JPS63241554A - Electrophotographic sensitive body - Google Patents

Abstract

PURPOSE:To obtain an electrophotographic sensitive body good in carrier transferability and resistivity, and superior in electric chargeability characteristics by using superlattice structure formed by laminating thin films different in optical band gap from each other for a photoconductive layer. CONSTITUTION:The electrophotographic sensitive body is composed of a conductive supporting body 1 and the photoconductive layer 3 composed of an electric charge generating layer 6 formed by alternately laminating 2 kinds of microcrystalline silicon thin films different in crystallization degree from each other, and a charge retaining layer 5 formed by alternately laminating microcrystalline silicon thin films and amorphous silicon thin films containing at least one of C, O, and N, and each of said microcrystalline thin films being different in crystallization degree from each other in the film thickness direction, thus permitting the photoconductive layer to be enhanced in carrier transferability and extended in carrier life, and sensitivity of the photosensitive body to be enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object 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) Amorphous silicon (hereinafter referred to as a) containing hydrogen (H)
-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, ZnO, Se, or 5e-Te, or poly-N-vinylcarbazole (PVC) have been used as materials constituting the photoconductive layer of electrophotographic photoreceptors.
Organic materials such as z ) or 1 to linitrofluorenone < TNF) have been used.

However, compared to these inorganic or organic materials, a-8i:H is a non-polluting substance and does not require recovery treatment, has a high spectral grn in the visible light region, and has a high surface altitude. It has advantages such as excellent wear resistance and impact resistance. Therefore, a-8i:
H is attracting attention as a photoreceptor material for electrophotographic processes.

This a-8i: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 a single photoreceptor, 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 met by creating a multilayer structure.

(Problems to be Solved by the Invention) By the way, a-8i:H is usually formed by a glow discharge decomposition method using a silane gas, but at this time,
a-3i: Hydrogen is incorporated into Hg3, and the electrical and optical properties vary greatly due to the difference in the amount of hydrogen. That is, as the amount of hydrogen entering the a-8t:H film increases, the optical bandgap increases, and the a-8i:H film increases.
As the resistance increases, the photosensitivity to long wavelength light decreases, making it difficult to use, for example, in a laser beam printer equipped with a semiconductor laser. Also, a-3i:HIl! When the hydrogen content in the film increases, depending on the film forming conditions, those having bonding structures such as (3iH2)n and SiH2 may occupy most of the area in the film.

In this case, voids increase and silicon dangling bonds increase, resulting in deterioration of photoconductive properties and rendering the material unusable as an electrophotographic photoreceptor. Conversely, lowering the amount of hydrogen incorporated into a-3i:H reduces the optical band gap and its resistance, but increases the photosensitivity to long wavelength light. However, when the hydrogen content is low, there is less hydrogen to combine with and reduce the dangling bonds of silicon. For this reason, the mobility of the generated carriers is lowered, the lifetime is shortened, and the photoconductive properties are deteriorated, making it difficult to use as an electrophotographic photoreceptor.

In this way, the photoconductive layer of the electrophotographic photoreceptor is formed into a single a-3
If it is composed only of i:HWJ, there is a problem that the characteristics change greatly depending on the manufacturing conditions of the a-8i:8 layer, and desired characteristics cannot be obtained.

The present invention has been made in view of such circumstances, and
To provide an electrophotographic photoreceptor that has excellent charging ability, low residual potential, high sensitivity to a wide wavelength range up to the near infrared region, good adhesion to a substrate, and excellent environmental resistance. The purpose is to

[Structure of the Invention] (Means for Solving the Problems) As a result of various studies, the present inventor has constructed a photoconductive layer of an electrophotographic photoreceptor by a charge retention layer and a charge generation layer, and has developed a method for each of them. The inventors have discovered that the above object can be achieved by stacking a plurality of predetermined semiconductor films, that is, by forming a superlattice structure region, and have completed the present invention.

That is, the electrophotographic photoreceptor of the present invention is an electrophotographic photoreceptor comprising an electrically conductive support and a photoconductive layer, the photoconductive layer comprising a charge generation layer and a charge retention layer, The generation layer consists of two types of microcrystalline silicon rg with different crystallinity.
The charge retention layer is composed of an amorphous silicon thin film containing at least one element selected from carbon, oxygen, and nitrogen and microcrystalline silicon'';
4 M! and the microcrystalline silicon 1ilfi! It is characterized in that the degree of crystallinity changes for each M# in the layer thickness direction.

The microcrystalline silicon (μC-8i) used in the present invention is thought to be formed from a mixed phase of microcrystalline silicon and amorphous silicon with a grain size of about several tens of angstroms, and has the following properties. It has physical characteristics. First, X-ray diffraction measurements show a crystal diffraction pattern with 2θ in the vicinity of 28 to 28.5°, which is clearly distinguishable from amorphous a-3i in which only a halo appears. Second, μC
The dark resistance of −3i can be adjusted to 10 10 Ω·1 or more, and is clearly distinguished from polycrystalline silicon, which has a dark resistance of 10 5 Ω·α.

The optical bandgap (E9°) of the μc-8i used in the present invention is preferably 1.550 V, for example. However, it can be set arbitrarily within a certain range. In order to obtain a desired Eg', it is preferable to add a predetermined amount of hydrogen to each of them and use them as μc-8i:H. This results in silicon dangling bonds? li is compensated, dark resistance and bright resistance are balanced, and photoconductive properties are improved.

The crystallinity of the microcrystalline silicon thin film constituting the N charge generation layer and the M charge retention layer is preferably 60 to 90%, more preferably 60 to 80%.

The concentration of carbon, oxygen, and nitrogen contained in the amorphous silicon thin film constituting the charge retention layer is preferably 0.1 to 40 atomic %, more preferably 0.5 to atomic %.

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

In this way, carrier mobility in the photoconductive layer increases,
Furthermore, the sensitivity of the electrophotographic photoreceptor is significantly improved by improving the life of the carrier.

(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 consisting of a charge retention layer 5 and a charge generation layer 6 is formed thereon.

Further, a surface layer 4 is formed on the charge generation layer 6.

Note that both the charge retention layer 5 and the charge generation layer 6 have a superlattice IM structure.

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

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

The barrier 12 may be formed using μc-3i or a-8i:H, or a-BN:H (amorphous boron to which nitrogen and hydrogen are added). Furthermore, an insulating film may be used. For example, μc-3i:H and a-3
By containing one or more elements selected from carbon C1 nitrogen N and oxygen O in i:1-1, a resistive insulating barrier layer can be formed. The thickness of the barrier layer 2 is preferably 100 to 10 μm.

The barrier layer 2 is formed to suppress the flow of charges between the conductive support 1 and the charge generation layer 5, thereby increasing the charge retention function of the photoreceptor surface and increasing the lightning charging ability of the photoreceptor. It is something that Therefore, when forming a Carlson type photoreceptor using a semiconductor layer as a barrier layer, the barrier Fm2
is P 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 charge generation layer.

Conversely, when the surface is negatively charged, the barrier layer 2 is made of N type,
This prevents holes that neutralize surface charges from being injected into the charge generation layer. Since carriers injected from the barrier layer 2 become noise with respect to carriers generated in the charge generation layer 6 upon incidence of light, preventing carrier injection as described above improves sensitivity. In addition, μc-8i:H
or a-8i: In order to make H into a P-type part, an element belonging to Group Ⅰ of the periodic table, such as boron B, aluminum A℃
, gallium Ga, indium In1, thallium TQ, etc. are preferably doped. Also, μC-3i
: )-19a-8i: In order to make H type N-type, an element belonging to Group V of the periodic table, such as nitrogen, phosphorus P1
It is preferable to dope with arsenic AS, antimony Sb, bismuth 13i, or the like.

The charge generation layer 6 generates carriers upon incidence of light, and one polarity of these carriers neutralizes the charges on the surface of the photoreceptor, and the other carriers travel within the charge retention H5 and become conductive. The support 1 is reached.

The charge retention layer M5 and the charge generation layer 6 are constructed by laminating two types of thin films. These ams have different optical bandgaps, and their thicknesses range from 30 to 500 nm. In this way, by stacking thin films with different optical bandgaps, it is possible to create a film with a large optical bandgap compared to a film with a small optical bandgap, regardless of the size of the optical bandgap itself. A superlattice structure having a periodic potential barrier acting as a barrier is formed. In this superlattice structure, the barrier (W) is so thin that the carriers pass through the barrier and travel in the superlattice structure due to the carrier tunneling effect in the thin film. Furthermore, in such a superlattice structure, a large number of carriers are generated by the incidence of light.

Therefore, the light is 11 degrees. Note that by changing the bandgap and layer thickness of the tI intestine of the superlattice structure, the apparent bandgap of the layer having the heterojunction superlattice H4 structure can be freely adjusted.

a-8i constituting the charge retention layer 5 and charge generation layer 6
The hydrogen content in :H and μc-8i:H is
0.01 to 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 properties of the light guide layer.

a-8i: To form the H layer by the glow discharge decomposition method, silane gases such as SiH4 and 5i2f-1s are introduced into the reaction chamber as raw materials, and H is formed in the thin layer by glow discharge using high frequency. Can be added. If necessary, hydrogen or helium gas can be used as a carrier gas for silanes.

On the other hand, silicon halides such as SiF4 gas and 3i (1!4 gas) can be used as the raw material gas.Also, even if the reaction is performed with a mixed gas of silane gas and silicon halide gas, H a-8i containing :)
Note that these thin films can be formed not only by the glow discharge decomposition method but also by physical methods such as sputtering.

(, tc 5iillfW also, a-3i: Ham
Similarly, a film can be formed using silane gas as a raw material by a high frequency glow discharge decomposition method. In this case, if the temperature of the support is set higher than in the case of forming a-8i:H and the high frequency power is also set higher than in the case of a-8i nide, it becomes easier to form μc-8i:H. .Also,
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, by using gas obtained by diluting high-order silane gas such as S i H4 and 5i2H's as raw material gas, μC
-8i:H can be formed with higher efficiency.

To make μC-5i:H and a-3i:H P-type, elements belonging to Group Ⅰ of the periodic table, such as boron B1 aluminum 82, gallium Qa.

It is preferable to dope with indium In, thallium M2, etc., and μc-8i:H and a-8i:H are doped with n
In order to form a mold, it is preferable to dope with elements belonging to Group V of the periodic table, such as nitrogen N, phosphorus P, arsenic AS, antimony 3b, and bismuth BiW. Doping with this p-type impurity or n-type impurity prevents charges from moving from the support side to the optical SN layer.

On the other hand 1. By incorporating at least one element selected from carbon C nitrogen N and oxygen O into czc-8i:l-1 and a-8i:H, it is possible to increase the resistance and surface charge retention ability. can. The content of these elements is 0.1 to 40 atomic %, preferably 0.5 to 30 atomic %.

A surface layer 4 is provided on the charge generation layer 6.

Since the a-3i:@ etc. of the charge generation layer 6 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 or the charge generation layer decreases, resulting in increased light loss. For this reason, it is preferable to provide the surface H4 to prevent reflection. Further, by providing the surface layer 4, the charge generation layer 6 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. The material forming the surface layer is a-
8i N :H, a-8i O:)-1, and a-8i
There are inorganic compounds such as C:)4 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 superlattice structure of the charge generation layer 6.

Electrons in the conduction band are transferred to the surface layer 4 due to the electric field in the photoreceptor.
The holes are accelerated towards the conductive support IBI. In this case, the number of carriers generated at the boundary between thin films with different optical bandgaps is significantly greater than the number of carriers generated in the bulk. Therefore, this superlattice structure has high photosensitivity. In addition, in the potential well layer, due to the mother-child effect, the lifetime of carriers is 55% lower than in the case of a single layer without a superlattice structure.
It is 10 to 10 times longer. Furthermore, in a superlattice structure, a periodic barrier layer is formed due to bandgap discontinuity, but carriers easily pass through the bias layer due to the channel effect, so the effective carrier mobility in the bulk is The carrier has excellent mobility.

Similarly, in the case of the charge retention layer 5, the lifetime of carriers in the potential well layer is 5 to 10 times longer than in the case of a single layer without a superlattice structure due to the m-son effect.

In addition, in the superlattice structure, a periodic barrier layer is formed due to bandgap discontinuity, but carriers easily pass through the bias layer due to the tunnel effect, so the effective mobility of carriers is reduced by the shift in the bulk. The carrier has excellent runnability. As described above, according to the superlattice structure in which la layers are formed of thin layers having different optical band gaps, it is possible to obtain high photoconductivity and to obtain images that are clearer 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, Si H4, 82H6, H2,
A raw material gas such as CH4 is contained. The gas in these gas cylinders is supplied to a mixer 28 via an outflow regulating valve 26 and piping 27. A pressure gauge 25 is installed in each cylinder, and by adjusting the pulp 26 while monitoring the pressure gauge 25, the mixer 28
It is possible to adjust the outflow and mixing ratio of each raw material gas to be supplied.

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 two reaction vessels so as to be rotatable in the vertical direction. At the upper end of the rotating shaft 30, a disk-shaped support base 32 has its surface aligned with the rotating shaft 3.
It is fixed perpendicular to 0. 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 power source 36 is connected between the electrode 33 and the drum base 34, so that a high frequency current is supplied between the N pole 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 manufacturing apparatus, the drum base 34 is placed in the reaction vessel 29, and then the gate valve 39 is opened to evacuate the inside of the reaction vessel 29 to a pressure of about 0.1 Torr or less. Next, cylinders 21, 22, 23
．． A required reaction gas is heated at a predetermined mixing ratio from 24 and introduced into a reaction vessel 29 . In this case, the gas flow introduced into the reaction vessel 29 is set so that the pressure within the reaction vessel 29 is 0.1 to 1.0 Torr. 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 power supply 36 supplies high frequency current between the ff1ff133 and the drum base 34, thereby saving both. A glow discharge is formed in between. As a result, a-
8i: H is deposited. Note that N20. N.H.
3, NO2, N2.

By using CH4, C2H4,02 gas, etc.
Carbon, oxygen and nitrogen can be included in a-3i:H.

As described above, the electrophotographic photoreceptor according to the present invention can be manufactured using a closed system manufacturing apparatus, and therefore is safe for the human body.

Next, an electrophotographic photoreceptor according to the present invention was formed into a film.

The results of testing the photographic characteristics of one child will be explained below.

Test Example 1 A diameter of 80 m was subjected to acid treatment, alkali treatment, and sandblasting treatment to prevent interference as necessary.
A 350 m+ wide aluminum drum substrate was mounted within the reaction vessel and the reaction vessel was evacuated to a vacuum of approximately 10-5 Torr. Heating the drum base to 250℃, 10rll1m
5008 CCM of SiH+ gas, 82
IJI ratio of H5 gas to 3iH+ gas is 10-3
It was introduced into the reaction vessel at a flow rate of 100%, and the pressure inside the reaction vessel was adjusted to ITorr. and 13.56 MHZ
Plasma was generated by applying high-frequency power of 200 mL to form a p-type a-8i C:H barrier layer on the drum substrate.

Next, 3iH4 at 500SCCM, CH4 gas at 30S
It was introduced at a flow rate of CCM, and a high frequency power of 400 W was applied to form an a-8t C:H thin film of 120 s. Next, 35 SCCM of SiH+ gas and 500 SCCM of H2 gas
3CCM was introduced and a high frequency power of 1.2KW was applied to form a 240 μc-3i:)l thin film. Such operations were repeated to form a charge retention layer having a superlattice structure of 15 μm. In addition, when forming the μc-3i:@thin film, 3i H was used for each WeMA formation.
4 Increase the gas flow rate and finally 2O3 (, CM,
The crystallinity was changed from 70% to 85%.

Next, SiH+ gas was introduced at a flow rate of 508 CCM and 1-12 gas was introduced at a flow rate of 500 SCCM, and a high frequency power of 1.2 KW was applied to form a 100 μC-3i:H thin film. Next, 5it-14 gas is set to 308CCM,
100 μc-8i:H thin films with different crystallinity were formed. These operations were repeated to form a charge generation layer of 5 μm.

Finally, a surface layer consisting of a 0.1 μm a S + C:HR film 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 charge generation 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.

The photoreceptor manufactured in this manner has high sensitivity even to long wavelength light of 780 to 790n+11, 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 produced at t9 even when the exposure amount on the photoreceptor surface was 25 ergci.

Test Example 2 An electrophotographic photoreceptor was manufactured in the same manner as Test Example 1, except that the crystallinity of the μc-3i:H thin film constituting the charge retention layer was changed as shown in FIG.

When images were formed using these photoreceptors in the same manner as in Test Example 1, high-quality images with bright red colors were obtained.

Note that the types of thin films constituting the charge retention layer and the charge generation layer are not limited to two types as in the above test example, but three or more types of thin films may be laminated, and in short, they have different optical band gaps. It is sufficient to form the boundary of sun.

[Effects of the Invention] According to this invention, since a superlattice structure formed by laminating thin films with mutually different optical band gaps is used in the light guiding N layer, carrier mobility is high and high efficiency is achieved. An electrophotographic photoreceptor with excellent resistance and charging characteristics can be obtained. In particular, the present invention has the advantage that by appropriately combining materials forming the thin film, it is possible to obtain a photoreceptor having optimal photoconductive properties for light in any wavelength band.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing an electrophotographic photoreceptor according to an embodiment of the present invention, FIG. 2 is a diagram showing an apparatus for manufacturing an electrophotographic photoreceptor according to an embodiment of the present invention, and FIG. 3 is a diagram showing a microcrystalline photoreceptor. FIG. 3 is a diagram showing changes in the crystallinity of a silicon thin film. 1: conductive support, 2: barrier layer, 3: photoconductive layer. 4: Surface layer, 5: Charge retention layer, 6: Charge generation layer. Applicant's representative Patent attorney Takehiko Suzue Layer thickness (a), J#4 (C)

Claims (8)

[Claims] (1) In an electrophotographic photoreceptor having a conductive support and a photoconductive layer, the photoconductive layer is composed of a charge generation layer and a charge retention layer, and the charge generation layer has two types of crystallinity different from each other. The charge retention layer is composed of alternating layers of microcrystalline silicon thin films, and the charge retention layer is made of alternating layers of amorphous silicon thin films and microcrystalline silicon thin films containing at least one element selected from carbon, oxygen, and nitrogen. 1. An electrophotographic photoreceptor comprising a microcrystalline silicon thin film, wherein the degree of crystallinity of the microcrystalline silicon thin film varies from film to film in the layer thickness direction. (2) The electrophotographic photoreceptor according to claim 1, wherein the thin film has a thickness of 30 to 500 Å. (3) The electrophotographic photoreceptor according to claim 1 or 2, wherein the photoconductive layer contains at least one element selected from elements belonging to Group III and Group V of the periodic table. . (4) Any one of claims 1 to 3, wherein the microcrystalline silicon thin film contains at least one element selected from carbon, oxygen, and nitrogen.
The electrophotographic photoreceptor described in . (5) A patent claim characterized in that a barrier layer made of an amorphous material or a semiconductor material in which at least a portion thereof is microcrystallized is formed between the conductive support and the photoconductive layer. The electrophotographic photoreceptor according to item 1. (6) The electrophotographic photoreceptor according to claim 5, wherein the barrier layer contains at least one element selected from elements belonging to Group III and Group V of the periodic table. (7) The electrophotographic photoreceptor according to claim 5 or 6, wherein the barrier layer contains at least one element selected from carbon, oxygen, and nitrogen. (8) The electrophotographic photoreceptor according to claim 1, wherein a surface layer is formed on the photoconductive layer.