JPS63187258A - Electrophotographic sensitive body - Google Patents

Abstract

PURPOSE:To improve the traveling property of a carrier in a surface layer by alternately laminating thin amorphous Si films and thin amorphous Si films contg. N, thereby forming the surface layer. CONSTITUTION:A photoconductive layer 3 and the surface layer 4 are formed on a conductive base 1. The layer 4 is formed into the superlattice structure alternately laminated with the thin amorphous Si (a-Si:H) films and thin amorphous Si (a-SiN:H) films contg. N respectively to 30-500Angstrom film thicknesses. >=1 Kinds of elements belonging to group III or V of periodic table are incorporated into this layer 4. The layer 3 is preferably formed of a-SiH or muc-Si:H. A barrier layer 2 consisting of a-Si:H, muc-Si or a-BN:H is preferably provided between the base 1 and the layer 3.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to an electrophotographic photoreceptor having excellent charging characteristics, dark decay characteristics, photosensitivity characteristics, environmental resistance, etc. [Prior Art] Hydrogen (H ) containing amorphous silicon (hereinafter referred to as a)
-8i:H) has recently attracted attention as a photoelectric conversion material, and has been applied to photoreceptors in electrophotographic processes as well as solar cells, thin film transistors, image sensors, and the like.

Conventionally, inorganic materials such as CdS, ZnOSe, or 5e-Te, or organic materials such as poly-N-vinylcarbazole (PVCZ) or trinitrofluorenone (TNF) have been used as materials constituting the photoconductive layer of an electrophotographic photoreceptor. It was used.

However, compared to these inorganic or organic materials, a-8t: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. For this reason, a Si
: H is attracting attention as a photoreceptor material for electrophotographic processes.

This a-8i:H is being studied as a material for a photoreceptor based on the Carlson method, but in this case, the photoreceptor is required to have high resistance and photosensitivity. However, it is difficult to satisfy both of these characteristics with a single photoreceptor layer, so a barrier layer is provided between the photoconductive layer and the conductive support, and the surface protection, antireflection, and surface potential are improved. For these purposes, such requirements are satisfied by forming a laminated structure in which a surface layer is provided on the photoconductive layer.

[Problem that the invention attempts to solve] By the way, conventionally, the surface layer is a-3iC.

An insulating single layer made of a-8i N, a-8i O, etc. is used, but such a surface layer has many structural defects such as dangling bonds and voids, which may affect the photoreceptor characteristics. is having an unfavorable impact on For example, when a photoreceptor is charged and irradiated with light, photocarriers are generated in the photoconductive layer. Among the photocarriers, holes travel toward the conductive support, and electrons travel toward the surface layer. In this case, electrons tunnel through the surface layer and neutralize the charge on the surface of the photoreceptor. Therefore, if the surface layer is thick, carriers cannot pass through the surface layer, resulting in poor sensitivity and image memory. Furthermore, as described above, since the surface layer contains many defects, carriers are trapped in the defects, resulting in an increase in residual potential. Furthermore, when light irradiation is performed in the next cycle, some of the carriers trapped in the surface layer travel toward the photoreceptor surface.
Since the surface charge is neutralized, the charging ability decreases.

Conversely, if the surface layer is thin, the surface potential of the photoreceptor decreases, creating a burden on the process design of copying machines, printers, and the like.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an electrophotographic photoreceptor that has excellent charging ability, low residual potential, and high sensitivity.

[Structure of the Invention] (Means for Solving the Problems) As a result of various studies, the present inventors have found that the above object can be achieved by using a superlattice structure as the surface layer of an electrophotographic photoreceptor. This discovery led to the completion of the present invention.

That is, the electrophotographic photoreceptor of the present invention is an electrophotographic photoreceptor having a conductive support, a photoconductive layer, and a surface layer, wherein the surface layer includes an amorphous silicon thin film and a nitrogen-containing amorphous silicon thin film. It is characterized in that it is constructed by laminating layers alternately, and each thin film has a thickness of 30 to 500 layers.

The nitrogen concentration in the nitrogen-containing amorphous silicon (a-8IN) thin film is preferably 1 to 30 atomic %, more preferably 5 to 15 atomic %.

(Function) In the electrophotographic photoreceptor of the present invention, the surface layer has a superlattice structure, and a-81 and a-
In the 8iN thin film, the carrier lifetime is 5 to 10 times longer than in the bulk layer due to quantum effects. In addition, since the respective a-S+ and a-8iN thin films are thin, carriers can easily pass through the a-8i and a-8iN thin films due to the tunnel effect, so the effective mobility of carriers is lower than that in the bulk layer. In other words, the mobility of the carrier is excellent.

As described above, since the life of the carrier in the surface layer is long and the carrier has excellent running properties, the sensitivity of the electrophotographic photoreceptor is significantly improved.

(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, 1 is a conductive support. A barrier layer 2 is formed on the conductive support, and a photoconductive layer 3 is formed thereon. Furthermore, 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 is made of μc-8i (microcrystalline silicon) or a-8i:
Alternatively, a-BN:H (amorphous boron to which nitrogen and hydrogen are added) may be used. Furthermore, an insulating film may be used. For example, μC
A high-resistance insulating barrier layer can be formed by including one or more elements selected from carbon C1 nitrogen N and oxygen 0 in -S+:+ or a-8i:H. The thickness of the barrier layer 2 is preferably 100 to 10 μm.

μc-8i is considered to be formed of a mixed layer of microcrystalline silicon and amorphous silicon with a grain size of about several tens of angstroms, and has the following physical characteristics. First, in X-ray diffraction measurement, 2θ is 28 to 28
．． It shows a crystal diffraction pattern at around 5° and is clearly distinguished from amorphous a-8i where only a halo appears. Second, the dark resistance of μc-8i can be adjusted to more than 10 EIΩ·α, and it is clearly distinguished from polycrystalline silicon, which has a dark resistance of 10 Ω·α.

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 charged negatively rather than positively 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. In addition, uc-8l:H and a-
In order to make 8i:H P-type, it is preferable to dope it with an element belonging to Group Ⅰ of the periodic table, such as boron B1 aluminum Af, gallium Ga, indium In, and thallium TI. Also, μC-8l :H and a-
8i: In order to make H type N, elements belonging to Group V of the periodic table, such as nitrogen, phosphorus P1 arsenic AS1 antimony Sb
, bismuth B1, etc. are preferably doped.

The photoconductive layer 3 formed on the barrier layer 2 is a-8i:H
Alternatively, it can be composed of μC-8i:H.

When light enters the photoconductive layer 3, carriers are generated. Among these carriers, those of one polarity neutralize the charges on the surface of the photoreceptor, and those of the other polarity travel along the photoconductive layer 113 and become conductive. Reach the support.

A surface layer 4 is formed on the photoconductive layer. The surface layer 4 has a superlattice structure formed by alternately stacking a-8i:HwII and J:C7a-8iN:H thin films. Since a-3i:)-1 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 proportion of the amount of light absorbed by the photoconductive layer 3 decreases, increasing optical loss. For this reason, a surface layer 4 is provided to prevent reflection.

In addition, by providing the surface layer 4, photoconductive! 13 is protected from damage. Furthermore, by forming the surface layer, the charging ability is improved, and the charge can be easily deposited on the surface.

a-8 constituting the barrier layer 2, photoconductive layer 3 and surface layer 4
The hydrogen content in i:HSa-8IN:H and μc-8i:H is preferably 0.01 to 30 at%,
More preferably 1 to 25 atom %. Such hydrogen content compensates for the dangling bonds of silicon,
Dark resistance and bright resistance become harmonious, and photoconductive properties are improved.

a-8+: To form 8 layers by the glow discharge decomposition method, silane gases such as 5IH4 and 5I2H6 are introduced into the reaction chamber as raw materials, and H is added into the thin layer by glow discharge with high frequency. be able to. If necessary, hydrogen or helium gas can be used as a carrier gas for silanes. On the other hand, silicon halides such as S i F4 gas and S i Cf+ gas can be used as the source gas. Furthermore, a-8i:H containing H can be similarly formed by reacting with a mixed gas of silane gas and silicon halide gas. Note that these thin layers can be formed not by the glow discharge decomposition method but also by a physical method such as sputtering.

In order to form a-8IN:H, which is one of the thin films constituting the surface layer 4, in the above method, N2 is added to the raw material gas.
0, NH3, NO2, N2, etc. may be added.

Similarly to a-8t:H, the μc-8+ layer can also be formed using silane gas as a raw material by the high-frequency glow discharge decomposition method. In this case, the temperature of the support is a-8t:
The high frequency power is set higher than when forming H, and the high frequency power is also a-
If set higher than the case of 8i:H, μc-8i: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. Further, by using a gas obtained by diluting high-order silane gas such as S I H4 and 512H6 as a raw material gas with hydrogen, μC-8IGH can be formed with even higher efficiency.

The surface of the electrophotographic photoreceptor constructed in this manner is charged with a positive voltage of approximately 500 V by corona discharge, and then exposed to light (
hv), electron and hole carriers are generated in the photoconductive layer 3. Electrons in the conduction band are accelerated toward the surface layer 4 side by the electric field within the photoreceptor, and holes are accelerated toward the conductive support 1 side. In this case, if a conventional surface layer consisting of a single resistive insulating layer is used, as mentioned above, if the film is thick, carriers flowing from the photoconductive layer to the surface cannot pass through the surface layer, resulting in a decrease in sensitivity. In addition, carriers are trapped in defects such as dangling bonds, leading to an increase in residual potential. On the other hand, if the film thickness is thin, the surface potential of the photoreceptor decreases, creating a burden on process design for copying machines, printing, etc. On the other hand, when the surface layer has a superlattice structure as in the photoreceptor of the present invention, the lifetime of carriers in the potential well layer becomes shorter than that of a single layer without a superlattice structure due to quantum effects. It is 5 to 10 times longer. In addition, in a superlattice structure, a periodic barrier layer is formed due to discontinuity in the band gap, but carriers easily pass through the bias layer due to the tunnel effect, so the effective mobility of carriers is determined by the mobility in the bulk. The carrier has excellent runnability. As mentioned above, according to the superlattice structure made of laminated thin layers,
It is possible to obtain high photoconductivity properties, and it is possible to obtain clearer images than conventional photoreceptors.

Referring to FIG. 3, 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, S i H4, B2 Hs, H
2. Contains raw material gas such as CH4. The gas in these gas cylinders is controlled by a valve 26 for flow rate adjustment and piping 2.
7 to a mixer 28.

A pressure gauge 25 is installed in each cylinder, and the pressure gauge 25 is installed in each cylinder.
By adjusting the valve 26 while monitoring 5, the flow rate and mixing ratio of each raw material gas supplied to the mixer 28 can be adjusted. The gases mixed in the mixer 28 are supplied to a reaction vessel 29. A rotating shaft 30 is attached to the bottom 31 of the reaction vessel 29 so as to be rotatable around the vertical direction. A disk-shaped support 32 is fixed to the upper end of the rotating shaft 30 with its surface perpendicular to the rotating shaft 30. 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 30.

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 cylinder 136 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 to a suitable evacuation means such as a vacuum pump via a gate valve 388.

When manufacturing a photoreceptor using the above manufacturing apparatus, the drum base 34 is placed in the reaction vessel 29, and then the gate pulp 39 is opened to exhaust the inside of the reaction vessel 29 to a pressure of about 0.1 Torr or less. Next, cylinder 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 to be OT orr. Next, the motor 38 is operated to rotate the drum base 34, the heater 35 heats the drum base 34 to a constant temperature, and the high frequency cylinder 1i36 supplies high frequency current between the electrode 33 and the drum base 34. A glow discharge is formed between the two. As a result, μc-8i:
H and a-8i:H are deposited. Note that N2 is present in the raw material gas.
0, NH3, NO2, N2, CH4, C2H4,02
By using Fr, nitrogen, carbon, and oxygen can be converted to μC-81:H? a-8i: Can be contained in H.

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 If necessary, to prevent interference, an aluminum drum base with a diameter of 80 mm and a width of 350 m, which has been subjected to acid treatment, alkali treatment, and sandblasting, is installed in the reaction vessel. It was evacuated to a vacuum level of 10 liters. While heating the drum base to 250°C and rotating it at 10 rpm, SiH+ gas was introduced into the reactor at a flow rate of 500 SCCM and BZ H6 gas at a flow rate of 10"3 to SiH+ gas, and the pressure inside the reactor was set to 1 Torr. A high frequency power of 13.56 MH2 was applied to generate plasma, and a barrier layer made of P-type a-8i:H was formed on the drum base.

Next, SiH4 gas was introduced into the reaction chamber at a flow rate of 5008CCM, 1H2 gas was introduced at 200SCCM, and B2H6 gas was introduced into the reaction chamber at a flow rate ratio of 10''B to SiH4 gas, and 500W of high-frequency power was applied to generate 30μ-1 type a-8l:H. A photoconductive layer was formed.

Next, 3008CCM of 5I84 gas and 30CCM of H2 gas.
08 CCM was introduced, the pressure in the reaction chamber was set to 1 Torr, and 450 W of high frequency power was applied to 50 people a-3+:
A H thin film was formed. Next, SiH+ gas was heated to 1508C.
CM, N2 gas 450SCCM, H2 gas 1508
CCM was introduced to form 50 a-8i N:H thin films (nitrogen concentration 10 at%). By repeating this operation, 20 layers of a-8i:)l thin film and 20 layers of a-8iN were formed.
A surface layer of 2,000 layers consisting of a :H thin film was formed.

When the surface of the photoreceptor thus formed is positively charged at about 500 μm 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 life of the carriers was extended, 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. Proven to be excellent.

Test Example 2 As one of the thin films constituting the surface layer, a nitrogen concentration of 15 at% was used instead of the a-8iN:H thin layer with a nitrogen concentration of 10 at%.
a-8i N: except that a thin layer of H was formed.
An electrophotographic photoreceptor was manufactured in the same manner as in Test Example 1. Note that the a-8iC:81 layer with a nitrogen concentration of 15 at% is Si
11008CC of H+ gas, 6008CCM of N2 gas
, was obtained by introducing 11008 CC of H2 gas.

The photoreceptor manufactured in this manner has high sensitivity even to long wavelength light of 780 to 790 nm, which is the oscillation wavelength of a semiconductor laser. When this photoreceptor was installed in a semiconductor laser printer and an image was formed by the Carlson process, a clear, high-resolution image could be obtained even when the exposure amount on the photoreceptor surface was 25 ergai.

When this photoreceptor was repeatedly charged, the transferred image had high reproducibility and stability, and had excellent durability such as corona resistance, moisture resistance, and abrasion resistance.

Note that the types of thin layers are not limited to two types as in the above test example, but three or more types of thin layers may be repeatedly laminated. In short, it is sufficient that the boundary between the a-3ii1 layer and the a-s i N1 layer is formed.

[Effects of the Invention] According to the present invention, since a superlattice structure is used in the surface layer, carrier mobility in the surface layer is good, the carrier has a long life, and an electrophotographic photosensitive material with excellent charging characteristics can be obtained. You can get a body.

[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. 1 is a diagram showing an apparatus for manufacturing an electrophotographic photoreceptor according to an embodiment of the invention. DESCRIPTION OF SYMBOLS 1... Conductive support body, 2... Barrier layer, 3... Photoconductive layer, 4... Surface layer.

Claims (8)

[Claims] (1) In an electrophotographic photoreceptor having a conductive support, a photoconductive layer, and a surface layer, the surface layer is composed of alternating layers of amorphous silicon thin films and nitrogen-containing amorphous silicon thin films. , and the thickness of each thin film is 30 to 500
An electrophotographic photoreceptor characterized by having . (2) The electrophotographic photoreceptor according to claim 1, wherein the surface layer contains at least one element selected from elements belonging to Group III or V of the periodic table. (3) The electrophotographic photoreceptor according to claim 1, wherein the photoconductive layer contains at least one element selected from elements belonging to Group III or V of the periodic table. . (4) The electrophotographic photoreceptor according to claim 1, wherein the photoconductive layer contains at least one of carbon, oxygen, and nitrogen. (5) The electrophotographic photoreceptor according to claim 1, wherein at least a portion of the photoconductive layer is made of an amorphous semiconductor or at least a portion of a microcrystalline semiconductor. (6) A barrier layer made of an amorphous semiconductor or at least a partially microcrystalline semiconductor is provided between the conductive support and the photoconductive layer. electrophotographic photoreceptor. (7) The electrophotographic photoreceptor according to claim 1, wherein the barrier layer contains at least one element selected from elements belonging to Group III or V of the periodic table. (8) The electrophotographic photoreceptor according to claim 1, wherein the barrier layer contains at least one of carbon, oxygen, and nitrogen.