JP2014143261A - Photoelectric conversion element and imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a photoelectric conversion element capable of reducing generation of an afterimage or burning while preventing generation of a white flaw due to crystallization of amorphous selenium; and the like.SOLUTION: A photoelectric conversion element includes a photoelectric conversion layer 13 which mainly comprises amorphous selenium and in which an electric charge is generated by incident light. The photoelectric conversion layer 13 includes a first arsenic-containing region 131 containing arsenic, a second arsenic-containing region 132 containing arsenic with a concentration different from that of arsenic in the first arsenic-containing region 131, and a sulfide region 133 comprising a sulfide, in the order from an incident side, on the opposite side of the incident side.

Description

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

Conventionally, a target portion that is mainly composed of amorphous selenium and has an amorphous photoconductive film that generates charges by incident light, and an electron beam that scans the electron beam from the side opposite to the light incident side with respect to the target portion An imaging apparatus including a generation unit is known. In this imaging apparatus, 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 amorphous photoconductive film. Of these, holes are amplified by avalanche multiplication in an amorphous photoconductive film to which a high electric field is applied, and are accumulated on the electron beam scanning 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 through 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.
The amorphous photoconductive film has a heat-resistant reinforcing layer containing 10 to 40% by weight of arsenic and a beam landing layer in this order from the light incident side. This heat-resistant reinforcing layer prevents thermal change (crystallization) of amorphous selenium that causes image defects (so-called white scratches). Here, since arsenic forms an electron capture level in amorphous selenium, if it is added to the entire region in the film thickness direction of the amorphous photoconductive film, an afterimage or seizure occurs. The reinforcing layer is provided on a part of the amorphous photoconductive film (on the side opposite to the light incident side) (see Patent Document 1).

JP 2002-319354 A

  In a conventional target unit (photoelectric conversion element), when an electron emitted from an electron beam generating unit (electron emitting unit) is combined with a hole in a beam landing layer (scanning sulfide region), an afterimage or a burn-in In practice, however, electrons may enter the heat-resistant reinforcing layer (second arsenic-containing region). In particular, when there are a large number of electrons that have entered, since the electrons are captured at the electron capture level formed by arsenic containing 10 to 40% by weight in the heat-resistant strengthening layer, afterimages and image sticking have occurred. It was.

  An object of the present invention is to provide a photoelectric conversion element capable of reducing the occurrence of afterimages and image sticking while preventing the generation of white scratches due to crystallization of amorphous selenium, and an image pickup element including the photoelectric conversion element.

  The photoelectric conversion element of the present invention is composed mainly of amorphous selenium, and includes a photoelectric conversion layer that generates charges by incident light. The photoelectric conversion layer contains arsenic on the side opposite to the incident side. One arsenic-containing region, a second arsenic-containing region containing arsenic at a concentration different from that of the first arsenic-containing region, and a sulfide region composed of sulfides are arranged in this order from the incident side. .

It is sectional drawing which shows the image pick-up element which concerns on embodiment. It is a figure which shows an electron emission part.

  Hereinafter, with reference to the accompanying drawings, a photoelectric conversion element according to an embodiment of the present invention and an imaging element including the photoelectric conversion element will be described. The imaging device of the present embodiment is incorporated in an imaging device such as a camera and constitutes image data of an imaging target.

  As shown in FIG. 1, the 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 that is disposed in close proximity to the photoelectric conversion element 10, and a photoelectric conversion element. 10 and the electron emission part 20, and a mesh electrode 30 that controls the trajectory of the 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 briefly 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 a photoelectric conversion layer 13 (described later) of the photoelectric conversion element 10.

  Next, the photoelectric conversion element 10 will be described with reference to FIG. The photoelectric conversion element 10 includes a light-transmitting substrate 11, a light-transmitting electrode film 12, and a photoelectric conversion layer 13 in this order from the light incident side.

  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).

The translucent electrode film 12 is formed to have a thickness of 15 to 30 nm, for example, and a predetermined positive voltage is applied via a connection terminal (not shown) to apply a high electric field (for example, 10 ⁸ V / m) to the photoelectric conversion layer 13. Above). 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. Further, the translucent electrode film 12 can be formed of a metal thin film.

  The photoelectric conversion layer 13 is made of a material mainly composed of amorphous selenium, and charges (electron / hole pairs) are generated by incident light, and the generated holes are amplified. That is, when light enters the photoelectric conversion layer 13, electron / hole pairs corresponding to the light intensity (light quantity) of the incident light are generated in the photoelectric conversion 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). Thereby, the amplified holes are accumulated on the electron emission portion 20 side of the photoelectric conversion 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.

  In the photoelectric conversion layer 13, a photoconductive region 130, a first arsenic-containing region 131, a second arsenic-containing region 132, and a sulfide region 133 are formed in this order from the light incident side. . Although details will be described later, crystallization of amorphous selenium constituting the photoelectric conversion layer 13 is suppressed by the arsenic contained in the first arsenic-containing region 131 and the second arsenic-containing region 132.

  Then, each area | region in the photoelectric converting layer 13 is demonstrated. First, the photoconductive region 130 is made of amorphous selenium, but may contain various additives such as arsenic as necessary.

  The sulfide region 133 is made of sulfide (for example, antimony sulfide), and makes the electrons emitted from the electron emission unit 20 land. The sulfide region 133 also functions as an electron injection blocking layer that prevents the injection of unnecessary electrons from the outside into the photoelectric conversion layer 13 that causes dark current. Note that the sulfide region 133 may contain amorphous selenium, arsenic, or the like.

  The first arsenic-containing region 131 and the second arsenic-containing region 132 contain arsenic that increases the crystallization temperature of amorphous selenium. In the case where the first arsenic-containing region 131 and the second arsenic-containing region 132 are not provided, the amorphous selenium forming the main body of the photoelectric conversion layer 13 has a low crystallization temperature, and thus crystallization proceeds gradually even at room temperature. Since the resistance of the crystallized portion is lowered, current flows easily, and image defects (so-called white scratches) in which dark current is locally concentrated are generated. In contrast, by providing the first arsenic-containing region 131 and the second arsenic-containing region 132 in the photoelectric conversion layer 13, the crystallization temperature of amorphous selenium increases due to arsenic contained in both regions, and white scratches are generated. It is suppressed.

In addition, since arsenic forms an electron capture level in amorphous selenium, if it is added to the entire region in the thickness direction of the photoelectric conversion layer 13, afterimages and seizures are generated, so that arsenic contains a first arsenic The region 131 and the second arsenic-containing region 132 may be provided in a part of the photoelectric conversion layer 13, that is, on the side opposite to the light incident side (on the side of the electron emission unit 20), and in the vicinity of the sulfide region 133. It is preferable to provide it.
Here, “close to the light incident side” means closer to the light incident side than the intermediate position in the thickness direction (light incident direction) of the photoelectric conversion layer 13.

  The first arsenic-containing region 131 is formed, for example, to a thickness of 500 nm or less, and the arsenic content concentration is higher than the content concentration in the second arsenic-containing region 132 described later, and is 10 wt% or more and 40 wt% or less. It is preferable that

  On the other hand, the second arsenic-containing region 132 is formed to have a thickness of 50 nm or less, for example, and the arsenic content concentration is preferably 0.1 wt% or more and 3 wt% or less.

  When the electrons emitted from the electron emitting portion 20 are combined with holes in the sulfide region 133 described above, no afterimage or seizure occurs, but actually, the electrons are present in the second arsenic-containing region 132. May enter. In particular, when there are a large number of entering electrons and the concentration of arsenic in the second arsenic-containing region 132 is high, the electrons that have entered the electron capture level formed by arsenic are captured, which may cause afterimages and image sticking. However, if the concentration of arsenic in the second arsenic-containing region 132 is 3% by weight or less, afterimages and image sticking due to electrons entering the second arsenic-containing region 132 are reduced.

  Moreover, if the content density | concentration of the arsenic in the 2nd arsenic content area | region 132 is 0.1 weight% or more, crystallization of the amorphous selenium which comprises the photoelectric converting layer 13 can be suppressed appropriately. Furthermore, the first arsenic-containing region 131 having an arsenic concentration higher than that of the second arsenic-containing region 132 is provided on the light incident side of the second arsenic-containing region 132, whereby amorphous selenium constituting the photoelectric conversion layer 13 is provided. Can be reliably suppressed. Further, if the arsenic concentration in the first arsenic-containing region 131 is 40% by weight or less, the occurrence of image defects due to high concentration of arsenic can be prevented.

  Note that the second arsenic-containing region 132 is preferably provided in contact with the sulfide region 133, whereby the thermal stability of the sulfide region 133 can be improved and the landing characteristics can be maintained.

  In this embodiment, the arsenic concentration in the first arsenic-containing region 131 close to the photoconductive region 130 is high, and the arsenic content in the second arsenic-containing region 132 close to the sulfide region 133 is low. On the contrary, the arsenic content concentration in the first arsenic-containing region 131 may be lowered and the arsenic content concentration in the second arsenic-containing region 132 may be increased. In the photoelectric conversion element 10, other layers may be interposed between the above-described layers and regions. For example, a hole injection blocking layer that prevents injection of unnecessary holes from the translucent electrode film 12 to the photoelectric conversion layer 13 is provided between the translucent electrode film 12 and the photoelectric conversion layer 13. Also good.

Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.
[Example 1]
As shown in FIG. 1, the light-transmissive electrode film 12 and the photoelectric conversion layer 13 were sequentially laminated on the light-transmissive substrate 11 to manufacture the photoelectric conversion element 10.
・ Translucent electrode film 12
The translucent electrode film 12 was formed to a thickness of 20 nm by IZO.
-Photoelectric conversion layer 13
The photoconductive region 130 was made of amorphous selenium and formed to a thickness of 14.5 μm. The first arsenic-containing region 131 was composed of arsenic selenide (As ₂ Se ₃ ) (arsenic concentration was 39% by weight) and formed to a thickness of 460 nm. The second arsenic-containing region 132 was composed of amorphous selenium and arsenic (the concentration of arsenic was 2.3 wt%), and was formed to a thickness of 33 nm. The sulfide region 133 was made of antimony sulfide and formed to a thickness of 1 μm.
In the image pickup device 1 including the photoelectric conversion element 10 of Example 1, no white flaws occurred, and no afterimage or image sticking occurred. Further, the landing characteristics did not change before and after heating at 50 ° C.

[Example 2]
The photoelectric conversion element 10 was manufactured in the same manner as in Example 1 except that the concentration of arsenic in the first arsenic-containing region 131 was 10%.
In the image pickup device 1 including the photoelectric conversion device 10 of Example 2, the generation of white scratches due to crystallization of amorphous selenium was slightly observed, but the level was not a problem as an image pickup device.

[Example 3]
A photoelectric conversion element 10 was manufactured in the same manner as in Example 1 except that the concentration of arsenic in the second arsenic-containing region 132 was 5%.
In the image pickup device 1 including the photoelectric conversion device 10 of Example 3, generation of white scratches was not recognized. In addition, the occurrence of afterimages and image sticking was slightly observed, but the level was satisfactory for an imaging device.

[Comparative Example 1]
The photoelectric conversion element 10 was manufactured in the same manner as in Example 1 except that the sulfide region 133 was provided on the first arsenic-containing region 131 without providing the second arsenic-containing region 132.
In the image pickup device 1 including the photoelectric conversion element 10 of Comparative Example 1, no white flaws were generated, but afterimages and image sticking occurred. Further, the landing characteristics did not change before and after heating at 50 ° C.

[Comparative Example 2]
The photoelectric conversion element 10 was manufactured in the same manner as in Example 1 except that the second arsenic-containing region 132 was provided on the photoconductive region 130 without providing the first arsenic-containing region 131.
In the imaging device 1 including the photoelectric conversion element 10 of Comparative Example 2, no afterimage or image sticking occurred, but white scratches occurred. Further, the landing characteristics did not change before and after heating at 50 ° C.

[Comparative Example 3]
The photoelectric conversion element 10 was manufactured in the same manner as in Example 1 except that the sulfide region 133 was provided on the photoconductive region 130 without providing the first arsenic-containing region 131 and the second arsenic-containing region 132.
In the image sensor 1 including the photoelectric conversion element 10 of Comparative Example 3, no afterimage or image sticking occurred, but white scratches occurred. In addition, the landing characteristics after heating at 50 ° C. deteriorated.

  As described above, according to the imaging device 1 of Example 1, the first arsenic-containing region 131 having a high arsenic content concentration is provided, and the sulfide region 133 side (electron emission unit 20) from the first arsenic-containing region 131. The second arsenic-containing region 132 having a low arsenic concentration is provided on the side), while suppressing generation of white scratches due to crystallization of amorphous selenium constituting the photoelectric conversion layer 13. It was possible to reduce the occurrence of afterimages and image sticking due to electrons entering the surface.

  1: imaging device, 10: photoelectric conversion device, 13: photoelectric conversion layer, 130: photoconductive region, 131: first arsenic-containing region, 132: second arsenic-containing region, 133: sulfide region

Claims (5)

A photoelectric conversion layer that is mainly composed of amorphous selenium and generates charges by incident light,
The photoelectric conversion layer is closer to the side opposite to the incident side,
A first arsenic-containing region containing arsenic;
A second arsenic-containing region containing arsenic in a concentration different from the first arsenic-containing region;
A sulfide region composed of sulfides;
In this order from the incident side. One of the first arsenic-containing region and the second arsenic-containing region has an arsenic content concentration of 0.1 wt% or more and 3 wt% or less,
2. The photoelectric conversion element according to claim 1, wherein the other region has an arsenic concentration higher than that of the one region and 40% by weight or less. The first arsenic-containing region is the other region;
The photoelectric conversion element according to claim 2, wherein the second arsenic-containing region is the one region. The first arsenic-containing region is the one region;
The photoelectric conversion element according to claim 2, wherein the second arsenic-containing region is the other region. The photoelectric conversion element according to any one of claims 1 to 4,
An electron emitting portion that emits electrons from the side opposite to the incident side with respect to the photoelectric conversion element,
An image pickup device comprising:

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