JP2014127444A - Photoelectric conversion element, image pickup element, and image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-sensitivity photoelectric conversion element, etc.SOLUTION: The photoelectric conversion element comprises a charge generation layer 13 in which an electric charge is generated by incident light, and a near-field photoelectric conversion layer 14 in which near-field light is generated by incident light, and an electric charge is generated by the generated near-field light. The charge generation layer 13 may preferably be configured from an amorphous Se as main constituent, in which case it is preferable that, in the near-field photoelectric conversion layer 14, the near-field light is generated by a 600 nm-750 nm wavelength component among incident light.

Description

  The present invention relates to a photoelectric conversion element that performs photoelectric conversion, an imaging element that includes the photoelectric conversion element, and an imaging apparatus that includes the imaging element.

  2. Description of the Related Art Conventionally, there has been known an imaging apparatus including a target unit provided with a face plate, a target electrode, and a photoconductive film, and a scanning electron beam generating unit that irradiates the target unit with an electron beam. In this imaging device, when light is incident on the target portion, charges (electron / hole pairs) corresponding to the light intensity of the incident light are generated in the photoconductive film near the target electrode. Of these, the holes are amplified by avalanche multiplication and accumulated on the electron beam irradiation side of the target portion. Then, the holes accumulated in the target unit and the electrons of the electron beam are combined, and a current flowing in the external circuit at the time of combination is taken out as an output, thereby obtaining a video signal corresponding to the incident light image (see Patent Document 1). .

Japanese Patent Laid-Open No. 7-029507

  The conventional imaging device has a peak of photoelectric conversion efficiency at a wavelength of around 400 nm due to the characteristics of amorphous Se (selenium) constituting the photoconductive film (first photoelectric conversion layer) (band gap is about 2.0 eV). In the vicinity of 650 nm (red light) having a wavelength longer than 620 nm, almost no photoelectric conversion is performed. For this reason, the sensitivity to red light is low, which causes a problem particularly in colorization of the imaging device. To solve this problem, it has been proposed to add Te (tellurium) having a band gap of about 0.3 eV as a sensitizer to improve sensitivity to red light. However, as the amount of Te added is increased, dark current increases, burn-in and image defects (so-called white flaws) occur. Therefore, improvement in sensitivity due to Te addition has a limit.

  An object of the present invention is to provide a high-sensitivity photoelectric conversion element, an image pickup element including the photoelectric conversion element, and an image pickup apparatus including the image pickup element.

  The photoelectric conversion element of the present invention includes a first photoelectric conversion layer in which charges are generated by incident light, and a second photoelectric conversion layer in which near-field light is generated by incident light and charges are generated by the generated near-field light. And.

It is a figure which shows the imaging device which concerns on embodiment. It is a figure which shows the electron emission part of each image pick-up element in an imaging device. It is a figure which shows the image pick-up element which concerns on the 1st modification of an imaging device. It is a figure which shows the image pick-up element which concerns on the 2nd modification of an imaging device.

  Hereinafter, a photoelectric conversion element according to an embodiment of the present invention, an imaging element including the photoelectric conversion element, and an imaging apparatus including the imaging element will be described with reference to the accompanying drawings. The imaging apparatus according to the present embodiment is, for example, a color imaging camera, and includes a plurality of (for example, three) imaging elements and constitutes color image data of an imaging target.

  As shown in FIG. 1, the imaging apparatus 100 is incident from three imaging elements 1 (red imaging element 1R, green imaging element 1G, and blue imaging element 1B) corresponding to RGB three colors and an object to be imaged. And an optical element 2 (for example, a color separation prism) that splits the separated light into RGB three-color branched light. In the imaging apparatus 100, the light incident from the imaging target is split into RGB three-color branched light (red light R, green light G, and blue light B) by the optical element 2, and the red light R is applied to the red imaging element 1R. The green light G is incident on the green image sensor 1G, and the blue light B is incident on the blue image sensor 1B.

  Each imaging element 1 includes a photoelectric conversion element 10 on which light from an object to be imaged is incident, an electron emission unit 20 disposed in close proximity to the photoelectric conversion element 10, and the photoelectric conversion element 10 and the electron emission unit 20. And a mesh electrode 30 that controls the trajectory of emitted electrons.

  Although details will be described later, in the photoelectric conversion element 10, holes are generated by the incident light, and a hole pattern corresponding to the incident light image is accumulated on the electron emission unit 20 side of the photoelectric conversion element 10. On the other hand, the electron emission unit 20 emits electrons to the photoelectric conversion element 10 through the mesh electrode 30. When the holes accumulated in the photoelectric conversion element 10 and the electrons emitted from the electron emission unit 20 are combined, a current flows in the external circuit, and this is taken out as an output to obtain a video signal corresponding to the incident light image. It is done. First, the electron emission unit 20 will be described.

  The electron emission unit 20 may be a thermal electron source or the like, but a cold cathode array type can be suitably used as shown in FIG. The electron emission unit 20 includes an electron emission substrate 21 made of a silicon substrate, a drive circuit layer (not shown) formed on the electron emission substrate 21, and a plurality of elements arranged in a matrix on the drive circuit layer. (For example, 640 × 480) electron sources 22 and a horizontal scanning circuit 23 and a vertical scanning circuit 24 formed around the electron emission substrate 21.

  Although not shown, each electron source 22 is composed of a MIS (Metal-Insulator-Semiconductor) type cold cathode electron source, and includes a lower electrode and an upper electrode, and a higher voltage is applied to the upper electrode than the lower electrode. Then, electrons are emitted from the emission sites 26 (recesses) provided on the surface in a plurality (for example, 3 × 3). The lower electrode is formed for each electron source 22, and the upper electrode is common to all the electron sources 22.

  The drive circuit layer is formed of a MOS (Metal-Oxide-Semiconductor) transistor, the drain electrode is connected to the lower electrode, and the gate electrode and the source electrode are connected to the horizontal scanning circuit 23 and the vertical scanning circuit 24, respectively. Yes. A positive voltage is applied to the upper electrode, and the drain potential of each electron source 22 is controlled by the horizontal scanning circuit 23 and the vertical scanning circuit 24 based on an external clock signal, synchronization signal, etc. Sequentially, electrons can be emitted. The emitted electrons are drawn out to the photoelectric conversion element 10 side through the mesh electrode 30 and reach the charge generation layer 13 (described later) of the photoelectric conversion element 10.

  Next, the photoelectric conversion element 10 and the video signal output from the photoelectric conversion element 10 will be described with reference to FIG. The photoelectric conversion element 10 of each imaging element 1 is provided with a translucent substrate 11, a translucent electrode film 12, and a charge generation layer 13 in this order from the light incident side. Furthermore, the photoelectric conversion element 10 of the red imaging element 1 </ b> R includes a near-field photoelectric conversion layer 14 between the translucent electrode film 12 and the charge generation layer 13. The charge generation layer 13 in the red imaging device 1R is an example of the “first photoelectric conversion layer” in the claims, and the near-field photoelectric conversion layer 14 is the “second photoelectric conversion layer” in the claims. It is an example.

  The translucent substrate 11 only needs to be made of a material that allows incident light to pass therethrough, and glass, quartz glass, or the like can be selected as appropriate in accordance with an imaging application (light wavelength).

A predetermined positive voltage is applied to the translucent electrode film 12 via a connection terminal (not shown), and a high electric field (for example, 10 ⁸ V / m or more) is generated in the charge generation layer 13. The translucent electrode film 12 only needs to be made of a material that transmits incident light and has a low electrical resistance. For example, ITO (Indium Tin Oxide), IZO (Indium Zinc Oxide), and AZO (Aluminium doped Zinc Oxide). ) Etc. can be used.

  The charge generation layer 13 is not particularly limited as long as charges (electron / hole pairs) are generated by incident light, but those having an action of amplifying the generated holes are preferable in order to improve sensitivity. Amorphous Se that causes avalanche multiplication can be preferably used.

  When light enters the charge generation layer 13, electron / hole pairs corresponding to the light intensity (light quantity) of the incident light are generated in the charge generation layer 13 in the vicinity of the translucent electrode film 12. Among these holes, holes are accelerated by a high electric field applied through the translucent electrode film 12, and are amplified by repeating collision ionization with Se atoms (avalanche multiplication). As a result, amplified holes are accumulated on the electron emission portion 20 side of the charge generation layer 13 and a hole pattern reflecting the incident light image is formed. The electrons sequentially emitted from each electron source 22 and the holes accumulated in the region corresponding to each electron source 22 are sequentially combined. A video signal corresponding to the incident light image can be obtained by taking out the current flowing in the external circuit as an output at the time of the coupling. That is, a video signal corresponding to the incident light image is output in units of the electron source 22.

  Note that various additives may be added to the amorphous Se in order to impart various characteristics to the charge generation layer 13. For example, As (arsenic) is added to improve the thermal stability of the amorphous Se. Alternatively, fluoride or the like may be added to control the electric field in the charge generation layer 13. The various additives need not be contained uniformly in the charge generation layer 13, and the composition distribution may occur in the film thickness direction.

Furthermore, the charge generation layer 13 may have a layer made of other materials having various functions in addition to a layer mainly composed of amorphous Se. For example, CeO ₂ (cerium oxide) is formed on the translucent electrode film 12 side of the charge generation layer 13 in order to prevent the injection of holes and electrons from the outside to the charge generation layer 13 which causes dark current (noise). May be provided, or an electron injection blocking layer formed of Sb ₂ S ₃ (antimony sulfide) or the like may be provided on the electron emission portion 20 side of the charge generation layer 13. Good.

  Here, amorphous Se causes avalanche multiplication under a high electric field as described above. On the other hand, since the band gap is about 2.0 eV, there is a peak of photoelectric conversion efficiency in the vicinity of 400 nm, and a wavelength of 620 nm or more. Almost no photoelectric conversion is performed on the light. Therefore, when green light G or blue light B is incident on the charge generation layer 13, holes are accumulated, but even when red light R is incident on the charge generation layer 13, almost no holes are accumulated. Therefore, among the three image pickup devices 1, the photoelectric conversion element 10 of the red image pickup device 1R generates near-field light by the incident red light R and charges (electron / hole pairs) by the generated near-field light. The near-field photoelectric conversion layer 14 is generated.

  The near-field photoelectric conversion layer 14 is configured by a nanostructure so that near-field light is generated when light in a wavelength region of 600 nm to 750 nm including red light R is incident. The material of the near-field photoelectric conversion layer 14 is not particularly limited as long as charges are generated by near-field light. For example, a metal, a transparent electrode, a semiconductor, a conductive polymer, or the like can be used. .

  When the red light R hits the near-field photoelectric conversion layer 14, near-field light is generated on the surface (nanostructure). The generated near-field light (virtual photons) is combined with free electrons on the surface of the near-field photoelectric conversion layer 14 to become dressed photon photons (dressed photons). The energy level of the atoms in the vicinity of the dressed photon photon is excited, and an electron / hole pair is generated. The holes generated in the near-field photoelectric conversion layer 14 are also amplified by avalanche multiplication when injected into the charge generation layer 13.

  Among the image pickup devices 1 configured as described above, in the red image pickup device 1R, in the charge generation layer 13, almost no charge is generated by the incident red light R, but in the near-field photoelectric conversion layer 14, Near-field light is generated by the red light R, and electric charges are generated by the near-field light. Then, the holes generated in the near-field photoelectric conversion layer 14 are amplified in the charge generation layer 13, and an amount of holes corresponding to the light intensity of the red light R is accumulated. By combining these holes and electrons, an image signal reflecting the light intensity of the red light R is output. Based on this red video signal, the light intensity of the red light R can be obtained.

  In the green image sensor 1G, when the green light G is incident on the charge generation layer 13, holes in an amount corresponding to the light intensity of the green light G accumulate in the charge generation layer 13. By combining the holes and the electrons, a video signal (green video signal) reflecting the light intensity of the green light G is output. Based on the green video signal, the light intensity of the green light G can be obtained. Similarly, when the blue light B is incident on the blue image sensor 1B, a video signal (blue video signal) reflecting the light intensity of the blue light B is obtained, and the light intensity of the blue light B is determined based on the blue video signal. Can be obtained.

  As described above, according to the imaging apparatus 100 of the present embodiment, the red imaging element 1R among the plurality of imaging elements 1 generates near-field light not only from the charge generation layer 13 but also from the incident red light R. In addition, by providing the near-field photoelectric conversion layer 14 in which charges are generated by the generated near-field light, the sensitivity to the red light R can be improved. Furthermore, the light intensity of the wavelength component of the green light G and the light intensity of the wavelength component of the blue light B can be obtained from the green image sensor 1G and the blue image sensor 1B. Color image data can be constructed.

  The green image sensor 1G and the blue image sensor 1B are not particularly necessary because the green light G and the blue light B having high photoelectric conversion efficiency in the charge generation layer 13 are incident. Similarly, the photoelectric conversion element 10 may include a near-field photoelectric conversion layer 14. In this case, the wavelength of the light generated by the dressed photon photons can be controlled by optimizing the size of the unevenness of the nanostructure (the wavelength at which the most near-field light is generated). That is, the near-field photoelectric conversion layer 14 in the red image sensor 1R, the near-field photoelectric conversion layer 14 in the red image sensor 1R, the near-field photoelectric conversion layer 14 in the green image sensor 1G, and the blue image sensor 1B. What is necessary is just to change the magnitude | size of the unevenness | corrugation of a nanostructure with the near field photoelectric conversion layer 14. FIG.

When the green imaging element 1G includes the near-field photoelectric conversion layer 14, charges are also generated in the near-field photoelectric conversion layer 14, and therefore, in the charge generation layer 13, holes generated in the charge generation layer 13 are generated. In addition, since holes generated in the near-field photoelectric conversion layer 14 are amplified and accumulated, the sensitivity to the green light G can be further improved. Similarly, when the blue imaging element 1B includes the near-field photoelectric conversion layer 14, the sensitivity to the blue light B can be further improved.
Of course, by optimizing the size of the unevenness of the nanostructure, it is possible to improve the sensitivity to wavelength regions other than RGB including ultraviolet rays and infrared rays.

  Then, the modification of the photoelectric conversion element 10 which concerns on this embodiment is demonstrated. About each modification, it demonstrates centering on a different point from the above-mentioned image sensor 1. FIG. Similar components are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the imaging device 100 of the first and second modified examples, the position of the near-field photoelectric conversion layer 14 in the photoelectric conversion element 10 of the red imaging element 1R is different from that of the photoelectric conversion element 10 described above.

  As shown in FIG. 3, the photoelectric conversion element 10 of the red imaging element 1 </ b> R according to the first modified example includes a light-transmitting substrate 11, a light-transmitting electrode film 12, and a charge generation layer 13 from the light incident side. The near-field photoelectric conversion layer 14 is provided in the charge generation layer 13 in order.

  As shown in FIG. 4, the photoelectric conversion element 10 of the red imaging element 1 </ b> R according to the second modified example includes a translucent substrate 11, a translucent electrode film 12, a charge generation layer 13, and a near field from the light incident side. The photoelectric conversion layer 14 is provided in this order. That is, the near-field photoelectric conversion layer 14 is provided on the electron emission unit 20 side.

  Also in the first modification and the second modification described above, the sensitivity to the red light R can be improved because the photoelectric conversion element 10 includes the near-field photoelectric conversion layer 14 in the red imaging element 1R.

  In the above embodiment and its modification, the case where the imaging apparatus 100 includes a plurality of imaging elements 1 has been described. However, the present invention is not limited to this, and a single imaging element 1 is provided. It may be a thing. In this case, when the near-field photoelectric conversion layer 14 is viewed from the light incident side, near-field light is generated by a certain wavelength component (for example, red light R) of the incident light, and charges are generated by the generated near-field light. And a non-near field region in which near-field light is not generated (no charge is generated) by the wavelength component (red light R) of incident light, for example, is divided into stripes or dots. It is preferable. In this case, the imaging device 1 is obtained based on the video signal (reflecting the light intensity of the wavelength component of the red light R) obtained based on the light incident on the near-field region and the light incident on the non-near-field region. The light intensity of the red light R can be calculated based on the difference from the video signal (not reflecting the light intensity of the wavelength component of the red light R). By doing in this way, the color image data of an imaging target object can be comprised with the single image pick-up element 1. FIG.

  1: imaging element, 2: optical element, 10: photoelectric conversion element, 13: charge generation layer, 14: near-field photoelectric conversion layer, 20: electron emission unit, 100: imaging element

Claims (8)

A first photoelectric conversion layer in which charges are generated by incident light;
A second photoelectric conversion layer in which near-field light is generated by the incident light and a charge is generated by the generated near-field light;
A photoelectric conversion element comprising: The first photoelectric conversion layer is mainly composed of amorphous Se,
2. The photoelectric conversion element according to claim 1, wherein the second photoelectric conversion layer generates the near-field light with a wavelength component of 600 nm to 750 nm in the light. A substrate,
An electrode for applying an electric field to the first photoelectric conversion layer,
3. The device according to claim 1, wherein the substrate, the electrode, the second photoelectric conversion layer, and the first photoelectric conversion layer are provided in this order from the light incident side. Photoelectric conversion element. A substrate,
An electrode for applying an electric field to the first photoelectric conversion layer,
The substrate, the electrode, and the first photoelectric conversion layer are provided in this order from the light incident side, and the second photoelectric conversion layer is provided in the first photoelectric conversion layer. The photoelectric conversion element according to claim 1, wherein: A substrate,
An electrode for applying an electric field to the first photoelectric conversion layer,
4. The device according to claim 1, wherein the substrate, the electrode, the first photoelectric conversion layer, and the second photoelectric conversion layer are provided in this order from the light incident side. 5. Photoelectric conversion element. The photoelectric conversion element according to any one of claims 1 to 5,
An electron emission portion for emitting electrons to the photoelectric conversion element;
An image pickup device comprising:   An image pickup apparatus comprising the image pickup device according to claim 6. A plurality of image sensors;
A spectroscopic element that splits the incident light into a plurality of branched lights and enters the plurality of imaging elements, and
An image pickup apparatus, wherein at least one of the plurality of image pickup elements includes the image pickup element according to claim 6.

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