices that can be used under high temperature and radiation environments where conventional semiconductors are not good. However, the characteristics obtained so far are far from those of conventional semiconductor devices, and do not extend to actual device applications. The main causes are listed below.
1. 通常の半導体デバイスにおいて用いられるシリコンやゲルマニウムのよ うに不純物の種類を変えることによって n型、 p型半導体を自由に作り分 けることが困難であるため、 ホモ接合素子が作製できない。  1. Since it is difficult to freely form n-type and p-type semiconductors by changing the type of impurities such as silicon and germanium used in ordinary semiconductor devices, homojunction devices cannot be manufactured.
2. 二種の酸化物から良質なヘテロ接合が得られた例は少なく、 従来の半導 体へテロ接合と比較してその接合特性が低い。  2. Few heterojunctions have been obtained from two types of oxides, and their bonding characteristics are lower than those of conventional semiconductor heterojunctions.
3. n型、 p型半導体として優れた材料が見つかっていない。 特に p型半導 体として適当な材料は少なく、 G.aと Nをドープした Z ηθや S r C u 2 02などの報告があるが、 それらの特性は十分ではない。 3. No excellent material has been found for n-type and p-type semiconductors. Particularly suitable materials are less as p-type semiconductor material, there are reports on Z Itashita and S r C u 2 0 2 doped with Ga and N, their properties are not sufficient.
具体的には、 ① H. Tanaka, J. Zhang and T. Kawai: Phys. Rev. Lett. 88 (2002) 027204、 ② Y. Watanabe and M. Okano: Appl. Phys. Lett. 78 (2001) 1906、 ③ H. Ohta, M. Orita, M. Hirano and H. Hosono: J. Appl. Phy's. 89 (2001) 5720, などの報告がなされている。 発明の開示  Specifically, ① H. Tanaka, J. Zhang and T. Kawai: Phys. Rev. Lett. 88 (2002) 027204, ② Y. Watanabe and M. Okano: Appl. Phys. Lett. 78 (2001) 1906 ③ H. Ohta, M. Orita, M. Hirano and H. Hosono: J. Appl. Phy's. 89 (2001) 5720. Disclosure of the invention
本発明は、 遷移金属酸化物へテロ接合を用いて、 簡便で特に紫外線に対して高 感度な光センサ一を提供する。 基板結晶として、 大型で良質な単結晶の得られるチタン酸化物 （T i 02また は S rT i〇3) を用いる。 これらに Nb， Ta， As , S b， W または、 L aを少量ドープして n型半導体特性を持たせる。 The present invention provides a simple and highly sensitive ultraviolet light sensor using a transition metal oxide heterojunction. As the substrate crystal, titanium oxide obtained a high-quality single crystals with large (T i 0 2 or S rT I_〇 3) used. These are doped with a small amount of Nb, Ta, As, Sb, W or La to have n-type semiconductor characteristics.
上記 n型基板の上に、 p n接合またはこれと類似する特性を有する接合を形成 することを目的として、 遷移金属酸化物をェピタキシャル成長させる。 pn接合 またはこれと類似する特性を有する接合とするには、 接合部の結晶構造が同一若 しくは近似させることが必要で、 このようにすることで接合界面を通して電子ま たはホールが相手側部材に移動する。  A transition metal oxide is epitaxially grown on the n-type substrate for the purpose of forming a pn junction or a junction having similar characteristics. In order to form a pn junction or a junction having similar characteristics, it is necessary that the crystal structure of the junction be the same or similar, and this allows electrons or holes to pass through the junction interface to the other side. Move to the member.
遷移金属酸化物としては、二酸化バナジウム（V02)、三酸化二バナジウム（V 2〇3)、 二酸化クロム （C r 02)、 マンガン、 鉄、 コバルト、 ニッケルを含むぺ ロブスカイト型酸化物 （AB〇3 ： Aは Y、 希土類元素、 Τ 1、 P b、 B i、 B a, S r， C aの単体または固溶体、 Bは Mn、 F e、 Co、 または、 N i)、 銅 酸化物 （AXC uOy： Aは L a, Y, B i , T l , P b, P r, Nd, B a， S r， C aの単体または固溶体）、 または、 二酸化ルテニウム （Ru02) が有効で あるとの知見を得た。 The transition metal oxide, vanadium dioxide (V0 2), dinitrogen trioxide, vanadium (V 2 〇 3), chromium Dioxide (C r 0 2), manganese, iron, cobalt, perovskite oxide containing nickel (AB 〇 3: a is Y, rare earth elements, Τ 1, P b, B i, B a, S r, alone or solid solutions of C a, the B Mn, F e, Co or,, N i), copper oxide (a X C uO y: a is L a, Y, B i, T l, P b, P r, Nd, B a, S r, alone or solid solutions of C a), or ruthenium dioxide (Ru0 2) Was found to be effective.
二酸化バナジウム （V〇2)、 二酸化クロム （C r〇2)、 または、 二酸化ルテニ ゥム （Ru02) の場合には、 基板として、 同じ結晶構造 （ルチル型構造） を有 する二酸化チタン結晶を使用する。 また、 マンガン、 鉄、 コバルト、 ニッケルを 含むベロブスカイト型酸化物 （ 8〇3 :八は丫、 希土類元素、 Tし P b、 B i、 B a, S r, C aの単体または固溶体、 Bは Mn、 F e、 Co、 または、 N i)、 または、 銅酸化物 （AxCuOy： Aは L a, Y, B i， T 1， Pb, P r， Nd, B a, S r , C aの単体または固溶体） の場合には、 基板としてチタン酸 ストロンチウム （ベロブスカイト構造） を使用する。 各場合に薄膜と基板結晶が 同一の結晶構造を持っため、 良質なヘテロ接合を形成することが出来る。 Vanadium dioxide (V_〇 2), chromium dioxide (C R_〇 2), or, in the case dioxide Ruteni © beam (Ru0 2) as a substrate, a titanium dioxide crystal have the same crystal structure (rutile structure) use. Further, manganese, iron, cobalt, perovskite-type oxides containing nickel (8_Rei 3: bees丫, rare earth elements, T and P b, B i, B a , S r, alone or solid solutions of C a, B the Mn, F e, Co or, N i), or copper oxide (A x CuO y: A is L a, Y, B i, T 1, Pb, P r, Nd, B a, S r , Strontium titanate (velovskite structure) is used as the substrate. In each case, since the thin film and the substrate crystal have the same crystal structure, a high quality heterojunction can be formed.
本発明に係る光センサーにおける遷移金属酸化物/ n型チタン酸化物へテロ接 合の大きな特徴は、 その接合バンド構造にある。 チタン酸化物が 3 eV程度の大 きなバンドギャップを持つのに対し、 遷移金属酸化物は 1 eV程度の小さなバン ドギャップを持つ。 両者の接合を作製したとき、 価電子帯のトップと伝導帯のポ トムは共に遷移金属酸化物側が高い位置に来る。 ところがバンドギヤップの値が 大きく異なること、 および、 チタン酸化物のフェルミ準位が伝導帯の直下にある ことから、 接合近傍において特に荷電子帯に大きなポテンシャル勾配が生じる。 以上のような特徴的なバンド構造から、 本接合デパイスは通常の半導体 p n接 合と同様の整流特性を示すことがわかる。 A major feature of the transition metal oxide / n-type titanium oxide heterojunction in the optical sensor according to the present invention lies in its junction band structure. Titanium oxide has a large band gap of about 3 eV, while transition metal oxide has a small band gap of about 1 eV. When the two junctions were fabricated, the top of the valence band and the conduction band Both Toms are higher on the transition metal oxide side. However, since the band gap value is greatly different and the Fermi level of titanium oxide is directly below the conduction band, a large potential gradient is generated near the junction, especially in the valence band. From the characteristic band structure described above, it can be seen that the present junction device exhibits the same rectification characteristics as a normal semiconductor pn junction.
この接合に紫外線を照射した場合、 チタン酸化物基板内で生成した電子とホー ルのうち、 ホールのみが遷移金属酸化物薄膜に移動し、 これが伝導に寄与する。 よって、 紫外線照射により遷移金属酸化物薄膜の電気抵抗が減少し、 光伝導セル として機能する。 また、 この時、 基板と薄膜の間には接合を通して光起電力が生 じるため、 フォトダイオードとして機能する。 図面の簡単な説明  When this junction is irradiated with ultraviolet light, of the electrons and holes generated in the titanium oxide substrate, only holes move to the transition metal oxide thin film, which contributes to conduction. Therefore, the electric resistance of the transition metal oxide thin film is reduced by the irradiation of ultraviolet rays, and the thin film functions as a photoconductive cell. Also, at this time, a photovoltaic force is generated between the substrate and the thin film through the junction, and thus functions as a photodiode. BRIEF DESCRIPTION OF THE FIGURES
第 1図は、 本発明に係る光センサーを用いた光伝導セルの基本となる部分を示 す図である。  FIG. 1 is a diagram showing a basic part of a photoconductive cell using an optical sensor according to the present invention.
第 2図は、 本発明に係る光センサ一を用いた光起電力セルの基本となる部分を 示す図である。  FIG. 2 is a diagram showing a basic part of a photovoltaic cell using the optical sensor 1 according to the present invention.
第 3図は、 本発明に係る光センサーの基本となるバンド構造を示す図である。 第 4図は、遷移金属薄膜を形成するレーザアブレーション装置の概略図である。 第 5図は、 本発明に係る光センサーの V02/T i 02： Nbヘテロ接合におけ る光誘起電流の紫外線強度依存性を示した図である。 FIG. 3 is a diagram showing a basic band structure of the optical sensor according to the present invention. FIG. 4 is a schematic view of a laser ablation apparatus for forming a transition metal thin film. Fig. 5, the optical sensor according to the present invention V0 2 / T i 0 2: is a diagram showing an ultraviolet intensity dependence of the photo-induced current that put the Nb heterojunction.
第 6図は、 V02/T i 02： Nbヘテロ接合における紫外線照射によるバンド 構造の変化を示した図である。 FIG. 6 is, V0 2 / T i 0 2 : is a view showing a change in band structure due to UV irradiation in Nb heterojunction.
第 7図は、 V02/T i 02： Nbヘテロ接合における光起電力の光量依存性を 示した図である。 Figure 7 is, V0 2 / T i 0 2 : is a diagram showing the light intensity dependence of the photovoltaic in Nb heterojunction.
第 8図は、 V02/T i 02： Nbヘテロ接合において光をオン 'オフしたとき の光起電力の時間変化を示す図である。 発明を実施するための最良の形態 以下に本発明の実施の形態を添付図面に基づいて説明する。 センサ一の基本と なる部分は、 Nb, T a, As, Sb、 W、 または、 L aを添加したルチル型二 酸化チタン （Ti02) または、 チタン酸ストロンチウム （S r T i 03) 基板上 に、 二酸化バナジウム （vo2)、 三酸化二バナジウム （V203)、 二酸化クロム (C r〇2)、 マンガン、 鉄、 コバルト、 ニッケルを含むベロブスカイト型酸化物 (AB03 ： Aは Y、 希土類元素、 T l、 P b、 B i、 B a, S r , C aの単体 または固溶体、 Bは Mn、 F e、 Co、 または、 N i)、 銅酸化物 （AxCuOy : Aは L a, Y, B i， T l， P b, P r , Nd, B a, S r， C aの単体または 固溶体）、 または、 二酸化ルテニウム （Ru〇2) の薄膜がェピタキシャル成長し ている。 Figure 8 is, V0 2 / T i 0 2 : is a graph showing a temporal change in the photovoltaic when turned 'off light in Nb heterojunction. BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Underlying portion of the sensor-is, Nb, T a, As, Sb, W or rutile titanium dioxide which was added L a (Ti0 2) or strontium titanate (S r T i 0 3) substrate, above, vanadium dioxide (vo 2) trioxide, vanadium (V 2 0 3), chromium dioxide (C R_〇 2), manganese, iron, cobalt, perovskite-type oxides containing nickel (AB0 3: a is Simple element or solid solution of Y, rare earth element, Tl, Pb, Bi, Ba, Sr , Ca, B is Mn, Fe, Co, or Ni), copper oxide (A x CuO y : a-L a, Y, B i, T l, P b, P r, Nd, B a, S r, alone or solid solution of C a), or, a thin film of ruthenium dioxide (Ru_〇 2) Epitakisharu Growing.
基板の厚さは 1 mmから 1 mである。 薄膜の厚さは数 nmから数百 nmであ る。 基板中の Nbの濃度は 0. lwt %以下が好ましい。  The thickness of the substrate is from 1 mm to 1 m. The thickness of the thin film is several nm to several hundred nm. The concentration of Nb in the substrate is preferably 0.1 wt% or less.
第 1図に光伝導セルの基本構造を示す。 チタン酸化物基板上に成長させた遷移 金属酸化物薄膜上に 1対の電極 A， Bを作製する。 この電極間に数ミリ Vから数 Vの電圧を印加し、流れる電流値の紫外線照射による変化を出力として取り出す。 第 2図に光起電力セルの基本構造を示す。 遷移金属酸化物薄膜表面とチタン酸 化物基板底面に作製した電極 A， B間の電圧を測定する。 紫外線照射による電圧 の変化をセンサー出力として取り出す。  Fig. 1 shows the basic structure of the photoconductive cell. A pair of electrodes A and B are fabricated on a transition metal oxide thin film grown on a titanium oxide substrate. A voltage of several millivolts to several volts is applied between the electrodes, and a change in the flowing current value due to irradiation with ultraviolet light is extracted as an output. Fig. 2 shows the basic structure of the photovoltaic cell. The voltage between the electrodes A and B formed on the surface of the transition metal oxide thin film and the bottom of the titanium oxide substrate is measured. The change in voltage due to UV irradiation is extracted as sensor output.
第 3図に本デバイスの基本となるチタン酸化物と遷移金属酸化物からなるへテ 口接合の模式的なバンド構造を示す。 チタン酸化物は 3 eV程度の大きなバンド ギャップを持つのに対し遷移金属酸化物は 1 e V程度の小さなバンドギャップを 持つ。 両者の接合を作製したとき、 第 3図のように価電子帯のトップと伝導帯の ポトムは共に遷移金属酸化物側が高い位置に来る。 ところがバンドギャップの値 が大きく異なること、 および、 チタン酸化物のフェルミ準位が伝導帯の直下にあ ることから、 特に荷電子帯に大きなポテンシャル勾配が生じる。  Figure 3 shows a schematic band structure of a heterojunction consisting of titanium oxide and transition metal oxide, which is the basis of this device. Titanium oxide has a large band gap of about 3 eV, while transition metal oxide has a small band gap of about 1 eV. When both junctions are fabricated, the top of the valence band and the potion of the conduction band are both higher on the transition metal oxide side as shown in Fig. 3. However, the large difference in band gap value and the fact that the Fermi level of titanium oxide is directly below the conduction band causes a large potential gradient, especially in the valence band.
第 4図は遷移金属酸化物薄膜を形成するためのレーザアブレーション装置の概 略図である。 遷移金属酸化物薄膜を形成するレーザアブレーシヨン装置は、 処理 チャンバ一 1の周囲に、 加熱装置 2、 KrFエキシマレーザ照射装置 3、 パルスモ 一夕 4及び O 2/〇 3供給管 5を設けている。 前記加熱装置 2は処理チャンパー 1 内に臨む先端で基板 Wを保持し、 その近傍には厚みモニタ 6を配置し、 前記パル スモ一タ 4は処理チャンバ一 1内に臨むロッド 7を進退せしめ、 このロッド 7先 端にはターゲット Tのホルダ 8を備えている。 FIG. 4 is a schematic view of a laser ablation apparatus for forming a transition metal oxide thin film. The laser ablation device that forms the transition metal oxide thin film is composed of a heating device 2, a KrF excimer laser irradiation device 3, and a pulse motor around the processing chamber 1. One night 4 and O 2 / 〇 3 supply pipe 5 are provided. The heating device 2 holds the substrate W at the tip facing the processing chamber 1, and arranges a thickness monitor 6 in the vicinity thereof, and the pulse monitor 4 advances and retreats the rod 7 facing the processing chamber 11. The rod 7 has a holder 8 for the target T at the end.
上記のレ一ザアブレーシヨン装置を用い、 以下の条件で Nbをドープした T i 02基板の （00 1) 面上にルチル型 V〇2薄膜を形成した。 成膜条件は、 温度を 370°C, 酸素分圧を 1 Pa、 成膜速度を 0. 1 5 nm/min 膜厚を 10 nmと した。 Using the above, single-Zaabureshiyon device, to form a rutile V_〇 2 thin film on the following conditions of T i 0 2 substrate doped with Nb of (00 1) plane. The film formation conditions were a temperature of 370 ° C, an oxygen partial pressure of 1 Pa, a film formation rate of 0.15 nm / min, and a film thickness of 10 nm.
上記のレ一ザアブレーション装置を用い、 以下の条件で Nbをドープした S r T i 03基板の （001) 面上にマンガン酸化物 L a0. 9S r 0.
Figure imgf000008_0001
薄膜を 形成した。 成膜条件は、 温度を 700°C、 酸素分圧を 10 Pa、 成膜速度を 1 nm /min、 膜厚を 30 nmとした。 Manganese oxide to the above-les using one The ablation device, Nb-doped S r T i 0 3 of the substrate under the following conditions (001) surface L a 0. 9 S r 0 .
Figure imgf000008_0001
A thin film was formed. The film formation conditions were a temperature of 700 ° C, an oxygen partial pressure of 10 Pa, a film formation rate of 1 nm / min, and a film thickness of 30 nm.
上記のレ一ザアブレーシヨン装置を用い、 以下の条件で Nbをドープした S r T i 03基板の （00 1) 面上に銅酸化物 C a Cu02薄膜を形成した。 成膜条件 は、 温度を 600°C、 酸素分圧を 10 Pa、 成膜速度を 1 n m/min、 膜厚を 50 nmとした。 Using the above, single-Zaabureshiyon device, to form a C a Cu0 2 thin copper oxide (00 1) on the surface of the S r T i 0 3 substrate doped with Nb in the following conditions. The film formation conditions were a temperature of 600 ° C, an oxygen partial pressure of 10 Pa, a film formation rate of 1 nm / min, and a film thickness of 50 nm.
第 5図に上記の V02/T i〇2： Nb接合における V02の光誘起電流の紫外線 強度依存性を示した。 波長 365 nmの弱い紫外線に対して光誘起電流は直線的 に変化し、 波長 300- 400 nmの強い紫外線に対しては直線から徐々に上に ずれる傾向を示す。 これは第 6図のように光照射によってチタン酸化物内に発生 したホールが V02薄膜に移動したため、 V〇2膜が p型となってその電気抵抗が 減少したためである。 注入されたホール量は入射光強度に比例するため、 光誘起 電流は弱光量下において入射光量にほぼ比例する。 Figure 5 of the above V0 2 / T I_〇 2: shows the ultraviolet intensity dependence of V0 2 photoinduced current in Nb junction. The photoinduced current changes linearly for weak ultraviolet light with a wavelength of 365 nm, and tends to gradually deviate from the straight line for strong ultraviolet light with a wavelength of 300-400 nm. This is because the electric resistance is reduced by a sixth order holes generated has moved to V0 2 thin film in the titanium oxide by light irradiation as shown in the illustration V_〇 2 film p-type. Since the amount of injected holes is proportional to the intensity of the incident light, the photo-induced current is almost proportional to the amount of incident light at low light amounts.
第 7図に紫外線照射により V02/T i 02 ： Nb接合に生じる光起電力の光量 依存性を示す。 波長 365 nmの光に対して、 光量の小さいときには直線的に変 化し、 光量が大きくなるとその増大が飽和する傾向を示す。 紫外線照射により最 高 0. 5 Vの光起電力が生じていることがわかる。 これは第 6図のように光照射 によってチタン酸化物内に発生した電子とホールのうちホールのみが V02薄膜 に移動したため、 V〇2膜とチタン酸化物基板の間に起電力が生じたためである。 第 8図は室温において光をスィツチングしたときの光起電力の時間変化を示す。 光照射時の立ち上がりは数マイク口秒と早く、 オフ時の減衰は数百マイク口秒で ある。 この値は典型的なシリコンフォトダイォードの緩和時間数マイクロ秒より 大きく、 光伝導デバイスとして用いられている硫化カドミウムの減衰時間 3 0〜 1 0 0ミリ秒より小さい。 このオン ·オフは数千回以上繰り返しても衰えること なく再現性が極めて高かつた。 7 by UV irradiation in FIG V0 2 / T i 0 2: shows the amount dependency of photovoltaic occurring Nb junction. For light with a wavelength of 365 nm, it changes linearly when the light amount is small, and the increase tends to be saturated when the light amount is large. It can be seen that a maximum of 0.5 V photoelectromotive force is generated by ultraviolet irradiation. This hole only V0 2 thin film of electrons and holes generated in the titanium oxide by light irradiation as FIG. 6 Since it moved to, because the electromotive force is generated between the V_〇 2 film and a titanium oxide substrate. FIG. 8 shows the time change of photovoltaic power when light is switched at room temperature. The rise at the time of light irradiation is as fast as a few microseconds, and the decay when off is several hundreds of microseconds. This value is more than a few microseconds for the relaxation time of a typical silicon photodiode and less than 30 to 100 milliseconds for the decay time of cadmium sulfide used as a photoconductive device. This on / off operation was extremely high with no regression even after repeated thousands of times.
上記と同様な手法によって、 N bをド一プした S r T i 0 3基板上にベロブス カイト型マンガン酸化物 L a。. 9 S r 0 . i M n O g薄膜を形成したヘテロ接合デバ イスにおいても第 5図， 第 7図と同様の特性が見られた。 基本的には V 0 2 /T i〇2系と同じバンド構造が期待される。 By the same technique, and the N b De and one-flop S r T i 0 3 Berobusu kite type manganese oxide on a substrate L a. . 9 S r 0. I M n O g thin Figure 5 also in the heterojunction device formed with the same characteristics as the Figure 7 was observed. Basically the same band structure as V 0 2 / T I_〇 2 system is expected.
上記と同様な手法によって、 N bをドープした S r T i 0 3基板上に銅酸化物 C a C u〇2薄膜を形成したデバイスにおいても上記と同様の特性が得られた。 本発明に係る光センサ一はフォトダイォ一ド特性を示すことから、 高感度な光 センサーとして機能する。 特に紫外光に対して高い感度を有し、 今後発展が予想 される紫外線を利用したリソグラフィ一や通信などの分野に有用である。 さらに X線などの放射線に対しても感度を有することが確かめられている。 また、 適当 な吸収剤を導入することで中性子線などの高エネルギー粒子に対しても使用可能 である。 一方、 可視光にも十分な感度を有している。 産業上の利用可能性 By the same technique, the same characteristics as above in the device forming the C a C U_〇 2 thin copper oxide on S r T i 0 3 substrate doped with N b is obtained. Since the optical sensor according to the present invention exhibits photodiode characteristics, it functions as a highly sensitive optical sensor. In particular, it has high sensitivity to ultraviolet light, and is useful in fields such as lithography and communications that use ultraviolet light, which is expected to grow in the future. Furthermore, it has been confirmed that it has sensitivity to radiation such as X-rays. It can also be used for high energy particles such as neutron beams by introducing an appropriate absorbent. On the other hand, it has sufficient sensitivity to visible light. Industrial applicability
以上に説明したように本発明に係る光センサーは、 酸化物のみからなるととも に特に紫外光に対して高感度で簡便な光センサーとして応用することができる。  As described above, the optical sensor according to the present invention can be applied as a simple optical sensor that is made of only an oxide and has high sensitivity particularly to ultraviolet light.

Claims

請求の範囲 The scope of the claims
1. n型半導体特性を有するチタンを含む酸化物に、遷移金属酸化物薄膜を積層 することで形成されるへテロ接合を備えたことを特徴とする光センサー。 1. An optical sensor comprising a heterojunction formed by stacking a transition metal oxide thin film on an oxide containing titanium having n-type semiconductor characteristics.
2. 請求の範囲第 1項に記載の光センサ一において、前記チタンを含む酸化物は 二酸化チタン（T i 02)またはチタン酸ストロンチウム（S r T i 03)であり、 これらに Nb， T a, As, S b, W、 または、 L aを少量ドープして n型半導 体特性を持たせたことを特徴とする光センサ一。 2. The optical sensor one according to claim 1, oxide containing titanium is titanium dioxide (T i 0 2) or strontium titanate (S r T i 0 3) , Nb thereto, An optical sensor characterized in that a small amount of Ta, As, Sb, W, or La is doped to have an n-type semiconductor characteristic.
3. 請求の範囲第 1項及至第 2項に記載の光センサーにおいて、前記遷移金属酸 化物は二酸化バナジウム （vo2)、 三酸化二バナジウム （V203)、 二酸化クロ ム （C r〇2)、 マンガン、 鉄、 コバルト、 ニッケルを含むぺロブスカイト型酸化 物 （AB03 ： Aは Y、 希土類元素、 T l、 Pb、 B i、 B a， S r , C aの単 体または固溶体、 Bは Mn、 F e、 Co、 または、 N i)、 銅酸化物 （AxCuO y : Aは L a, Y, B i， Τ 1 , P b, P r, Nd， B a, S r, C aの単体ま たは固溶体）、 または、 二酸化ルテニウム （Ru〇2) であることを特徵とする光 センサ一。 3. The optical sensor according to paragraph 1及至claim 2, wherein the transition metal oxides is vanadium dioxide (vo 2), trioxide, vanadium (V 2 0 3), dioxide chromium (C R_〇 2), manganese, iron, cobalt, perovskite oxide containing nickel (AB0 3: a is Y, rare earth elements, T l, Pb, B i , B a, S r, single body or solid solution of C a, B is Mn, Fe, Co, or Ni), copper oxide (A x CuOy: A is La, Y, Bi, Τ1, Pb, Pr, Nd, Ba, Sr An optical sensor characterized by being a simple substance or a solid solution of Ca, or ruthenium dioxide (Ru 2 ).
4. 請求の範囲第 1項及至第 3項に記載の光センサ一において、この光センサ一 は紫外線等の光照射による遷移金属酸化物薄膜の電気抵抗の変化を利用して光を 検出する光伝導セルであることを特徴とする光センサ一。  4. The optical sensor according to any one of claims 1 to 3, wherein the optical sensor detects light using a change in electrical resistance of the transition metal oxide thin film due to irradiation with light such as ultraviolet light. An optical sensor comprising a conduction cell.
5. 請求の範囲第 1項及至第 3項に記載のデバイスにおいて、この光センサーは 紫外線等の光照射によって遷移金属酸化物へテロ接合に生じる光起電力を利用し て光を検出するフォトダイオードであることを特徴とする光センサ一。  5. The device according to claims 1 to 3, wherein the optical sensor detects light using photoelectromotive force generated in a transition metal oxide heterojunction by irradiation with light such as ultraviolet rays. An optical sensor, characterized in that:
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