JP4096059B2 - Photon detector and manufacturing method thereof - Google Patents

Description

  The present invention relates to a photon detector capable of detecting one photon and a manufacturing method thereof.

  High-sensitivity photodetectors are currently used in many fields such as optical measurement devices and communication technologies. Detectors that can detect single photons include photomultiplier tubes and avalanche photodiodes.

  However, since the photomultiplier tube utilizes the external photoelectric effect, it is difficult to reduce the size and requires a high voltage. In addition, the avalanche photodiode is weak against thermal noise, and has a drawback that the element needs to be cooled to a very low temperature in order to detect photons with high sensitivity, and requires a large applied voltage.

  In recent years, a photon detector using a single electron transistor (hereinafter referred to as “SET”), which will be described later, has been developed, and it is becoming possible to detect a photon with a smaller size and higher sensitivity.

  A. N. Cleland et al. Manufactured a device in which a light detection portion and SET as an amplifying element are connected to detect weak light having a wavelength of 650 nm (see Non-Patent Document 1 below). However, since this photodetector is manufactured by an electron beam lithography method, it is limited to an operation at an extremely low temperature of 20 mK and is difficult to operate at room temperature. Further, the photodetection device has a complicated structure, and is difficult to mass-produce and integrate.

  Also, S. Komiyama et al. Can detect photons of far-infrared light with a wavelength of 200μm by amplifying the charge polarization caused by photons incident on a minute conductor into a macroscopic current by the action of SET. (See Non-Patent Document 2 below). However, in order to cause charge polarization, application of a strong magnetic field is essential, and the wavelength range of photons that can be measured is limited to around 200 mm. In addition, since the structure of the apparatus is complicated, the fabrication method using the lithography technique has a limit on miniaturization of elements, and is limited to operation at an extremely low temperature of 0.4K.

  Takada et al. Produced a self-polarizing quantum dot by combining a titanium oxide fine particle and a light absorber such as an organometallic complex without applying an external electric field, and set the light with a wavelength of 540 nm incident on the quantum dot at room temperature. (See Patent Document 1 below). By using fine particles as quantum dots, high-sensitivity detection is achieved with a simple structure, but the electrodes need to be placed precisely by electron beam lithography, which is expensive and not suitable for mass production. . In addition, since the light receiving part is limited to a minute region between the source and drain electrodes, it is expected that a device for condensing incident light on the light receiving part is required for highly sensitive measurement.

As described above, the conventional photodetection method using SET requires a severe operating environment such as extremely low temperature or in a strong magnetic field, has a complicated structure, and has a small light receiving part. was there.
"Very low noise based on the single electron transistor", Appl. Phys. Lett., Vol. 61, 1992, 2820-2822 `` A single-photon detector in the far-infrared range '', Nature, Vol.403, 2000, 405-407 Japanese Patent Laid-Open No. 2003-243692

  An object of the present invention is to solve the above-mentioned problems and to provide a photon detection device capable of detecting ultra-weak light at room temperature, having a wide light receiving area, and capable of being easily manufactured and integrated. And

  It is an object of the present invention to dispose metal fine particles two-dimensionally through an insulating layer between two upper and lower electrodes, which are transparent electrodes, and are covered with an insulating film so as to be adjacent to the metal fine particles. This is achieved by realizing a configuration in which the semiconductor fine particles are arranged.

  A bias voltage is applied between the upper and lower electrodes in order to separate electron-hole pairs generated by photons incident on the semiconductor fine particles and to generate a tunnel current via the metal fine particles between the electrodes.

  The present invention has a configuration in which single electron transistors (hereinafter referred to as “SET”) having a common source electrode and drain electrode are connected in parallel two-dimensionally. The upper and lower electrodes are the drain and source electrodes, respectively, and the semiconductor fine particles are the gate electrodes.

SET has a structure in which a source and a drain electrode are tunnel-joined at both ends of a minute conductor (island electrode), and a gate electrode is installed at a position where no tunnel coupling occurs in the vicinity of the island electrode. When the voltage applied to the gate electrode is 0, if the voltage applied between the source and drain is less than e / 2C (e: elementary charge, C: capacitance of the entire island electrode), one island electrode Unless thermal energy kT (k: Boltzmann constant, T: absolute temperature) corresponding to the increase in electrostatic energy e ² / 2C due to tunneling to the outside is provided from outside, electrons are prohibited from tunneling. This is called the Coulomb blockade phenomenon. In order to develop Coulomb blockade at room temperature, C must be made minute, that is, the area of the tunnel junction between the island electrode and the source and drain must be about 10 nm square. When a positive voltage is applied to the gate electrode in the Coulomb blockade state, the electrostatic energy of the tunnel junction is (-ne + CgVg) ² / 2C (n: number of electrons present in the island electrode, Cg: gate capacitance, Vg: gate voltage), and when CgVg = e / 2, 3e / 2, 5e / 2, ..., the electrostatic energy is n = N, N + 1 (N = 0, 1, 2, ...) Because it is minimized, the Coulomb blockade is broken and a tunnel current flows between the source and drain. That is, the current between the source and the drain can be controlled by applying a weak voltage enough to attract several electrons to the gate electrode.

  In the present invention, the holes that are generated by the incidence of photons on the semiconductor fine particles and drift to the lower side of the semiconductor fine particles due to the electric field applied between the upper and lower electrodes attract the charges in the adjacent metal fine particles. Electrons tunnel through the fine metal particles to the drain electrode, and current flows. By measuring this current, photons can be detected.

  According to the present invention, when a photon is incident on any one of a large number of two-dimensionally arranged semiconductor fine particles, it can be detected as an electric current, so that a light receiving surface can be widened and an optical for condensing incident light. It is possible to detect photons with high sensitivity without using any parts.

  Since the structure of the present invention is a structure in which an insulating layer between electrodes is formed of alkanethiol or a polymer material, and metal and semiconductor fine particles are arranged in a self-organized manner, an easy manufacturing method that does not require semiconductor processing or the like Is provided.

  The structure formed by metal fine particles, semiconductor fine particles, and insulating layers is uniformly formed between the upper and lower electrodes, so the area of the light-receiving surface can be arbitrarily formed, and can be formed on curved surfaces as well. It is.

  By arranging either one of the upper and lower electrodes in an array, a two-dimensional array of elements can be produced, and the incident position of a photon can be detected.

  Embodiments of a photon detector according to the present invention will be described below with reference to the drawings. 1 is a cross-sectional view of the element, and FIG. 2 is an equivalent circuit diagram of FIG.

  A method of manufacturing a photon detector according to the present invention will be described with reference to FIG. First, the insulating layer 102 is formed on the metal substrate 101. On the insulating layer, the metal fine particles 103 whose surfaces are covered with the insulating film 104 are fixed so that they are scattered without being in close contact with each other. The total thickness of the insulating layer on the metal substrate and the insulating layer on the surface of the metal fine particles is set to several nm or less so that electron tunneling easily occurs. The diameter of the metal fine particle is set to about 1 to 20 nm so that the electrostatic energy that changes when one electron tunnels through the tunnel junction with the upper and lower electrodes is comparable to the thermal energy at room temperature. Thereafter, the semiconductor fine particles 105 whose surfaces are covered with the insulating film 106 are arranged on the insulating layer on the metal substrate so as to be adjacent to the metal fine particles. The film thickness of the insulating film on the surface of the semiconductor fine particles is such that electron-hole pairs generated by photons are held inside without tunneling to the outside of the semiconductor fine particles, and in the metal fine particles adjacent to the generated holes. 10-20 nm is preferable so that an electrostatic interaction may easily act between these electrons. The diameter of the semiconductor fine particles is preferably about 2 to 3 times the diameter of the metal fine particles. Subsequently, in order not to cause direct tunneling of electrons from the metal substrate to the upper transparent electrode, which will be described later, it is desirable that the insulating layer on the metal substrate has an insulation of preferably 10 nm or more in a region where the metal particles and the semiconductor particles are not deposited. Layer 107 is deposited. Finally, a transparent electrode 108 is deposited on the top of the device.

Semiconductor fine particles are substances that have the effect of forming electron-hole pairs when irradiated with light, such as intrinsic semiconductors such as Si and Ge, GaAs, GaP, CdS, ZnS, ZnSe, CdSe, InP, InSb, PbS. III-V, II-VI, I-VII, I-III-VI, II-IV-V semiconductors such as PbSe, TiO ₂ , ZnO, etc., but corresponding to the wavelength of photons to be detected It is not limited to these as long as it has an energy gap smaller than the energy to be applied.

  When charge separation in the semiconductor is low efficiency, by bonding a metal complex dye or organic dye to the surface of the semiconductor fine particles, the electrons photoexcited by these dyes immediately move to the conduction band of the semiconductor. Stays in the dye, so that more efficient charge separation can be achieved. As a method for bonding the dye, the dye is automatically bonded to the surface of the semiconductor fine particles simply by mixing the semiconductor fine particles into the dye solution.

  Examples of the metal fine particles include metals composed of Group VIa to IVb elements such as gold, silver, copper, platinum, palladium, ruthenium, rhodium, iridium, osmium, iron, nickel, chromium, tin, aluminum, lead, and alloys thereof. However, gold that can easily control the size of the fine particles and can easily cover the self-assembled film of alkanethiol described later is particularly preferable.

As the upper and lower electrodes, the metal electrodes are the same as the above metal fine particles, such as gold, silver, copper, platinum, palladium, ruthenium, rhodium, iridium, osmium, iron, nickel, chromium, tin, aluminum, lead, etc. Examples thereof include metals composed of elements and alloys thereof, and gold that can easily cover an alkanethiol self-assembled film described later is particularly preferable. For transparent electrodes, ZnO, SnO ₂ , In ₂ O ₃ doped with Al ³⁺ , Sb ⁵⁺ , Sn ⁴⁺ respectively to make an n-type semiconductor can be used, but the transmittance with respect to the wavelength of the photon to be detected Higher one is desirable.

Examples of the insulating layer on the metal electrode and the surface of the metal fine particle include a self-assembled film of a molecule having thiol or disulfide, a polymer thin film, an oxide film such as SiO ₂ , Al ₂ O ₃ , ZrO _2, etc. Alkanethiol self-assembled films are preferred because they are easy to control and form. Examples of the insulating layer on the surface of the semiconductor fine particles include the above-mentioned examples. However, since a thickness of about 10 nm or more is required, a polymer alternating laminated film is preferable.

(Operation) The operation of the present invention will be described with reference to FIG. When photons having energy equal to or greater than the energy gap of the semiconductor fine particles are incident on the semiconductor fine particles 203, electron-hole pairs are generated by the photoelectric effect. Due to the voltage applied to the upper and lower electrodes, electrons separate upward and holes separate downward to drift. The holes that have moved downward in the semiconductor fine particles attract the electrons in the metal fine particles, and the electrons move from the metal substrate 201 through the metal fine particles to the transparent electrode 202 according to the SET operating principle, so the holes between the upper and lower electrodes Current flows.

  Examples of production and evaluation of a photon detection device according to the method of the present invention will be described below.

(1) Preparation of self-assembled film-coated gold fine particles In this example, gold fine particles were used as the metal fine particles. G. Tsutsui (Jpn. J. Appl. Phys., Vol. 40, 2001, 346-349) et al. 50 μl of an approximately 11 nm diameter gold colloid solution (1 mg / ml) prepared with 0.5 mM N- The solution was dropped into 4 ml of Fmoc-Aminohexanethiol / N, N-dimethyl formamide (DMF) solution, stirred and allowed to stand for 24 hours to form a self-assembled film of N-Fmoc-Aminohexanethiol on the surface of the gold fine particles. Add 1 ml piperidine and let stand for 1 hour to deprotect Fmoc, then replace DMF with water and remove unreacted Aminohexanethiol by repeating 35,000 xg for 30 minutes three times to obtain the final volume. 0.88 ml.

(2) Preparation of polymer alternate layer-coated titanium dioxide fine particles In this example, titanium dioxide (TiO ₂ ) fine particles were used as semiconductor fine particles. After adding 0.2 ml of 10% Acetylacetone aqueous solution of chelating agent to 0.6 g of titanium dioxide fine particles (Degussa P25) with a diameter of about 25 nm, grind it in a mortar, add 60 ml milli-Q water, and perform ultrasonic treatment for 1 hour with an ultrasonic cleaner Centrifugation was performed at 4000 × g for 15 minutes to remove the precipitate, thereby preparing a titanium dioxide colloidal solution. Add 30ml / ml poly (sodium 4-styrenesulfonate) (PSS) / 1M NaCl solution 1ml to this colloidal solution, sonicate with ultrasonic cleaner for 1 hour, then centrifuge at 30000 × g for 30 minutes and remove the supernatant. Removed and redispersed with Milli-Q water. This washing operation by centrifugation was performed three times. As a result, TiO ₂ fine particles whose surface was coated with PSS were produced. To this colloidal solution, 1 ml of 30 mg / ml poly (allylamine hydrochloride) (PAH) / 1M NaCl solution was added, and TiO ₂ fine particles whose surface was coated with PSS / PAH were prepared in the same manner. This series of operations was alternately performed for PSS and PAH, and TiO ₂ fine particles were coated with a five-layer film of PSS and PAH. The diameter of the fine particles was determined to be about 58 nm by the dynamic light scattering method.

(3) Production of Photodetector In this example, gold was used as the metal substrate, Indium Tin Oxide (ITO) was used as the transparent electrode, and alkanethiols were used as the insulating layer. Gold was deposited at 330 ° C. by sputtering on a glass substrate (Corning 7059) with a chromium adhesive layer in between. The film thicknesses of chromium and gold were 300 nm and 450 nm, respectively. After the gold thin film was formed, heat treatment was performed with a gas burner.

The gold substrate was immersed in 20 ml of 1 mM carboxy-pentanethiol / ethanol solution at 60 ° C. for 2 hours, and then immersed at room temperature for about 100 hours to form a self-assembled film of carboxy-pentanethiol on the gold substrate. The gold substrate was immersed in a phosphate buffer solution (pH7.5), (1) a was prepared by the process self-assembled film-coated gold colloid solution ^{0.17ml, 10 -12 mol N-hydroxysuccinimide} (NHS), 2 × 10 - ¹² mol 1- [3- (Dimethylamino) propyl] -3-ethylcarbodiimide (EDC) was added, and the amino group of the self-assembled film formed on the surface of the gold fine particles and the self-assembled film formed on the gold substrate surface A carboxyl group was attached. After 24 hours, 0.1 mmol NHS and 0.2 mmol EDC were added to activate all carboxyl groups on the gold substrate. After 1 hour, 1 ml of the TiO ₂ colloid solution prepared in the step (2) diluted to 0.17 g / l was added to a gold substrate washed with water and immersed in milli-Q water, and washed with water after 24 hours. The TiO ₂ fine particles are expected to be disposed adjacent to the gold fine particles due to electrostatic interaction between the negative charge of the outermost PSS and the positive charge of the amino group on the gold fine particle surface. The gold substrate was immersed in a 1 mM amino-undecanethiol aqueous solution for 64 hours to form a self-assembled film in the gap between the gold and TiO ₂ fine particles.

A self-assembled film and fine particles fixed on the above gold substrate are formed by sputtering so as to partially cover the SiO ₂ insulating film, and the ITO film slightly protrudes from the SiO ₂ film thereon. Thus, it was formed by sputtering. This protruding portion becomes the light detection portion, and the area is about 0.2 mm ² .

(4) Evaluation of photon detector
A function generator (HP 33120A) and a multimeter (HP 3458A) were connected in series to the gold and ITO electrodes of the photon detection device fabricated in (3), and the change in current when the applied voltage was changed was measured. Changes in current were measured when light was irradiated for a certain period of time at a certain voltage and with several light intensities.

  FIG. 3 shows the results of measuring the current-voltage characteristics between the source and drain under no light irradiation. In the configuration of this example, the electron tunnel path portion of the gold fine particle-alkanethiol insulating film-ITO electrode has a structure of a MIS (Metal-Insulator-Semiconductor) diode, and current is difficult to flow in the case of a positive voltage. Coulomb blockade appeared only in the case of negative voltage. Irradiation excites the valence electrons in the ITO and breaks this rectifying action. When gold was vapor deposited instead of the ITO electrode and used as an electrode, Coulomb blockade was observed at voltages in both directions as shown in (b), confirming that the gold fine particles functioned as quantum dots.

FIG. 4 shows an example in which a change in current when light is irradiated at a bias voltage of 0.5 V is measured. The light irradiation was continued until there was almost no change in the current value. Measurements are made with three types of incident light intensity, and the UV intensity is approximately 4 × 10 ⁹ , 3 × 10 ⁵ , and 6 × 10 ² per second in terms of the number of photons incident on the light receiving surface. . The relationship between the number of incident photons and the maximum value of the current is as shown in FIG. 5, and it was confirmed that measurement was possible in a wide range of incident light intensities. In this example, up to about 10 ³ photons could be detected per second.

  It can be used in a technical field that requires detection of a single photon, or in a technical field that requires detection of extremely weak light.

Conceptual illustration of a photon detector according to the present invention 1 is an equivalent circuit diagram of the photon detector of FIG. Current-voltage characteristics between source and drain under non-light irradiation Measurement diagram of change in current when irradiated with light at a bias voltage of 0.5V Relationship between the number of incident photons and the maximum current

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Metal substrate 102 Insulating layer 103 Metal fine particle 104 Insulating layer 105 Semiconductor fine particle 106 Insulating layer 107 Insulating layer 108 Transparent electrode 201 Metal substrate used as a source electrode 202 Transparent electrode used as a source electrode 203 Semiconductor fine particle

Claims (12)

In the photon detector, at least one of the transparent electrodes is a two-dimensional arrangement of metal fine particles covered with an insulating film between two upper and lower electrodes through an insulating layer and insulated so as to be adjacent to the metal fine particles. By arranging the semiconductor fine particles covered with the film, the holes generated by the incidence of photons on the semiconductor fine particles and drifting downward under the semiconductor fine particles due to the electric field applied between the upper and lower electrodes are adjacent to the metal fine particles. A photon detector for detecting a photon by measuring that an electric current flows when one of the electrodes passes through the metal fine particles and flows into the other electrode .   The photon detector according to claim 1, wherein a bias voltage is applied between the upper and lower electrodes.   2. The photon detector according to claim 1, wherein the upper and lower electrodes are drain or source electrodes, respectively, and the semiconductor fine particles are gate electrodes.   2. The photon detector according to claim 1, wherein the semiconductor fine particles have an energy gap smaller than energy corresponding to a wavelength of a photon to be detected. The semiconductor fine particles include gallium arsenide (GaAs), gallium phosphide (GaP), cadmium sulfide (CdS), indium phosphide (InP), indium gallium arsenide (InGaAs), gallium indium nitrogen arsenide (GaInNAs), and zinc oxide (ZnO). The photon detector according to claim 1, wherein the photon detector is titanium oxide (TiO ₂ ).   6. The photon detector according to claim 5, wherein a dye is bonded to the surface of the fine particle.   The metal fine particle is gold, silver, copper, platinum, palladium, ruthenium, rhodium, iridium, osmium, iron, nickel, chromium, tin, aluminum, lead, or an alloy thereof. Photon detector.   The metal electrode is gold, silver, copper, platinum, palladium or ruthenium, rhodium, iridium, osmium, iron, nickel, chromium, tin, aluminum or lead, or an alloy thereof. Photon detector. The transparent electrode is an n-type semiconductor in which zinc oxide (ZnO), tin oxide (SnO ₂ ), or indium oxide (In ₂ O ₃ ) is doped with Al ³⁺ , Sb ⁵⁺ , and Sn ⁴⁺ , respectively. The photon detector according to claim 1.   2. The photon detection according to claim 1, wherein the insulating layer on the metal electrode and the insulating film on the surface of the metal fine particle are a self-assembled film, a polymer thin film, or an oxide film of a molecule having thiol or disulfide. vessel. The photon detector according to claim 9, wherein the oxide film is silicon oxide (SiO ₂ ), aluminum oxide (Al ₂ O ₃ ), or zirconium oxide (ZrO ₂ ). The metal fine particles covered with the insulating film are two-dimensionally arranged on the metal electrode through the insulating layer, and the semiconductor fine particles covered with the insulating film are arranged so as to be adjacent to the metal fine particles. A method of manufacturing a photon detector coated with a conductive film, wherein the semiconductor fine particles are fixed so as to be adjacent to the metal fine particles after the metal fine particles are fixed on the metal electrode. Manufacturing method of the detector.

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