JPS63243955A - Electrophotographic sensitive body - Google Patents

Abstract

PURPOSE:To increase the degree of transfer of carriers in an electric charge retaining layer by alternately laminating thin films of amorphous Si contg. a prescribed element and thin films of microcrystalline Si so as to form the electric charge retaining layer and by continuously varying the concn. of the element. CONSTITUTION:A photoconductive layer 3 consisting of an electric charge retaining layer 5 and an electric charge generating layer 6 is formed on an electrically conductive support 1. The layer 5 is formed by alternately laminating thin films of amorphous Si contg. one or more among C, O and N, e.g., a-SiC:H and thin films of microcrystalline Si, e.g., muc-Si:H and the concns. of the elements are continuously varied in the vicinity of the interface between the thin films. The layer 6 is formed by alternately laminating thin films of amorphous Si such as a-Si:H and thin films of microcrystalline Si such as muc-Si:H. The pref. thickness of each of the thin films is 30-500Angstrom . A barrier layer 2 of a-Si:H or muc-Si:H and a surface layer 4 of a-Si:H or the like are preferably preferably formed between the support 1 and the layer 5 and on the layer 6, respectively.

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) Hydrogen (H)'! Amorphous silicon (hereinafter abbreviated as a-8t: H) contained in
In addition to image sensors and other devices, it is also applied to photoreceptors in electrophotographic processes.

Conventionally, CDS #ZnOp asp or 5e-Te has been used as a material constituting the photoconductive layer of an electrophotographic photoreceptor.
or poly-N-vinylcarbazole (PV
Organic materials such as C2) or trinitrofluorenone (TNF) were used. However, a-81:
Compared to these inorganic or organic materials, H is a non-polluting substance, so it does not require recovery treatment, has high spectral sensitivity in the visible light region, and has a high surface hardness that makes it resistant to wear and impact. It has advantages such as excellent properties. For this reason, a-81:H is attracting attention as a photoreceptor for electrophotographic processes.

This a-8t: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 gold film is formed as a surface charge retention layer on the photoconductive layer. These requirements are satisfied by creating a multi-layered structure.

(Problems to be Solved by the Invention) By the way, a-8t:H is usually formed in large quantities by a glow discharge decomposition method using a silane-based gas, but at this time, a-8i:H in the a-8i:H film is Hydrogen is taken in, and the difference in the amount of hydrogen causes the stain's atmospheric and optical properties to vary greatly. That is,
As the amount of hydrogen that enters the a-8t:H film increases, the optical bandgap becomes narrower and the resistance of a-8t:H increases, but as a result, the photosensitivity to long wavelength light decreases. Therefore, for example, it is difficult to mount a semiconductor radar and then use it in a beam printer.

Also, when the hydrogen content in a-8i:H& increases,
Depending on the film forming conditions, those having bonding structures such as (SiH2)n and 5IH2 may occupy most of the area in the film. Then, voids increase, silicon dangling increases, and the photoconductive properties deteriorate, making it unusable as an electrophotographic photoreceptor.

Conversely, decreasing the amount of hydrogen incorporated into a-8l2H reduces the optical bandgap and reduces its resistance, but increases its photosensitivity to long wavelength light. However, the lower hydrogen content leaves less hydrogen to combine with and reduce the silicon dangling dends.

For this reason, the mobility of the generated carriers is reduced, the life span 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 can be formed into a single a-8
If it is composed of only the l:H layer, there is a problem that the characteristics change greatly depending on the manufacturing conditions of a-8t:HJu, and desired characteristics cannot be obtained.

The present invention has been made in view of such circumstances, and
To provide an electrophotographic photoreceptor with excellent charging ability, low residual potential, high photosensitivity over 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] (Ninth Means for Solving Problems) As a result of extensive research, the present inventors have discovered that the photoconductive layer of a single-child photographic photoreceptor is composed of a charge retention layer and a charge generation layer. ,
By constructing the charge retention layer as a product of a plurality of semiconductor films containing carbon, etc. and having different concentrations; that is, a superlattice structure, and continuously changing the concentration of carbon, etc. near the interface of these semiconductor films, the above-mentioned The inventors discovered that the object could be achieved and completed the present invention.

That is, the electrophotographic photoreceptor of the present invention is an electrophotographic photoreceptor comprising a conductive support and a photoconductive layer, wherein the photoconductive layer has a charge generation layer and a charge retention layer, and the photoconductor has a charge generation layer and a charge retention layer. The generation layer is composed of alternating layers of amorphous silicon thin films and microcrystalline silicon thin films, and the charge retention layer is composed of carbon, oxygen,
and amorphous silicon thin film and a microcrystalline silicon thin film containing at least one element selected from nitrogen, and the concentration of the element is continuous near the interface of the amorphous silicon thin film. It is characterized by a change in.

The concentration of carbon, oxygen, and nitrogen contained in the amorphous silicon thin film is preferably 0.1 to 40 atoms, more preferably 0.5 to 30 atoms.

The microcrystalline silicon (μc-8t) used in the present invention is thought to be formed by 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-8i in which only a halo appears. Second, μc-8i
The dark resistance can be adjusted to 1010Ω or more,
It can also be clearly distinguished from polycrystalline silicon, which has a dark resistance of 105Ω.

The optical bandgap (Eg') of the μc-8t used in the present invention is desirably 1.55 eV, for example. However, it can be set arbitrarily within a certain range. In order to obtain the desired EgO, it is preferable to add a predetermined amount of hydrogen to each and use it as μc-8i:H.

This compensates for silicon dangling, balances dark resistance and bright resistance, and improves photoconductive properties.

(Function) In the electrophotographic photoreceptor of the present invention, since the charge retention 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, carrier mobility in the charge retention layer increases υ
Furthermore, the sensitivity of the electrophotographic photoreceptor is significantly improved due to the longer life of the carrier.

In addition, in the present invention, carbon, oxygen,
Since it contains at least one type of nitrogen, it is possible not only to adjust the band gap as described above, but also to increase the resistance of the photoconductive layer and enhance the charge retention ability of the surface.

(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 same figure, conductive support 1
A barrier layer 2 is formed on the barrier layer 2, and a photoconductive layer hj3 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 the charge retention layer 5 and the charge generation layer 6 have a superlattice structure.

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 may be formed using .mu.c-8t or a-8l:H, or a-BN:H (amorphous boron to which nitrogen and hydrogen are added). Furthermore, an insulating film may be used. For example, by incorporating one or more elements selected from carbon C1 nitrogen N and oxygen O into μc-8i:H and a-8l:H, a high-resistance insulating barrier layer can be formed.

The thickness of the barrier layer 2 is preferably 100X to 10 μm.

The above barrier No. 2 consists of a conductive support 1 and a charge generating JWI 5.
It is formed to enhance the charge retention function of the surface of the photoreceptor by suppressing the flow of charge between the photoreceptor and the charging ability of the photoreceptor. Therefore, when a Carlson type photoreceptor is constructed using a semiconductor layer as a barrier layer, the barrier layer 2 is made to be P type or N type in order not to reduce the ability to retain charges charged on the surface. That is, when the surface of the photoreceptor is positively charged, the barrier layer 2 is changed to P-type to prevent electrons that neutralize the surface charge from being injected into the charge generation layer.

On the other hand, when the surface is negatively charged, barrier layer 2 is made of 8th layer,
This prevents holes that neutralize surface charges from being injected into the charge generation layer. Since carriers injected from the barrier layer 2 act as a nozzle for carriers generated in the charge generation layer 6 upon incidence of light, preventing carrier injection as described above improves sensitivity. In addition, μc-8i:
In order to make H or a-8t:H P-type, elements belonging to Group Ⅰ of the periodic table, such as boron B, aluminum At
, gallium Ga, indium In, thallium Tt, etc. are preferably doped. Also, μc-8i
: In order to make H or a-81:H N-type, it is preferable to dope it with an element belonging to Group V of the periodic table, such as nitrogen, phosphorus P, arsenic As, antimony sb, and bismuth Bi.

The charge generation layer 6 generates carriers when light is incident thereon, and carriers of one polarity neutralize the charges on the surface of the photoreceptor, and the other carriers travel within the charge retention layer 5 and become conductive. The sexual support 1 is reached.

The charge retention layer 5 and the charge generation layer 6 are constructed by alternately laminating two types of thin layers. These thin layers have different optical bandgaps and each have a thickness in the range of 30-500X.

The superlattice structure constituting the charge retention layer 5 ideally has a second
As shown in the figure, for example, it is desirable that thin films with different optical band gaps form discontinuous periodic potentials.

However, in order to form such a superlattice structure, it is necessary to evacuate the atmosphere in the reaction chamber after each thin film is formed to prevent impurities from entering the thin film during the next film formation. Therefore, the film formation time is extremely long, and there is a drawback that mass productivity is poor. In addition, when forming a film by plasma CVD, ion bombardment occurs constantly on the film forming surface, which causes impurities to diffuse into the thin film, resulting in the discontinuous periodic potential shown in Figure 2. cannot be formed.

In contrast, in the superlattice structure according to the present invention, as shown in FIG. 3, the element concentration, that is, the optical band gap, near the interface of each thin film is continuously changed. Such a superlattice structure is created by slightly lowering the radio frequency power to weaken ion bombardment, introducing a large amount of H2, and changing the flow rate of gas containing impurities while keeping the radio frequency power constant. Alternatively, it can be obtained by changing the high frequency power while keeping the gas flow rate constant. By forming a film using such a method, ion bombardment is weakened, and a periodic potential as shown in FIG. 3, in which the characteristics near the interface change continuously, can be obtained.

In this way, near the interface of the thin film, the degree of mystery of carbon, etc.
Therefore, by adopting a superlattice structure in which the optical bandgap is continuously changed, films can be deposited one after another without waiting for the deposition conditions to become stable. The time can be significantly shortened, resulting in excellent mass productivity. Furthermore, since the film formation is continuous, the adhesion between each thin film is improved.

As explained above, by stacking thin layers with mutually different optical bandgaps, the optical bandgap can be set as a standard for a layer with a small optical bandgap, regardless of the size of the optical bandgap itself. A superlattice structure is formed with a periodic potential barrier in which the large layer acts as a barrier. In this superlattice structure, since the barrier thin film is extremely thin, carriers pass through the barrier and travel through the superlattice structure due to the carrier tunneling effect in the thin layer. Furthermore, in such a superlattice structure, a large number of carriers are generated by incident light. Therefore, it has high photosensitivity. Note that by changing the bandgap and layer thickness of the thin layer of the superlattice structure, the apparent bandgap of the layer having the heterojunction superlattice structure can be freely adjusted.

a-8i constituting the charge retention layer 5 and charge generation layer 6:
H and μc-8t: The content of hydrogen in H is
It is preferably 0.01 to 30 atoms, more preferably 1 to 25 atoms. 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 a-8t S H layer by glow discharge decomposition method, silane gases such as SiH4 and S1□H6 are introduced into the reaction chamber as raw materials, and H is generated 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 for the silanes. On the other hand, SiF4
Silicon halides such as gas and 5ICt4 gas can be used as source gases. Furthermore, a-8t:H containing H can be similarly formed by reacting with a mixed gas of silane gas and silicon halide gas. Note that these thin films can be formed not by the glow discharge decomposition method but also by a physical method such as sputtering.

Similarly to a-8t:H, the μc-8i 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-8l:
The high frequency power is set higher than when forming H, and the high frequency power is also a-
In the case of 81:H, if the value is set high, μc-81:
It becomes easier to form H. 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, by using gas obtained by diluting high-order silane gas such as SiH4 and 512H6 as raw material gas,
μc-8i: H can be formed with higher efficiency.

μc-8i: H and a-8t: In order to make H into pm, elements belonging to Group Ⅰ of the periodic table, such as boron B1 aluminum AA, gallium G&, indium I
n.

It is preferable to dope with thallium Tt, etc.
In order to make fia-8l:H and a-81:H n-type, elements belonging to group Ⅰ of the periodic table, such as nitride IN,
Phosphorus P1 HgAs, Antimony Sb, and Bismuth B1
It is preferable to dope. 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, μc-8
By incorporating at least one element selected from carbon C1 nitrogen N and zero oxygen into l:H and a-8i:H, high resistance can be achieved and the surface charge retention ability can be increased.

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

Since a-8i:H and the like of the charge generation layer 6 has 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 charge generation layer decreases, and light loss increases. For this reason, it is preferable to provide the surface layer 4 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.

Materials forming the surface layer include a-stN: H, a
There are inorganic compounds such as -8iO:Hl and a-8IC:H, and organic materials such as polyvinyl chloride and polyamide.

When the surface of the electrophotographic photoreceptor constructed in this way is charged with a positive voltage of about 5 oov by corona discharge, what happens? A tensile barrier is formed. When light (h) is incident on this photoreceptor, carriers of electrons and holes are generated in the charge generation layer 6.The electrons in the conduction band are accelerated toward the surface layer 4 by the electric field in the photoreceptor. , holes are accelerated toward the conductive support 1 side.In this case, in the charge retention layer, in the potential well layer, due to the quantum effect, compared to the case of a single layer without a superlattice structure, Furthermore, in a superlattice structure where the lifetime of carriers is 5 to 10 times longer, 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. , the effective mobility of carriers is similar to that in the bulk, and carrier mobility is excellent.As described above, a superlattice structure consisting of laminated thin layers with different optical band gaps has a high photoconductivity. It is possible to obtain clearer images than conventional photoreceptors.

Referring to FIG. 4, an apparatus and 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, SiH4, B2H6, H
2, raw material gas such as CH4 is accommodated. 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.
By adjusting the pulp 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. The drum base 34 of the photoreceptor is placed on the support base 32 with its axial center being the rotation axis 30.
A heater 35 for heating the drum base is disposed inside the drum base 34. 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, and the pressure inside the reaction vessel 29 is monitored by a pressure gauge 37.
9 is connected to a suitable exhaust means such as a vacuum denso via a dirt pulp 38.

When manufacturing a photoreceptor using the above-mentioned manufacturing apparatus, after installing the drum base 34 in the reaction vessel 29, the Y-tower valve 39 is opened and the inside of the reaction vessel 29 is heated to approximately Q, l Torr.
Evacuate to below pressure. Next, cylinder 21.22,2
3 and 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 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, and the heater 35 rotates the drum base 34.
is heated to a constant temperature, and a high frequency electric current is supplied between the stain electrode 33 and the drum base 34 by the high frequency power source 36 to form a glow discharge between them. As a result, a-8t:H is deposited on the drum base 34. Note that N20°NH5, No2. N2. CH4,0
These elements can be contained in a-8t:H by using 2H4,0□ 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 An aluminum split 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 as necessary, is installed in a reaction vessel to prevent interference, and the reaction vessel is heated to approximately 10 torr. It was evacuated to a degree of vacuum. While heating the drum base to 250 °C and rotating it at 10 rpm, SiH4 was introduced into the reaction vessel at a flow rate of 500 SCCM, B2H6 was introduced into the reaction vessel at a flow rate of 10 SCCM to SiH4, and the pressure inside the reaction vessel was increased. was adjusted to 1 torr. Then, a high frequency power of 13.56 MHz is applied to generate a noise, and a p.
:H barrier layer was formed.

Next, the flow rates of 5IH4 gas and H2 gas were set to 50SCCM and 500SCCM, respectively, the pressure inside the reaction vessel was set to ITorr, and the high frequency power of 1 kW was set to 5
The voltage was applied for 1 minute to form a μc-8t:H thin film. Next, CH4 gas with a flow rate of 15 SCCM was introduced for 2 minutes, and a
-8iC: A thin H film (carbon concentration: 2 atoms) was formed. Such operations were repeated to form a charge retention layer of 20 μm in which the carbon concentration near the interface of the a-8iC:H thin film was continuously changed.

After that, SiH4 gas was set to 400 SCCM, H2 gas was set to 500 SCCM, and a high frequency power of 300 W was applied to form 50 a-81:H thin films. Then 5
50 SCCM of IH4 gas, 500 S of H2 gas
CCM, applying high frequency power of 800W,
A μc-8i:H thin film of X was formed. These operations were repeated to form a charge generation layer of 5 μm.

Finally, a surface layer consisting of a-81:H with a thickness of 0.5 μm 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. It has been proven that it has excellent durability.

Test Example 2 An electrophotographic photoreceptor was prepared in the same manner as Test Example 1, except that an a-8iN:H thin film (nitrogen concentration: 2 atoms) was formed instead of the a-8iC:H thin film constituting the charge retention layer. was manufactured. Note that the 1-8iN:H thin film was obtained by introducing 20 SCCM of N2 gas while applying high frequency power.

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.

The above describes a test example in which the charge retention layer is composed of two types of thin films. However, the present invention is not limited to this, and three or more types of thin films may be laminated. In short, a boundary between thin films with different optical band gaps is formed. Just do it.

[Effects of the Invention] According to the present invention, since the photoconductive layer uses a superlattice structure composed of laminated thin films with mutually different optical band gaps, carrier mobility is high and the resistance is high. An electrophotographic photoreceptor with excellent charging characteristics can be obtained.

In particular, it adopts a structure that continuously changes the concentration of carbon, etc. near the interface of the amorphous silicon thin film that makes up the charge retention layer, making it easy to remove. , the adhesion between each thin film is good. Furthermore, the electrophotographic photoreceptor of the present invention has the advantage that by appropriately combining materials forming the thin film, a photoreceptor having optimal photoconductive properties for light in any wavelength band can be obtained. .

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an electrophotographic photoreceptor according to an embodiment of the present invention, FIGS. 2 and 3 are diagrams showing energy bands of a superlattice structure, and FIG. FIG. 2 is a diagram showing a manufacturing apparatus for nine photographic photosensitive bodies. 1: conductive support, 2: barrier layer, 3: photoconductive layer, 4: surface layer, 5: charge-retaining layer, 6: charge generation layer. Applicant's agent Patent attorney Takeshi Suzue Music Figure 1 Figure 2 Figure 3

Claims (9)

[Claims] (1) In an electrophotographic photoreceptor comprising a conductive support and a photoconductive layer, the photoconductive layer has a charge generation layer and a charge retention layer, and the charge generation layer is composed of an amorphous silicon thin film and a microstructure. The charge retention layer is formed by alternately laminating amorphous silicon thin films and microcrystalline silicon thin films containing at least one element selected from carbon, oxygen, and nitrogen. 1. An electrophotographic photoreceptor, characterized in that the concentration of the element changes continuously near the interface of the amorphous silicon thin film. (2) The electrophotographic photoreceptor according to claim 1, wherein the thin film has a thickness of 30 to 500 Å. (3) The electrophotographic photosensitive material according to claim 1 or 2, wherein the photoconductive layer contains at least one element selected from elements belonging to Group III or V of the periodic table. body. (4) Claims 1 to 3, wherein the microcrystalline silicon thin film constituting the charge generation layer and the charge retention layer contains at least one element selected from carbon, oxygen, and nitrogen. The electrophotographic photoreceptor according to any one of the above. (5) In the charge generation layer, the crystallinity of each thin film changes continuously in the vicinity of the interface of each thin film. Photographic photoreceptor. (6) A barrier layer made of an amorphous material or at least a partially microcrystalline semiconductor material is provided between the conductive support and the photoconductive layer. electrophotographic photoreceptor. (7) The electrophotographic photoreceptor according to claim 6, 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 6, wherein the barrier layer contains at least one element selected from the group consisting of carbon, oxygen, and nitrogen. (9) The electrophotographic photoreceptor according to claim 1, further comprising a surface layer on the photoconductive layer.