JPS6357784B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a PN junction type electrophotographic photoreceptor having an amorphous silicon photoconductor layer produced by a glow discharge decomposition method. Various types of electrophotographic photoreceptors have already been proposed, but one that has been widely put into practical use is one in which selenium or selenium alloys are deposited on a conductive substrate to a thickness of several tens of microns by vacuum evaporation or oxidized. There is a single-layer photoreceptor made by coating zinc or cadmium sulfide together with a resin binder to a thickness of several tens of microns. All of these photoreceptors have relatively excellent electrophotographic properties in general, but on the other hand, they have drawbacks such as problems in environmental pollution, heat resistance, surface hardness, and abrasion resistance. have In other words, in a photoreceptor whose photoconductor layer is made of selenium or a selenium alloy, when the temperature inside the copying machine increases, crystallization is promoted, and this thermal instability not only deteriorates the photoreceptor to an unusable state, but also selenium is harmful to the human body. Photoreceptors with exposed selenium on their surfaces must be handled with great care in view of environmental pollution. Furthermore, photoreceptors using a photoconductor layer made of zinc oxide or cadmium sulfide combined with a resin also have the problem of toxicity, and this type of photoreceptor also has the drawback of an extremely complicated manufacturing process. Furthermore, selenium and zinc oxide have insufficient surface hardness and abrasion resistance, and cannot be used repeatedly over a long period of time in copying machines that use fur brushes or elastic blades as means for removing residual toner. However, as mentioned above, photoreceptors with a single-layer structure in which selenium or a selenium alloy is used as a photoconductor layer are not charged to a sufficient surface potential depending on the type of use; in other words, the charge retention ability and dark decay characteristics are poor. The disadvantage is that it is not sufficient. For this reason, a so-called P-N junction type photoreceptor in which an intermediate layer having a majority carrier of charges opposite to the majority carrier of the photoconductor layer is formed between the conductive substrate and the photoconductor layer. It is thought that this is effective in improving charge retention and dark decay characteristics. This is US Patent No. 3041166
As shown in the specification, if a P-type material is selected for the photoconductor layer, an N-type material is used as the intermediate layer and the material is negatively charged, and a P-type intermediate layer is used for the N-type photoconductor layer. This is used to positively charge the battery, thereby improving charging and dark decay characteristics. However, even in this type of P-N junction photoreceptor, pure selenium is used as the P-type material, and a mixture of selenium and Te, As, As ₂ S ₃ , etc. is used as the N-type material, so the result is Environmental pollution resistance, heat resistance,
This means that there is no improvement in terms of surface hardness, abrasion resistance, etc. The present invention has been made in view of the above facts.
The purpose is to provide an electrophotographic photoreceptor that is excellent in environmental pollution resistance, heat resistance, surface hardness, etc., and also has outstanding charging and dark decay characteristics. An object of the present invention is to provide an electrophotographic photoreceptor in which a photoconductor layer and an intermediate layer are made of amorphous silicon, which is both P-type and N-type. In order to achieve the above object, an electrophotographic photoreceptor according to the present invention is made of amorphous silicon having a thickness of 10 to 100 microns and containing no boron or an amount of boron that becomes an intrinsic semiconductor. An amorphous silicon intermediate layer with a thickness of 0.2 to 5 microns is provided between the N-type photoconductor layer and the conductive substrate, which carries many charges of opposite polarity to the photoconductor layer. It is characterized by a P-type photoconductor layer having a thickness of 10 to 100 microns and containing up to 1000 ppm of boron, which is P-type, as a matrix, and a conductive substrate. In between, there is provided an amorphous silicon intermediate layer having a thickness of 0.2 to 5 microns and carrying a majority of charges of opposite polarity to that of the photoconductor layer. The present invention will be explained below. As a result of searching for a photosensitive material with excellent environmental pollution resistance, heat resistance, surface hardness, etc., the inventor of the present invention discovered that the glow discharge decomposition method, which is currently being researched and developed in the semiconductor field, was developed. The amorphous silicon produced
We have focused on silicon (hereinafter abbreviated as a-Si) and have been researching its application to the field of electrophotographic photoreceptors. A-Si produced by the glow discharge decomposition method has a low density of defect levels in the energy gap, and general amorphous amorphous metal exhibits rather exceptional electrical properties as a semiconductor, as well as being relatively low cost. Because it is also useful in terms of manufacturing, allowing the production of large-area films, technology using a-Si has been widely used in semiconductor application technology fields such as solar cells and photocells, which have traditionally been based on crystalline silicon. Development is progressing rapidly. In this way, a-Si, whose usefulness is being recognized in the field of semiconductor application technology, is used as a photosensitive material for electrophotography.
In particular, as a result of research into its application as a photoconductor, it was discovered that it has ideal properties in terms of pollution-free properties, heat resistance, surface hardness, and abrasion resistance, which conventional photoconductors lacked. As will be explained in detail later, a-Si is formed in the form of a film on a substrate by a glow discharge decomposition method, but in a pure a-Si film containing no impurities, its structural defects form a donor level, and normally N In terms of spectral sensitivity, it has an extremely excellent photoconductivity, with a peak at about 5,700 angstroms, which is close to the relative luminous efficiency, as will be described later. Therefore, it is conceivable to form this a-Si to a thickness of several tens of microns on a conductive substrate and use it as a so-called single-layer photoconductor, but a-Si itself generally has a low volume resistivity and cannot be used as a normal corona. When charging, it is difficult to charge the surface to a sufficient surface potential, and the dark decay rate is also fast, making it difficult to obtain good image contrast. However, by adding boron (chemical symbol B) to this a-Si, its originally N-type semiconductor property approaches that of an intrinsic semiconductor, and by adding a larger amount of boron, it becomes a P-type semiconductor. Becomes a semiconductor. Conversely, by adding phosphorus (chemical symbol P), it becomes more N-type, and depending on the amount of each addition, a
-The volume resistance value of Si changes. This fact is WE
Published in 1976 by Spear and PGLe Comber.
Philosophical Magazine (Vol.33, No.6)
On pages 935 to 949, “Electronic properties of
substitutionally doped amorphous Si and Ge”
The research has been published under the title. Furthermore, the volume resistance of a-Si also changes depending on the setting of manufacturing conditions in the glow discharge decomposition method, particularly the set temperature of the substrate on which the a-Si film is formed. Therefore, it can be expected that by adding an appropriate amount of impurities such as boron and setting the substrate temperature appropriately, an a-Si film with relatively high resistance can be obtained. In reality, as will be clear from the examples described later, an a-Si film having a maximum volume resistance of about 10 ¹³ Ω·cm can be obtained and can be used satisfactorily as a photoreceptor with a single layer structure in the Carlson method. However, if this situation continues, the application of a-Si to electrophotography will be severely restricted. This is because, as mentioned above, the amount of impurities added and the setting of the substrate temperature are limited in order to provide a-Si with the high resistance required for a single-layer photoreceptor. However, a-Si containing no impurities
Of course, a-Si containing boron or phosphorus in amounts other than those mentioned above cannot be used in electrophotographic photoreceptors. Furthermore, even if a-Si has a sufficiently high resistance and can be charged to a surface potential of, for example, 500 to 600 volts, it may be charged to an even higher potential depending on the copying machine used. may be requested. The present invention focuses on the fact that, in addition to the excellent advantages of a-Si in terms of non-polluting properties and heat resistance, a-Si easily changes its properties into P-type and N-type by adding boron or phosphorus. , a-Si is used as a P-N junction type photoreceptor to improve charging and dark decay characteristics. That is, as shown in FIG. 1, the P-N junction type electrophotographic photoreceptor according to the present invention is formed on a conductive substrate 1 by a glow discharge decomposition method, and has a thickness of about 0.2 to 5 microns. An amorphous silicon intermediate layer 2 and a P layer formed thereon by a glow discharge decomposition method and having a thickness of about 10 to 100 microns and having a majority carrier of charges having a polarity opposite to that of the majority carrier of the intermediate layer 2. It is constructed by sequentially stacking type or N type amorphous silicon photoconductor layers 3. When P-type a-Si is selected as the photoconductor layer 3, the intermediate layer 2 is made of a-Si having N-type properties.
-Si is used and is negatively charged in the image forming process. On the other hand, when a-Si having N-type properties is used as the photoconductor layer 3, P-type a-Si is used as the intermediate layer 2 and is positively charged. In the above configuration, the N-type photoconductor layer 3 and the P
To explain the effect using a photoreceptor having a mold intermediate layer 2 as an example, the photoconductor layer is positively charged by positive corona charging in a dark state, while the conductive substrate 1 is negatively charged. be guided. At this time, an electric field is applied at the interface junction between the photoconductor layer 3 and the intermediate layer 2, thereby causing the majority carriers of opposite polarity to move in opposite directions. In other words, electrons move toward the surface of the N-type photoconductor layer 3, and holes move toward the substrate 1 side of the P-type intermediate layer 2, resulting in a state in which neither electrons nor holes exist in both layers, that is, a depletion state. This significantly improves charging and dark decay properties.
From another perspective, the charge induced in the conductive substrate 1 is always of the opposite polarity to the majority carrier charge in the intermediate layer 2, so the injection of charge from the substrate is reliably suppressed, so that charging and Dark decay characteristics are improved. If the photoconductor layer and the intermediate layer are of the opposite type to those described above, the effects will simply be reversed and the same excellent PN effect will be achieved. Now, if we consider the case where a photoconductor charged to a high potential as described above is imagewise exposed, in the present invention, the N-type photoconductor layer is positively charged, and the P-type photoconductor layer is positively charged. On the other hand, due to negative polarity charging and so-called reverse bias charging, among the holes and electrons generated by exposure, the majority carrier charge moves toward the surface side of the photoconductor layer to neutralize the charged charge. , and the minority carriers move to the substrate side. However, minority carriers usually have a short lifespan and cannot be moved much. In other words, for example, among the holes and electrons generated by exposure near the surface of the N-type photoconductor layer, the electrons are majority carriers and therefore easily move toward the surface, but the holes cannot substantially move, resulting in a good result. This means that you will not be able to obtain a good image. This becomes more pronounced as the N-type or P-type tendency of the photoconductor layer becomes stronger, and conversely, the weaker the tendency, the longer the life of minority carriers becomes. In other words, in a P-type or N-type semiconductor located close to an intrinsic semiconductor, holes and electrons can move to almost the same extent.
As the P-type or N-type tendency becomes stronger, the life of the minority carrier decreases. Therefore, the N-type or P-type photoconductor layer 3 in the present invention has a relatively weak N-type or P-type tendency, respectively. It needs to be P-type or N-type a-Si that can have a life span long enough to allow movement. By the way, a produced by glow discharge decomposition method
-As mentioned above, Si is originally an N-type semiconductor, but by adding boron, the N-type tendency gradually weakens and it becomes an intrinsic semiconductor, and by further increasing the amount of boron added, it becomes a P-type semiconductor. . On the other hand, by adding phosphorus, it becomes stronger N-type. The addition of boron and phosphorus changes the volume resistivity of a-Si itself, and the substrate temperature conditions in the glow discharge method also have a large effect on the volume resistivity. That is, as can be understood from the examples described later, a-Si has a substrate temperature of approximately 50°C to 250°C.
By setting it in the range of 10 8 Ω・cm to nearly 10 11 Ω・cm as the substrate temperature decreases even when no impurities are included, the volume resistivity increases from approximately 10 ⁸ Ω・cm to nearly 10 ¹¹ Ω・cm. By adding phosphorus, the volume resistivity decreases to 10 ⁵ Ω・cm with approximately 50 ppm phosphorus content.
On the other hand, by adding boron, the volume resistivity improves, and the N-type tendency gradually weakens, and when a certain amount of boron is contained, for example, about 90 to 160 ppm, a-Si becomes a substantially intrinsic semiconductor. However, with a higher boron content, a-Si becomes a P-type semiconductor and its volume resistivity decreases; with a boron content of 1000 ppm, it becomes approximately 10 ⁹ Ω・cm,
At more than 10000ppm, it decreases to about 10 ⁵ Ω・cm and has a strong P.
Becomes a mold. Incidentally, the change in volume resistivity due to the addition of boron or phosphorus has some error depending on the manufacturing conditions, and in this respect, the constant boron content at which a-Si becomes an intrinsic semiconductor must also have some range. On the other hand, from the viewpoint of charging and dark decay characteristics, the photoconductor layer 3 needs to be relatively weak P-type or N-type as described above, but it is also necessary to avoid lateral leakage during charging. Therefore, it is necessary to have a certain volume resistance. This is supported by the experiments described later, as long as it has a volume resistance of about 10 ⁹ Ω·cm, and a-Si having a resistance up to this level has a sufficient minority carrier life. On the other hand, the intermediate layer may be of strong P type or N type, and its volume resistivity can be up to about 10 ⁵ Ω·cm. Based on these facts, in the present invention, when N-type a-Si is selected as the photoconductor layer 3, a-Si containing no impurities or a-Si containing an amount of boron to become an intrinsic semiconductor is selected. Can be used. Although there are some manufacturing errors here, according to the embodiments of the present invention, a-Si becomes an intrinsic semiconductor at a point containing about 90 to 160 ppm of boron.
a- containing boron from about 90 to 160 ppm
Si can be used. For the P-type intermediate layer 2 adjacent to the N-type photoconductor layer 3, a-Si containing boron can be used in an amount that makes it more P-type than an intrinsic semiconductor, and up to about 10,000 ppm at most. In other words, since a certain point containing about 90 to 160 ppm of boron becomes an intrinsic semiconductor, a-Si containing boron of more than 90 to 10,000 ppm is used. On the other hand, when P-type a-Si is selected as the photoconductor layer 3, a-Si containing up to 1000 ppm of boron is used as the P-type, whereas for the N-type intermediate layer, boron is from 0 to 1000 ppm. a- containing enough boron to become an intrinsic semiconductor
Si, a-Si containing no impurities or approx.
A-Si containing up to 50 ppm phosphorus can be used. The amount of boron and phosphorus added affects the volume resistivity of a-Si, so from another perspective, as a P-type or N-type semiconductor layer, it is approximately 10 ⁹ Ω・cm or more regardless of its composition. a-Si with a volume resistivity of
and about 10 ⁵ as a P-type or N-type intermediate layer.
A-Si having a volume resistivity of Ω·cm or more can be used. Here, P generated by glow discharge decomposition method
The manufacturing method of type and N type a-Si will be explained. Fig. 2 shows a glow discharge decomposition device for producing a-Si, and the first, second, and third pumps 4, 5, and 6 in the figure are supplied with SiH ₄ , PH ₃ , and B ₂ H ₆ gas, respectively. is sealed. These gases are released by opening the corresponding first, second, and third regulating valves 7, 8, and 9, and the flow rate is adjusted to the metering valve 10,
11 and 12 and sent to the main pipe 13. Note that 14, 15, and 16 are flow meters, and 17 is a stop valve. The gas flowing through the main pipe 13 is sent into the reaction tube 18, and a resonance vibration coil 19 is wound around the reaction tube, and its resonance vibration power is suitably, for example, 100 to 300 Watts. Inside the reaction tube 18, a substrate 20 made of, for example, aluminum or NESA glass, on which an a-Si film is formed, is placed on a turntable 22 that can be rotated by a motor 21. 20 itself is about 50 to 250 depending on a suitable heating means.
It is heated to a temperature of °C. Furthermore, the interior of the reaction tube 18 is in a highly vacuum state (gas pressure:
0.5 to 2.0 Torr) and is connected to the rotary pump 23 and the diffusion pump 24. In the glow discharge decomposition apparatus having the above configuration, when forming a pure a-Si film on the substrate 20, the first
The regulating valve 7 is opened to supply SiH ₄ gas from the first pump 4, and when phosphorus or boron is contained, the second or third regulating valves 8 and 9 are also opened to supply the second and third pumps 5 and 6. Releases _PH3 gas and _{B2H6 gas} .
The amount of discharge is regulated by metering valves 10, 11, 12, and the amount of discharge is regulated by metering valves _{10, 11} , and ₁₂ .
The mixed gas with PH ₃ or B ₂ H ₆ gas is in the reaction tube 18.
sent to. And the inside of the reaction tube 18 is 0.5 to
Gas pressure around 2.0Torr, substrate temperature 50 to 250℃,
Also, the power of the resonant vibration coil is 100 to 300 watts.
In combination with the setting, glow discharge occurs, and when the fed gas is only SiH ₄ ,
A pure a-Si film is formed by the reaction of SiH ₄ →Si+2H ₂ .
In the case of a mixed gas, the reaction of 2(SiH ₄ + PH ₃ ) → 2Si + 7H ₂ or SiH ₄ + B ₂ H ₆ → Si + B ₂ + 5H ₂ forms an a-Si film containing phosphorus or boron at a rate of about 0.1 to 0.5 microns/min. The film is then formed on the substrate 20. Since P-type and N-type a-Si films are formed in this way, the photoreceptor of the present invention has a thickness of 0.2 to 5.
A micron-thick a-Si intermediate layer is formed, and then an a-Si photoconductor layer with a thickness of 10 to 100 microns is formed in which the majority carriers are of opposite polarity to the majority carriers in the intermediate layer. In the above, the setting of the substrate temperature has a great influence on the volume resistance of the obtained a-Si film, and the volume resistance tends to decrease almost in proportion to the increase in the substrate temperature. Therefore, in the present invention, the substrate temperature is approximately 50 to 250°C.
It is desirable to do so. Examples will be described below. Example 1 SiH ₄ was decomposed using the glow discharge decomposition apparatus shown in FIG. 2 described above to form a pure a-Si film with a thickness of 1 micron on an aluminum substrate. still,
The manufacturing conditions are: gas pressure of 0.5Torr, aluminum substrate temperature of 200℃, and resonance vibration power of 100watts.
Film formation rate was set at 0.1 microns per minute. Next, under the same conditions, B ₂ H ₆ was added to SiH ₄ at 50, 200, 500, 800, 1000, 1500, 2000, respectively.
A mixed gas containing 5,000, 10,000, 20,000, and 100,000 ppm was decomposed by the glow discharge method, and 5,
20, 50, 80, 100, 150, 200, 500, 1000, 2000,
A 1 micron thick a-Si film containing 10000 ppm boron was formed on an aluminum substrate. still,
Boron content was measured using a Hitachi ion microanalyzer. Similarly, a mixed gas containing appropriate amounts of PH ₃ and SiH ₄ was decomposed by glow discharge to produce 5 ppm,
1 micron thick a-Si films containing 10 ppm and 50 ppm phosphorus were formed. Next, the relationship between these a-Si films and the volume resistance value (electrical conductivity) was investigated, and the results shown by the solid line A in FIG. 3 were obtained. In the figure, the contents of boron and phosphorus are shown in molar ratios of B ₂ H ₆ /SiH ₄ and PH ₃ /SiH ₄ , respectively, and the ppm content is shown in parentheses. In other words,
B ₂ H ₆ /SiH ₄ is 10 ^-6 with 2 ppm boron, 10 ^-5 is
20ppm, 10 ^-4 is 200ppm, 10 ^-3 is 2000ppm, 10 ^-2
contains 20000ppm boron and has a PH ₃ /
SiH ₄ is 10 ^-6 is 1 ppm phosphorus, 10 ^-5 is 10 ppm, 10 ^-4
indicates that it contains 100ppm, and 10 ^-3 indicates that it contains 1000ppm of phosphorus. The results of solid line A in Figure 2 are as described above.
The results almost correspond to those shown by WESpear and PGLeComber. Separately, increase the aluminum substrate temperature to 120℃
All under the same conditions except that the thickness was 1
Micron pure a-Si film, 5, 20, 50, 80,
A-Si films containing 150, 200, 500, 1000, 2000, and 10000 ppm of boron, and further a-Si films containing 5, 10, and 50 ppm of phosphorus, respectively, were formed. and these a
-When we measured the relationship between the Si film and the volume resistance, we found that
The results shown by the dotted curve B in the figure were obtained. From the results shown in Figure 3, first, a pure a-Si film containing no impurities formed at a substrate temperature of 200°C has a volume resistivity of approximately 8 × 10 ⁸ Ω・cm; Then, it is about 10 ¹⁰ Ω・cm, and both N
It can be understood that it belongs to type semiconductor. Furthermore, a-Si containing 5 ppm boron produced under the condition of a substrate temperature of 200°C has a volume resistivity of approximately 2×10 ⁹ Ω・cm,
Approximately 3×10 ¹⁰ Ω・cm when containing 20 ppm boron, approximately 6×10 ¹⁰ Ω・cm when containing 50 ppm, and approximately 10 ¹¹ when containing 80 ppm
Ω・cm, at 100ppm, it becomes 4×10 ¹¹ Ω・cm, approaching from an N-type to an intrinsic semiconductor. and 8x at 150ppm
Improved to 10 ¹¹ Ω・cm and passed through the intrinsic semiconductor to P.
Becomes a mold. However, after this point, the volume resistivity suddenly decreased to 5×10 ¹⁰ Ω・cm with 200 ppm boron content.
10 ⁸ Ω・cm with 500ppm content, 6×10 ⁶ with 1000ppm
Ω・cm, 2×10 ⁵ Ω・cm at 2000ppm, and
At 10,000 ppm, it becomes less than 10 ⁵ Ω·cm, and the so-called P-type tendency becomes stronger. Furthermore, as the amount of a-Si containing phosphorus increases, its N-type tendency becomes stronger, but on the other hand, the volume resistivity gradually decreases to approximately 9 x 10 ⁷ Ωcm at a phosphorus content of 5 ppm. 5×10 ⁶ Ω・cm at 10ppm,
It exhibited a volume resistivity of 10 ⁵ Ω·cm at 50 ppm. On the other hand, an a-Si film containing boron produced at a substrate temperature of 120°C has a volume resistivity approximately 10 to 100 times greater than that at 200°C. That is, 5ppm generated under a substrate temperature of 120℃
The a-Si film containing boron has a volume resistivity of approximately 2
×10 ¹⁰ Ω・cm, 4×10 ¹¹ Ω・with 20ppm boron content
cm, 9×10 with 50ppm ¹¹ Ω・cm9× with 100ppm
10 ¹² Ω・cm, approaching from N-type to intrinsic,
At 150 ppm, it becomes a P-type semiconductor with a volume resistance of 8 x 10 ¹² Ωcm. If the boron content exceeds that amount, the P-type tendency of a-Si becomes stronger and its volume resistivity decreases. In other words, with 200ppm boron content, the volume resistance is 2×
10 ¹¹ Ω・cm, 500ppm Approximately 10 ¹⁰ Ω・cm, 1000ppm
10 ⁹ Ω・cm at 2000ppm, 3×10 ⁷ Ω・cm at 2000ppm, and
At 10000ppm, it becomes 6×10 ⁵ Ω・cm. On the other hand, a-Si containing phosphorus showed almost the same volume resistance value as when the substrate temperature was 200°C. From the above measurement results, a which is originally an N-type semiconductor
-As Si contains boron, its volume resistivity gradually increases and its N-type tendency weakens.
100 to 150ppm, approximately 90% considering some manufacturing errors
It can be seen that it becomes an intrinsic semiconductor at a point containing boron of 160 ppm to 160 ppm. Therefore, as the N-type photoconductor layer, a-Si containing up to a certain amount of boron, that is, until it becomes an intrinsic semiconductor, can be used, while as the P-type photoconductor layer, a-Si containing boron of up to a certain amount can be used. a-Si, that is, a-Si containing at least an amount of boron that makes it more P-type than an intrinsic semiconductor.
Si can be used. However, it is necessary for the N-type and P-type photoconductor layers to have a certain lifespan with respect to holes and electrons, which are minority carriers, respectively, and in this respect, the degree of P-type and N-type photoconductor layers must not be too strong. Based on experiments on light attenuation characteristics described later, the lower limit for the N-type photoconductor layer is a that does not contain any boron.
It was confirmed that up to -Si can be used, and a-Si containing up to about 1000 ppm of boron can be used as the P-type photoconductor layer. In relation to FIG. 3, this means that the volume resistivity of a-Si is approximately 10 ⁹ Ω·cm or more. The P-type and N-type intermediate layers are approximately 10 ⁵ as will be understood from the experiments described later.
Since a-Si, which has a volume resistivity of Ω cm or more, can be used, a-Si containing boron at a minimum amount of about 10,000 ppm as a P-type, and a maximum of about 10,000 ppm, can be used.
-Si, and as the N type, a-Si containing up to about 50 ppm phosphorus, pure a-Si, or a-Si containing boron in an amount that makes it an intrinsic semiconductor can be used. Example 2 In this example, the spectral sensitivity characteristics of a-Si were investigated. First, by the glow discharge decomposition method shown in Example 1, a pure a-Si film with a thickness of 30 microns was formed on an aluminum substrate at a substrate temperature of 120°C.
This photoreceptor sample is referred to as (C). Next, this photoreceptor was charged to a surface potential of about 100 volts by corona charging and irradiated with light. The irradiation light was sequentially varied within a wavelength range of 4,000 to 8,000 angstroms using a filter, and the relationship with the photocurrent was measured. This result is shown by curve C in Figure 4, and as is clear from this, a-Si has a luminous efficiency of about 5700, which is close to the relative luminous efficiency.
It has a peak at angstroms and has excellent spectral sensitivity characteristics. then on an aluminum substrate under the same conditions.
30 micron thick a-Si containing 20 ppm boron
A film was formed and the spectral sensitivity was measured in the same manner.
The result is shown by curve D in FIG. 4, which has a peak of about 6000 angstroms, which also has good spectral sensitivity characteristics. Therefore, it was confirmed that a-Si can be satisfactorily used in photoreceptors from the viewpoint of sensitivity characteristics. Example 3 Using the glow discharge decomposition apparatus shown in FIG. 2, a total of 16 types of PN junction type photoreceptor samples were prepared as shown in Table 1. First, samples (E) to (I) have a substrate temperature of 200℃.
In both cases, a P-type a-Si intermediate layer is formed on an aluminum substrate, and an N-type a-Si intermediate layer is formed on the aluminum substrate.
-Si photoconductor layer is formed, and as can be seen from Table 1, for example (E) is a P-type intermediate layer.
This refers to a sample consisting of a-Si containing 200 ppm of boron, which means a sample consisting of pure a-Si as an N-type photoconductor layer, and sample (F) containing 500 ppm as a P-type intermediate layer.
a-Si containing boron, as an N-type photoconductor layer
It shows that it is made of a-Si containing 50 ppm of boron. Samples (J) to (N) also consist of a P-type intermediate layer and an N-type photoconductor layer, but all were prepared at a substrate temperature of 120°C. Unlike these, samples (O) to (T) consist of a P-type photoconductor layer and an N-type intermediate layer. R) to (T) were produced at 120°C. In each sample, aluminum was used as the substrate, the thickness of the intermediate layer was 1 micron, and the thickness of the photoconductor layer was 30 microns. As a comparison sample, a photoreceptor having a single layer structure made of pure a-Si and having a thickness of 30 microns was prepared at a substrate temperature of 120°C. This is designated as sample (U).

[Table] Next, experiments were conducted on the charging ability and dark decay characteristics of each of these samples (E) to (T) and the comparative sample (U). First, experiments on chargeability characteristics were conducted by charging each sample in the dark with a corona charger connected to a 5.5KV high voltage source and measuring the surface potential. The characteristics of the dark decay rate were determined by leaving each charged sample in a dark place and measuring the decay of the surface potential. These measurement results are shown in Figures 5 to 7.
As shown in the figures, Fig. 5 shows samples (E) to (I), Fig. 6 shows samples (J) to (N), and Fig. 7 shows samples (O) to (T). Show the results. In addition, comparative sample (U)
Only the measurement results are shown in both FIG. 5 and FIG. 6 to facilitate comparison with the present invention. First, looking at Figure 5, which shows the characteristics of samples (E) to (I), all of them except sample (I) have excellent charging and dark decay properties, and sample (G) in particular has excellent charging and dark decay properties. It is charged to the highest potential (approximately 790 volts) and has an extremely fast dark decay rate. In addition, even in sample (E), which uses pure a-Si with a volume resistivity of only 10 ⁹ Ω・cm as the photoconductor layer, it is charged to more than 600 volts due to the stacking with the intermediate layer, and the dark decay rate is extremely high. In good condition. This difference is remarkable when compared with sample (U), which has a single layer structure of pure a-Si and has a volume resistance of about 10 ¹⁰ Ω·cm, which was produced at a substrate temperature of 120°C. In other words, as shown by the dotted line curve, sample (U) has a charged potential of less than 400 volts and a fast dark decay rate. Although sample (I) is a P-N junction type, its charging and dark decay characteristics are poor, but this is because the volume resistivity of the N-type photoconductor layer is approximately 9×10 ⁷ Ω・
It is recognized that this is because the leakage occurs in the lateral direction of the photoconductor as a result. Next, as is clear from FIG. 6, which shows the measurement results of samples (J) to (N), all of them have excellent charging and dark decay characteristics. Except for sample (M), all the samples have improved charging and dark decay characteristics compared to samples (E) to (H) shown in FIG. This is considered to be because both the photoconductor layer and the intermediate layer were formed at a substrate temperature of 120° C., and their volume resistivity increased. It should be noted that sample (M) has inferior characteristics compared to the other samples, but this is because the volume resistivity of the intermediate layer is as low as about 6×10 ⁵ Ω·cm. However, since it is charged to nearly 500 volts and its dark decay rate is relatively good, it can be used satisfactorily as a photoreceptor. However, on the contrary, it is said that the minimum volume resistance of the intermediate layer is about 10 ⁵ Ω・cm, and from this it is desirable that the P-type intermediate layer be a-Si containing up to about 10,000 ppm of boron. . Figure 7 shows the measurement results of photoreceptor samples (O) to (T) consisting of a P-type photoconductor layer and an N-type intermediate layer, and it can be seen that all except sample (T) have good characteristics. . Sample (T) cannot be used as a photoconductor because the volume resistivity of the photoconductor layer is 3×10 ⁷
It is recognized that this is because there is only Ω・cm. On the other hand, the material (S) in which the photoconductor layer is made of a-Si having a volume resistivity of 10 ⁹ Ω·cm and containing 1000 ppm of boron has improved charging characteristics to about 500 volts and is practical.
However, this is almost the limit and the photoconductor layer has about 10 ⁹
This proves that it has a volume resistivity of Ω・cm or more. In addition, material (Q) has poor dark decay characteristics, but this is because it uses a-Si containing phosphorus with a volume resistivity of approximately 10 ⁵ Ωcm as the intermediate layer. This confirms that a volume resistance of 10 ⁵ Ω・cm or more is required. Finally, among the samples charged as above,
Experiments were conducted on the optical attenuation characteristics of (E), (I), (K), (P), (S), and (T). This is to check the tolerance level of P type and N type as a photoconductor layer.
The experiment was carried out by irradiating the entire surface of the charged sample with a 2800° tungsten lamp. Naturally, the light attenuation characteristics of the photoconductor layer will depend on the migration lifetime of the minority carriers. Figure 8 shows the results. Among these, samples (K) and (P), which use a-Si close to the intrinsic semiconductor region as the photoconductor layer, show the best optical attenuation characteristics, and are This shows that it has a long moving life. The optical attenuation characteristics decrease as the P-type or N-type characteristics of the photoconductor layer become stronger.
Samples with photoconductor layers made of a-Si containing
When it comes to (I) and (T), the contrast decreases significantly and a contrast image cannot be obtained. However, pure a-Si
Samples (E) and (S) in which the photoconductor layer is made of a-Si containing 1000 ppm of boron, respectively, exhibit acceptable light attenuation characteristics. However, in order to obtain a good image, the characteristics exhibited by samples (E) and (S) are the limit, and from this point of view, as an N-type photoconductor layer, the amount of a-Si or intrinsic semiconductor must be reduced. a-Si containing boron
As the P-type photoconductor layer, a-Si containing boron in a minimum amount of P-type up to about 1000 ppm can be used. Taking this result into consideration with the result shown in FIG. 3, it is confirmed that a-Si having a volume resistivity of approximately 10 ⁹ Ω·cm or more can be used as a photoconductor layer.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an electrophotographic photoreceptor according to the present invention, Fig. 2 is a schematic diagram of a glow discharge decomposition device for producing amorphous silicon, and Fig. 3 is a schematic diagram of a glow discharge decomposition device for producing amorphous silicon. FIG. 4 is a diagram showing the spectral sensitivity characteristics of the amorphous silicon film, and FIGS. 5 to 7 are the charging and dark decay characteristics of the electrophotographic photoreceptor according to the present invention. 8 are diagrams showing optical attenuation characteristics. DESCRIPTION OF SYMBOLS 1... Conductive substrate, 2... Intermediate layer, 3... Photoconductor layer, 4, 5, 6... First, second, third pump, 13... Main pipe, 18... Reaction tube, 19 ...Resonant vibration coil, 20... Board.

Claims (1)

[Scope of Claims] 1. An N-type photoconductor layer with a thickness of 10 to 100 microns and made of amorphous silicon that does not contain boron or contains boron in an amount that makes it an intrinsic semiconductor, and conductivity. There is a layer between the substrate and the photoconductor layer that has a thickness that carries many charges of opposite polarity to that of the photoconductor layer.
An electrophotographic photoreceptor comprising an amorphous silicon intermediate layer of 0.2 to 5 microns. 2. Between the conductive substrate and a P-type photoconductor layer whose base material is amorphous silicon containing up to 1000 ppm of boron, which is P-type with a thickness of 10 to 100 microns. 1. An electrophotographic photoreceptor comprising an amorphous silicon intermediate layer having a thickness of 0.2 to 5 microns and carrying a large number of charges of opposite polarity.