WO1999016098A1 - Semiconductor photoelectric surface - Google Patents

Semiconductor photoelectric surface Download PDF

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Publication number
WO1999016098A1
WO1999016098A1 PCT/JP1998/004119 JP9804119W WO9916098A1 WO 1999016098 A1 WO1999016098 A1 WO 1999016098A1 JP 9804119 W JP9804119 W JP 9804119W WO 9916098 A1 WO9916098 A1 WO 9916098A1
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WIPO (PCT)
Prior art keywords
active layer
layer
semiconductor photocathode
photocathode
semiconductor
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Application number
PCT/JP1998/004119
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French (fr)
Japanese (ja)
Inventor
Tokuaki Nihashi
Original Assignee
Hamamatsu Photonics K.K.
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Publication date
Application filed by Hamamatsu Photonics K.K. filed Critical Hamamatsu Photonics K.K.
Priority to DE69807103T priority Critical patent/DE69807103T2/en
Priority to EP98941849A priority patent/EP1024513B1/en
Priority to AU90029/98A priority patent/AU9002998A/en
Publication of WO1999016098A1 publication Critical patent/WO1999016098A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J40/00—Photoelectric discharge tubes not involving the ionisation of a gas
    • H01J40/02—Details
    • H01J40/04—Electrodes
    • H01J40/06—Photo-emissive cathodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J1/00—Details of electrodes, of magnetic control means, of screens, or of the mounting or spacing thereof, common to two or more basic types of discharge tubes or lamps
    • H01J1/02—Main electrodes
    • H01J1/34—Photo-emissive cathodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2201/00—Electrodes common to discharge tubes
    • H01J2201/34—Photoemissive electrodes
    • H01J2201/342—Cathodes
    • H01J2201/3421—Composition of the emitting surface
    • H01J2201/3423—Semiconductors, e.g. GaAs, NEA emitters

Definitions

  • the present invention relates to a semiconductor photocathode that emits photoelectrons into a vacuum upon incidence of photons, in particular a III-V semiconductor photocathode.
  • a semiconductor photocathode used for a photomultiplier tube has a high photoelectron emission efficiency.
  • One such semiconductor photocathode is disclosed in US Pat. No. 3,387,161.
  • This semiconductor photocathode has an active layer obtained by activating the surface of a p-type semiconductor having a doping concentration of 1 ⁇ 10 18 cm 3 or more and 1 ⁇ 10 19 cm ′′ 3 or less with an alkali metal. With this configuration, downward energy band bending is formed on the vacuum emission side surface of the photocathode, which lowers the vacuum level barrier on the surface to facilitate the escape of photoelectrons and separates from the vacuum emission side surface. Even photoelectrons generated inside the active layer are more likely to reach the emission side surface because the diffusion length can be increased without lowering the electron emission probability.
  • the doping concentration is low. This is because the lower the doping concentration, the more the decrease in crystallinity can be suppressed.
  • the dopant concentration is low, the diffusion length can be increased, but the probability of electron emission decreases, resulting in a decrease in quantum efficiency. For this reason, conventionally, It was difficult to further reduce the concentration.
  • an object of the present invention is to provide a semiconductor photocathode having a low doping concentration and a high quantum efficiency.
  • the semiconductor photocathode of the present invention is a semiconductor photocathode which emits photoelectrons into a vacuum in response to incident photons, wherein the surface on the photoelectron emission side is a P-type doped III activated with alkali metal or alkali metal oxide.
  • An active layer comprising a Group V compound semiconductor is provided, and the surface doping concentration on the photoelectron emission side of the active layer is 1 ⁇ 10 17 cm 3 or less.
  • the diffusion length increases.
  • the crystal is good, the probability of electrons reaching the emission side surface is high, the deterioration of the electron emission probability can be prevented, and the quantum efficiency can be kept high.
  • the energy band gap of the active layer is preferably at least twice the work function of the alkali metal or alkali metal oxide of the surface layer. In this case, electrons are easily emitted from the surface.
  • An electron supply layer may be provided on a side different from the photoelectron emission side of the active layer.
  • the doping concentration of the active layer may be 1 ⁇ 10 17 cm 3 or less in the vicinity of the photoelectron emission surface and 1 ⁇ 10 to 1 ⁇ 10 cm ′′ ′ on the back side.
  • the doping concentration of the active layer may be gradually increased from the vicinity of the photoelectron emitting surface toward the back, and the doping concentration at the deepest portion on the back side may be 1 ⁇ 10 to 1 ⁇ 10 cm.
  • the diffusion length is further increased, and the electric field inside the diffusion layer is configured to move the electrons toward the emission surface side, so that the probability of the electrons reaching the emission surface is improved.
  • the thickness of the region having a doping concentration of 1 ⁇ 10 18 to 1 ⁇ 10 19 cm ′ 3 on the back side of the active layer is several nm or less.
  • the amount of photoelectrons that migrate to the side opposite to the emission-side surface and disappear is suppressed. For this reason, Applicable to over-type photocathode structure.
  • a Schottky electrode formed on the surface of the active layer may be provided, and an external bias may be applied to the active layer. According to this, the photoelectrons generated inside the active layer due to the external bias are efficiently guided to the emission side surface.
  • FIG. 1 is a schematic diagram of a phototube using the photocathode of the present invention.
  • FIG. 2 is a diagram showing a dopant concentration distribution of the active layer on the photocathode of FIG.
  • FIG. 3 is a diagram comparing wavelength characteristics of the photoelectric surface of the present invention and a conventional product.
  • FIG. 4 is a graph showing the relationship between the dopant concentration and the quantum efficiency.
  • FIG. 5 is a diagram showing an example of the dopant concentration distribution of the active layer of the photocathode of the present invention.
  • FIG. 6 is a diagram showing another example of the dopant concentration distribution of the active layer of the photocathode of the present invention.
  • FIG. 7 is a diagram showing still another example of the dopant concentration distribution of the active layer of the photocathode of the present invention.
  • FIG. 1 is a schematic diagram of a transmission type phototube using a semiconductor photocathode according to the present invention.
  • the phototube 10 is configured such that a photocathode 30 and an anode 40 using a semiconductor photocathode according to the present invention are accommodated in a sealed container 20 whose inside is evacuated.
  • This vacuum container
  • the photocathode 30 is supported by metal lead pins 51 via a metal support plate 31 having a hole at the center and a metal support base 50.
  • the anode 40 is a metal electrode formed in a rectangular frame shape, and is supported by a metal lead pin 52.
  • the lead pins 51 and 52 penetrate the bottom of the vacuum vessel 20 and are connected to external power sources, respectively, and apply a voltage higher than that of the photocathode 30 to the anode 40.
  • the photocathode 30 is a substrate formed of sapphire on a rectangular frame-shaped metal support plate 31.
  • a matching layer 33, an active layer 34, and a surface layer 35 are sequentially laminated thereon.
  • the matching layer 33 is made of, for example, amorphous A 1 N grown on the substrate 32 by epitaxial growth.
  • the matching layer 33 has a thickness of about 10 nm, and is lattice-matched with the active layer 34 to allow the active layer 34 to grow well. Further, it is provided for the purpose of preventing backward movement of photoelectrons generated in the active layer 34.
  • the active layer 34 is formed from p-type GaN epitaxially grown on the matching layer 33.
  • the thickness of the active layer 34 is 100 nm or more, and Mg or Zn is doped as a p-type dopant. Its concentration distribution is as shown in Fig. 2.It has a first layer with a thickness of lOOnm near the surface and a second layer with a thickness of lnm formed at least deeper than the light incident surface.
  • the dopant concentration near the surface is 1 ⁇ 10 16 cm 3
  • the concentration increases toward the second layer
  • the concentration at the boundary with the second layer is 5 ⁇ 10 17 cm 3
  • the dopant concentration in the second layer is 1 ⁇ 10 18 cm 3 higher than in the first layer.
  • the growth of the matching layer 33 and the active layer 34 is performed by MOCVD, MBE, HWE, etc. Various crystal growth methods can be used.
  • a surface layer 35 made of an alkali metal or an oxide thereof, for example, Cs or Cs0 is formed by vapor deposition. This surface layer 35 is formed as a monoatomic layer.
  • the energy band gap of the vacuum discharge of the surface layer 35 when C s is used as the metal is 1.4 eV, and when C s O is used, the energy band gap is 0.9 eV.
  • the band gap is less than half of 3.4 eV.
  • the operation of the photoelectric tube will be described.
  • the incident light passes through the hole of the metal support plate 31, passes through the substrate 32, the matching layer 33, and enters the active layer 34.
  • Photons are absorbed mainly in the first layer of the active layer 34 to generate photoelectrons.
  • the distribution of the band gap energy in the active layer 34 substantially corresponds to the dopant concentration.
  • the photoelectrons generated in the first layer move in the first layer so as to slide down the slope and reach the surface layer 35, and have a large band gap with the surface layer 35. Is extremely thin, so it is easily released into a vacuum.
  • the emitted photoelectrons reach the anode 40 by an electric field between the photocathode 30 and the anode 40 and are detected as a current.
  • the present inventor compared the wavelength characteristics of the conventional photocathode and the photocathode of the present invention shown in FIG. The results are shown in comparison with FIG.
  • a comparison was made with a conventional product in which the active layer was one layer and the dopant concentration was 1 ⁇ 10 18 cm 3 .
  • the broken line shows the wavelength characteristics of the quantum efficiency of the photocathode of the present invention, and the straight line shows the wavelength characteristics of the quantum efficiency.
  • the product of the present invention has a higher quantum efficiency at a wavelength of 350 nm or less than the conventional product, has a low quantum efficiency at a wavelength of 400 ⁇ or more, improves sharp cut properties, and improves characteristics in a low wavelength region. It was confirmed that. This is thought to be due to the fact that, as the diffusion length increases, the probability of photoelectrons reaching the surface increases due to the improvement in crystallinity, thereby improving the photoelectron emission efficiency from the surface.
  • Figure 4 shows various prototypes with different dopant concentrations in the active layer.
  • 5 is a graph comparing quantum efficiency at 254 nm. The quantum efficiency varies considerably depending on the prototype, but the overall high dopant concentration (1 ⁇ 18 to 1X)
  • the concentration distribution of the active layer 34 may be composed of a first layer and a second layer as shown in FIG. 5 in addition to that shown in FIG. 2, and the concentration of each may be changed stepwise. . With this configuration, photoelectrons generated by photons incident from the opposite side of the emission surface can be effectively guided to the emission side.
  • the photocathode of the present invention can be applied to a reflection photocathode which emits photoelectrons on the same side as the incident direction of photons.
  • the matching layer 33 may be formed of, for example, amorphous A 1 N or GaN epitaxially grown on the substrate 32.
  • FIGS. 6 and 7 show the concentration distribution of the active layer on the reflection type photoelectric surface corresponding to the transmission type photoelectric surface of FIGS. 2 and 5, respectively. In either case, photoelectrons generated in the high dopant concentration layer can be efficiently guided to the emission side surface.
  • Control of these dopant concentrations can be easily set by controlling the supply of the dopant material. Although it is preferable to provide a high-concentration region in a portion away from the emission surface, it is not essential and may not be provided. Alternatively, by applying an external bias voltage to the active layer, the internal energy-bandgap level may be graded to force photoelectrons to the emission surface. In this case, the internal dopant concentration may be uniform, or the predetermined distribution may be provided as described above.
  • G a N As the active layer
  • G a, In, A l, B, etc. are used as group III materials
  • N, P, As, etc. are used as V group materials. Can be used.
  • alkali metal of the surface layer Cs, Cs0, etc. can be used. You.
  • the active layer having a low dopant concentration stabilizes the crystallinity and increases the diffusion length, so that the photocathode having high quantum efficiency and improved sharp cut property can be obtained. can get.
  • the photoelectric surface according to the present invention can be applied not only to a photoelectric tube but also to a photoelectric surface performing various photoelectric conversions.

Abstract

A phototube (10) comprises a photocathode (30) having photoelectric surface. In a sealed enclosure (20) whose inside is vacuum, the photoelectric cathode (30) and an anode (40) are opposed to each other. Voltages are applied to them through lead pins (51 and 52). The photocathode (30) includes a metallic support plate (31) to which is secured a sapphire plate (32) on which are formed an a-AlN matching layer (33), a p-type GaN active layer (34), and a CsO surface layer (35). The active layer (34) has a dopant concentration that increases from 1 x 1016 cm-3 in the surface up to 5 x 1017 cm-3 at a depth of 100 nm. The dopant concentration only at the deepest region over a thickness of several nanometers is 1 x 1018 cm-3. The crystallinity of the active layer (34) is improved, and the diffusion length is increased, improving the quantum efficiency and sharp-cut property.

Description

明糸田書 半導体光電面 技術分野  Akira Itoda Semiconductor Photocathode Technology
本発明は、光子の入射により真空中に光電子を放出する半導体光電面、特に III 一 V族半導体光電面に関する。 背景技術  The present invention relates to a semiconductor photocathode that emits photoelectrons into a vacuum upon incidence of photons, in particular a III-V semiconductor photocathode. Background art
光電子増倍管などに用いられる半導体光電面は光電子放出効率が高いことが好 ましい。 こうした半導体光電面として米国特許 3,387, 161号で開示されているも のがある。 この半導体光電面は、 ド一プ濃度 1 X 1018cm 3以上 1 X 1019cm"3以下 の p型半導体の表面をアル力リ金属で活性化した活性層を有している。 このよう な構成とすることにより、 光電面の真空放出側表面において下向きのエネルギー バンドベンディングが形成され、 表面における真空準位障壁を低下させて光電子 の脱出を容易にするとともに、 真空放出側表面から離れた活性層内部で発生した 光電子でも放出側表面に達しやすくなつている。 これは、 電子放出確率を下げる ことなく、 拡散長を増大させることができるからである。 発明の開示 It is preferable that a semiconductor photocathode used for a photomultiplier tube has a high photoelectron emission efficiency. One such semiconductor photocathode is disclosed in US Pat. No. 3,387,161. This semiconductor photocathode has an active layer obtained by activating the surface of a p-type semiconductor having a doping concentration of 1 × 10 18 cm 3 or more and 1 × 10 19 cm ″ 3 or less with an alkali metal. With this configuration, downward energy band bending is formed on the vacuum emission side surface of the photocathode, which lowers the vacuum level barrier on the surface to facilitate the escape of photoelectrons and separates from the vacuum emission side surface. Even photoelectrons generated inside the active layer are more likely to reach the emission side surface because the diffusion length can be increased without lowering the electron emission probability.
しかし、 ド一プ濃度を高濃度にすると、 結晶中に発生する欠陥等によるバンド 端付近の吸収が発生し、光吸収特性のシャープカツト性が損なわれる傾向がある。 また、 ソーラーブラインド性の点からは、 ド一プ濃度が低いことが好ましい。 ド ―プ濃度が低いほうが結晶性の低下を抑えることができるからである。 しかし、 低ド一プ濃度にすると、 拡散長は増大させることができるが、 電子放出確率が低 下するために、 結果的に量子効率が低下してしまう。 このため、 従来は、 ドープ 濃度をさらに低下させることが困難だった。 However, when the doping concentration is increased, absorption near the band edge occurs due to defects or the like generated in the crystal, and the sharp cut property of the light absorption characteristics tends to be impaired. Further, from the viewpoint of solar blindness, it is preferable that the doping concentration is low. This is because the lower the doping concentration, the more the decrease in crystallinity can be suppressed. However, when the dopant concentration is low, the diffusion length can be increased, but the probability of electron emission decreases, resulting in a decrease in quantum efficiency. For this reason, conventionally, It was difficult to further reduce the concentration.
本発明は、 上記の問題点に鑑みて、 低ドープ濃度で量子効率の高い半導体光電 面を提供することを課題とする。  In view of the above problems, an object of the present invention is to provide a semiconductor photocathode having a low doping concentration and a high quantum efficiency.
本発明の半導体光電面は、 入射光子に応じて真空中に光電子を放出する半導体 光電面において、 光電子放出側の表面がアル力リ金属あるいはアルカリ金属酸化 物で活性化された P型ドープの III一 V族化合物半導体からなる活性層を備え、 活性層の光電子放出側の表面ドープ濃度が 1 X 1017cm 3以下であることを特徴と する。 The semiconductor photocathode of the present invention is a semiconductor photocathode which emits photoelectrons into a vacuum in response to incident photons, wherein the surface on the photoelectron emission side is a P-type doped III activated with alkali metal or alkali metal oxide. An active layer comprising a Group V compound semiconductor is provided, and the surface doping concentration on the photoelectron emission side of the active layer is 1 × 10 17 cm 3 or less.
これによれば、 結晶性の低下が防止されるので、 拡散長が増大する。 また、 結 晶が良好なので放出側表面に電子が到達する確率が高く、 電子放出確率の劣化が 防げ、 量子効率を高く保つことができる。  According to this, since a decrease in crystallinity is prevented, the diffusion length increases. In addition, since the crystal is good, the probability of electrons reaching the emission side surface is high, the deterioration of the electron emission probability can be prevented, and the quantum efficiency can be kept high.
さらに、 活性層のエネルギーバンドギャップが表面層のアルカリ金属又はアル 力リ金属酸化物の仕事関数の 2倍以上であることが好ましい。このようにすれば、 表面から電子が放出されやすい。  Further, the energy band gap of the active layer is preferably at least twice the work function of the alkali metal or alkali metal oxide of the surface layer. In this case, electrons are easily emitted from the surface.
活性層の光電子放出側と異なる側に、 電子供給層を備えていてもよい。  An electron supply layer may be provided on a side different from the photoelectron emission side of the active layer.
または、 活性層のド一プ濃度は、 光電子放出面近傍が 1 X 1017cm 3以下、 その 奥側が 1 X 10 ~ 1 X 10 cm"'であつてもよい。 Alternatively, the doping concentration of the active layer may be 1 × 10 17 cm 3 or less in the vicinity of the photoelectron emission surface and 1 × 10 to 1 × 10 cm ″ ′ on the back side.
あるいは、 活性層のドープ濃度を光電子放出面近傍から奥に向かって次第に増 加させており、 奥側の最深部のドープ濃度は 1 X 10 〜 1 X 10 cm であっても よい。  Alternatively, the doping concentration of the active layer may be gradually increased from the vicinity of the photoelectron emitting surface toward the back, and the doping concentration at the deepest portion on the back side may be 1 × 10 to 1 × 10 cm.
これらの構成によれば、 より拡散長が大きくなるとともに、 拡散層内部の電界 は、 放出表面側に向かって電子を移動させる構成となり、 放出表面への電子到達 確率が向上する。  According to these configurations, the diffusion length is further increased, and the electric field inside the diffusion layer is configured to move the electrons toward the emission surface side, so that the probability of the electrons reaching the emission surface is improved.
活性層の奥側のドープ濃度 1 X 1018〜 1 X 1019cm'3の領域の厚みは数 nm以下 であればさらに好ましい。この場合は、高濃度ド一プ層で発生した光電子のうち、 放出側表面と反対側に移行して消失する光電子の量が抑制される。 このため、 透 過型光電面構造に適用できる。 More preferably, the thickness of the region having a doping concentration of 1 × 10 18 to 1 × 10 19 cm ′ 3 on the back side of the active layer is several nm or less. In this case, of the photoelectrons generated in the high-concentration doping layer, the amount of photoelectrons that migrate to the side opposite to the emission-side surface and disappear is suppressed. For this reason, Applicable to over-type photocathode structure.
あるいは、 活性層表面に形成されたショットキー電極を備え、 前記活性層に外 部バイアスを印加してもよい。 これによれば、 外部バイアスにより、 活性層内部 で発生した光電子は、 放出側表面に効率的に導かれる。  Alternatively, a Schottky electrode formed on the surface of the active layer may be provided, and an external bias may be applied to the active layer. According to this, the photoelectrons generated inside the active layer due to the external bias are efficiently guided to the emission side surface.
本発明は以下の詳細な説明および添付図面によりさらに十分に理解可能となる c これらは単に例示のために示されるものであって、 本発明を限定するものと考え るべきではない。 The present invention will become more fully understood from the detailed description and the accompanying drawings, which follow are presented by way of illustration only and should not be taken as limiting the invention.
本発明のさらなる応用範囲は、 以下の詳細な発明から明らかになるだろう。 し かしながら、 詳細な説明および特定の事例は本発明の好適な実施形態を示すもの ではあるが、 例示のためにのみ示されているものであって、 本発明の思想および 範囲における様々な変形および改良はこの詳細な説明から当業者には明らかであ ることははつきりしている。 図面の簡単な説明  Further areas of applicability of the present invention will become apparent from the detailed description below. However, while the detailed description and specific examples illustrate preferred embodiments of the present invention, they are provided by way of example only, and various modifications within the spirit and scope of the present invention may be made. It is obvious that variations and modifications will be apparent to those skilled in the art from this detailed description. BRIEF DESCRIPTION OF THE FIGURES
図 1は、 本発明の光電面を利用した光電管の概略図である。  FIG. 1 is a schematic diagram of a phototube using the photocathode of the present invention.
図 2は、 図 1の光電面の活性層のド一パント濃度分布を示す図である。  FIG. 2 is a diagram showing a dopant concentration distribution of the active layer on the photocathode of FIG.
図 3は、 本発明の光電面と従来品の波長特性を比較した図である。  FIG. 3 is a diagram comparing wavelength characteristics of the photoelectric surface of the present invention and a conventional product.
図 4は、 ドーパント濃度と量子効率の関係を示すグラフである。  FIG. 4 is a graph showing the relationship between the dopant concentration and the quantum efficiency.
図 5は、本発明の光電面の活性層のドーパント濃度分布の一例を示す図である。 図 6は、 本発明の光電面の活性層のドーパント濃度分布の別の例を示す図であ る。  FIG. 5 is a diagram showing an example of the dopant concentration distribution of the active layer of the photocathode of the present invention. FIG. 6 is a diagram showing another example of the dopant concentration distribution of the active layer of the photocathode of the present invention.
図 7は、 本発明の光電面の活性層のドーパント濃度分布のさらに別の例を示す 図である。 発明を実施するための最良の形態  FIG. 7 is a diagram showing still another example of the dopant concentration distribution of the active layer of the photocathode of the present invention. BEST MODE FOR CARRYING OUT THE INVENTION
以下、 図面を参照して本発明の実施の形態を説明する。 図 1は、 本発明による半導体光電面を利用した透過型光電管の概略図である。 光電管 1 0は、 内部を真空にした密閉容器 2 0内に、 本発明による半導体光電面 を利用した光電陰極 3 0と陽極 4 0が収容されて構成されている。 この真空容器Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram of a transmission type phototube using a semiconductor photocathode according to the present invention. The phototube 10 is configured such that a photocathode 30 and an anode 40 using a semiconductor photocathode according to the present invention are accommodated in a sealed container 20 whose inside is evacuated. This vacuum container
2 0は、 中空円柱状のガラス製容器であり、 内部は圧力約 10'8Torr 以下に保持 されている。 光電陰極 3 0は、 中央に穴の空いた金属製支持板 3 1と金属製支持 台 5 0を介して金属製のリードピン 5 1によって支持されている。 一方、 陽極 4 0は、 矩形枠状に成型された金属製電極であり、 金属製リードピン 5 2によって 支持されている。 リードピン 5 1、 5 2は真空容器 2 0の底部を貫通して外部電 源にそれぞれ接続されており、 陽極 4 0に光電陰極 3 0より高い電圧を印加する ものである。 2 0 is a hollow cylindrical glass container, inside thereof is kept below a pressure of about 10 '8 Torr. The photocathode 30 is supported by metal lead pins 51 via a metal support plate 31 having a hole at the center and a metal support base 50. On the other hand, the anode 40 is a metal electrode formed in a rectangular frame shape, and is supported by a metal lead pin 52. The lead pins 51 and 52 penetrate the bottom of the vacuum vessel 20 and are connected to external power sources, respectively, and apply a voltage higher than that of the photocathode 30 to the anode 40.
光電陰極 3 0は、 矩形枠状の金属支持板 3 1にサファイアから形成された基板 The photocathode 30 is a substrate formed of sapphire on a rectangular frame-shaped metal support plate 31.
3 2が固定され、 その上に、 整合層 3 3、 活性層 3 4、 表面層 3 5が順次積層さ れて形成されている。 32 is fixed, and a matching layer 33, an active layer 34, and a surface layer 35 are sequentially laminated thereon.
整合層 3 3は、 例えば、 基板 3 2上にェビタキシャル成長させたアモルファス 状の A 1 Nから形成されている。 この整合層 3 3は、 層厚約 10nm であり、 活 性層 3 4と格子整合し、 活性層 3 4の結晶成長を良好に行わせる。 また、 活性層 3 4で発生した光電子の逆行を防ぐ目的で設けられている。  The matching layer 33 is made of, for example, amorphous A 1 N grown on the substrate 32 by epitaxial growth. The matching layer 33 has a thickness of about 10 nm, and is lattice-matched with the active layer 34 to allow the active layer 34 to grow well. Further, it is provided for the purpose of preventing backward movement of photoelectrons generated in the active layer 34.
活性層 3 4は、 この整合層 3 3上に、 ェピタキシャル成長させた p型 G a Nか ら形成されている。 この活性層 3 4の厚みは lOOnm以上であり、 p型ドーパン トとして M gまたは Z nがドープされている。 その濃度分布は図 2に示す通りで あり、 表面付近の厚さ lOOnmの第 1層と、 少なくともその光入射面より奥側に 形成された厚さ l nm の第 2層とを有しており、 第 1層は、 表面付近でのド一パ ント濃度が 1 X l016cm 3で、 第 2層側ほど濃度が高くなり、 第 2層との境界の濃 度は 5 X 1017cm 3に達する。 第 2層のドーパント濃度は、 第 1層より高い 1 X 1018cm 3である。 The active layer 34 is formed from p-type GaN epitaxially grown on the matching layer 33. The thickness of the active layer 34 is 100 nm or more, and Mg or Zn is doped as a p-type dopant. Its concentration distribution is as shown in Fig. 2.It has a first layer with a thickness of lOOnm near the surface and a second layer with a thickness of lnm formed at least deeper than the light incident surface. In the first layer, the dopant concentration near the surface is 1 × 10 16 cm 3 , the concentration increases toward the second layer, and the concentration at the boundary with the second layer is 5 × 10 17 cm 3 Reach The dopant concentration in the second layer is 1 × 10 18 cm 3 higher than in the first layer.
これらの整合層 3 3、 活性層 3 4の成長は、 M O C V D、 M B E、 HW E等の 各種の結晶成長方法を用いることができる。 The growth of the matching layer 33 and the active layer 34 is performed by MOCVD, MBE, HWE, etc. Various crystal growth methods can be used.
この活性層 3 4の表面には、 アルカリ金属またはその酸化物、 例えば C sある いは C s 0からなる表面層 3 5が蒸着により形成されている。この表面層 3 5は、 単原子層として形成されている。 アル力リ金属として C sを利用したときの表面 層 3 5の真空放出のエネルギーバンドギャップは 1.4eVであり、 C s Oを利用 したときは 0.9eV であり、 活性層の G a Nのエネルギーバンドギャップ 3.4eV の半分以下である。  On the surface of the active layer 34, a surface layer 35 made of an alkali metal or an oxide thereof, for example, Cs or Cs0 is formed by vapor deposition. This surface layer 35 is formed as a monoatomic layer. The energy band gap of the vacuum discharge of the surface layer 35 when C s is used as the metal is 1.4 eV, and when C s O is used, the energy band gap is 0.9 eV. The band gap is less than half of 3.4 eV.
次に、 この光電管の動作を説明する。 光電陰極 3 0の基板 3 2側から光を入射 させると、 入射光は、 金属製支持板 3 1の穴を通過し、 基板 3 2、 整合層 3 3を 透過して、 活性層 3 4に達する。 この活性層 3 4の主に第 1層で光子が吸収され て光電子が発生する。 活性層 3 4内のバンドギャップエネルギーの分布は、 ほぼ ドーパント濃度に対応した形になる。 この結果、 第 1層で発生した光電子は、 ち ようどスロープを滑り落ちるように第 1層内を移動して表面層 3 5に達し、 表面 層 3 5とのバンドギャップが大きく、 表面層 3 5が極端に薄いので、 容易に真空 中に放出される。 放出された光電子は、 光電陰極 3 0と陽極 4 0間の電界によつ て陽極 4 0に達して、 電流として検知される。  Next, the operation of the photoelectric tube will be described. When light enters from the substrate 32 side of the photocathode 30, the incident light passes through the hole of the metal support plate 31, passes through the substrate 32, the matching layer 33, and enters the active layer 34. Reach. Photons are absorbed mainly in the first layer of the active layer 34 to generate photoelectrons. The distribution of the band gap energy in the active layer 34 substantially corresponds to the dopant concentration. As a result, the photoelectrons generated in the first layer move in the first layer so as to slide down the slope and reach the surface layer 35, and have a large band gap with the surface layer 35. Is extremely thin, so it is easily released into a vacuum. The emitted photoelectrons reach the anode 40 by an electric field between the photocathode 30 and the anode 40 and are detected as a current.
本願発明者は、 従来の光電面と図 1に係る本願発明の光電面の性能を比較する ため、 両者の波長特性を比較した。 その結果を図 3に比較して示す。 ここでは、 従来品として活性層を 1層としてそのドーパント濃度を 1 X l018cm 3とした製品 と比較した。 破線が従来品、 直線が本願発明の光電面の量子効率の波長特性を示 している。 本願発明品は、 従来品に比べて波長 350nm以下の量子効率は高く、 400ηιη 以上の波長では、 量子効率が低く、 シャープカット性の向上と、 低波長 領域での特性の向上が図られていることが確認された。 これは、 拡散長が増大す るとともに、 結晶性の向上により光電子の表面への到達確率が向上し、 それによ り表面からの光電子の放出効率も向上するためとみられる。 The present inventor compared the wavelength characteristics of the conventional photocathode and the photocathode of the present invention shown in FIG. The results are shown in comparison with FIG. Here, a comparison was made with a conventional product in which the active layer was one layer and the dopant concentration was 1 × 10 18 cm 3 . The broken line shows the wavelength characteristics of the quantum efficiency of the photocathode of the present invention, and the straight line shows the wavelength characteristics of the quantum efficiency. The product of the present invention has a higher quantum efficiency at a wavelength of 350 nm or less than the conventional product, has a low quantum efficiency at a wavelength of 400 ηιη or more, improves sharp cut properties, and improves characteristics in a low wavelength region. It was confirmed that. This is thought to be due to the fact that, as the diffusion length increases, the probability of photoelectrons reaching the surface increases due to the improvement in crystallinity, thereby improving the photoelectron emission efficiency from the surface.
図 4は、 活性層のドーパント濃度を変えた各種の試作品について例えば波長 254nm における量子効率を比較したグラフである。 試作品により量子効率にか なりばらつきがあるが、 全体として従来の高ドーパント濃度 （ 1 χ ιο18〜 1 XFigure 4 shows various prototypes with different dopant concentrations in the active layer. 5 is a graph comparing quantum efficiency at 254 nm. The quantum efficiency varies considerably depending on the prototype, but the overall high dopant concentration (1 ιιο 18 to 1X)
1019cm'3) の場合に比較して、 本発明の低ドーパント濃度 （ 1 X l017cm 3以下） の製品の量子効率は同等もしくは上回っていることが確認された。 It was confirmed that the quantum efficiency of the product having a low dopant concentration (1 × 10 17 cm 3 or less) of the present invention was equal to or higher than that of 10 19 cm ′ 3 ).
次に、 本発明の他の実施形態について説明する。 活性層 3 4の濃度分布として は、 図 2に示したものの他、 図 5に示すように、 第 1層と第 2層から構成し、 そ れそれの濃度をステップ状に変化させてもよい。 このように構成することで、 放 出面の反対側から入射した光子により発生した光電子を放出側に効果的に導くこ とができる。  Next, another embodiment of the present invention will be described. The concentration distribution of the active layer 34 may be composed of a first layer and a second layer as shown in FIG. 5 in addition to that shown in FIG. 2, and the concentration of each may be changed stepwise. . With this configuration, photoelectrons generated by photons incident from the opposite side of the emission surface can be effectively guided to the emission side.
また、 本発明の光電面は、 光子の入射方向と同じ側に光電子を放出する反射型 の光電面についても適用できる。 その場合には、 整合層 3 3は例えば基板 3 2上 にェピタキシャル成長させたアモルファス状の A 1 Nあるいは G a Nで形成して もよい。 図 6、 図 7は、 それぞれ図 2、 図 5の透過型光電面に対応する反射型光 電面の活性層濃度分布を示したものである。 いずれの場合も高ドーパント濃度層 で発生した光電子を効率的に放出側表面に導くことができる。  Further, the photocathode of the present invention can be applied to a reflection photocathode which emits photoelectrons on the same side as the incident direction of photons. In this case, the matching layer 33 may be formed of, for example, amorphous A 1 N or GaN epitaxially grown on the substrate 32. FIGS. 6 and 7 show the concentration distribution of the active layer on the reflection type photoelectric surface corresponding to the transmission type photoelectric surface of FIGS. 2 and 5, respectively. In either case, photoelectrons generated in the high dopant concentration layer can be efficiently guided to the emission side surface.
これらのドーパント濃度の制御は、 ドーパント材料の供給を制御することで容 易に設定することができる。 なお、 放出面から離れた部分に高濃度領域を設ける ことは好ましいことではあるが、 不可欠のものではなく、 設けなくともよい。 あるいは、 活性層に外部バイアス電圧を印加することにより、 内部のエネルギ —バンドギャップレベルに勾配をつけて、 光電子を放出側表面に強制的に導いて もよい。 この場合は、 内部のドーパント濃度を一様にしても、 上記のように所定 の分布をつけてもよい。  Control of these dopant concentrations can be easily set by controlling the supply of the dopant material. Although it is preferable to provide a high-concentration region in a portion away from the emission surface, it is not essential and may not be provided. Alternatively, by applying an external bias voltage to the active layer, the internal energy-bandgap level may be graded to force photoelectrons to the emission surface. In this case, the internal dopant concentration may be uniform, or the predetermined distribution may be provided as described above.
以上の説明では、 活性層として G a Nを用いた例について説明してきたが、 III 族材料として G a、 I n、 A l、 B等を、 V族材料として N、 P、 A s等を使用 することができる。  In the above description, an example using G a N as the active layer has been described. However, G a, In, A l, B, etc. are used as group III materials, and N, P, As, etc. are used as V group materials. Can be used.
また、 表面層のアルカリ金属としては、 C s、 C s 0等を使用することができ る。 In addition, as the alkali metal of the surface layer, Cs, Cs0, etc. can be used. You.
以上、 説明したように本発明によれば、 低ド一パント濃度の活性層により結晶 性が安定して、 拡散長も増加するので、 量子効率が高く、 シャープカット性の向 上した光電面が得られる。  As described above, according to the present invention, the active layer having a low dopant concentration stabilizes the crystallinity and increases the diffusion length, so that the photocathode having high quantum efficiency and improved sharp cut property can be obtained. can get.
さらに、 活性層にワイ ドエネルギーバンドの半導体を使用することにより、 表 面からの光電子放出が確実に行われる。  Furthermore, by using a semiconductor having a wide energy band for the active layer, photoelectrons are reliably emitted from the surface.
また、 活性層のド一パント濃度分布を調整することにより、 活性層の奥で発生 した光電子を放出側表面に確実に導くことができる。  In addition, by adjusting the dopant concentration distribution of the active layer, photoelectrons generated in the back of the active layer can be reliably guided to the emission side surface.
以上の本発明の説明から、 本発明を様々に変形しうることは明らかである。 そ のような変形は、 本発明の思想および範囲から逸脱するものとは認めることはで きず、 すべての当業者にとって自明である改良は、 以下の請求の範囲に含まれる ものである。 産業上の利用可能性  It is apparent from the above description of the invention that the present invention can be variously modified. Such modifications cannot be deemed to depart from the spirit and scope of the invention, and modifications obvious to those skilled in the art are intended to be within the scope of the following claims. Industrial applicability
本発明に係る光電面は、 光電管への使用のほか、 各種の光電変換を行う光電面 への適用が可能である。  The photoelectric surface according to the present invention can be applied not only to a photoelectric tube but also to a photoelectric surface performing various photoelectric conversions.

Claims

請求の範囲 The scope of the claims
1 . 入射光子に応じて真空中に光電子を放出する半導体光電面において、 光電子放出側の表面がアル力リ金属あるいはアル力リ金属酸化物で活性化され た p型ドープの III一 V族化合物半導体からなる活性層を備え、 前記活性層の光 電子放出側の少なくとも表面のドープ濃度が 1 X 1017cm 3以下であることを特徴 とする半導体光電面。 1. A p-type doped III-V compound in which the surface on the photoelectron emission side is activated by an alkali metal or an alkali metal oxide on a semiconductor photocathode that emits photoelectrons into a vacuum in response to incident photons. A semiconductor photocathode having an active layer made of a semiconductor, wherein a doping concentration of at least a surface of the active layer on the photoelectron emission side is 1 × 10 17 cm 3 or less.
2 . 前記活性層のエネルギーバンドギヤップが前記表面層のアル力リ金属又 はアル力リ金属酸化物の仕事関数の 2倍以上であることを特徴とする請求項 1記 載の半導体光電面。 2. The semiconductor photocathode according to claim 1, wherein the energy band gap of the active layer is at least twice the work function of the metal or the metal oxide of the surface layer.
3 . 前記活性層の光電子放出側と異なる側に、 電子供給層を備えている請求 項 1記載の半導体光電面。 3. The semiconductor photocathode according to claim 1, further comprising an electron supply layer on a side different from the photoelectron emission side of the active layer.
4 . 前記活性層のド一プ濃度は、 光電子放出面近傍が 1 X 1017cm 3以下、 そ の奥側が 1 X 1018〜 l X 1019cm 3であることを特徴とする請求項 1記載の半導体 光電面。 4. The doping concentration of the active layer is 1 × 10 17 cm 3 or less near the photoelectron emission surface and 1 × 10 18 to l × 10 19 cm 3 on the back side. The semiconductor photocathode as described.
5 . 前記活性層の奥側のド一プ濃度 1 X 1018〜 1 X 10lacm 3の領域の厚みは 数 nm以下であることを特徴とする請求項 4記載の半導体光電面。 5. The semiconductor photocathode according to claim 4, wherein the depth of the region having a doping concentration of 1 × 10 18 to 1 × 10 lacm 3 on the back side of the active layer is several nm or less.
6 . 前記活性層のド一プ濃度を光電子放出面近傍から奥に向かって次第に増 加させており、 奥側の最深部のド一プ濃度は 1 X 1018〜 1 X 1019cm 3であること を特徴とする請求項 1記載の半導体光電面。 6. The concentration of the dopant in the active layer is gradually increased from the vicinity of the photoelectron emission surface toward the back, and the concentration of the deepest part on the back side is 1 × 10 18 to 1 × 10 19 cm 3 . 2. The semiconductor photocathode according to claim 1, wherein:
7 . 前記活性層の奥側のドープ濃度 1 X 1018〜 1 X 1019cm 3の領域の厚みは 数 nm以下であることを特徴とする請求項 6記載の半導体光電面。 7. The semiconductor photocathode according to claim 6, wherein a thickness of a region having a doping concentration of 1 × 10 18 to 1 × 10 19 cm 3 on the back side of the active layer is several nm or less.
8 . 前記活性層表面に形成されたショットキ一電極を備え、 前記活性層に外 部バイアスを印加することを特徴とする請求項 1記載の半導体光電面。 8. The semiconductor photocathode according to claim 1, further comprising a Schottky electrode formed on a surface of the active layer, wherein an external bias is applied to the active layer.
PCT/JP1998/004119 1997-09-24 1998-09-11 Semiconductor photoelectric surface WO1999016098A1 (en)

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