JP2011023399A - Organic-inorganic hybrid junction type photoelectric transducer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic-inorganic hybrid junction type photoelectric transducer of high sensitivity, which has signal gain G and has a visible-ultraviolet optical wave band having superior response and low dark current property such as a p-i-n or Schottky type. <P>SOLUTION: A basic junction structure is made into a p<SP>*</SP>-i-p (n<SP>*</SP>-i-n) symmetric junction structure formed of a p<SP>*</SP>(n<SP>*</SP>)-type organic semiconductor thin film being a hole transportation-type organic semiconductor thin film functioning as an emitter layer-cum-window layer of a hole, an i-type inorganic semiconductor photoelectric transducing layer being an inorganic semiconductor layer of low carrier concentration and high resistance, and a p(n)-type inorganic semiconductor collector layer from above an element. The organic-inorganic hybrid junction type photoelectric transducer applying bias voltage of DC or AC of several V to dozens of V is obtained. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an organic-inorganic semiconductor hybrid junction photoelectric conversion element that operates in the visible-ultraviolet light band and exhibits a significant signal gain.

<Conventional technology of light receiving element in hybrid structure of organic-inorganic semiconductor>
With the progress of EL light-emitting devices using organic semiconductor thin films, organic semiconductor thin film synthesis and thin film forming techniques have been advanced. The background of this technology is the steady development of hole transport or electron transport control in organic semiconductor thin films. The hole transport organic semiconductor thin film is referred to as “p ^* type”, and the electron transport organic semiconductor thin film is referred to as “n ^* type”.

  In the development of photovoltaic photoelectric conversion elements having an organic-inorganic hybrid structure, research on light-receiving elements using organic solar cells and all-organic semiconductor thin films has also progressed. On the other hand, research on organic-inorganic hybrid junction type photoelectric conversion elements has also made steady progress although it is in the basic research stage. In these conventional organic-inorganic semiconductor composite elements, the role of the organic semiconductor thin film is utilized as a transparent organic conductive thin film rather than a semiconductor function, and a Schottky junction with an inorganic semiconductor is often used.

  That is, in the organic-inorganic composite element, the role of the organic thin film plays the role of excellent permeability as a window layer and good Schottky junction with the inorganic semiconductor. In fact, in recent years, good Schottky contact (rectification) due to contact between an organic conductive thin film that is transparent in the ultraviolet-visible range and a wide gap compound semiconductor has been found, and organic semiconductors such as ZnO and inorganic using this A wide-gap semiconductor Schottky junction type ultraviolet light-receiving element has also been proposed by a research group of Tohoku University (see, for example, Patent Document 1).

The semiconductor light-receiving element that operates on the principle of the above-mentioned organic-inorganic semiconductor Schottky junction replaces an inorganic semiconductor window layer having a large absorption loss, for example, a p ⁺ window layer with an organic semiconductor thin film having a low absorption loss, and applies an external bias. The operation is performed using the high electric field / depletion layer region formed at the Schottky junction interface formed in step (b).

  In other words, the conventional organic-inorganic hybrid light receiving element can be said to be a Schottky type light receiving element in which a normal Schottky junction at the metal-semiconductor contact is replaced with a transparent organic / thin film.

A problem of the organic-inorganic semiconductor Schottky junction type light-receiving element proposed so far is that no signal gain G of current is generated. That is, the limit value of the external quantum efficiency η _ex that governs the light receiving sensitivity of the Schottky junction type organic-inorganic composite light receiving element, as in the case of a conventional p-i-n light receiving element made of an inorganic semiconductor. However, even if the absorption and reflection loss of the organic window layer are completely controlled, η _ex <100%.

<Principle and problem of conventional semiconductor photo detector with signal gain>
In order to dramatically improve the light receiving sensitivity, a signal multiplication type light receiving element exceeding the upper limit of the quantum efficiency of 100% is required, but a photovoltaic type semiconductor light receiving element that expresses this signal gain G is required. There are pnp type or npn type phototransistor elements and avalanche multiplication type APD elements composed of inorganic semiconductors such as Si, Ge, and the like.

  The junction structure of the phototransistor type light receiving diode by Si or the like is a p-n-p junction or an n-p-n junction. The operating principle of the npn type is that electrons that are minute minority carriers are injected into the base region by light incident from the outside of the device, and these electrons flow from the base layer to the emitter side due to the diffusion effect, and at the same time increase. The doubled hole current flows from the emitter into the base, passes through the base layer while diffusing, and generates a large current toward the collector. A so-called bipolar transistor current multiplication operation is used.

  However, these phototransistor type light receiving elements such as Si and Ge generate a signal gain G, but the biggest drawback is that the operation speed is slow. In addition, there are disadvantages such as a large dark current and a low S / N ratio in high-speed response. The fact that the device response speed is extremely slow compared to the p-i-n or Schottky type is due to the operating mechanism of the phototransistor device, which is an essential drawback, and their applications are limited. Limited.

  As is well known, the biggest factor that determines the response speed of npn phototransistors, for example, is the speed at which carriers such as electrons generated in the base layer move to the emitter layer due to excitation by light, and the multiplication factor. This is because the moving speed of holes flowing from the emitter layer through the base layer to the collector layer is limited by the diffusion speed in the base layer. In order to reduce this problem as much as possible, the base layer has been designed to be as thin as possible and the impurity concentration has been given a gradient. However, the improvement is limited to a few MHz. ing. In addition, as described above, the problem that the dark current governing the S / N of the light receiving element is large has not been overcome.

<APD type semiconductor light receiving element>
As another photovoltaic-type semiconductor light-receiving element that exhibits signal gain, there are APD elements such as Si and Ge. In this device, a DC bias of 200 V or higher is applied, the electric field strength of the photoelectric conversion layer is increased to an electric field strength (> 10 ⁶ / cm) at which avalanche multiplication occurs, and the photocurrent signal is avalanche multiplied by 2-3 digits. It is operated by multiplying. However, the problem of this APD element having this multiplication function is that it has a higher operating voltage than that of a p-i-n element or a Schottky element operated at several volts to several tens of volts, and the manufacture of the APD element. The process requires complicated processes such as the formation of a buried guard ring to prevent discharge and dark current, and the integration of elements is not easy and the cost is high. It is limited to special applications such as part of the system and scientific light measurement field.

  As described above, devices such as the pin structure, the Schottky structure, the APD structure, and the phototransistor each have advantages and disadvantages, and are designed and manufactured to the limit value of each characteristic. ing. The problem of the semiconductor light-receiving element having the signal gain G is the development of a new element that does not reduce the signal gain G and enables high-speed response, integration, low cost, and the like. -An inorganic hybrid junction type semiconductor light-receiving element.

JP 2008-211203 A

  The subject of the present invention is a highly sensitive organic-inorganic light-wave band having a signal gain G, excellent response such as p-i-n and Schottky type, and low dark current characteristics. A hybrid junction photoelectric conversion element is provided.

In the organic-inorganic hybrid junction photoelectric conversion element of the present invention, the basic junction structure is formed from the upper part of the element with a p ^* type organic semiconductor thin film that is a hole transport type organic semiconductor thin film that functions as a hole emitter layer and window layer. As a p ^* -i-p symmetrical junction structure comprising an i-type inorganic semiconductor photoelectric conversion layer, which is an inorganic semiconductor layer having a low carrier concentration and high resistance, and a p-type inorganic semiconductor collector layer, a direct current of several V to several tens of V Alternatively, the signal gain of the photocurrent is expressed by applying an alternating bias voltage.

In the organic-inorganic hybrid junction photoelectric conversion element of the present invention, the basic junction structure is an n ^* -type organic semiconductor thin film that is an electron transport type organic semiconductor thin film that functions as an electron emitter layer and window layer from the top of the element. And an n ^* -i-n symmetric junction structure comprising an i-type inorganic semiconductor photoelectric conversion layer, which is an inorganic semiconductor layer having a low carrier concentration and a high resistance, and an n-type inorganic semiconductor collector layer. By applying a direct current or alternating current bias voltage, the signal gain of the photocurrent is expressed.

  Furthermore, in the organic-inorganic hybrid junction photoelectric conversion element of the present invention, by changing the application direction of the bias voltage, the signal multiplication type light-receiving characteristic mode that generates the signal gain of the photocurrent and the normal that does not generate the signal gain. Another feature is that the PIN type light receiving characteristic mode can be selected.

Further, in the organic-inorganic hybrid junction photoelectric conversion element of the present invention, the basic junction structure is formed from the top of the element, a transparent p ^* type organic semiconductor thin film that is a hole transport type organic semiconductor thin film, and a low carrier concentration and high resistance. An n-type wide gap inorganic semiconductor layer, a p ^* -i-n junction as an n-type wide gap inorganic semiconductor layer, or a transparent n ^* -type organic semiconductor thin film that is an electron transport type organic semiconductor thin film; High resistance i-type wide gap inorganic semiconductor layer and p-type wide gap inorganic semiconductor layer n ^* -i-p junction. By applying DC bias voltage to this basic junction structure, carrier avalanche multiplication type signal Gain was expressed.

  Further, an integrated light receiving element in which a plurality of the organic-inorganic hybrid junction type photoelectric conversion elements are formed on the same semiconductor substrate in a linear or planar manner at a predetermined interval, and the whole is covered with an antireflection film or a protective film. And the organic-inorganic hybrid junction photoelectric conversion element or the integrated light receiving element, and a high-efficiency scintillation material that converts high-energy radiation such as deep ultraviolet rays, X-rays, and gamma rays into the ultraviolet region and the visible light region. This is an all-solid-type deep ultraviolet and radiation high-speed and high-sensitivity detection device that does not use a photomultiplier tube constructed by combining the above.

  ADVANTAGE OF THE INVENTION According to this invention, the highly sensitive organic-inorganic hybrid junction type photoelectric conversion element of the visible-ultraviolet light wave band which has the signal gain G, was equipped with the outstanding responsiveness and low dark current property can be provided. .

It is a cross-sectional schematic diagram of the organic-inorganic hybrid junction type photoelectric conversion element which concerns on this invention. It is a cross-sectional schematic diagram of the organic-inorganic hybrid junction type photoelectric conversion element of 1st Embodiment. It is a graph of the sensitivity spectrum of the organic-inorganic hybrid junction type photoelectric conversion element of 1st Embodiment. It is a cross-sectional schematic diagram of the organic-inorganic hybrid junction type photoelectric conversion element of 2nd Embodiment. It is a cross-sectional schematic diagram of the organic-inorganic hybrid junction type photoelectric conversion element of 3rd Embodiment. It is a cross-sectional schematic diagram of the organic-inorganic hybrid junction type photoelectric conversion element of 4th Embodiment. It is explanatory drawing of the operation principle of the organic-inorganic hybrid junction type photoelectric conversion element of 4th Embodiment. It is a graph which shows the measurement result of the dark current of the organic-inorganic hybrid junction type photoelectric conversion element of 4th Embodiment. It is a graph of the sensitivity spectrum of the organic-inorganic hybrid junction type photoelectric conversion element of 4th Embodiment. It is a cross-sectional schematic diagram of the organic-inorganic hybrid junction type photoelectric conversion element of 5th Embodiment. 1 is a schematic diagram of a radiation detection apparatus according to the present invention. It is a graph of the measurement result of the X-ray-spectral spectrum of the ZnSSe crystal thin film measured with the radiation detector concerning the present invention. It is a cross-sectional schematic diagram of the integrated light-receiving element according to the present invention.

  In order to overcome the above problems, the organic-inorganic hybrid junction photoelectric conversion element of the present invention is roughly classified into two new methods.

  One of them is a technique in which a conventional phototransistor having a signal gain G due to Si or the like, or a light-receiving element having a multiplication function similar to that is composed of an organic-inorganic hybrid junction. Therefore, it is necessary to change the role of the organic semiconductor thin film in the light receiving element in the conventional organic-inorganic hybrid configuration, that is, the low resistance window layer, the organic Schottky junction, the element protective layer, and the like.

In particular, in the present invention, a junction structure is formed in which the function of the organic semiconductor thin film functions as a carrier / emitter to the active layer or the collector layer of the inorganic semiconductor that forms the organic semiconductor thin film. For this purpose, the junction structure is a symmetric p ^* -i-p structure or n ^* -i-n structure, and n layer, which is an intermediate base layer in the conventional pnp structure, or p, which is an intermediate base layer in the npn structure. The layer is composed of an extremely high resistance i layer.

Here, the i layer corresponding to the n layer in the pnp structure is composed of an n ⁻ -type intrinsic semiconductor layer having a low carrier concentration of 1 × 10 ¹⁶ / cm ³ or less, thereby increasing the resistance. Similarly, the i layer corresponding to the p layer in the npn structure is formed of a p ⁻ -type intrinsic semiconductor layer having a low carrier concentration of 1 × 10 ¹⁶ / cm ³ or less and has a high resistance.

These organic-inorganic hybrid symmetric junction structures such as p ^* -i-p structure or n ^* -i-n structure generate a signal gain G that is characteristic of conventional inorganic semiconductor phototransistors, It was verified that the junction structure enables high-speed response, which was a problem with conventional phototransistors.

The reason why the p ^* -i-p structure or the n ^* -i-n structure with such an organic-inorganic hybrid structure exhibits high-speed response is that the base layer is formed of a high-resistance i layer. This high-resistance i layer corresponds to the base layer serving as a photoactive layer, and a high electric field can be applied to the photoactive layer by a bias voltage of several tens to several tens of volts from the outside of the device. Carriers generated by being excited can be accelerated by an electric field instead of diffusion and moved at high speed.

As will be described in detail in the experimental examples, wide-gap compound semiconductors such as Si, ZnSSe, GaN, and ZnO are selected as the inorganic semiconductors constituting the i layer to be the photoactive layer, and the organic semiconductor thin film is visible-ultraviolet and transparent. The following excellent light-receiving characteristics have been demonstrated in a light-receiving element having a p ^* -ip junction structure using PEDOT (trade name), which is a hole-transporting p ^* -type semiconductor.

(1) Generates a large photocurrent signal gain G ranging from one to three digits by functioning as a pseudo bipolar transistor under DC or AC bias conditions of several volts to several tens of volts. Works with.
The signal multiplication function in an organic-inorganic hybrid junction transistor is thought to be similar to that of an inorganic semiconductor. However, in order to clarify the exact signal multiplication mechanism, further basic research on organic-inorganic hybrid junction elements is needed. It seems necessary.
(2) The dark current of the light receiving element was several pA / mm ² to several tens of nA / mm ² in the region of several volts to several tens of volts.
(3) The response speed of several hundred MHz or more was verified by the direct current or alternating current bias in the light receiving element with the element capacitance reduced to 10 pF or less.

As mentioned before, the point of caution in the element structure of the organic-inorganic hybrid junction photoelectric conversion element of the present invention is that a high-resistance i layer composed of an inorganic semiconductor is used in an actual p ^* -ip junction structure. n is the carrier concentration becomes 10 ¹⁶ / cm ³ or lower carrier concentration ^- constitute a layer, n ^* in the -i-n junction structure, i layer is low carrier concentration in the carrier concentration 10 ¹⁶ / cm ³ or less It is necessary to be composed of p ^- layers. In the present description, these n ⁻ layers and p ⁻ layers are described as i layers in accordance with semiconductor conventions.

  The organic-inorganic hybrid junction photoelectric conversion element that generates another signal gain G in the present invention is an avalanche multiplication type short wavelength APD light-receiving element that operates with high sensitivity in a blue-ultraviolet light wave band. As for the APD element, practical light receiving elements in the near infrared and visible light wave bands have been developed for inorganic semiconductors such as Si and Ge, but there are no practical light receiving elements in the ultraviolet region of 350 nm or less. An APD element using an organic-inorganic semiconductor composite element has not been developed yet.

In the present invention, an organic-inorganic hybrid junction type APD element in a blue-ultraviolet light band is used for the first time by an asymmetric junction of an organic semiconductor and an inorganic / wide gap compound semiconductor with a p ^* -i-n structure and an n ^* -ip structure. And an extremely high signal gain G were achieved. These organic-inorganic hybrid junction avalanche multiplication elements have a large leak current due to reverse bias in a simple organic-inorganic semiconductor contact, and a stable APD operation is difficult. However, a guard ring structure using a metal such as Pt is difficult. It was realized by applying process technology such as insulating film such as SiO ₂ film and protective film on the element surface.

  The basic junction structure, characteristics, and outline of the fabrication process of the organic-inorganic semiconductor hybrid element that generates the signal gain G have been described above. Another feature of these elements is that the light receiving elements can be easily integrated. is there. The ease of integration is effective when the present invention is formed on a large wafer such as a large-area Si crystal or GaAs.

  That is, an i layer is formed on a predetermined wafer by an inorganic semiconductor, and an organic semiconductor thin film is formed on the surface of the i layer semiconductor crystal by a simple process such as a spin coating method, a vacuum deposition method, or a direct polymerization method. did. When a guard ring such as Pt for preventing leakage current is formed, it is formed in the shape of a ring pattern or the like on the surface of the i-layer inorganic semiconductor before the formation of the organic semiconductor thin film. Further, high density integration is possible using this metal guard ring.

  The signal gain G, high speed, and integration that are the characteristics of the present invention can pioneer a new application field that has not existed in the past, but one of them is deep ultraviolet rays using an integrated light receiving element and a scintillation material, And X-ray detection device

  In the organic-inorganic hybrid junction photoelectric conversion element of the present invention, an excellent carrier-synthetic film can be obtained by simply forming an organic semiconductor thin film on the surface of an inorganic / wide gap semiconductor by a spin coating method, a vacuum deposition method, or a direct polymerization method. A heterojunction interface that functions as an emitter is obtained, which is surprising. This is because, when a phototransistor consisting of a hetero-bipolar transistor such as a pnp structure is formed at a heterojunction interface between inorganic semiconductors, a high concentration of interface defects contributes to the disappearance of carriers and the high-efficiency emitter action is inhibited. This is because it is well known.

  As will be described later, the inorganic semiconductor is not limited to a wide gap semiconductor such as ZnSe or ZnO, and an efficient organic-inorganic hybrid junction can be realized even in Si having a small band gap value. This can be an advantageous feature.

  However, a point to be noted at the organic-inorganic composite interface is that carriers accumulate at the organic-inorganic bonding interface. This is due to the fact that the organic semiconductor thin film functions as a carrier block layer for electrons and holes, but this accumulation effect depends on the interface characteristics between the organic semiconductor thin film and the inorganic semiconductor to be joined. It occurs in gap semiconductors. This accumulation effect leads to a decrease in the response speed of the light receiving element and a decrease in the signal gain G. In such a case, high sensitivity and high speed response can be achieved by superimposing an AC bias such as a pulse on the DC bias. It becomes possible.

  In order to form an organic-inorganic clean interface, it is necessary to clean the surface of the inorganic semiconductor, remove the oxide layer, and, in the case of an oxide semiconductor such as ZnO, an appropriate surface treatment to prevent reaction due to oxygen on the surface. However, they can all be performed by simple wet and dry processes including cleaning and etching.

  As described above, the relationship between the present invention and the prior art, the basic operation principle of the present invention, the process for actually creating the element, and the like have been described. The following is a description of the present invention based on specific embodiments. I will explain the effect.

<Types of organic semiconductor thin films>
In this experiment, several kinds of organic semiconductor thin films were tried. Many organic semiconductor thin films have been pioneered in the development of organic EL, and among them, as an electron transport organic semiconductor thin film that has become a practical product, 2- (4-tert-butylphenyl) -5- (4-Biphenylyl) -1,3,4-oxadiazole is known, and as a hole transport organic semiconductor thin film, PEDT / PSS (polymer of 3,4 ethylenedioxythiophene and polystyrene sulfonic acid is used. ) Or p ^* type CuPc is known.

  In particular, PEDT / PSS used as a polymer organic semiconductor thin film has already been pioneered as a product and is actively applied to organic EL devices, etc., and can be formed on many inorganic semiconductors by spin coating and appropriate heat treatment have. For low molecular organic semiconductor thin films, CuPc-based materials were formed by vacuum deposition. This organic material is a proven material used in organic EL elements, but when used in an organic-inorganic hybrid junction type light receiving element in the present invention, it is lower than PEDT / PSS due to poor transparency in the ultraviolet region. Sensitivity was shown.

The selection of a suitable organic semiconductor thin film material for maximizing the light receiving function or the light emitting function in the photoelectric conversion element of the present invention may differ depending on the type of inorganic semiconductor that forms a junction interface with the organic semiconductor thin film. In the case of forming a p ^* type organic semiconductor thin film, PEDT / PSS has a good bonding interface with many semiconductors of different species and can be formed by a simple process such as spin coating and thermal annealing. Visible-ultraviolet and excellent transparency.

<Description of basic structure>
FIG. 1 is a schematic cross-sectional view of a basic organic-inorganic hybrid junction photoelectric conversion element of the present invention.

  This organic-inorganic hybrid junction photoelectric conversion element has an inorganic semiconductor layer 3, a photoelectric conversion layer 4 made of an inorganic semiconductor layer, and an organic semiconductor thin film 5 on the upper surface of an inorganic semiconductor substrate 2 having a lower electrode 1 provided on the back surface. Are sequentially laminated, and the upper electrode 6 is connected to the organic semiconductor thin film 5 to provide it. The lower electrode 1 and the upper electrode 6 are connected to a bias applying means 7 in order to apply an appropriate bias voltage.

  Here, the organic semiconductor thin film 5 is an emitter layer / window layer, and the inorganic semiconductor layer 3 is a collector layer. Hereinafter, the emitter layer / window layer is simply referred to as the organic semiconductor thin film 5, and the collector layer is simply referred to as the inorganic semiconductor layer 3.

When the inorganic semiconductor substrate 2 is p-type, the inorganic semiconductor layer 3 is p-type, the photoelectric conversion layer 4 is n ^- type, and the organic semiconductor thin film 5 is p ^* -type and has a p ^* -ip symmetrical structure. When the inorganic semiconductor substrate 2 is n-type, the inorganic semiconductor layer 3 is n-type, the photoelectric conversion layer 4 is p ^- type, and the organic semiconductor thin film 5 is n ^* -type and has an n ^* -i-n symmetric junction structure. It is said.

In particular, the inorganic semiconductor layer 3 and the organic semiconductor thin film 5 have a carrier concentration of 1 × 10 ¹⁷ / cm ³ or more, while the photoelectric conversion layer 4 has a carrier concentration of 1 × 10 ¹⁶ / cm ³ or less as a high resistance i layer. Yes.

  As can be seen from the basic structure of FIG. 1, a photoelectric conversion layer 4 to be an i layer is formed on an inorganic semiconductor layer 3 with an inorganic semiconductor, and an organic semiconductor thin film is formed thereon by spin coating, vacuum deposition, or chemical polymerization. Thus, the organic semiconductor thin film 5 is formed.

  Although only the basic structure of the organic-inorganic hybrid junction photoelectric conversion element of the present invention is shown in FIG. 1, practical device fabrication is actually made with II-VI, III-V wide gap semiconductors, Si, and the like. However, it is necessary to devise the arrangement of an additional insulating film for stable operation, a passivation film for the element, a metal guard ring, and an upper metal electrode to enable ultrasonic bonding.

<First Embodiment>
FIG. 2 is a schematic cross-sectional view of a light-receiving element having a p ^* -ip structure, which is a more specific photoelectric conversion element according to the first embodiment and is configured using ZnSSe, which is a semiconductor having a wide gap.

  In the photoelectric conversion element of this embodiment, the barrier conversion buffer layer B, the inorganic semiconductor layer 3, and the photoelectric conversion layer 4 composed of the inorganic semiconductor layer are formed on the upper surface of the inorganic semiconductor substrate 2 provided with the lower electrode 1 on the back surface. And the organic semiconductor thin film 5 are sequentially laminated, and the upper electrode 6 is connected to the organic semiconductor thin film 5 and provided. The lower electrode 1 and the upper electrode 6 are connected to a bias applying means 7 in order to apply an appropriate bias voltage.

  Furthermore, in the photoelectric conversion element of the present embodiment, a guard ring R in which an opening through which light is incident is formed between the photoelectric conversion layer 4 and the organic semiconductor thin film 5 by forming a ring shape.

The inorganic semiconductor substrate 2 is a p-GaAs substrate cut along the (100) plane, has a thickness of about 0.3 mm, and a carrier concentration of about 1 × 10 ¹⁸ / cm ³ .

The buffer layer B is a ZnTe—ZnSe superlattice layer formed on the upper surface of the inorganic semiconductor substrate 2, and a p-Zn _1-x S _x Se layer constituting the p-GaAs and the inorganic semiconductor layer 3 of the inorganic semiconductor substrate 2. Is used to eliminate a barrier of about 1.0 eV due to the hole flow flowing at the interface, and the interface superlattice of the buffer layer B causes a resonant tunneling effect, I let it pass.

The inorganic semiconductor layer 3 is a p-Zn _1-x S _x Se layer formed on the upper surface of the buffer layer B by the epitaxial growth method, and the carrier concentration is set to about 5 × 10 ¹⁷ / cm ³ by adding active nitrogen. Yes.

The photoelectric conversion layer 4 is an i-Zn _1-x S _x Se layer formed on the upper surface of the inorganic semiconductor layer 3 without addition by epitaxial growth, has a thickness of about 0.4 μm, and has an electron concentration of 2 × 10 ¹⁵ / About ³ cm.

Before the organic semiconductor thin film 5 is formed, a Pt metal film is formed on the upper surface of the photoelectric conversion layer 4 by sputtering or the like, and the guard ring R is formed by patterning the Pt metal film. This guard ring R is Schottky joined to the i-Zn _1-x S _x Se layer of the photoelectric conversion layer 4 and can prevent the occurrence of dark current.

  After formation of the guard ring R, liquid PEDT / PSS is applied to the upper surface of the photoelectric conversion layer 4 by a spin coating method, and is heated to 180 ° C. to be cured, thereby forming the organic semiconductor thin film 5. The formation of the organic semiconductor thin film 5 is not limited to the spin coating method, and may be an appropriate method such as a vacuum deposition method. . In the present embodiment, the thickness of the organic semiconductor thin film 5 is about 250 nm.

After the formation of the organic semiconductor thin film 5, an insulating protective film 8 made of Al ₂ O ₃ or an anti-reflective film made of SiO ₂ is formed on the upper surface of the organic semiconductor thin film 5 by vacuum deposition using an electron gun. Provided. The thickness of the insulating protective layer 8 is about 0.06 μm.

  Further, an opening for exposing a part of the organic semiconductor thin film 5 is formed in the insulating protective layer 8, and the upper electrode 6 is formed by vacuum-depositing Ag in the opening.

In the p ^* -i-p type photoelectric conversion element shown in FIG. 2, even if the direction of the bias voltage is changed, either one of the junctions is in the reverse direction. Therefore, the dark current is, for example, several pA to several tens pA under a 5V bias condition. It is an extremely low value of about / mm ² and shows different light receiving characteristics in the bias direction.

  That is, in the light receiving element of this embodiment, a signal gain G is generated when the organic semiconductor thin film 5 on the element is positively biased. Further, under the condition that the organic semiconductor thin film 5 is negatively biased, no signal gain is generated, and the device operates as a PIN type element with high speed and low dark current.

Here, the light receiving characteristics when the organic semiconductor thin film 5 is negatively biased and the signal gain G is not generated will be described. Under this bias condition, the external quantum efficiency η _ex = 85% -75% is obtained in the incident light wavelength range of 450-300 nm, and the light receiving sensitivity S is high-speed and stable operation as an element with S = 0.15-0.1 A / W. Was verified. In the light receiving mode similar to the p-i-n type, the signal gain G is absent, but the external quantum efficiency and sensitivity are superior to those of existing Si ultraviolet photodiodes.

  On the other hand, with a bias with the organic semiconductor thin film 5 being positive, the light receiving sensitivity shows a very large change. That is, under the condition that the organic semiconductor thin film 5 is positively AC biased by 1 V or more, it increases 5-120 times compared with the photocurrent signal in the above-described p-i-n operation. The signal gain G appears above a certain AC bias value, and if the bias value is satisfied, the constant signal gain G is maintained regardless of the AC bias value. The AC bias may be a square type or a sine wave. This AC bias serves to discharge weak charges accumulated at the organic-inorganic semiconductor interface, and the bias frequency is preferably several Hz to several hundred MHz.

  Thus, by selectively switching the output of the bias voltage output from the bias applying means 7, the signal multiplication type light receiving characteristic mode for generating the signal gain of the photocurrent, and the normal PIN type for generating no signal gain. The light receiving characteristic mode can be switched.

  In order to realize a high-speed response in the mode in which the signal gain G is generated, it is necessary to optimize the AC bias and set the bias frequency high. On the other hand, when carrier accumulation does not occur at the organic-inorganic semiconductor interface, or when the organic semiconductor thin film does not function as a carrier block layer, it can be operated at high speed under normal DC bias conditions.

  Fig. 3 shows the sensitivity (A / W) spectrum when light in the blue (450nm) -ultraviolet region (300nm) is irradiated with a 0-5V AC bias applied to the organic semiconductor thin film 5 of the light receiving element. Shown in The frequency of the AC bias is 100 MHz. In FIG. 3, the triangle marks are the light receiving elements of the present embodiment.

  For comparison, in FIG. 3, the sensitivity of a p-i-n photodiode using Si, which is currently used practically, is shown by a square mark, and the sensitivity of a pin structure photodiode made of ZnSSe is shown by a black circle. Since the signal gain G is expressed, it can be seen that extremely high external quantum efficiency is achieved in the light receiving element of this embodiment. In particular, it can be seen that the ultraviolet light receiving element, which is currently in practical use in the ultraviolet region with a wavelength of 300 to 350 nm, greatly exceeds the pin type light receiving element using Si having the highest sensitivity.

As described above, the p ^* -i-p structure light-receiving element exhibits a blue-ultraviolet sensitivity of 1-2 digits or more as compared with the conventional high-sensitivity p-i-n type light-receiving element. In the light receiving element having this signal gain, the antireflection film or the like has not been optimized, and it is possible to further increase the sensitivity by optimizing it, and it has an extremely excellent ultraviolet light receiving sensitivity. I understand that.

  When the high-speed response of the light-receiving element of this embodiment was examined with a light-receiving element having a light-receiving region with a diameter of 30 μm, a high-speed response of about 400 MHz was confirmed. The response of the light receiving element is not limited by the carrier travel time because the i layer is completely covered with the high electric field region, and is limited by the CR time constant. The response speed can be further improved by reducing the element capacitance. This high-speed response shows that the problem of low response speed, which is a drawback of the phototransistor having the signal gain G due to conventional Si or the like, is greatly improved.

The condition that the p ^* -ip type photoelectric conversion element of this embodiment generates a remarkable signal gain G is a case where the bias voltage is set with the organic semiconductor thin film 5 side being positive. This bias condition corresponds to the condition that the organic semiconductor thin film operates as a carrier emitter, the organic semiconductor thin film 5 exhibits the function as a p-type semiconductor, and the current multiplication effect known for pnp bipolar transistors such as Si. Is considered to have occurred. The p ^* -i-p type photoelectric conversion element of this embodiment is different from the Si pnp bipolar transistor in that the base layer is i-type and has high resistance, and the external bias is i. Applied to the layer, the carrier can move at high speed, and high speed driving is possible.

Second Embodiment
FIG. 4 is a schematic cross-sectional view of a light-receiving element having a p ^* -ip structure, which is a photoelectric conversion element according to the second embodiment and uses GaN having a band gap larger than that of ZnSSe.

  In the photoelectric conversion element of this embodiment, the buffer layer B for barrier removal, the inorganic semiconductor layer 3, the photoelectric conversion layer 4 made of an inorganic semiconductor layer, and the organic semiconductor thin film 5 are sequentially formed on the upper surface of the inorganic semiconductor substrate 2. The upper electrode 6 is provided between the photoelectric conversion layer 4 and the organic semiconductor thin film 5 with the intermediate insulating layer 9 interposed therebetween. Furthermore, an insulating protective layer 8 that covers the organic semiconductor thin film 5 is provided on the upper surface of the organic semiconductor thin film 5.

  In particular, the upper electrode 6 and the organic semiconductor thin film 5 are provided along the surface direction on the photoelectric conversion layer 4, and it is possible to suppress the formation of a thick protective film on the upper surface of the organic semiconductor thin film 5. Makes it easier to suppress the absorption of light.

  Furthermore, the upper electrode 6 is provided in a frame shape surrounding the organic semiconductor thin film 5 to form an opening through which light is incident. Since the upper electrode 6 itself becomes a light shielding body, there is no need to separately provide a light shielding body. Thus, it is possible to prevent the generation of current due to light excitation outside the light receiving region.

  The lower electrode 1 is provided on the exposed surface of the inorganic semiconductor layer 3 exposed by etching back the photoelectric conversion layer 4 and the inorganic semiconductor layer 3, and bias applying means 7 is connected to the upper electrode 6 and the lower electrode 1. The bias applying means 7 applies a predetermined bias voltage to the light receiving element.

  The inorganic semiconductor substrate 2 is composed of a sapphire substrate, and a buffer layer B made of a GaN layer is formed on the upper surface of the inorganic semiconductor substrate 2 by MOCVD (Metal Organic Chemical Vapor Deposition).

The inorganic semiconductor layer 3 is a p-GaN layer formed on the upper surface of the buffer layer B while adding Mg as an acceptor by MOCVD, and has a thickness of about 2 μm and a carrier concentration of about 7 × 10 ¹⁷ / cm ³ . .

The photoelectric conversion layer 4 is an i-GaN layer formed by MOCVD while adding a small amount of Mg to the upper surface of the inorganic semiconductor layer 3. The photoelectric conversion layer 4 has a thickness of about 0.4 μm and an electron concentration of about 8 × 10 ¹⁵ / cm ^3. It is said.

Before forming the organic semiconductor thin film 5, an Al ₂ O ₃ film and an SiO ₂ film are sequentially formed on the upper surface of the photoelectric conversion layer 4 by electron gun vapor deposition to form an intermediate insulating layer 9. A Ti metal film and a Pt / Au metal film are sequentially formed on the upper surface of the substrate by vacuum deposition, and a ring-shaped upper electrode provided on the photoelectric conversion layer 4 via the intermediate insulating layer 9 by patterning them. 6 is formed.

  Further, before forming the Ti metal film and the Pt / Au metal film by vacuum deposition, the photoelectric conversion layer 4 is etched by dry etching to expose the inorganic semiconductor layer 3, and further the inorganic semiconductor layer 3 is etched, A recess for forming the lower electrode 1 is provided, and a Ti metal film and a Pt / Au metal film are formed to form the lower electrode 1 together with the upper electrode 6.

  The cross sections of the photoelectric conversion layer 4 and the inorganic semiconductor layer 3 that are exposed as a result of the formation of the recesses are processed into a mesa shape to suppress the generation of dark current.

  The organic semiconductor thin film 5 is formed by applying liquid PEDT / PSS to the upper surface of the photoelectric conversion layer 4 by spin coating after the formation of the upper electrode 6 and heating to 180 ° C. to cure. The formation of the organic semiconductor thin film 5 is not limited to the spin coating method, and may be an appropriate method such as a vacuum deposition method. . In the present embodiment, the thickness of the organic semiconductor thin film 5 is about 800 nm.

After the organic semiconductor thin film 5 is formed, an insulating protective layer 8 is formed on the entire upper surface of the organic semiconductor thin film 5 by forming an insulating protective film made of Al ₂ O ₃ or an antireflection film made of SiO ₂ . .

Similar to the light receiving element of the first embodiment, the light receiving element of this embodiment does not generate a signal gain G of photocurrent under the condition that the organic semiconductor thin film 5 is negatively biased, and is a normal Schottky type without gain. Or, it showed light receiving characteristics similar to a p-i-n type light receiving element. Under this bias condition, the external quantum efficiency η _ex = 60% -50% at a wavelength of 360 nm-250 nm. This external quantum efficiency in the ultraviolet region is slightly better than η _ex = 55% -45% in the GaN p-i-n type light receiving element reported in papers.

  Under the condition that the organic semiconductor thin film 5 was positively biased, when an AC bias of 0-12V was applied, the sensitivity spectrum rose from around the wavelength of 360 nm, and the signal gain G was about 5-45. Under this bias condition, a high value of sensitivity S = 1 A / W−2 A / W is shown in the ultraviolet region of the wavelength region from 360 nm to 280 nm. 360 nm, which is the long wavelength end of sensitivity, corresponds to the fundamental absorption edge of GaN, and the short wavelength limit (270 nm) of sensitivity is limited by the ultraviolet absorption of the organic semiconductor thin film (PEDT / PSS) window layer.

The dark current I _d in the light receiving element of this embodiment is several nA / mm ² under a bias condition of 5 V, which is a dark current that is about one digit higher than that of the light receiving element of the first embodiment. This can be attributed to components generated from defects at the organic-GaN interface and components generated from GaN itself having high density of macro defects such as dislocations. Although the light receiving sensitivity and dark current control are inferior to the light receiving element of the first embodiment, the UV sensitivity can be further greatly improved by controlling the defects of the GaN crystal film and improving the interface between the photoelectric conversion layer 4 and the organic semiconductor thin film 5. I can expect.

<Third Embodiment>
FIG. 5 is a schematic cross-sectional view of a light-receiving element having an n ^* -in structure using ZnO having a band gap equivalent to that of GaN, which is the photoelectric conversion element of the third embodiment.

  In the photoelectric conversion element of this embodiment, an inorganic semiconductor layer 3, a photoelectric conversion layer 4 made of an inorganic semiconductor layer, and an organic semiconductor thin film 5 are sequentially formed on the upper surface of an inorganic semiconductor substrate 2 provided with a lower electrode 1 on the back surface. The upper electrode 6 is connected to the organic semiconductor thin film 5 and is formed. The lower electrode 1 and the upper electrode 6 are connected to a bias applying means 7 in order to apply an appropriate bias voltage.

  Furthermore, in the photoelectric conversion element of this embodiment, an intermediate insulating layer 9 in which an opening through which light enters is formed between the photoelectric conversion layer 4 and the organic semiconductor thin film 5 is provided.

  The inorganic semiconductor substrate 2 is an n-ZnO substrate cut at the c-plane.

The inorganic semiconductor layer 3 is an n-ZnO layer formed by homo-epitaxial growth method (MBE method) while adding Ga as a donor to the upper surface of the inorganic semiconductor substrate 2 and has a thickness of about 2 μm and a carrier concentration of 8 × 10 ¹⁷ / cm ³ or so.

The photoelectric conversion layer 4 is a p ⁻ -type i-ZnO layer formed by adding N and As acceptors at a low concentration on the upper surface of the inorganic semiconductor layer 3, and has a thickness of about 0.3 μm and a hole concentration of 2 × 10 ¹⁵ / cm ³ or so.

Before the organic semiconductor thin film 5 is formed, an Al ₂ O ₃ film and a SiO ₂ film are sequentially formed on the upper surface of the photoelectric conversion layer 4 by a CVD method or the like to form an intermediate insulating layer 9. By patterning, an opening for receiving light is formed.

  Furthermore, before the organic semiconductor thin film 5 is formed, a surface treatment using a silane coupling agent is performed on the upper surface of the photoelectric conversion layer 4.

  The organic semiconductor thin film 5 is subjected to surface treatment with a silane coupling agent, and then liquid 2- (4-tert-butylphenyl) -5- (4-biphenyl) -1,3,4 on the upper surface of the photoelectric conversion layer 4. -Oxadiazole is applied by spin coating and heated to 150 ° C to cure. The formation of the organic semiconductor thin film 5 is not limited to the spin coating method, and may be an appropriate method such as a vacuum deposition method. . In the present embodiment, the thickness of the organic semiconductor thin film 5 is about 200 nm.

After the organic semiconductor thin film 5 is formed, an insulating protective layer 8 is formed on the entire upper surface of the organic semiconductor thin film 5 by forming an insulating protective film made of Al ₂ O ₃ or an antireflection film made of SiO ₂ . .
Further, an opening for exposing a part of the organic semiconductor thin film 5 is formed in the insulating protective layer 8, and the upper electrode 6 is formed by vacuum-depositing Ag in the opening.

  Since the light receiving element of the present embodiment uses ZnO, which is an oxide semiconductor, there has been a problem that the interface becomes remarkably rough when the organic semiconductor thin film 5 is directly formed on the ZnO surface. In order to reduce this, the organic semiconductor thin film 5 is formed after the ZnO surface is treated with a silane coupling agent for a short time.

In the light receiving element of this embodiment, the i-ZnO layer having p ⁻ type carriers constituting the photoelectric conversion layer 4 is an extremely high resistance layer, and the dark current in the light receiving element is several pA / mm. ² and a value two orders of magnitude lower than that of the GaN-based light receiving element of the second embodiment. This value is almost constant under the bias condition of 0-10V regardless of the bias direction. This low dark current suggests that the macro defect density of ZnO crystals is lower than that of GaN and that the organic-ZnO interface is superior.

  Furthermore, the light receiving element of this embodiment generates sensitivity at an ultraviolet wavelength of 365 nm or less and operates up to a deep ultraviolet wavelength of about 200 nm. As in the light receiving element of the first and second embodiments, the light receiving characteristic in the ultraviolet light band generates the n-ip type without the signal gain G and the signal gain G by selecting the bias direction. Gain mode can be selected.

In the case where there was no signal gain G, high external quantum efficiency η _ex = 90-85% was obtained in the ultraviolet region, which is a wavelength region of 360 nm-250 nm, at a DC bias voltage of 10 V. This external quantum efficiency is similar to the characteristics of the already reported nZnO-organic thin film Schottky type light receiving element.

  A significant improvement in UV sensitivity was verified under conditions in which a bias voltage generating signal gain was applied. That is, a signal gain G of 50 or more was manifested at a direct current and alternating current bias of 18V. When converted to external quantum efficiency, an extremely high efficiency of 5000% or more was obtained. When the organic semiconductor thin film, which is a feature of the present invention, is used as an effective carrier / emitter instead of a Schottky metal, the light receiving element of the present embodiment has a sensitivity S = 2A / W− in the ultraviolet light region up to 200 nm. It was found to have a high UV sensitivity of 5 A / W.

When ZnO is used as in this embodiment, p-type conversion by N and As acceptors has not reached the device level, and the carrier concentration of the p-ZnO layer is as low as 2 × 10 ¹⁵ / cm ^3. In addition, since the uniformity of the carrier concentration is inferior, the signal multiplication function of the present invention has not been sufficiently exhibited.

If complete p-type control of ZnO crystal is realized, a p ^* -i-p structure becomes possible by combining with PEDT / PSS which has excellent transparency in the ultraviolet region, which is comparable to current photomultiplier tubes. A signal multiplication type high-sensitivity, solid-state light-receiving element is expected to be possible.

<Fourth embodiment>
FIG. 6 is a schematic cross-sectional view of a light receiving element which is the photoelectric conversion element of the fourth embodiment and is an APD element having a p ^* -in structure.

  In the photoelectric conversion element of this embodiment, the barrier conversion buffer layer B, the inorganic semiconductor layer 3, and the photoelectric conversion layer 4 composed of the inorganic semiconductor layer are formed on the upper surface of the inorganic semiconductor substrate 2 provided with the lower electrode 1 on the back surface. And the organic semiconductor thin film 5 are sequentially laminated, and the upper electrode 6 is connected to the organic semiconductor thin film 5 and provided. The lower electrode 1 and the upper electrode 6 are connected to a bias applying means 7 in order to apply an appropriate bias voltage.

  Furthermore, in the photoelectric conversion element of the present embodiment, a guard ring R in which an opening through which light is incident is formed between the photoelectric conversion layer 4 and the organic semiconductor thin film 5 by forming a ring shape.

The inorganic semiconductor substrate 2 is an n-GaAs crystal substrate cut along the (100) plane, has a thickness of about 0.3 mm, and a carrier concentration of about 3 × 10 ¹⁸ / cm ³ .

The buffer layer B is an n-GaAs epilayer formed on the upper surface of the inorganic semiconductor substrate 2 using a two-chamber MBE growth apparatus. By providing the buffer layer B, the dislocation of the first semiconductor layer 62 provided on the buffer layer B can be reduced to 10 ⁵ / cm ² or less, and in the light receiving element of this embodiment used in a high electric field. Generation of dark current can be reduced.

The inorganic semiconductor layer 3 is an n-Zn _1-x S _x Se layer formed while adding chlorine as a donor to the upper surface of the buffer layer B.

The photoelectric conversion layer 4 is an i-Zn _1-x S _x Se layer formed on the upper surface of the inorganic semiconductor layer 3 without addition, and has a thickness of about 0.25 μm and an electron concentration of about 2 × 10 ¹⁵ / cm ^3. It is said.

Before the organic semiconductor thin film 5 is formed, a Pt metal film is formed on the upper surface of the photoelectric conversion layer 4 by sputtering or the like, and the guard ring R is formed by patterning the Pt metal film. The guard ring R is formed into a ring shape by patterning and is Schottky joined to i-Zn _1-x S _x Se of the photoelectric conversion layer 4. By providing this guard ring R, the generation of dark current can be prevented.

  After forming the guard ring R, the organic semiconductor thin film 5 is formed by applying liquid PEDT / PSS to the upper surface of the photoelectric conversion layer 4 by a spin coating method and heating to 180 ° C. to cure. The formation of the organic semiconductor thin film 5 is not limited to the spin coating method, and may be an appropriate method such as a vacuum deposition method. . In the present embodiment, the thickness of the organic semiconductor thin film 5 is about 350 nm.

After the organic semiconductor thin film 5 is formed, an insulating protective film made of Al ₂ O ₃ or an antireflection film made of SiO ₂ is formed on the entire upper surface of the organic semiconductor thin film 5 by CVD or the like to form an insulating protective layer 8. Is provided.

  Further, an opening for exposing a part of the organic semiconductor thin film 5 is formed in the insulating protective layer 8, and the upper electrode 6 is formed by vacuum-depositing Ag in the opening.

The basic principle of the light receiving element of this embodiment is shown in FIG. The light receiving element of this embodiment is an APD element having a p ^* -i-n junction, and all the DC bias applied by the bias applying means 7 is applied to the n ⁻ type photoelectric conversion layer 4, and FIG. As shown in Fig. 2, the avalanche multiplication phenomenon occurs when the band is tilted greatly and the electric field intensity is in the region of ~ 10 ⁶ / cm. The APD operating voltage in the light receiving element of this embodiment is characterized by being as low as about 25-40V. This APD operating voltage is about 1/5, while Si-based APD elements require about 200 V, and high-density integration of APD elements is also possible.

  Further, as can be seen from the band diagram of FIG. 7, electrons multiplied in the i-layer photoelectric conversion layer 4 are absorbed into the inorganic semiconductor layer 3, and holes are absorbed into the organic semiconductor thin film 5. There is no effect. For this reason, the bias to the APD element may be a normal DC bias, and the response speed is several hundred MHz or more.

  The problem of the organic-inorganic high-abbreviated junction type APD element is the control of dark current at the APD operating voltage, and the dark current characteristics are shown in FIG.

Conventionally, a large reverse bias is required for an APD type element, a leak current is generated at an organic-inorganic semiconductor interface, a dark current is increased, and there is a problem that a true avalanche multiplication is hindered. By developing a key guard ring structure, this problem can be avoided. That is, as in this embodiment, a guard ring R that is Schottky bonded to the photoelectric conversion layer 4 is provided between the photoelectric conversion layer 4 and the organic semiconductor thin film 5. FIG. 9 shows how the dark current during an APD operation in which an avalanche multiplication occurs is reduced to about 10 pA / mm ² in an organic-inorganic high-abbreviated APD provided with a guard ring R. By providing the guard ring R in this way, the organic-inorganic hybrid APD element can be operated with high sensitivity and stability.

Moreover, the spectrum of the sensitivity of the organic-inorganic hybrid junction type APD using ZnSSe of this embodiment is shown in FIG. The light receiving element of this embodiment has an external quantum efficiency η _ex = 60-30% in the 450-300 nm wavelength band at 5 V bias. In an APD operation of 37 V or more, η _ex = 1500% (blue) −1000% (ultraviolet) has been verified that is 20 times larger than that. The sensitivity of this APD element can be easily realized at 5 A / W in the blue region and 3 A / W in the 300 nm ultraviolet. These sensitivities increase to 1.5 times the sensitivity when the APD operating voltage is increased to 40V, but the dark current also increases.

  Furthermore, another feature of the organic-inorganic hybrid APD element of this embodiment is a high-speed response, and a high-speed response of ˜550 MHz has been confirmed with a circular APD element having a diameter of 25 μm.

<Fifth Embodiment>
FIG. 10 is a cross-sectional view of a light receiving element which is a photoelectric conversion element according to the fifth embodiment, and which includes an APD element having a p ^* -in structure in which sensitivity in the ultraviolet region deeper than that of the photoelectric conversion element according to the fourth embodiment is improved. It is a schematic diagram.

  In the photoelectric conversion element of this embodiment, an inorganic semiconductor layer 3, a photoelectric conversion layer 4 made of an inorganic semiconductor layer, and an organic semiconductor thin film 5 are sequentially formed on the upper surface of an inorganic semiconductor substrate 2 provided with a lower electrode 1 on the back surface. The upper electrode 6 is connected to the organic semiconductor thin film 5 and is formed. The lower electrode 1 and the upper electrode 6 are connected to a bias applying means 7 in order to apply an appropriate bias voltage.

  Furthermore, in the photoelectric conversion element of the present embodiment, a guard ring R in which an opening through which light is incident is formed between the photoelectric conversion layer 4 and the organic semiconductor thin film 5 by forming a ring shape.

  The inorganic semiconductor substrate 2 is an n-ZnO substrate cut at the c-plane.

The inorganic semiconductor layer 3 is an n-ZnO layer formed by MBE or MOCVD while adding Ga as a donor to the upper surface of the inorganic semiconductor substrate 2 and has a carrier concentration of about 5 × 10 ¹⁷ / cm ³ .

The photoelectric conversion layer 4 is an i-ZnO layer formed on the top surface of the inorganic semiconductor layer 3 without addition by MBE or MOCVD, has a thickness of about 0.2 μm, and a carrier concentration of about 1 × 10 ¹⁵ / cm ^3. It is said.

Before the organic semiconductor thin film 5 is formed, an SiO ₂ film is formed on the upper surface of the photoelectric conversion layer 4, and the guard ring R is formed by patterning the SiO ₂ film. By providing this guard ring R, the generation of dark current can be prevented.

  After forming the guard ring R, the organic semiconductor thin film 5 is formed by applying liquid PEDT / PSS to the upper surface of the photoelectric conversion layer 4 by a spin coating method and heating to 200 ° C. to cure. The formation of the organic semiconductor thin film 5 is not limited to the spin coating method, and may be an appropriate method such as a vacuum deposition method. . In the present embodiment, the thickness of the organic semiconductor thin film 5 is about 200 nm.

After the organic semiconductor thin film 5 is formed, an insulating protective layer 8 is formed on the entire upper surface of the organic semiconductor thin film 5 by forming an insulating protective film made of Al ₂ O ₃ or an antireflection film made of SiO ₂ . .

  Further, an opening for exposing a part of the organic semiconductor thin film 5 is formed in the insulating protective layer 8, and the upper electrode 6 is formed by vacuum-depositing Ag in the opening.

  The upper part of the light receiving element of this embodiment is subjected to mesa processing by a wet process to control the side leakage current. The operating voltage of the light receiving element of the present embodiment varies greatly depending on the thickness of the photoelectric conversion layer 4, but is about 65-90V, which is larger than that of the light receiving element of the fourth embodiment is 35-40V. An operating voltage is required.

The reverse dark current in the APD region was several hundred pA / mm ² to 50 nA / mm ² , but these dark currents were caused by the guard ring R provided between the photoelectric conversion layer 4 and the organic semiconductor thin film 5. It could be reduced by 1-2 digits. By this guard ring structure and an appropriate organic semiconductor thin film processing process, an organic-ZnO hybrid junction type APD element with stable operation becomes possible.

The external quantum efficiency η _ex of the light receiving element of the present embodiment showed an extremely high efficiency of 85% to 65% in the ultraviolet wavelength range of 360 to 250 nm under a DC bias condition of several volts.

Under the APD operating conditions, the signal gain G showed a value of G = 45 at a wavelength of 350 nm and G = 15-30 at a wavelength of 250 nm. These signal gains are gains when the electric field intensity is ˜5 × 10 ⁶ / cm, and can be further improved by further dark current control in the future.

  As described above, the basic structure and characteristics of APD elements in the short wavelength band by hybrid junctions of wide gap semiconductors such as ZnSSe and ZnO and organic semiconductor thin films have been explained. The feature of these elements is that the element fabrication process is simple. Thus, high density integration of APD is easy.

  This feature is that the integrated APD element is extremely useful in the future detection of weak ultraviolet light, considering that the integration of Si and Ge alone is difficult due to the complicated process and the difficulty of dark current control. It becomes a light detection element.

  In particular, an all-solid-state X-ray detector can be realized by combining these APD elements with scintillation materials.

  Conventionally, high sensitivity light-receiving elements for deep ultraviolet and radiation have been used in many fields such as Si-VLSI, liquid crystal and other ultraviolet exposure processes, ultraviolet irradiation sterilizers, various X-ray diagnostic devices in the medical field, In the detection of high-energy radiation such as X-rays, the combination of scintillation materials and photomultiplier tubes that have been put to practical use is advantageous. The advantage of replacing photomultiplier tubes with highly sensitive semiconductor light-receiving elements is Some are extremely large in terms of low cost.

  In the all-solidification of the high-sensitivity detection element in the deep ultraviolet or radiation region, the high-sensitivity light-receiving element having an organic-inorganic semiconductor hybrid structure that exhibits a remarkable signal gain of the present invention has the ability to replace a photomultiplier tube. In particular, the development of a new all-solid-state radiation detection system is expected by combining with scintillation materials that convert radiation into the ultraviolet region.

FIG. 11 is a schematic diagram of a radiation detection apparatus configured using the above-described light receiving element. In particular, the light receiving element is an APD element having a p ^* -in structure according to the fourth embodiment. In addition, instead of the light receiving element, an integrated light receiving element in which a plurality of light receiving elements are integrated may be used, and higher sensitivity can be expected by using the integrated light receiving element.

  The radiation detection apparatus according to the present embodiment includes a detector main body 11 and an analysis apparatus 13 connected to the detector main body 11 via an appropriate wiring 12. Note that the detector main body 11 and the analysis device 13 may be configured integrally.

The detector main body 11 is a scintillation crystal and a photomultiplier tube assembled in a general X-ray diffraction spectrometer, and only the photomultiplier tube is removed. As an alternative, the detector body 11 has the p ^* -in structure. An APD element is mounted, specifically, a cylindrical housing 11a having a bottom, and in this housing 11a, a filter 11b for cutting light in the visible-ultraviolet region, an X-ray scintillation plate 11c The slit plate 11d and the light receiving element 11e are sequentially provided from the opening side of the housing 11a.

  The housing 11a is a shield tube, and shields radiation other than light incident through the filter 11b.

  In this embodiment, a bulk scintillation crystal having a high conversion efficiency from X-rays to a blue-ultraviolet region is used for the X-ray scintillation plate 11b.

  The light receiving element 11e is placed at a predetermined position on a holding base 11f provided in the housing 11a. The light receiving element 11e is connected to the analyzing device 13 through the wiring 12, applies a predetermined bias voltage to the light receiving element 11e, and inputs the output signal of the light receiving element 11e to the analyzing device 13.

  The semiconductor crystal film evaluated by X-ray diffraction spectroscopy using the radiation detection apparatus of the present embodiment is a ZnSSe crystal thin film formed by MBE growth on GaAs, and is performed in the X-ray rocking curve measurement mode. The X-ray spectrum is shown in FIG.

  In this experiment, the scintillation material and the device configuration have not been optimized, but it can be seen that the weak blue-near ultraviolet light from the X-ray scintillation crystal is clearly detected. By combining the high-sensitivity light-receiving element of the present invention with scintillation such as X-rays, an all-solid-state, low-cost, high-performance X-ray or higher-energy radiation detector that does not use a vacuum tube such as a photomultiplier is realized. I understand that it is possible.

  Although still under experiment, the application of organic-ZnO hybrid structure APD elements to X-rays and high-energy radiation detectors can be integrated two-dimensionally and with high density, and the UV sensitivity is even better. Therefore, an effective radiation detection apparatus can be realized. In the future, the radiation detection apparatus of the present embodiment will be a light-weight and low-cost, without using a photomultiplier tube, an ultraviolet CCD apparatus in a short wavelength light wave band, an accurate two-dimensional distribution measuring apparatus of radiation intensity such as X-rays. It shows that it can be realized in all solid form.

  In addition, the organic-inorganic hybrid light-receiving element has the advantage that a high-speed, high-sensitivity element can be realized in a wide range of visible-ultraviolet by selecting an organic thin film and an inorganic semiconductor under the element. Because it is easy to integrate, it can be applied in the fields of radiation medicine, scientific measurement, and many other industrial fields.

<Sixth Embodiment>
In the embodiment described above, one light receiving element has been described. However, these light receiving elements can be arranged side by side while providing appropriate element separating means, and can be easily integrated. FIG. 13 is a schematic cross-sectional view of an integrated light-receiving element formed by integrating light-receiving elements. Specifically, a cross-sectional schematic diagram of an integrated light-receiving element formed by integrating light-receiving elements having a p ^* -ip structure. It is.

  The integrated light receiving element of this embodiment includes an inorganic semiconductor layer 3, a photoelectric conversion layer 4 made of an inorganic semiconductor layer, and an organic semiconductor thin film 5 on the upper surface of an inorganic semiconductor substrate 2 having a lower electrode 1 provided on the back surface. The upper electrode 6 is provided between the photoelectric conversion layer 4 and the organic semiconductor thin film 5 with an intermediate insulating layer 9 interposed therebetween. The lower electrode 1 and the upper electrode 6 are connected to a bias applying means 7 in order to apply an appropriate bias voltage. Furthermore, an insulating protective layer 8 that covers the organic semiconductor thin film 5 is provided on the upper surface of the organic semiconductor thin film 5.

The inorganic semiconductor substrate 2 is a p-Si substrate cut in 100 planes, has a thickness of about 0.3 mm, and is doped with B to a carrier concentration of about 2 × 10 ¹⁸ / cm ³ .

The inorganic semiconductor layer 3 is a p-Si epilayer formed by adding B to the upper surface of the inorganic semiconductor substrate 2 by CVD, with a thickness of about 2 μm and a carrier concentration of about 5 × 10 ¹⁷ / cm ^3. Yes.

The photoelectric conversion layer 4 is an i-Si layer formed on the upper surface of the inorganic semiconductor layer 3 without addition by CVD growth, has a thickness of about 0.7 μm, and an electron concentration of about 5 × 10 ¹⁴ / cm ³ . .

Before forming the organic semiconductor thin film 5, an intermediate insulating layer 9 made of a SiO ₂ film is formed on the upper surface of the photoelectric conversion layer 4 by thermal oxidation. Further, an Al metal is formed on the upper surface of the intermediate insulating layer 9 by vacuum deposition. An upper electrode layer is formed by sequentially forming a film and an Ag metal film, the upper electrode layer is formed at a predetermined position by patterning the upper electrode layer, and the intermediate insulating layer 9 is further patterned to form an organic semiconductor. A joining region to which the thin film 5 is joined is formed. This junction region is an opening through which light is incident. In the present embodiment, the joining region has a circular shape with a diameter of 0.3 mm.

  The organic semiconductor thin film 5 is formed by applying liquid PEDT / PSS to the upper surface of the photoelectric conversion layer 4 by a spin coating method and heating to 180 ° C. to cure. The formation of the organic semiconductor thin film 5 is not limited to the spin coating method, and may be an appropriate method such as a vacuum deposition method. . In this embodiment, the thickness of the organic semiconductor thin film 5 is about 100 to 200 nm.

  When the organic semiconductor thin film 5 is formed, it is necessary not to contact the upper electrode 6 of the adjacent light receiving element, and an appropriate mask (not shown) is formed in advance before the organic semiconductor thin film is formed by spin coating. ) To selectively form an organic semiconductor thin film.

After the organic semiconductor thin film 5 is formed, an insulating protective layer 8 is formed on the entire upper surface of the organic semiconductor thin film 5 by forming an insulating protective film made of Al ₂ O ₃ or an antireflection film made of SiO ₂ . .

  In this way, an integrated light receiving element having a large number of light receiving elements can be obtained. In particular, by using the organic semiconductor thin film 5, the manufacturing process can be simplified and the cost can be reduced, and it can be integrated at a higher density.

  In the integrated light receiving element of this embodiment, ten light receiving elements are formed side by side on a straight line, and one light receiving element is formed with a circular light receiving surface having a diameter of 0.3 mm.

Receiving characteristics of the 10 integrated light-receiving device that the light-receiving element are integrated is similar to the characteristics of the single light receiving element, the dark current I _d is a ~300pA / mm ^2, the dark at a unit of the light-receiving element The value was 2-3 times larger than the current. This increase in dark current means that the photolithography process is not complete, the shape of the aperture for the light receiving surface provided in SiO ₂ is uneven, and the uniform formation of the organic semiconductor thin film cannot be controlled. Is the cause.

  The signal gain of the photocurrent in the integrated light receiving element of the present embodiment is generated when the organic semiconductor thin film 5 is operated under a bias condition that is positive, and the bias that makes the organic semiconductor thin film 5 negative under a bias condition of about 10V. It is multiplied by 5-50 times the photocurrent value when voltage is applied. The sensitivity wavelength reaches the visible-purple light wave, and the visible range sensitivity is 1.3 A / W (purple light wave) to 3 AA / W (red light wave), and it is 0.8 A / W for 400-350 nm near-ultraviolet purple light wave. High ultraviolet sensitivity was shown.

  The response speed of the integrated light receiving device of this embodiment is an AC bias method, the carrier traveling speed in the photoelectric conversion layer 4 is sufficiently fast, and the response speed of the device is limited by the CR time constant of the diode. In particular, when the light-receiving surface was circular with a diameter of 0.1 mm, a high-speed response of 200 MHz was confirmed. This response speed can be improved by integration with a reduced effective light receiving area.

  As can be seen from the integrated structure shown in FIG. 13, the light receiving element in the integrated light receiving element of this embodiment can easily realize the formation process of the organic semiconductor thin film 5 only by spin coating or vacuum deposition, and the integration process is also possible. Since it is simple, higher density two-dimensional integration is possible.

In particular, integration of the Si-organic semiconductor hybrid junction type photodetecting element has been attempted with p ^* -type CuPc in addition to PEDT / PSS. In this case, the organic semiconductor thin film is a low molecular organic material, and has an advantage that it can be formed with a uniform film thickness by a vacuum deposition method. The single or integrated light receiving element of the Si-organic semiconductor hybrid junction type photodetecting element can be applied to a highly sensitive CCD element up to the ultraviolet region. Si-Organic Semiconductor Hybrid Junction Photodetectors, whether single or integrated, can be selected from visible to ultraviolet by selecting organic semiconductor thin films with excellent Si-organic interface properties and establishing precision processing processes for organic films. High-sensitivity CCD is realized.

DESCRIPTION OF SYMBOLS 1 Lower electrode 2 Inorganic semiconductor substrate 3 Inorganic semiconductor layer 4 Photoelectric conversion layer 5 Organic semiconductor thin film 6 Upper electrode 7 Bias application means 8 Insulating protective layer 9 Intermediate insulating layer B Buffer layer R Guard ring

Claims (6)

In a photoelectric conversion element having an organic-inorganic hybrid junction structure,
The basic junction structure is composed of a p ^* type organic semiconductor thin film that is a hole transporting organic semiconductor thin film that functions as a hole emitter layer and window layer, and an inorganic semiconductor layer i that has a low carrier concentration and a high resistance. As a p ^* -i-p symmetrical junction structure composed of a p-type inorganic semiconductor photoelectric conversion layer and a p-type inorganic semiconductor collector layer,
A high-sensitivity organic-inorganic hybrid junction photoelectric conversion element that exhibits a signal gain of photocurrent by applying a DC or AC bias voltage of several to several tens of volts. In a photoelectric conversion element having an organic-inorganic hybrid junction structure,
The basic junction structure consists of an n ^* type organic semiconductor thin film which is an electron transport type organic semiconductor thin film functioning as an electron emitter layer and window layer, and an i type which is an inorganic semiconductor layer having a low carrier concentration and high resistance. As an n ^* -i-n symmetric junction structure composed of an inorganic semiconductor photoelectric conversion layer and an n-type inorganic semiconductor collector layer,
A high-sensitivity organic-inorganic hybrid junction photoelectric conversion element that exhibits a signal gain of photocurrent by applying a DC or AC bias voltage of several to several tens of volts.   By changing the application direction of the bias voltage, it is possible to select a signal multiplication type light receiving characteristic mode that generates a signal gain of photocurrent and a normal PIN type light receiving characteristic mode that does not generate a signal gain. The organic-inorganic hybrid junction photoelectric conversion element according to claim 1 or 2. In a photoelectric conversion element having an organic-inorganic hybrid junction structure,
Basic junction structure from the top of the device, transparent p ^* type organic semiconductor thin film which is a hole transport type organic semiconductor thin film, low carrier concentration and high resistance i type wide gap inorganic semiconductor layer, and n type wide gap inorganic semiconductor A transparent n ^* type organic semiconductor thin film which is a p ^* -i-n junction or an electron transport type organic semiconductor thin film, an i type wide gap inorganic semiconductor layer having a high carrier concentration and a high resistance, and a p type wide gap N ^* -i-p junction as an inorganic semiconductor layer,
An avalanche multiplication type blue-ultraviolet lightwave organic-inorganic hybrid junction type photoelectric conversion element characterized in that a signal avalanche multiplication type signal gain is developed by applying a DC bias voltage to the basic junction structure.   A plurality of organic-inorganic hybrid junction photoelectric conversion elements according to any one of claims 1 to 4 are formed on the same semiconductor substrate in a linear or planar manner at a predetermined interval, and the whole is formed with an antireflection film or protection. An integrated light-receiving element covered with a film. The organic-inorganic hybrid junction photoelectric conversion element according to any one of claims 1 to 4, or the integrated light receiving element according to claim 5,
All-solid-state deep ultraviolet and high-speed radiation that does not use a photomultiplier tube that is constructed by combining high-efficiency scintillation materials that convert high-energy radiation such as deep ultraviolet rays, X-rays, and gamma rays into the ultraviolet and visible light regions・ High sensitivity detection device.