JPH0216421A - Photodetector - Google Patents

Abstract

PURPOSE:To detect ultrafaint light by providing an electroluminescence body in contact with a photosensitive layer impressing a specified voltage between said body and said layer so that the wavelength of light made incident on the photosensitive layer is converted, detecting the light emission of said electroluminescence body and photoelectrically converting it. CONSTITUTION:The photosensitive layer 3 and the electroluminescence layer 2 are closely laminated and the electrostatic voltage V is impressed between transparent conductive films 4 and 1 which hold both sides of said layers between them so as to form a wavelength conversion part 5, then the wavelength hupsilon2 of incident light is converted into the wavelength hupsilon2. By making a photoelectric conversion part 6 abut on the transparent conductive film 1 and irradiating a photoelectric conversion film 9 with the light of the wavelength hupsilon2, a photoelectron is emitted into a glass tube. The photo-electron is multiplied in a dynode group 10 consisting of plural dynodes formed in the glass tube 8 and gathered in an anode 11 so as to obtain an output current. Thus, the ultrafaint light of near infrared light, which can not be detected by a photomultiplier tube, can be detected. The title photodetector becomes appropriate to detect the light emission of the living or chemical light emission.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a weak light detection device.

2. Description of the Related Art As an example of a conventional weak light detection device, the most sensitive photodetector in existence is a photomultiplier tube.

FIG. 4 shows a sectional view thereof. When the photocathode 50 is irradiated with light, photoelectrons are emitted into the vacuum region 51. The emitted photoelectrons are accelerated by the electric field generated by the first dynode 52 to which a voltage of about 100V is applied, and enter the first dynode 52, where a(3-6) secondary electrons are emitted.

These secondary electrons are now accelerated to the second dynode 53,
Collision and release 32 secondary electrons. This process is repeated until the kth stage has ak pieces (usually 106 pieces). These electrons are collected at the anode 54 and become an output current.

Typical materials for the photocathode 50 include, for example, CsCs-1 (115-200n,
Ag-0-Cs (400-1200nm), Na-8b-Cs (multialkali) (300-850n
m), GaAs (Cs) (300-910 nm), etc. The highest radiation sensitivity of these is 6060-8O/
It is W.

The photocathode can emit photoelectrons from the incident light (energy hν
) is defined by the sum Eg+χ of the band gap Eg of the photoelectron emitting material and the electron affinity χ. That is, light with hv≦Eg1χ cannot be detected.

Conventionally, photoelectric materials that can detect up to the longest wavelength range have been negative electron affinity materials (NBA materials). In this method, a monoatomic layer of Cs-0 is adsorbed onto the clean surface of a given semiconductor single crystal, creating band curvature on the surface, and the vacuum level is lower than the bottom of the conduction band (effectively is in a negative electron affinity state (NEA state).Currently, the negative electron affinity material (NBA material) in practical use is GaAs.
(Cs), but the bandgap Eg of GaAs is 1
．． 4 eV, and its detection limit on the long wavelength side is 910 nm.

Among the infrared detectors with longer wavelengths, the one with the highest sensitivity was the S1 avalanche photodiode. FIG. 5 shows its cross-sectional view.

The incident light is absorbed by the PN junction 55, which is reverse biased to a value close to the reverse breakdown voltage, and electron-hole pairs are generated within the depletion layer. These carriers, accelerated by the strong electric field in the depletion layer, bombard bound electrons one after another while traveling, and
Ionize. Such a mechanism occurs like an avalanche, and the current is multiplied.

However, its detection limit light intensity is about 104W. Further, the detection limit wavelength on the long wavelength side is 11050n.

Problems to be Solved by the Invention On the other hand, in recent years, there has been an increasing need for ultra-weak light sensors in the near-infrared region, for example. An example of this is a technique that attempts to capture extremely weak near-infrared chemiluminescence from living organisms.

However, none of the existing near-infrared light sensors have the sensitivity to detect these extremely weak lights.

Means for Solving the Problems In order to detect ultra-weak light of a predetermined wavelength, a photoreceptor layer having photosensitivity in that wavelength range, an electroluminescent body configured inside or in contact with the photoreceptor layer, and the aforementioned A photodetector comprising a wavelength converting section composed of a photoreceptor and an electrode provided so as to apply a predetermined electric field to the electroluminescent body, and a photoelectric conversion section that detects light emission from the electroluminescent body and converts it into an electric signal. Form a vessel. The electroluminescent body is made of a material that emits light at a wavelength to which the photoelectric conversion section has high sensitivity.

Operation A predetermined electric field is applied to the photoreceptor layer having sensitivity in a predetermined wavelength range and the electroluminescent body formed inside or in contact with the photoreceptor layer by an electrode pair provided close to the photoreceptor layer. The photoelectric conversion section is provided at a position where light emission from the electroluminescent body can be detected. The photoelectric conversion part material and the electroluminescent material are selected so that the photoelectric conversion part has a highly sensitive photoelectric conversion efficiency in the emission wavelength region of the electroluminescent material.

When light with a predetermined wavelength λ1 is incident on the photoreceptor layer, it is absorbed by the photoreceptor layer, and electron-hole pairs are generated.

These photocarriers drift due to the applied electric field.

Among the photocarriers, the electrons injected into the electroluminescent body are accelerated by the applied high electric field, obtain high energy, and collide with the base body of the electroluminescent body itself or an impurity center (luminescence center) therein. , ionizes this. The electrons generated at this time repeatedly collide one after another, producing new electron-hole pairs like an avalanche. Then, light is emitted by recombination of electron-hole pairs captured at the impurity center.

Alternatively, hot electrons collide with the luminescent center ion and excite its core electrons. Then, light is emitted due to core electron transition from the excited state of the luminescent center to the ground state.

The above electroluminescence (wavelength λ2) is received by the photoelectric conversion section, photoelectrically converted using a predetermined means, multiplied, and converted into an electric signal.

Embodiment An embodiment of the present invention is shown in FIG. This is a cross-sectional view of a high-sensitivity near-infrared photodetector in one embodiment of the present invention. Transparent conductive film 1, light emitting layer 2, photosensitive layer 3, and transparent conductive film 4
A wavelength conversion section 5 in which the photoelectric conversion section 6 is laminated is formed on the end face of the photoelectric conversion section 6 as shown in the figure.

As the photoelectric conversion section 6, a photomultiplier tube 7 is used in this embodiment. The photomultiplier tube 7 includes a photoelectric conversion film 9 formed on the inner surface of a glass tube 8, a group of dynodes 10 in several stages,
It consists of 11 anodes.

A predetermined electrostatic field is applied to the photosensitive layer 3 and the light emitting layer 2 by an electrode pair made of a transparent conductive film 1.4 as shown in the figure.

When light with a predetermined wavelength λ is incident on the photosensitive layer 3, it is absorbed by the photosensitive layer 3, and electron-hole pairs are generated.

Due to the applied electric field, these photocarriers drift electrons toward the light-emitting layer 2 and holes toward the transparent conductive film 4.

Among the photocarriers, the electrons injected into the light-emitting layer 2 are accelerated by the applied high electric field, obtain high energy, and collide with the matrix itself of the light-emitting layer 2 or the impurity center (light-emitting center) therein. , ionizes this. The electrons generated at this time repeatedly collide one after another, producing new electron-hole pairs like an avalanche. Then, light is emitted by recombination of electron-hole pairs captured at the impurity center. Alternatively, hot electrons collide with the luminescent center ion and excite its core electrons. Then, light is emitted due to core electron transition from the excited state of the luminescent center to the ground state.

The electroluminescence (wavelength λ2) from the light-emitting layer 2 is received by the photoelectric conversion film 9, and photoelectrons are emitted into vacuum using the external photoelectric effect. It is 106 with a group of 10 dynodes.
The signal is multiplied approximately twice as much, captured by the anode 11, and taken out as an electrical signal.

The photoelectric conversion unit 6 may be a photoelectric conversion element other than a photomultiplier tube as long as it is highly sensitive to light of wavelength λ2. As other embodiments of the photoelectric conversion section 6, other devices that utilize an external photoelectric effect or elements that utilize an internal photoelectric effect such as an avalanche photodiode may have similar effects.

The transparent conductive film 1.4 is a thin film such as ITO or metal mesh, and at least the transparent conductive film 1 has the electroluminescence (
The transparent conductive film 4 well transmits incident light (wavelength λ1). . The light emitting layer 2 is made of ZnS: Cu,
A L Z n S: M n, Z n S: Cut
CL ZnS: ZnS such as Mn, Cut, etc.
system, SrS: Ce, CaS: Ce,
Cab: Inorganic electroluminescent material represented by EU, etc.
Alternatively, it is an organic electroluminescent material typified by a metal chelate fluorescent material such as aluminum 8-hydroxyquinoline (hereinafter referred to as AIQ3), which emits visible light. The molecular structure of AIQa is as follows. (
For example, Tang (C, Tang) and VanSlyke (S, VanSlyke); Applied Physics Letter (Appl, Ph1s, Lett,)
51 (1987) 913P-915P). In this example, AIQa was used.

1q3 In this example, the photosensitive layer 3 is made of azulenium salt compound L-
(p-dimethylaminocinnamylidene)-5-inpropyl-3,8-dimethylazulenium iodine (hereinafter referred to as C
-GAZ-I) was used. The molecular structure of C-GAZ-I is as follows.

FIG. 2 shows its spectral sensitivity characteristics. C-GAZ-I has strong sensitivity in the near-infrared region. Other materials for the photosensitive layer 3 include organic photoreceptor materials such as phthalocyanine pigments such as α-titanyl phthalocyanine (αTi0Pc), azo pigments, and squalium salts, which have strong sensitivity in the near-infrared region. Also good.

The thickness of the light emitting layer 2 and the thickness of the photosensitive layer 3 are 2000A~
It is 1μ. On the other hand, the transparent conductive film 1.4 has a light emitting layer 2.
A bias voltage of several volts is applied so that the electric field applied to the photosensitive layer 3 is 10 6 to 10 7 V/m 2 .

As the photoelectric conversion film 9, GaAs (Cs) (300-9
10 nm) was used. This is Ag-0-Cs (40
0-1200 nm), Na--8b-C8 (fluoric alkali) (300-850 nm), etc. may also be used.

A sectional view showing the configuration of another embodiment of the present invention is shown in FIG. In this embodiment, the wavelength converter 5 includes the photosensitive layer 1 as shown in the figure.
It has a structure in which luminescent particles 16 are dispersed in 5. The luminescent particles 16 are fine powders made of an inorganic electroluminescent material or an organic electroluminescent material that emits visible light, similar to the embodiments described above.

Light with a wavelength λ1 is incident on the photosensitive layer 15 and absorbed, and the generated photocarriers drift toward the transparent conductive film 1, causing electrons to drift toward the transparent conductive film 1 and holes to drift toward the transparent conductive film 4 due to the applied electric field.

Some of the electrons that hit the luminescent particles 16 are injected into them and are accelerated by the applied high electric field, producing electroluminescence. The electroluminescence (wavelength λ2) from the luminescent particles 16 is photoelectrically converted and multiplied by the photomultiplier tube 7, and taken out as an electrical signal.

By measuring the signals from these photodetectors of the present invention using a single photoelectron counting method using a pulse height discriminator, it is possible to detect ultra-weak light in the near-infrared region, which is about a few photos and 77 minutes. became.

As described above, the present invention first converts incident light with a wavelength λ into light with a wavelength λ2 using a wavelength conversion unit comprising a photosensitive layer and a light emitting layer, and converts the incident light into light with a wavelength λ2. The photoelectric converter performs photoelectric conversion, multiplies the signal, and converts it into an electrical signal using an extremely sensitive photoelectric conversion unit. Therefore, for example, even for ultra-weak light in the near-infrared region for which conventional photodetectors could not obtain sufficient sensitivity, conventional charge conversion elements such as photomultiplier tubes can respond to light in the high-sensitivity wavelength range. By converting the wavelength and making it incident, extremely sensitive detection has become possible. Of course, as the material for the photosensitive layer 3.15, a photosensitive material having sufficient sensitivity to the wavelength of incident light is used.

For example, in this embodiment, a photoreceptor material having high sensitivity in the near-infrared region was used. In particular, many organic photoreceptor materials have high sensitivity in the near-infrared region, and are suitable as the photoreceptor material because they can be designed in such a manner.

Effects of the Invention The present invention has made it possible to detect ultra-weak light in the near-infrared region, which was impossible with conventional photodetectors such as photomultiplier tubes. This has made it possible, for example, to capture extremely weak chemiluminescence and bioluminescence.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the configuration of a photodetector in an embodiment of the present invention, FIG. 2 is a spectral sensitivity characteristic diagram of the organic photoreceptor material used in the embodiment, and FIG. FIG. 4 is a cross-sectional view showing the configuration of another embodiment of the photodetector of the invention. FIG. 4 is a cross-sectional view of a photomultiplier tube which is a conventional photodetector. FIG. 1 is a cross-sectional view of an avalanche photodiode. 2.5... Transparent conductive film, 3... Light emitting layer, 4... Photosensitive layer, 6... Wavelength conversion section, 7... Photoelectric conversion film, 9...
...Photoelectric conversion part, 16... Luminescent particle. Name of agent: Patent attorney Shigetaka Sangyo Haka1 person No. 1 (nm) Enumi Ozu

Claims (2)

[Claims] (1) A photoreceptor layer having photosensitivity in a predetermined wavelength range, and an electroluminescent body configured inside or in contact with the photoreceptor layer;
a wavelength conversion unit configured of an electrode provided to apply a predetermined electric field to the photoreceptor and the electroluminescent body;
A photodetector comprising a photoelectric conversion section that detects light emission from the electroluminescent body and converts it into an electric signal. (2) The photodetector according to claim 1, wherein a photoreceptor material having sensitivity in the near-infrared region is used as the material of the photoreceptor layer.