JPH0380305B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an electrophotographic photoreceptor that is sensitive to light of a wide range of wavelengths. Conventionally, various types of photoconductive layer materials for electrophotographic photoreceptors have already been proposed and put into practical use. As a photoconductive layer, it is important to have high sensitivity and high resistance, as well as heat resistance, abrasion resistance, non-pollution, and spectral characteristics close to visual sensitivity. Selenium or selenium alloys, zinc oxide, cadmium sulfide, etc., do not necessarily satisfy all of the above-mentioned conditions to a higher level. For example, electrophotographic image forming members that have a selenium-based photoconductive layer containing tellurium or arsenic in order to widen the spectral sensitivity range have large changes in electrical properties due to temperature and humidity, and also suffer from increased optical fatigue. It has drawbacks such as lack of uniformity and stability of copied images. However, selenium, especially arsenic, and tellurium are extremely harmful to the human body and are weak in strength.
It may get mixed into the copied image or be scattered inside the copying machine, causing it to come into contact with the human body. Furthermore, the selenium-based photoconductive layer is formed in an amorphous state in order to have high dark resistance as a photoconductive layer, but since selenium crystallization occurs at an extremely low temperature of 65°C, image formation during use is difficult. It also has a drawback in terms of heat resistance, in that it tends to crystallize under the influence of frictional heat with other members during the process, resulting in a decrease in dark resistance. On the other hand, an image forming member having a so-called binder-based photoconductive layer using zinc oxide, cadmium sulfide, etc. as a constituent material of the photoconductive layer has parameters that determine the electrical and photoconductive properties and physical and chemical properties of the photoconductive layer. In many cases, the reproducibility is poor, leading to a decrease in yield, and the humidity dependence is significant, resulting in deterioration of electrical characteristics and poor cleaning performance. Based on the above facts, the present invention has developed a glow discharge decomposition method that has ideal properties in terms of non-pollution, heat resistance, and abrasion resistance that conventional photoconductive layers lack, and has a wide photosensitivity range. An object of the present invention is to provide an electrophotographic photoreceptor whose photoconductive layer is amorphous silicon (hereinafter abbreviated as a-Si) produced by the present invention. The a-Si film is formed on the substrate by glow discharge decomposition method. The glow discharge decomposition method is a method of forming a film by decomposing silane gas in a glow discharge.There are two plasma generation methods: inductive coupling method and capacitive coupling method, but pure a-Si film containing no impurities is Normally, it acts as an N-type semiconductor, and its volume resistance is low and its dark decay rate is too fast, making it difficult to obtain good images. However, by mixing diborane gas into silane gas and decomposing it by glow discharge, boron is added to a-Si, making it an intrinsic semiconductor and even a P-type semiconductor, and the volume resistivity of a-Si changes depending on the amount of each addition. Furthermore, the volume resistance of a-Si also changes depending on the temperature set on the substrate during film formation. Therefore, if the amount of boron added and the substrate temperature are appropriately set, a high-resistance a-Si film can be obtained and can be used satisfactorily as a photoreceptor with a single layer structure in the Carlson system. On the other hand, in order to widen the photosensitivity region of the a-Si film, it is possible to narrow the optical forbidden band width, and this can be achieved by increasing the substrate temperature setting. However, increasing the board temperature setting
This lowers the volume resistance of the a-Si film. Based on these facts, in the present invention, the amount of boron added is set appropriately so as to obtain an a-Si film with high volume resistivity, and by changing the substrate temperature during the formation of the same film, the light of the electrophotographic photoreceptor is improved. A conductive layer with a wide photosensitivity region was created. Here, as a method for forming the a-Si film, a glow discharge decomposition apparatus shown in FIG. 1 was used to decompose silane gas mixed with ciborane gas to form an a-Si film on the surface of a clean aluminum substrate. Typical creation conditions are
Apply RF power 100~3000Watts at 13.56MHz, gas pressure 0.5~2.0Torr, gas flow rate 50~3000W/min
300 CC, film formation rate is 150 to 500 A per minute, substrate temperature is room temperature to 400°C, and film thickness is 7 to 20 μm. Examples will be explained below. Example 1 A film with a thickness of 10 μm was obtained on a clean aluminum substrate by mixing 100 ppm of diborane gas with silane gas and continuing glow discharge decomposition for 6 hours using the above-mentioned apparatus.
After heating the substrate temperature to 350°C, discharge was started, and during the discharge, the temperature was cooled at a rate of 0.5, 1.0, 1.5, and 2.0°C per minute, respectively, and when the temperature reached 120°C, the temperature remained constant. Table 1 shows the test results for the dark decay rate and light absorption coefficient of these a-Si films.

[Table] Judging from the corresponding nearby wavelengths, all good results are marked with a circle.
From this result, it is desirable that the region with high volume resistance (10 ¹¹ Ω·cm or more) be 1/3 to 1/2 of the film thickness. Example 2 Table 2 shows the results of Example 1 in which the substrate temperature after cooling was set to 200°C.

[Table] The same judgment as in Table 1 is made, and when the final substrate temperature is 200℃, the area with high volume resistance is 1/2 of the film thickness.
It is desirable that there be. In Example 1, after discharge decomposition at a substrate temperature of 350°C for 3 to 4 hours, the substrate temperature was increased to 120°C and subjected to discharge decomposition for 3 to 2 hours, and in Example 2, the substrate temperature was 350°C.
℃ for 3 hours and 200℃ for 3 hours give similarly good results. It is also good to add oxygen, nitrogen, carbon, etc. to control the volume resistance and photoelectric gain of the a-Si layer. As described above, the method for manufacturing an electrophotographic photoreceptor of the present invention includes forming an amorphous silicon photoconductive layer produced by decomposing silane gas mixed with a trace amount of diborane gas by a glow discharge decomposition method on a substrate. In the manufacturing method of photographic photoreceptors, the temperature of the substrate mixed with a trace amount of diborane gas is kept below 400℃.
A step of forming a first amorphous silicon layer by heating the substrate to a temperature of 350° C. or higher and continuing to cool the substrate temperature at a constant cooling rate at the same time as glow discharge starts, for forming the first amorphous silicon layer. Subsequently, the second amorphous silicon layer is formed by fixing the substrate temperature at a constant temperature in the range of 120°C to 200°C at the same time as the cooling of the substrate temperature is stopped. During film formation, the amorphous silicon layer is heated to a temperature of 400°C or higher and 350°C or higher, and at the same time as glow discharge begins, the substrate temperature is cooled to a constant temperature.
Since it is formed by continuous cooling to at least 200℃, the hydrogen ion concentration can be controlled over a wide range, and the optical forbidden band width can be controlled over a wide range from low to high, and resistivity can be varied over a wide range from low to high. The photoelectric effect is excellent for a wide range of light from short wavelengths to long wavelengths. Generally, the light source used in an apparatus using an electrophotographic photoreceptor is a red light-emitting diode on the long wavelength side, so it is well matched with the red light-emitting diode on the long wavelength side, and the second amorphous The silicon layer has a substrate temperature of 120°C to 200°C.
Since it is formed at a fixed temperature in the temperature range of °C, it has a constant and very high resistivity (specific resistance of 10 ¹¹ Ω cm or more), and the decay of the charged electric charge. The present invention provides an electrophotographic photoreceptor with very high performance, which has a small charge retention property and a low charge retention property, and satisfies both the photoelectric effect property and the charge retention property at the same time. Furthermore, since the first amorphous silicon layer and the second amorphous silicon layer can be formed successively within the same batch, there is an advantage that film formation can be made easily.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram for producing amorphous silicon. 1...Piping, 2...Valve, 3...Reaction tube, 4
... High frequency coil, 5 ... Board, 6 ... Board holder, 7 ... Pressure gauge, 8 ... Board holder support rod, 9 ... High frequency power supply.

Claims (1)

[Claims] 1. In a method for manufacturing an electrophotographic photoreceptor in which an amorphous silicon photoconductive layer is formed on a substrate by decomposing silane gas mixed with a trace amount of diborane gas by a glow discharge decomposition method, a substrate mixed with a trace amount of diborane gas is used. Temperature below 400℃350
℃ or higher, and at the same time as the start of glow discharge, the substrate temperature continues to be cooled at a constant cooling rate to form a first amorphous silicon layer, subsequent to the formation of the first amorphous silicon layer. As a result, the board temperature increases at the same time as cooling of the board temperature stops.
A method for manufacturing an electrophotographic photoreceptor, comprising the step of forming a second amorphous silicon layer at a constant temperature in the temperature range of 120°C to 200°C.