JPH0234019B2 - DENSHISHASHIN KANKOTAI - Google Patents

Description

[Detailed description of the invention]

1. Industrial Application Field The present invention relates to an electrophotographic photoreceptor particularly suitable for use with positive charging. 2. Prior Art Conventionally, electrophotographic photoreceptors have been made of Se or Se.
Photoreceptor doped with As, Te, Sb, etc., ZnO and CdS
Photoreceptors, etc., in which the compound is dispersed in a resin binder are known. However, these photoreceptors have problems in terms of environmental pollution, thermal stability, and mechanical strength. On the other hand, electrophotographic photoreceptors using amorphous silicon (a-si) as a matrix have been proposed in recent years. a-Si has so-called dangling bonds in which Si--Si bonds are broken, and many localized levels exist within the energy gap due to these defects. For this reason, hopping conduction of thermally excited carriers occurs, resulting in a small dark resistance, and photoexcited carriers are trapped in localized levels, resulting in poor photoconductivity. Therefore, the dangling bonds are filled by compensating for the defects with hydrogen atoms (H) and bonding H to Si. The resistivity of such amorphous hydrogenated silicon (hereinafter referred to as a-Si:H) in the dark is
It is 10 ⁸ to 10 ⁹ Ω-cm, which is about 1/10,000 times lower than that of amorphous Se. Therefore, a-Si:H
A photoreceptor consisting of a single layer has problems in that the dark decay rate of the surface potential is high and the initial charging potential is low. However, on the other hand, when irradiated with light in the visible and infrared regions, the resistivity is greatly reduced, so it has extremely excellent properties as a photosensitive layer of a photoreceptor. Therefore, in order to impart potential holding ability to such a-Si:H, it is possible to increase the resistivity to 10 ¹² Ω-cm by doping it with boron, etc., but the amount of boron etc. cannot be determined accurately. It is not easy to control. In addition, by introducing a small amount of oxygen together with boron, etc., it is possible to increase the resistance to about 10 ¹³ Ω-cm, but when this is used in the photoreceptor, the photosensitivity decreases, and the edge breakage becomes worse. The problem arises of the generation of residual potential. In addition, photoreceptors with a-Si:H surfaces are susceptible to the effects of long-term exposure to the atmosphere and moisture.
Up to now, sufficient studies have not been made regarding the chemical stability of the surface, such as the influence of chemical species generated by corona discharge. For example, it has been found that when left for more than one month, the acceptance potential decreases significantly due to the influence of moisture. On the other hand, regarding amorphous hydrogenated silicon carbide (hereinafter referred to as a-SiC:H), its manufacturing method and existence are disclosed in “Phil.Mag.Vol.35”.
(1978), etc., and its characteristics include:
It has high heat resistance and surface hardness, has a high dark resistivity (10 ¹² to 10 ¹³ Ω-cm) compared to a-Si:H, and has an optical energy gap of 1.6 to 2.8 depending on the carbon content. It is known that it varies over a range of eV. However, the band gap widens due to the carbon content, resulting in poor long wavelength sensitivity. An electrophotographic photoreceptor combining such a-SiC:H and a-Si:H has been proposed, for example, in Japanese Patent Laid-Open No. 127083/1983. According to this, a-
A functionally separated two-layer structure was created in which the Si:H layer was used as a photosensitive (photoconductive) layer, and the a-SiC:H layer was provided as a charge transport layer under this photoconductive layer, and the upper layer a-Si:H
Obtains photosensitivity in a wider wavelength range, and a-Si:
The lower a-SiC:H layer forms a heterojunction with the H layer.
This aims to improve the charging potential. However, the dark decay of the a-Si:H layer cannot be sufficiently prevented;
The charging potential is still insufficient to be practical, and the presence of the a-Si:H layer on the surface results in poor chemical stability, mechanical strength, heat resistance, etc. Become. Moreover, the carbon atom content of the charge transport layer has not been studied, nor has the thickness of each layer been taken into account, so it does not satisfy the various characteristics required for an electrophotographic photoreceptor. Not yet. On the other hand, JP-A-57-17952 discloses a-Si:
A first a-SiC:H layer is formed as a surface modification layer on the photoconductive layer consisting of H, and a second a-SiC:H layer is formed on the back surface (support electrode side) as a charge transport layer. As a result, the photoreceptor has a functionally separated three-layer structure. Regarding this known photoreceptor, a-Si:H
Although it has the effect of preventing dark decay of the layer, a-SiC:
Since the carbon atom content of the H layer, especially the charge transport layer, has not been studied, sensitivity may decrease depending on the bonding state with the a-Si:H layer, and the residual potential may also increase, making it difficult to copy a large number of sheets. It does not have the durability to withstand it. 3. Purpose of the Invention The present inventor has diligently investigated the problems of the prior art as described above, and has devised a photoreceptor with a novel structure that has the features of a functionally separated photoreceptor such as the three-layer structure described above, and particularly We discovered that the carbon atom content of the charge transport layer and the impurity concentrations of the charge transport layer and charge blocking layer greatly affect the characteristics of the photoreceptor, and decided to set the carbon atom and impurity contents within an appropriate range. As a result, we have succeeded in obtaining a photoreceptor that is excellent in photosensitivity, residual potential, potential holding ability, durability, etc. especially when positively charged. 4. Structure of the Invention That is, the present invention provides a flow rate ratio of diborane and monosilane on a substrate of [B ₂ H ₆ ]/[SiH ₄ ]=200 to
Formed into P-type by glow discharge decomposition under conditions of 2000ppm, with a carbon atom content of 10~
30 atomic%, and the hydrogen atom content is 10~
30 atomic% and a charge blocking layer made of amorphous hydrogenated and/or fluorinated silicon carbide with a thickness of 400 Å to 1 μm, and the flow ratio of diborane and monosilane to [B ₂ H ₆ ]/[SiH ₄ ]=5. Amorphous hydrogenated amorphous atom formed by glow discharge decomposition under conditions of ~100 ppm, with a carbon atom content of 10-30 atomic%, a hydrogen atom content of 10-30 atomic%, and a thickness of 10-30 μm. and/or a charge transport layer made of fluorinated silicon carbide;
Or a charge generation layer made of fluorinated silicon, with a carbon atom content of 10 to 70 atomic%, a hydrogen atom content of 10 to 30 atomic%, and a thickness of
The present invention relates to an electrophotographic photoreceptor characterized in that surface-modified layers made of amorphous hydrogenated and/or fluorinated silicon carbide having a thickness of 400 to 5000 Å are sequentially laminated. 5 Examples Hereinafter, the photoreceptor according to the present invention will be illustrated in detail, but first, the progress that led to the present invention will be explained. The photoreceptor shown in FIG. modified layer)
4 are sequentially laminated.
The a-SiC:H layer 2 mainly has the functions of holding potential, transporting charges, and improving adhesion to the substrate 1,
Its carbon atom content is 10-30 atomic% (Si and C
It is important that the thickness be set at a ratio of (to the total number of atoms), and it is preferably formed to have a thickness of 10 μm to 30 μm. The photoconductive layer 3 generates charge carriers in response to light irradiation, and
The thickness is preferably 2500 Å to 5 μm.
Furthermore, the a-SiC:H layer 4 improves the surface potential characteristics of this photoreceptor, maintains the potential characteristics over a long period of time, and maintains environmental resistance (prevents the effects of humidity, atmosphere, and chemical species generated by corona discharge). , improved printing durability due to high surface hardness, improved heat resistance when using photoreceptors,
It has functions such as improving thermal transferability (particularly adhesive transferability), and functions as a so-called surface modification layer. The thickness t of this a-SiC:H layer 4 is 400 Å~
It is important to make it thinner than the conventional one, to 5000 Å, especially 400 Å≦t<2000 Å. By configuring the photoreceptor in this way, it maintains a high potential with a thinner film than conventional Se photoreceptors, exhibits excellent sensitivity to light in the visible and infrared regions, and is heat resistant. This makes it possible to provide an a-Si photoreceptor (for example, for electrophotography) that has good durability, printing durability, and stable environmental resistance. Moreover, what is noteworthy is that by setting the carbon atom content of the charge transport layer within a specific range of 10 to 30 atomic percent, the photoreceptor has more than enough of the various properties required. That's true. This will be explained in detail below. First, it has been confirmed that the optical energy gap (Eg, opt) of a-SiC:H generally increases as the carbon atom content increases, as shown in FIG. This Eg corresponds to a band gap, and as the carbon atom content increases, the Eg of a-Si:H (approximately
1.71eV). On the other hand, the carbon atom content is a as shown in Figure 3.
- The specific resistance of SiC:H (ρ _D : dark resistivity, ρ _G : resistivity when irradiated with green light) is influenced by the carbon content (i.e.
If Eg) is increased, the photosensitivity (ρ _D /
ρ _G ) decreases, as shown in FIG. When the wavelength of the irradiated light is changed, the photosensitivity of a-SiC:H changes depending on the carbon content, as shown in FIG. FIG. 6 shows the energy band of the photoreceptor having the layer structure described in FIG. In this energy band diagram, as described above, the charge transport layer 2
Since the carbon atom content of the charge transport layer 2 is set to 10 to 30 atomic% (15 atomic% in the illustrated example: Eg = 2.1 eV), the Eg of the charge transport layer 2 itself has an appropriate size, and the a- Eg of Si:H layer 3 (approx.
1.71eV) forms a bandcap that does not substantially form a barrier to electrons. That is, when the surface of this photoreceptor is operated with a negative charge, holes indicated by a circle are injected from the substrate 1 side as shown by the dashed line, but these holes are injected into the a-SiC:H layer 2. As a result, the negative charge on the surface of the _{photoreceptor} is sufficiently retained, dark decay is reduced, and the potential retention ability is improved. Furthermore, carriers (holes indicated by ○, electrons indicated by ●) generated in the photoconductive layer 3 during light irradiation
Of these, for electrons, the conduction band Ec has almost no barrier between layers 2 and 3 (that is, the matching of energy levels is good), so a
-SiC: Can easily move to the substrate 1 side through the H layer 2 as shown by the dashed line, and holes can easily move to the surface side through the thin surface layer 4 to selectively neutralize surface negative charges. and efficiently form an electrostatic latent image. Therefore, this photoreceptor has good photosensitivity in addition to the above-mentioned potential holding ability. In order to obtain such remarkable effects, it has been revealed that the carbon atom content of the charge transport layer 2 must be specifically set to 10 to 30 atomic %.
That is, when the carbon atom content is less than 10 atomic%,
a-SiC: The specific resistance of H layer 2 is necessary for potential holding ability.
Since it is less than 10 ¹² Ω-cm (see Fig. 3), the charging potential is particularly insufficient, which is inappropriate. Furthermore, when the carbon atom content exceeds 30 atomic%, the resistivity decreases as well, and at the same time, the presence of too many carbon atoms increases defects in the a-SiC:H layer, resulting in poor carrier transport performance itself. . It is also important that in the photoreceptor shown in FIG. 1, the photoconductive layer 3 is not doped with any impurities such as those belonging to Group A of the periodic table. In other words, when the a-Si:H layer is doped with impurities to increase its resistance (ρ _D =10 ¹¹ to ^{10 12} Ω-cm) as in the conventional technology,
Impurity doping lowers the carrier range (μτ)e of electrons, that is, (mobility×lifetime), which causes the optical attenuation curve to tail, resulting in lower sensitivity and lower image quality. FIG. 7 shows the light attenuation characteristics of the above-mentioned photoreceptor in which the photoconductive layer 3 is not doped with impurities.
When impurities are doped (in the glow discharge method described later, for example, [B ₂ H ₆ ]/[SiH ₄ ]=
20 ppm), it was found that the attenuation curve tailed during light irradiation. The present inventor has discovered that although the functionally separated photoreceptor with the three-layer structure shown in FIG. 1 has the remarkable advantages described above, it also has the following problems. I stopped. That is, as understood from the energy band diagram of FIG. 6 and the above explanation, the photoreceptor shown in FIG. 1 is a photoreceptor for negative charging, and has low charging ability and dark decay for positive charging. It gets bigger. In other words, as is clear from FIG. 6, for example, if the carbon atom content of the charge transport layer 2 is 15 atomic%, Eg, opt is
When using the surface of the photoreceptor with a positive charge of 2.06eV, electrons are transferred from the substrate 1 side to the charge transport layer 2.
It easily overcomes Ec and is injected, neutralizing the positive charge on the surface and attenuating the surface potential. Moreover, among the carriers generated in the photoconductive layer 3 during light irradiation, holes are charge-transported from the photoconductive layer 3 due to the energy gap or energy barrier (△E) of _EV between both layers 3-2. It becomes difficult to move to layer 2 (Eg, opt of a-Si is 1.71eV, a-SiC
Eg, opt is 2.06eV). For these reasons, the above-mentioned photoreceptor has poor charging ability during positive charging, has a large amount of dark decay, and has poor photosensitivity, so only the attenuation curve shown in Figure 9 can be obtained, making it unsuitable for use in positive charging. be. Therefore, as shown in FIG. 10, in the photoreceptor shown in FIG. It was considered to provide a charge blocking layer. As a result, as shown in FIG. 11, it is possible to prevent the injection of electrons from the substrate 1 and maintain the positive charge on the surface of the photoreceptor (that is, to reduce dark decay). Due to the energy barrier (ΔE) similar to that shown in FIG. As a result of intensive study of the above-mentioned problems that occur during positive charging, the present inventor found that it is inappropriate to simply provide the charge blocking layer 5 to prevent the injection of carriers. It has been recognized that it is necessary to take effective means to efficiently move holes generated during irradiation to the charge transport layer 2 side. As such a means, one idea is to reduce the carbon content of a-SiC:H constituting the charge transport layer 2 based on the data shown in FIG. 2 to reduce the ΔE between both layers 3-2. However, in order to achieve this, it is necessary to significantly reduce the carbon atom content to less than 10 atomic%, which lowers the resistance of the a-SiC:H layer 2 and significantly lowers the charging potential of the photoreceptor. . The present inventor maintained the carbon atom content of the a-SiC:H layer 2 at 10 to 30 atomic% in order to achieve level matching of _EV between both layers 3-2 to improve charging characteristics and transport ability. While holding well, a-SiC:H
The present invention was achieved by discovering that the above-mentioned problems can be sufficiently overcome by doping layer 2 with a relatively small amount of Group A elements of the periodic table. That is, the photoreceptor according to the present invention basically has a first
Although it has the layer structure shown in Figure 0, a-
While the SiC:H layer 2 is doped with a relatively small amount of a periodic table group A element (e.g. boron), the a-SiC:H layer 5 for charge blocking is doped with a periodic table group A element (e.g. boron). It is heavily doped and the carbon atom content of the a-SiC:H layer 2 is 10~
It is characterized by being maintained at 30 atomic%. As a result, as shown in Fig. 13, a-SiC:H
Layer 2 is bonded to photoconductive layer 3 by boron doping.
This narrows the energy gap regarding _EV and allows for sufficient matching of energy levels between the two layers. As a result, holes generated in the photoconductive layer 3 during light irradiation are transferred to the charge transport layer 3.
This allows for smooth injection into the interior. In addition, due to the presence of the charge blocking layer 5, the substrate 1
It is also possible to effectively prevent injection of electrons from In this way, as shown in FIG. 14, it became possible for the first time to obtain a photoreceptor exhibiting sufficient attenuation characteristics for positive charging use. That is, in this photoreceptor, the photosensitivity increases, the residual potential decreases, the tailing of the optical attenuation curve disappears, and the charging potential can be maintained at a high level. The carbon atom content of the above a-SiC:H layer 2 should be set to 10 to 30 atomic% (for example, 15 atomic%) for the reasons mentioned above (i.e., retention of charged potential, improvement of transport ability). ), this is based on reasons specific to positive charging. In other words, if we increase the carbon content to more than 30 atomic%,
This widens the energy gap,
In order to match the energy level regarding _EV , it is necessary to increase the amount of boron doping. However, increasing the amount of boron doping in this way conversely lowers the resistance more than necessary, resulting in poor charging characteristics, and because it is difficult to control the amount of doping, it becomes difficult to match the energy level with the photoconductive layer. Become. In order to obtain the photoreceptor according to the present invention illustrated in FIG. 13, the amount of boron doped in each of the a-SiC:H layers 2 and 5 is important as described above. In particular, the charge transport layer controls the flow rate ratio of diborane and monosilane to [B ₂ H ₆ ]/[SiH ₄ ]=5 to 100 ppm (e.g.
The charge blocking layer is formed by glow discharge decomposition (described below) under conditions of 10 ppm), and the charge blocking layer has a flow rate ratio of diborane and monosilane of [B ₂ H ₆ ]/[SiH ₄ ]= It is preferable that the material be formed into a P type by glow discharge decomposition under conditions of 200 to 2000 ppm (for example, 1000 ppm). Next, each layer of the photoreceptor according to the present invention will be explained in more detail. First a-SiC:H layer (surface modified layer) This a-SiC:H layer 4 is used to modify the surface of the photoconductor to make the a-Si photoconductor practically superior. It is essential. That is, it enables the basic operations of an electrophotographic photoreceptor, such as charge retention on the surface and attenuation of the surface potential due to light irradiation. Therefore, the repetitive characteristics of charging and optical attenuation are very stable, and good potential characteristics can be reproduced even if left for a long period of time (for example, one month or more). On the other hand, in the case of a photoreceptor having an a-Si:H surface, it is easily affected by humidity, air, ozone atmosphere, etc., and the potential characteristics change significantly over time.
In addition, a-SiC:H has a high surface hardness, so it is resistant to abrasion during processes such as development, transfer, and cleaning, and it also has good heat resistance, so it can be used in processes that apply heat such as adhesive transfer. be able to. In order to achieve such excellent effects comprehensively, the film thickness of the a-SiC:H layer 4 must be 400 Å≦ as described above.
Within the range of t≦5000Å (especially 400Å≦t<2000Å)
It is extremely important to choose That is, when the film thickness is 5000 Å or more, the residual potential V _R becomes too high and the sensitivity E
A reduction of 1/2 (described later) also occurs, and good characteristics as an a-Si photoreceptor are lost. In addition, the film thickness
When the thickness is less than 400 Å, charges are no longer charged on the surface due to the tunneling effect, resulting in an increase in dark decay and a significant decrease in photosensitivity. Therefore, it is desirable that the thickness of the a-SiC:H layer 4 be 5000 Å or less (particularly less than 2000 Å) and 400 Å or more, but such a thickness range cannot be expected from conventionally known techniques. Furthermore, it has been found that it is also important to select the carbon composition of this a-SiC:H layer 4 in order to exhibit the above-mentioned effects. The composition ratio is a-
If expressed as Si ₁ -xCx:H, x should be 0.1 to 0.7 (carbon atom content is 10 atomic% to 70 atomic%).
) is desirable. In other words, if 0.1≦x, the optical energy gap will be approximately 2.0 eV or more, and the irradiated light will be absorbed by the a-Si:H layer (charge generating layer) due to the so-called optically transparent window effect for visible and infrared light. layer) 3 (Figures 4 and 5).
(see figure). Conversely, when x<0.1, a portion of the light is absorbed by the surface layer 4, and the photosensitivity of the photoreceptor tends to decrease. Furthermore, when x exceeds 0.7, most of the layer becomes carbon, and the semiconductor properties are lost, as well as a-
Since the deposition rate when forming the SiC:H film by the glow discharge method decreases, it is preferable that x≦0.7. Second a-SiC:H layer (charge transport layer) This a-SiC:H layer 2 has both the functions of potential retention and charge transport, has a dark resistivity of 10 ¹² Ω-cm or more, and has high durability. It has electric field properties and has a high potential maintained per unit film thickness, and the impurity doping (light doping) described above reduces the barrier to holes injected from the photosensitive layer 3, allowing the holes to have high mobility. Support 1 efficiently throughout its lifespan
Transport to the side. Also, the composition of carbon (10~
Since the size of the energy gap can be adjusted by 30 atomic %), holes generated in the photosensitive layer 3 in response to light irradiation can be efficiently injected without creating a barrier. Therefore, this a-SiC:H layer 2 maintains a high surface potential at a practical level and efficiently and quickly transports the charge carriers generated in the a-SiC:H layer 3, resulting in a photoreceptor with high sensitivity and no residual potential. It has the function of In order to fulfill these functions, the thickness of the a-SiC:H layer 2 is preferably 10 μm to 30 μm in order to apply a dry development method using the Carlson method, for example. If this film thickness is less than 10 μm, it is too thin and the surface potential necessary for development cannot be obtained.
Moreover, if the thickness exceeds 30 μm, the rate at which the carrier reaches the support 1 will decrease. However, even if the film thickness of this a-SiC:H layer is made thinner (for example, 10-odd μm) than that of the Se photoreceptor, a surface potential at a practical level can be obtained. a-Si:H layer (photoconductive layer or photosensitive layer) This a-Si:H layer 3 has high photoconductivity to visible light and infrared light, as shown in FIG. , the maximum value of ρ _D /ρ _L is ~10 ⁴ for red light at a wavelength of around 650 nm. By using this a-Si:H as a photosensitive layer, it is possible to create a photoreceptor that is highly sensitive to light in the entire visible region and in the infrared region. In order to absorb visible light and infrared light without waste and generate charge carriers in this manner, the thickness of the a-Si:H layer 3 is preferably 2500 Å to 5 μm. If the film thickness is less than 2500 Å, all of the irradiated light will not be absorbed and a portion of it will reach the underlying a-SiC:H layer 2, resulting in a significant decrease in photosensitivity. Also,
Although the a-Si:H layer 3 has a large charge transport ability,
Since the resistivity is ~10 ⁹ Ω-cm and it does not have potential retention properties by itself, there is no need to make it thicker than necessary for light absorption as a photosensitive layer, and the maximum thickness is 5 μm. It is sufficient. Moreover,
When the thickness exceeds 5 μm, carriers tend to diffuse laterally in the layer, and the sensitivity decreases on the contrary. Third a-SiC:H layer (charge blocking layer) This blocking layer 5 prevents injection of electrons from the substrate 1, and creates the necessary energy gap difference between the substrate 1 and the substrate 1. In order to form
A large amount of Group A elements of the periodic table is doped (heavy doping). Since this blocking layer is made of an a-SiC:H layer, it has the characteristics of good adhesion to the substrate 1 and good film adhesion. This blocking layer 5 is preferably provided with a thickness of 400 Å to 1 μm in order to fully exhibit its function. If it is less than 400 Å, it is too thin and the blocking function deteriorates, and if it exceeds 1 μm, it is thick and the layer itself has a low resistance, making it easy for carriers to diffuse laterally. Further, the carbon atom content in the blocking layer 5 is 10 to
It is desirable to set it to 30 atomic%. Next, an apparatus (glow discharge apparatus) that can be used to manufacture a photoreceptor according to the present invention will be described with reference to FIG. In the vacuum chamber 12 of this device 11, the above-described substrate 1 is fixed on the substrate holder 14, and the heater 1
5, the substrate 1 can be heated to a predetermined temperature. A high frequency electrode 17 is arranged opposite to the substrate 1, and a glow discharge is generated between the high frequency electrode 17 and the substrate 1. In addition, 20, 21, 22, 23, 24, 2 in the figure
5, 27, 28, 29, 30, 35, 36, 3
8 and 39 are respective valves; 31 is a supply source of SiH ₄ or a gaseous silicon compound; 32 is a supply source of CH ₄ or a gaseous carbon compound; 33 is a carrier gas supply source such as Ar or H ₂ ; and 34 is a B ₂ H ₆ sources, 37 are SiF ₄
It is a gas supply source (fluorine supply source). In this glow discharge device, first, a support such as Al
After cleaning the surface of the substrate 1, place it in a vacuum chamber 12, adjust the valve 36 so that the gas pressure in the vacuum chamber 12 becomes 10 ^-6 Torr, and evacuate the substrate 1.
is heated and maintained at a predetermined temperature, for example, 200°C. Next, a high purity inert gas is used as a carrier gas,
A mixed gas prepared by diluting an appropriate amount of SiH ₄ or a gaseous silicon compound and CH ₄ or a gaseous carbon compound is introduced into the vacuum chamber 12 together with B ₂ H ₆ if necessary,
High frequency power is applied by a high frequency power source 16 under a reaction pressure of 0.01 to 10 Torr. As a result, each of the above reaction gases is decomposed by glow discharge, and the boron-doped a-SiC:H containing hydrogen is formed on the substrate 1 as the above layers 5 and 2, and the a-SiC:H containing hydrogen is formed as the above layer 4. to be deposited. At this time, a-Si ₁ -xCx:H (for example x
(up to about 0.3 or 0.7) can be deposited at 1000 Å/
It is possible to deposit a-SiC:H at a rate of min or more. Furthermore, in order to deposit a-Si:H (photosensitive layer 3 above), the silicon compound may be decomposed by glow discharge without supplying the carbon compound. It is necessary that the above a-SiC:H layers 5, 2, and 4 contain hydrogen, but if they do not contain hydrogen, the charge retention characteristics of the photoreceptor will not be practical. . For this reason, it is desirable that the hydrogen content be 10 to 30 atomic%.
If it is less than 10 atomic %, compensation for dangling bonds is insufficient, and if it exceeds 30 atomic %, defects are more likely to occur. The hydrogen content in the photoconductive layer 3 is essential in order to compensate for dangling bonds and improve photoconductivity and charge retention, and is usually 10 to 10%.
30 atomic% is desirable for the same reason as above. In addition, in order to compensate for dangling bonds, fluorine is introduced into a-Si instead of the above-mentioned H or in combination with H (the source is
SiF ₄ ), a-Si:F, a-Si:H:F, a-SiC:
F, a-SiC:H:F can also be used. In this case, the amount of fluorine is preferably 0.5 to 10 atomic%. The above manufacturing method is based on the glow discharge decomposition method, but other methods include sputtering method, ion plating method, and vapor deposition of a-Si under the introduction of activated or ionized hydrogen in a hydrogen discharge tube. (In particular, the method of
The above-mentioned photoreceptor can also be produced by the method disclosed in Japanese Patent Application No. 78413 (Japanese Patent Application No. 152455/1982). Reactive gases used include SiH ₄ and SiF ₄ .
Other than Si ₂ H ₆ , SiHF ₃ or its derivative gas, CH ₄
Lower hydrocarbon gases such as C ₂ H ₆ and C ₃ H ₃ and CF ₄ can be used. Next, an example in which the present invention is applied to an electrophotographic photoreceptor will be specifically described. No. 10 was deposited on the Al support by glow discharge decomposition method.
An electrophotographic photoreceptor having the structure shown in the figure was manufactured. First, a clean Al support with a smooth surface was placed in a reaction (vacuum) chamber of a glow discharge device. Inside the reaction tank
Evacuate to a high vacuum level of 10 ^-6 Torr and lower the support temperature.
After heating to 200℃, high purity Ar gas was introduced.
A high-frequency power with a frequency of 13.56 MHz and a power density of 0.04 W/cm ² was applied under a back pressure of 0.5 Torr, and a preliminary discharge was performed for 15 minutes. Then _SiH4 and _{CH4 and B2H6}
By introducing a reactive gas consisting of (Ar + SiH ₄ + CH ₄ + B ₂ H ₆ ) and decomposing the mixed gas by glow discharge, the a-SiC:H layer, which plays a charge blocking function, potential retention and charge transport. The functional a-SiC:H layer was formed to a predetermined thickness at a deposition rate of 350 Å/min. To form the a-Si:H photosensitive layer, once the reaction layer is evacuated, CH ₄ is not supplied and SiH ₄ is discharge decomposed using Ar as a carrier gas.
An a-Si:H photosensitive layer of a predetermined thickness was formed. After that, CH ₄ was supplied again and the flow rate ratio was adjusted (Ar
+SiH ₄ +CH ₄ ) The mixed gas is decomposed by glow discharge,
A-SiC:H surface modification layer of a predetermined thickness is further provided,
Completed an electrophotographic photoreceptor. The photoconductor produced in this way is coated with positive polarity.
A 6KV corona discharge was performed and various electrophotographic characteristics were measured. In this case, when samples (Samples No. 1 to No. 15) were prepared with various compositions and film thicknesses of each layer of the photoreceptor, the results shown in the table below were obtained.

【table】

【table】

[Table] For this test, the electrophotographic photoreceptor prepared as described above was tested using an electrometer SP-428.
The photoconductor was mounted on a mold (manufactured by Kawaguchi Electric Co., Ltd.), the voltage applied to the discharge electrode of the charger was set to +6 KV, the charging operation was performed for 10 seconds, and the charged potential on the surface of the photoreceptor immediately after this charging operation was set to Vo (V), After dark decay for 2 seconds, the amount of irradiation light required to attenuate the charged potential to 1/2 was defined as the halving exposure amount E1/2 (1ux·sec). The light attenuation curve of the surface potential becomes flat at a certain finite potential, and may not become completely zero; this potential is called the residual potential V _R (V). Regarding image quality, the photoreceptor was made into a drum shape, and the electrophotographic copying machine U-BixV was used at 20℃ and 60%RH.
(manufactured by Konishiroku Photo Industry Co., Ltd.), an image was printed, and the initial image quality (image quality after 1000 copies) and image quality after multiple uses (image quality after 200,000 copies) were evaluated as follows. . Image density 1.0 or more ◎ (Very good image quality) 〃 0.6 to 1.0 〇 (Good image quality) 〃 Less than 0.6 △ (Blurred image occurs) 〃 ×
(The concentration is extremely low and cannot be determined.) As is clear from the data shown in this table, compared to sample No. 1 in which the charge transport layer is not doped with impurities,
It can be seen that Sample No. 2 of the present invention, which has an impurity-doped structure, exhibits excellent characteristics. In addition, samples No. 3 to No. 6
As is clear from Nos. 12 to 15, the doping amount of the blocking layer is set to [B ₂ H ₆ ]/[SiH ₄ ]=200 to
The doping amount of the charge transport layer was set to 2000 ppm, and the doping amount of the charge transport layer was set to 5.
If it is set to ~100 ppm, it is possible to significantly improve the durability when copying a large number of sheets while maintaining the photosensitivity and residual potential at good values. Furthermore, it can be seen that it is important to set the composition, thickness, etc. of each layer within the above-mentioned desirable ranges. 6 Effects of the Invention As described above, the present invention provides a photosensitive material using a laminate of an a-SiC surface-modified layer, an a-Si photoconductive layer, an a-SiC charge transport layer, and an a-SiC charge blocking layer. Because it consists of a thin film, it retains a high potential, exhibits excellent sensitivity to light in the visible and infrared regions, has good heat resistance and printing durability, and has stable environmental resistance. Therefore, it is possible to provide an a-Si photoreceptor (for example, for electrophotography) having the following properties. In addition, level matching with the photoconductive layer can be achieved by doping the charge transport layer with impurities, making it possible to smooth the movement of optical carriers and increasing photosensitivity. Since the energy barrier against undesired injection carriers is increased by increasing the number of injected carriers, the ability to hold the charged potential and the effect of preventing dark decay can be enhanced. Moreover, what is noteworthy is that by setting the carbon atom content of the charge transport layer within a specific range of 10 to 30 atomic%, various properties required for photoreceptors (especially high sensitivity, low residual potential, and high potential) can be achieved. It has more than enough properties (retention ability, repeated durability).

[Brief explanation of drawings]

1 to 12 are for explaining the present invention, in which FIG. 1 is a cross-sectional view of a part of an electrophotographic photoreceptor, and FIG. 2 is a-SiC:H according to the carbon atom content.
Figure 3 is a graph showing changes in the optical energy gap of a.
- A graph showing the change in resistivity of SiC:H, Figure 4 shows the change in resistivity of a-SiC:H due to the optical energy gap.
Figure 5 is a graph showing the photosensitivity characteristics of irradiated light by comparison, and Figure 6 is a graph showing the photosensitivity characteristics depending on the wavelength of the irradiated light.
The figure shows the energy band diagram of each layer of the photoreceptor, Figure 7 shows the potential attenuation characteristic diagram of the photoreceptor, Figure 8 shows the potential attenuation characteristic diagram of other photoreceptors, and Figure 9 shows the exposure of Figure 1 when positively charged. Figure 10 is a cross-sectional view of a part of another photoreceptor, Figure 11 is an energy band diagram of each layer of the photoreceptor in Figure 10, and Figure 12 is Figure 10 when positively charged. 13 to 16 illustrate the present invention. FIG. 13 is an energy band diagram of each layer of the photoreceptor, and FIG. 14 shows the photoreceptor when positively charged. FIG. 15 is a graph showing changes in characteristics depending on the thickness of the surface-modified layer, and FIG. 16 is a schematic cross-sectional view of a photoreceptor manufacturing apparatus. In addition, in the symbols shown in the drawings, 1...
...Support (substrate), 2...a-SiC:H layer (charge transport layer), 3...a-Si:H photosensitive layer (photoconductive layer),
4... a-SiC:H layer (surface modified layer), 5... Charge blocking layer, 11... Glow discharge device, 1
7... High frequency electrode, 31... Gaseous silicon compound supply source, 32... Gaseous carbon compound supply source, 3
3...Carrier gas supply source, 34... _B2H6 supply source, 37... _SiF4 supply source, Eg, opt...Optical energy gap, _ρD / _ρG ...Dark resistivity/ _light Resistivity at the time of irradiation, E1/2...half-reduced exposure amount, V _R ...residual potential.

Claims (1)

[Claims] 1. Formed into a P-type on a substrate by glow discharge decomposition under conditions where the flow rate ratio of diborane and monosilane is [B ₂ H ₆ ]/[SiH ₄ ]=200 to 2000 ppm. and the carbon atom content is 10-30 atomic%,
A charge blocking layer made of amorphous hydrogenated and/or fluorinated silicon carbide having a hydrogen atom content of 10 to 30 atomic% and a thickness of 400 Å to 1 μm, and the flow rate ratio of diborane and monosilane [B ₂ H ₆ ] / [SiH ₄ ] = 5 to 100 ppm, the carbon atom content is 10 to 30 atomic%, the hydrogen atom content is 10 to 30 atomic%, and the thickness is A charge transport layer made of amorphous hydrogenated and/or fluorinated silicon carbide with a thickness of 10 to 30 μm, and a charge transport layer made of amorphous hydrogenated and/or fluorinated silicon carbide with a hydrogen atom content of 10 to 30 atomic% and a thickness of 2500 Å to 5 μm.
Or a charge generation layer made of fluorinated silicon, with a carbon atom content of 10 to 70 atomic%, a hydrogen atom content of 10 to 30 atomic%, and a thickness of
An electrophotographic photoreceptor characterized in that a surface-modified layer made of amorphous hydrogenated and/or fluorinated silicon carbide having a thickness of 400 to 5000 Å is laminated in sequence.