JPH0218586B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a photoelectric conversion element. [Technical Background of the Invention] A photoelectric conversion element converts the amount of light projected onto a photoelectric conversion layer into an electrical signal amount corresponding to the amount of light from electrodes provided on the photoelectric conversion layer in parallel or sandwiching the photoelectric conversion layer. It can be extracted as The applications of such photoelectric conversion elements are wide-ranging, including photodiodes, image pickup tubes, and facsimile reading parts. Cadmium selenide (CdSe) is a photoconductive material that exhibits high photoelectric conversion efficiency in the visible region, and is used, for example, in image pickup tubes under the trade name Carnicon. FIG. 1 shows a simplified sectional view of the photoelectric conversion element of this carnicon. The substrate 1 is a transparent glass plate, and a NESA film is formed as an electrode 2 on one surface of the substrate 1. Furthermore , a cadmium selenide layer 4, a cadmium selenate layer 5 (CdSeO ₃ ) 5, and an arsenic trisulfide (As ₂ S ₃ ) layer 6 are sequentially superposed on this NESA electrode 2 as a photoelectric conversion layer 3. ing.
When the Nesa electrode 2 is used as one electrode, the other electrode is an electron beam 7 projected from an electron gun (not shown), focused on the upper surface of the arsenic trisulfide layer 6, and successively scanned. Flatten. When light 8 is projected onto the other surface of the substrate of such a photoelectric conversion element, the resistance of the photoelectric conversion layer 3 changes depending on the amount of light, and the resistance value of the portion onto which the light is projected becomes low. The change in resistance value can be read as the value of the current flowing between the NESA electrode 2 and the cathode by applying a constant voltage between the NESA electrode 2 and the cathode onto which the electron beam 7 is projected. This current is called photocurrent and is expressed as Ip. Also, the current that flows when light projection is stopped is called dark current and is expressed by Id. As a property of the photoelectric conversion layer 3 , when a certain amount of light 8 is projected, the larger Ip is, the better.
It is said to be a highly sensitive membrane. On the other hand, the smaller Id is, the better.
For example, when 1 lux of light 8 is projected onto the 1-inch photoelectric conversion layer 3 for an image pickup tube and a voltage of 25 V is applied to the Nesa electrode 2, Ip is 400 nA and Id is 1 nA. A part of this photoelectric conversion layer 3 will be changed as follows. First, cadmium selenide layer 4, cadmium selenide layer 5
After successively superimposing the cadmium selenate layer 5, a pair of electrodes 9 and 10 are formed on the cadmium selenate layer 5 as shown in the top view of FIG.
The a side is 2 mm, the b side is 5 mm, and the interval c is 0.25 mm. In this case, if a voltage of 1V is applied between electrode 9 and electrode 10 and light of 100 lux is projected, Ip = 3 x 10 ^-7 A and Id = 3 x 10 ^-12 A are obtained. At this time, the thickness of the photoelectric conversion layer consisting of the cadmium selenide layer 4 and the cadmium selenate layer 5 and lacking the arsenic trisulfide layer 6 is 1 μm, so the conductivity when light is projected is σp = 1.5×10 ^-4 /cm , and the conductivity when no light is projected is σd=1.5×10 ⁻⁹ /cm. [Problems with the background art] The conductivity σp of such a photoelectric conversion element when light is projected is a required value, for example, 1×10 ^-13 /cm
It is only a fraction of the above, and lacks sensitivity. [Purpose of the Invention] This invention improves the photoelectric conversion element whose main layer is cadmium selenide used in the above-mentioned form, and improves the photosensitivity by several times to several tens of times compared to the conventional one. The object of the present invention is to provide a photoelectric conversion element. [Summary of the Invention] That is, the present invention comprises a transparent substrate, a photoelectric conversion layer formed on at least one surface of this substrate and containing cadmium selenide as a main layer component, and an electrode formed on the surface of this photoelectric conversion layer. In the photoelectric conversion element, the photoelectric conversion layer is provided with a diffusion region between the substrate and the cadmium selenide layer. [Embodiments of the Invention] Examples will be described below. FIG. 3 is a cross-sectional view of this example, showing a transparent substrate 1, a photoelectric conversion layer 11 formed on one side surface of this substrate, and a photoelectric conversion layer 11 formed on one side surface of the substrate.
It consists of electrodes 9 and 10 formed on top of the electrodes 9 and 10. However, the shapes of the electrodes 9 and 10 are the same as those shown in FIG. The photoelectric conversion layer 11 includes a cadmium selenide layer 4 , a cadmium selenide layer 5 formed on the cadmium selenide layer, and a substrate 1 and the cadmium selenide layer 4 .
and a diffusion region 12 at the border. The substrate 1 is made of borosilicate glass having a thickness of 2 mm and a diameter of 26 mmφ and containing silicon dioxide and boron oxide as main components and containing aluminum oxide, iron oxide, calcium oxide, magnesium oxide, sodium oxide, potassium oxide, and arsenic oxide as other components. It consists of Above board 1
The thickness of the cadmium selenide layer 4 formed in
The thickness is preferably 0.5 μm to 3 μm, particularly 1 μm, and is formed by vapor deposition. The cadmium selenide layer 5 is obtained by heating the cadmium selenide in an oxygen and argon atmosphere containing selenium vapor, and may have a thickness of, for example, 0.1 μm. The diffusion region 12 formed between the substrate 1 and the cadmium selenide layer 4 is also formed during the above atmospheric treatment. A 10,000 times magnified electron micrograph of the diffusion region is shown in FIG. In the sample shown in the figure, cadmium selenide was deposited directly on a borosilicate glass substrate, then subjected to the heat activation treatment described above, and then the cadmium selenide layer was removed by etching to form a layer on the glass substrate. is exposed. The figure is a scanning electron micrograph of the surface of this substrate. From the figure, island-like regions corresponding to particles of the cadmium selenide layer can be seen on the surface of the glass substrate. This part is a layer of interdiffused regions of glass substrate material and cadmium selenide. Note that the dotted areas with strong contrast between white and black in the same figure correspond to the intersections of multiple grain boundaries.
It is mainly a concave part made of glass. The photoelectric conversion layer 11 having such a diffusion region exhibits particularly strong sensitivity to light and small dark current,
When used in an image pickup tube, the sensitivity is 60 times higher than that of the photoelectric conversion layer 3 shown in FIG. 1 whose main component is cadmium selenide. Electrodes 9 and 10 of the photoelectric conversion element shown in FIG.
When a voltage of 1V is applied between them and 100 lux of light is projected, Ip = 2 × 10 ^-5 A, Id = 1.6 × 10 ^-11 A are obtained, and the conductivity when light is projected is σp = 1 ×10 ^-2 /
cm, conductivity when no light is projected σd=8×10 ^-9 /
cm, and exhibits a photosensitivity 60 times that of the photoelectric conversion layer 3 in FIG. The reason why such high sensitivity is obtained can be explained as follows. Each sample had a tin oxide (SnO ₂ ) layer, a tantalum pentoxide (Ta ₂ O ₅ ) layer, or a silicon dioxide (SiO ₂ ) layer formed on the substrate 1, and a sample with the substrate 1 as it was. Prepare different types of samples. Each of the three components formed on the substrate 1 is
It is transparent with a thickness of 0.2-1 μm. A photoelectric conversion layer 11 and electrodes 9 and 10 are simultaneously formed on each of these samples by the same method as described in the example. After measuring Ip and Id for each sample, the photoelectric conversion layer 11
A part of the diffusion region 12 is removed by dissolving it with dilute nitric acid.
Detect the presence or absence of. View results. From this table, the presence or absence of the diffusion region 12 and the size of σp match well,
It can be seen that only the sample with a diffused region shows both high sensitivity and small dark current. It can be inferred that formation of such a diffusion region was prevented by the NESA electrode 2 in the case of the conventional image pickup tube. [Table] The diffusion region 12 is generated using cadmium selenide 4
is greatly influenced by the material of the substrate with which it comes in contact, but other factors include the presence or absence of oxygen and the temperature when heat-treating cadmium selenide 4. If the atmosphere during treatment does not contain oxygen, the diffusion region 12 No formation occurs, σp = 2×10 ^-5 /cm, σd = 1×10 ^-9 /cm, and the photosensitivity is also extremely low. Further, even in a mixed atmosphere of oxygen and selenium, at temperatures below 500° C., the diffusion region 12 is hardly formed and the photosensitivity is 1/100 or less. A photoelectric conversion element whose main layer component is cadmium selenide, which is distributed on the substrate by forming a diffusion region 12 between it and the substrate, has another advantage that it can be independently mounted on a single substrate as shown in FIG. When two or more of the photoelectric conversion elements 131 , 132 , . [Effects of the Invention] As described above, in a photoelectric conversion element whose main layer component is cadmium selenide, the sensitivity to light is significantly improved by forming a diffusion region between the substrate and the cadmium selenide layer. It also improves the adhesion strength to the substrate, and enables the formation of finer patterns when independent photoelectric conversion elements are formed on the same substrate.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of a conventional photoelectric conversion element whose main layer component is cadmium selenide, Figure 2 is a diagram of the shape of the electrode used for measurement, Figure 3 is a cross-sectional view of the photoelectric conversion element of the present invention, and Figure 4. 5 is an electron micrograph showing an enlarged diffusion region, and FIG. 5 is a sectional view of a photoelectric conversion element group of the present invention. DESCRIPTION OF SYMBOLS 1... Substrate, 2... Electrode Nesa film, 3 ... Photoelectric conversion layer, 4... Cadmium selenide layer, 5... Cadmium selenite layer, 6... Arsenic trisulfide layer, 7...
Electron beam, 8... Light, 9... Electrode, 10... Electrode, 11 ... Photoelectric conversion layer, 12... Diffusion region, 1
31-13n ...Photoelectric conversion element.

Claims (1)

[Claims] 1. A photoelectric conversion element comprising a transparent substrate, a photoelectric conversion layer formed directly on the surface of the substrate and having cadmium selenide as a main layer component, and an electrode formed on the surface of the photoelectric conversion layer. The substrate is made of borosilicate glass containing silicon oxide and boron oxide as main components, and an interdiffusion region of the transparent substrate material and cadmium selenide is formed between the substrate and the cadmium selenide layer. Features of photoelectric conversion elements.