JPS63292144A - Electrophotographic sensitive body - Google Patents

Abstract

PURPOSE:To obtain a photosensitive body not deteriorated in the mobility of carriers and life by increasing film thickness and good in electric chargeability to both polarities by alternately laminating 2 kinds of thin microcrystalline silicon films at least one of both containing conductivity governing element to form a barrier layer. CONSTITUTION:The photosensitive body is obtained by laminating on a conductive supporting body 1 the barrier layer 2 and on this layer a photoconductive layer 3, and further on this a protective layer 4, and the barrier layer 2 has a superlattice structure obtained by alternately laminating 2 kinds of thin microcrystalline silicon films at least one of both containing conductivity governing element, such as an element of III or V of the periodic table, and it may contain also one of C, O, and N. A preferable film thickness of the barrier layer 2 is 100Angstrom -10mum, and a preferable film thickness of each thin film is 30-500Angstrom , thus permitting the obtained electrophotographic sensitive body to be low in residual potential, good in adhesion between the barrier layer 2 and the conductive substrate, and good in chargeability.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention provides an electrophotographic method that has excellent charging characteristics, dark decay characteristics, photosensitivity characteristics, environmental resistance, etc., and is capable of being charged both positively and negatively. Regarding photoreceptors.

(Prior art) Amorphous silicon containing hydrogen (H) (hereinafter referred to as
a-Si (abbreviated as H) has recently attracted attention as a photoelectric conversion material, and has been applied to photoreceptors in electrophotographic processes, such as solar cells, thin film transistors, and image sensors.

Conventionally, materials constituting the photoconductive layer of electrophotographic photoreceptors include inorganic materials such as CdS, ZnO, Se, or 5e-Te, or poly-N-vinylcarbazole (PVCz).
Alternatively, organic materials such as trinitrofluorenone (TNF) have been used.

However, compared to these inorganic or organic materials, a-31:H is a non-polluting substance, so there is no need for recovery treatment, and it has high spectral sensitivity in the visible light region.
It also has advantages such as high surface hardness and excellent wear resistance and impact resistance. Therefore, a-51:H
is attracting attention as a photoreceptor for electrophotographic processes.

This a-31:H is being studied as a photoreceptor material based on the Carlson method, but in this case, high resistance and photosensitivity are required as photoreceptor characteristics. However, it is difficult to satisfy both of these characteristics with photoreceptors manufactured by heavy industries, so a barrier layer is provided between the photoconductive layer and the conductive support, and a surface charge retention layer is provided on the photoconductive layer. These requirements are satisfied by using a layered structure.

(Problems to be Solved by the Invention) Conventionally, a high-resistance insulating single layer has been used as a barrier layer, but when such a barrier layer is thick, it separates from the photoconductive layer to the support. Carriers flowing to the barrier layer cannot pass through the barrier layer, and as a result, the residual potential becomes high. On the other hand, if the film is thin, dielectric breakdown will occur due to the development bias. In addition, when a p-type or n-type semiconductor is used as a barrier layer, if the film is thick, carriers will be trapped in structural defects such as dangling bonds, resulting in a high residual potential, whereas if the film is thin, the residual potential will be high. In this case, carriers from the support cannot be blocked, resulting in a decrease in charging ability.

On the other hand, for purposes such as two-color copying and dual use as a printer and a copy, a photoreceptor that can be charged both positively and negatively is desired. When such a photoreceptor is formed of amorphous silicon, it is conceivable to add oxygen to the amorphous silicon or to provide an insulating layer between the photoconductive layer and the support. However, in the former case, the addition of oxygen increases film defects and deteriorates sensitivity, residual potential, etc. In the latter case, if the insulating layer is thick, carriers will be trapped and the residual potential will increase, whereas if it is thin, dielectric breakdown will occur during image development, which is not preferable.

The present invention has been made in view of such circumstances, and
Excellent charging ability, low residual potential, high photosensitivity over a wide wavelength range up to the near-infrared region, good adhesion to the substrate, excellent environmental resistance, and good charging performance in both positive and negative charging. The purpose of the present invention is to provide an electrophotographic photoreceptor having the following functions.

[Structure of the Invention] (Means for Solving the Problems) As a result of various studies, the present inventors have achieved the above object by using a superlattice structure as a barrier layer of an electrophotographic photoreceptor. They have discovered that it is possible to do so, and have completed the present invention.

That is, the electrophotographic photoreceptor of the present invention is an electrophotographic photoreceptor comprising an electrically conductive support, a photoconductive layer, and a barrier layer, wherein at least one of the barrier layers contains atoms dominating the conductivity type. To provide an electrophotographic photoreceptor capable of being charged both positively and negatively, characterized in that 82 layers of two types of microcrystalline silicon thin films are alternately formed, and the thickness of the thin film is 30 to 500. .

In the electrophotographic photoreceptor of the present invention, the element controlling the conductivity type contained in the microcrystalline silicon thin film constituting the barrier layer is, for example, an element belonging to Group 1 or Group 2 of the periodic table. The content of these elements is preferably 10-3 to 1 atomic %, more preferably 104 to 10-1 atomic %.

Microcrystalline silicon (μc-8i) is thought to be formed from a mixed phase of microcrystalline silicon and amorphous silicon with a grain size of approximately several tens of angstroms, and has the following physical properties. are doing.

First, X-ray diffraction measurements show a crystal diffraction pattern with a 2θ of around 28 to 28.5@, which is clearly distinguishable from amorphous a-St in which only a halo appears. Second, μc-
The dark resistance of No. 31 can be adjusted to 10 10 Ω, and is clearly distinguished from polycrystalline silicon, which has a dark resistance of 10 5 Ω (1).

The optical bandgap (Eg'') of the μc-Sl used in the present invention is preferably 1.55 e V, for example. However, it can be set arbitrarily within a certain range. It is preferable to add a predetermined amount of hydrogen to each to obtain μc-81:H. This compensates for silicon dangling bonds and
Dark resistance and bright resistance are balanced, and photoconductive properties are improved.

(Function) In the electrophotographic photoreceptor of the present invention, since the barrier layer is provided with the superlattice structure, carriers generated in this region have a long lifetime and a high mobility. Although the theory has not yet been fully established, there is no doubt that this is a quantum effect due to the periodic well potential characteristic of the superlattice structure, and this is particularly referred to as the superlattice effect.

In this way, the mobility of carriers in the barrier layer increases and the lifetime of the carriers increases, resulting in a marked improvement in the sensitivity of the electrophotographic photoreceptor.

(Example) FIG. 1 is a diagram showing a cross-sectional structure of an electrophotographic photoreceptor according to an example of the present invention. In the figure, conductive support 1
A barrier layer 2 is formed thereon, and a photoconductive layer 3 is formed thereon. Further, a surface layer 4 is formed on the photoconductive layer 3.

Hereinafter, the structure of the electrophotographic photoreceptor shown in FIG. 1 will be explained in more detail.

The conductive support 1 usually consists of a drum made of aluminum.

The barrier layer 2 has a superlattice structure composed of two types of microcrystalline silicon thin films. At least one of these contains an atom that dominates the conductivity type, for example, an atom belonging to Group I or V of the Periodic Table. Examples of elements belonging to Group Ⅰ of the periodic table include boron B1 aluminum AI!
, gallium Ga.

There are indium In, thallium T, ff, etc. In addition, examples of elements belonging to Group V of the periodic table include nitrogen,
Phosphorus P1 Arsenic A s s Antimony Sb1 and Bismuth 8
There is a first prize. μC-81 constituting the barrier layer can be one in which element 7 is added (μc-31:H).

Furthermore, the barrier layer 2 may contain at least one selected from carbon, oxygen, and nitrogen. The thickness of the barrier layer 2 is preferably 100 to 10 μm.

The barrier layer 2 is formed in order to suppress the flow of charges between the conductive support 1 and the photoconductive layer 3, thereby increasing the charge retention function of the photoreceptor surface and increasing the charging ability of the photoreceptor. It is something. Therefore, when forming a Carlson type photoreceptor using a semiconductor layer as a barrier layer, the barrier layer 2 must be made of
type or N type. That is, when the surface of the photoreceptor is positively charged, the barrier layer 2 is made of P type to prevent electrons that neutralize the surface charge from being injected into the photoconductive layer. Conversely, when the surface is negatively charged, the barrier layer 2 is made of N type to prevent holes that neutralize the surface charge from being injected into the photoconductive layer. Since the carriers injected from the barrier layer 2 become noise with respect to the carriers generated in the photoconductive layer 3 upon incidence of light, preventing carrier injection as described above improves the sensitivity.

The photoconductive layer 3 generates carriers by the incidence of light, and these carriers are of one polarity and form a band on the surface of the photoreceptor. I!
The charge is neutralized and the other one travels within the photoconductive layer 3 and reaches the conductive support 1 .

The photoconductive layer 3 has μc-8l:H, a-Sl:H
It can be configured by Further, the photoconductive layer 3 may contain at least one selected from carbon, oxygen, and nitrogen.

The hydrogen content in a-8l:H and μc-8l:H constituting the barrier layer 2 and the photoconductive layer 3 is 0, O1~
30 atom % is preferable, and 1 to 25 atom % is more preferable. Such hydrogen content compensates for the dangling bonds of silicon, brings the dark resistance and bright resistance into balance, and improves the photoconductive properties.

To form the a-SlrH layer by the glow discharge decomposition method, silane gases such as SiH4 and 512H6 are introduced into the reaction chamber as raw materials, and H can be added into the thin film by glow discharge using high frequency. . If necessary, hydrogen or helium gas can be used as a carrier gas for silanes. On the other hand, SiF4 gas and s
iCJ! .

Silicon halide such as gas can be used as the source gas. In addition, even if the reaction is performed with a mixed gas of silane gas and silicon halide gas, H-containing a
-Sl:H can be formed into a film. Note that these thin films can be formed not only by the glow discharge decomposition method but also by a physical method such as sputtering.

Similarly to a-5i:H, the μc-Si layer can also be formed by high-frequency glow discharge decomposition using silane gas as a raw material. In this case, the temperature of the support is a-8l;
The high frequency power is set higher than when forming H, and the high frequency power is also a-
When set higher than the case of St:H, μc-Si:H
becomes easier to form. Furthermore, by increasing the support temperature and high frequency power, the flow rate of source gas such as silane gas can be increased, and as a result, the film formation rate can be increased. In addition, SiH4 and Si of the raw material gas
By using a gas obtained by diluting a high-order silane gas such as 2H6 with hydrogen, μC-5i:H can be formed with higher efficiency.

In order to make 1tc-Sl:H and a-St:H p-type, elements belonging to Group 1 of the periodic table, such as boron B, aluminum A, 17, gallium Ga1 indium Ins, and thallium TJ, are added. Doping is preferable, and in order to make μc-St:H and a-8i:H n-type, elements belonging to Group Ⅰ of the periodic table, such as nitrogen N1 phosphorus P, arsenic A8. It is preferable to dope with antimony Sb1, bismuth B1, etc. This doping with p-type impurities or n-type impurities prevents charges from moving from the support side to the photoconductive layer. On the other hand, p
By incorporating at least one element selected from carbon C1 nitrogen N and oxygen O into c-Sl:H and a-Sl:H, high resistance can be achieved and the surface charge retention ability can be increased.

A surface layer 4 is provided on the photoconductive layer 3.

Since μc-Sl:H and the like constituting the photoconductive layer 3 have a relatively large refractive index of 3 to 3.4, light reflection easily occurs on the surface. When such light reflection occurs, the ratio of the amount of light absorbed by the photoconductive layer decreases, resulting in increased light loss.For this reason, it is preferable to provide the surface layer 4 to prevent reflection. By providing the surface layer 4, the photoconductive layer is protected from damage.Furthermore, by forming the surface layer, the charging ability is improved and the charge is better placed on the surface.Formation of the surface layer The material used is a-SI N:
These include inorganic compounds such as H, a-810:H, and a-8iC:H, and organic materials such as polyvinyl chloride and polyamide.

When the surface of the electrophotographic photoreceptor constructed in this manner is charged with a positive voltage of about 500 V by corona discharge, a potential barrier is formed. When light (hv) is incident on this photoreceptor, carriers of electrons and holes are generated in the photoconductive layer 3. Electrons in the conduction band are accelerated toward the surface layer 4 side, and holes are accelerated toward the conductive support 1 side by the electric field in the photoreceptor. In this case, if a conventional barrier layer consisting of a single high-resistance insulating layer is used, as mentioned above, if the film is thick, carriers flowing from the photoconductive layer to the support cannot pass through the Si2 layer. As a result, the residual potential becomes high. On the other hand, if the film is thin, dielectric breakdown will occur due to the development bias. Also, as a barrier layer, p-type or n-type
When using a type semiconductor, if the film is thick, carriers will be trapped in structural defects such as dangling bonds, resulting in a high residual potential, whereas if the film is thin, carriers from the support will be blocked. Otherwise, the charging ability will decrease. On the other hand, when the barrier layer has a superlattice structure as in the photoreceptor of the present invention, carriers in the potential well layer are less concentrated due to quantum effects than in the case of a single layer without a superlattice structure. The lifespan is 5 to 10 times longer. Furthermore, in the superlattice structure, due to bandgap discontinuity,
Although a periodic barrier layer is formed, carriers easily pass through the bias layer due to the tunnel effect, so the effective carrier mobility is similar to that in the bulk, and carrier mobility is excellent.

As described above, the superlattice structure in which thin films with different optical band gaps are laminated can provide high photoconductivity and provide clearer images than conventional photoreceptors.

Referring to FIG. 2, an apparatus and a manufacturing method for manufacturing the electrophotographic photoreceptor of the above embodiment by a glow discharge method will be described below. In the figure, gas cylinders 21, 22, 23.
24, for example, St H4, B2 H6, H2, respectively.
, CH4, and other raw material gases are contained therein. The gas in these gas cylinders is controlled by a valve 26 and piping 27 for adjusting the flow rate.
The water is supplied to the mixer 28 via the mixer 28. A pressure gauge 25 is installed in each cylinder, and the pressure gauge 25
mixer 2 by adjusting valve 26 while monitoring
The flow rate and mixing ratio of each raw material gas supplied to 8 can be set as: AwJ. The gases mixed in the mixer 28 are supplied to a reaction vessel 29. A rotating shaft 30 is provided at the bottom 31 of the reaction vessel 29.
is mounted rotatably around the vertical direction. A disk-shaped support 32 is fixed to the upper end of the rotating shaft 3o with its surface perpendicular to the rotating shaft 3o1. Inside the reaction vessel 29, a cylindrical electrode 33 is installed on the bottom 31 with its axial center aligned with the axial center of the rotating shaft 3o.

A drum base 34 of a photoreceptor is placed on a support base 32 with its axial center aligned with the axial center of the rotating shaft 30, and a heater 3 for heating the drum base is installed inside the drum base 34.
5 are arranged. A high frequency power source 36 is connected between the electrode 33 and the drum base 34, so that a high frequency current is supplied between the electrode 33 and the drum base 34. The rotating shaft 30 is rotationally driven by a motor 38. The pressure inside the reaction vessel 29 is monitored by a pressure gauge 37,
The reaction vessel 29 is connected via a gate valve 38 to a suitable exhaust means such as a vacuum pump.

When manufacturing a photoreceptor using the above-mentioned manufacturing apparatus, the drum base 34 is placed in the reaction container 29, and then the gate valve 39 is opened to exhaust the inside of the reaction container 29 to a pressure of about 0.1 orr or less. Next, cylinders 21, 22, 23.
24, the required reaction gases are mixed at a predetermined mixing ratio and introduced into the reaction vessel 29.

In this case, the flow rate of the gas introduced into the reaction container 29 is such that the pressure inside the reaction container 29 ranges from 0.1 to 1. Set it so that it is Oorr. Next, the motor 38 is operated to rotate the drum base 34, and the heater 35 rotates the drum base 34.
is heated to a constant temperature, and a high frequency current is supplied between the electrode 33 and the drum base 34 by the high frequency power supply 36 to form a glow discharge between them. As a result, a-Sl:H is deposited on the drum base 34. Note that N20. NH,,No2. N2. CH.

These elements can be contained in a-81:H by using C2H4,02 gas or the like.

As described above, since the electrophotographic photoreceptor according to the present invention can be manufactured using a closed system manufacturing apparatus,
Safe for humans.

Next, the results of testing the electrophotographic properties of an electrophotographic photoreceptor according to the present invention formed into a film will be described.

Test Example 1 A diameter of 80 mva was subjected to acid treatment, alkali treatment, and sandblasting treatment to prevent interference as necessary.
An aluminum drum base with a width of 350 + * m is installed in the reaction vessel, and the reaction vessel is heated to approximately 1O-5T orr.
It was evacuated to a degree of vacuum. Heating the drum base to 250°C,
While rotating at 10 rpm, SiH4 gas was heated to 305C.
CM and H2 gases were introduced into the reaction vessel at a flow rate of 9008 CCM, and the pressure inside the reaction vessel was adjusted to 1 Torr. Then, 13.58 MHz high frequency power was applied to generate plasma, and 100 μc-8
i:H thin III (crystallinity = 80%) was formed. Next, B2H6 gas was added to the SiH4 gas flow rate at 5x10-
100 p-type μC-8l thin films (crystallinity: 65%) were formed.

These operations were repeated to form a barrier layer having a superlattice structure of 3000 members.

Next, add 500 SCCMSH2 gas to 500 IH4 gas.
At a flow rate of 0 SCCM, B2H6 gas was introduced at a flow rate ratio of I x 10-' to 5IH4 gas flow rate,
A high frequency power of 400 W was applied to form a 30 μm photoconductive layer.

Finally, a 0.5 μm surface layer consisting of a-8iC:H was formed.

When the surface of the photoreceptor thus formed is positively charged at about 500 V and exposed to white light, this light is absorbed by the photoconductive layer and carriers of electron-hole pairs are generated. In this test example, a large number of carriers were generated, the carriers had a long life, and high running performance was obtained. This resulted in clear, high-quality images. In addition, when the photoreceptor manufactured in this test example was repeatedly charged, the reproducibility and stability of the transferred image were extremely good, and the durability such as corona resistance, moisture resistance, and abrasion resistance was also improved. It has been proven that the properties are excellent.

Test Example 2 Example 1 except that the barrier layer was formed as follows.
An electrophotographic photoreceptor was formed in the same manner as described above.

5IHa gas 30SCCM, H2 gas 900SCC
At a flow rate of M, B2H6 gas was introduced into the reaction vessel at a flow rate ratio of 10-3 to 5IH4 gas flow rate, the pressure in the reaction vessel was adjusted to ITorr, and a high frequency power of 1.2kW was applied. 100 p-type μc-81:H thin films (crystallinity near 0%) were formed. Next, B2H6 gas was introduced at a flow rate ratio of 5×10 −2 to 5IH4 gas flow rate to form a 100 p-type μC-31 thin film (crystallinity: 65%). Repeat these operations,
A barrier layer consisting of a superlattice structure of 3000 members was formed.

When an image was formed using this photoreceptor in the same manner as in Test Example 1, a clear and high quality image was obtained.

Test Example 3 An electrophotographic photoreceptor was formed in the same manner as in Example 1, except that the barrier layer was formed as follows.

5IH4 gas 30SCCM, H2 gas 6008CC
A flow rate of M was introduced into the reaction vessel, the pressure inside the reaction vessel was adjusted to ITorr, and a high frequency power of 600 W was applied to form a 60 μc-Si:H thin film (crystallinity: 60%).
was formed. Next, PH3 gas was introduced at a flow rate ratio of 10 to 5IH4 gas flow rate, and 100 n-type μC
-3L thin film (crystallinity: 80%) was formed. These operations were repeated to form a barrier layer having a superlattice structure of 2000 members.

When an image was formed using this photoreceptor in the same manner as in Test Example 1, a clear and high quality image was obtained.

Test Example 4 Example 1 except that the barrier layer was formed as follows.
An electrophotographic photoreceptor was formed in the same manner as described above.

After forming an n-type μc-8i thin film in the same manner as in Example 3, PH3 gas was introduced at a flow rate ratio of 10-3 to the SiH4 gas flow rate, and the n-type μc-Si thin film (crystallinity =70%).

These operations were repeated to form a barrier layer having a superlattice structure of 1000 members.

When an image was formed using this photoreceptor in the same manner as in Test Example 1, a clear and high quality image was obtained.

Above, we have explained the test example in which the superlattice structure of the barrier layer is composed of two types of thin films, but the invention is not limited to this, and three or more types of thin films may be laminated. Just form a boundary.

[Effects of the Invention] According to the present invention, since a superlattice structure formed by laminating thin films with different optical band gaps is used for the barrier layer, carrier mobility is high and the film thickness can be reduced. It is possible to obtain a photoreceptor having good charging ability in both positive and negative charging without deteriorating carrier mobility or life even if the thickness is increased.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an electrophotographic photoreceptor according to an embodiment of the present invention, and FIG. 2 is a diagram showing an apparatus for manufacturing an electrophotographic photoreceptor according to an embodiment of the invention. 1: Conductive support, 2: Barrier layer, 3: Photoconductive layer, 4: Surface layer. Applicant's agent Patent attorney Takehiko Suzue 1st rs 2nd prisoner

Claims (6)

[Claims] (1) In an electrophotographic photoreceptor comprising a conductive support, a photoconductive layer, and a barrier layer, the barrier layer is made of two types of microcrystalline silicon thin films, at least one of which contains atoms dominating the conductivity type. The thin film is laminated, and the thickness of the thin film is 3
An electrophotographic photoreceptor capable of being charged both positively and negatively, characterized in that it has a thickness of 0 to 500 Å. (2) The electrophotographic photoreceptor according to claim 1, wherein the barrier layer contains at least one element selected from elements belonging to Group III or Group V of the periodic table. (3) The electrophotographic photoreceptor according to claim 1 or 2, wherein the barrier layer contains at least one element selected from the group consisting of carbon, oxygen, and nitrogen. (4) The electrophotographic photoreceptor according to claim 1, wherein the photoconductive layer is made of an amorphous material and/or a semiconductor material that is at least partially microcrystalline. (5) Any one of claims 1 to 4, wherein the photoconductive layer contains at least one element selected from the group consisting of carbon, oxygen, and nitrogen.
The electrophotographic photoreceptor described in . (6) The electrophotographic photoreceptor according to claim 1, further comprising a surface layer on the photoconductive layer.