JPS63243960A - Electrophotographic sensitive body - Google Patents

Abstract

PURPOSE:To improve the traveling property of carriers in an electric charge retaining layer by alternately laminating thin microcrystalline Si films and thin films of amorphous Si contg. a prescribed element whose concn. varies continuously in the vicinity of the interface so as to form the retaining layer. CONSTITUTION:The photoconductive layer 3 of a sensitive body is composed of an electric charge retaining layer 5 and an electric charge generating layer 6. The layer 5 is formed by alternately laminating thin microcrystalline Si films and thin films of amorphous Si contg. one or more element among C, O and N and the concns. of the elements are continuously varied in the vicinity of the interface between the thin films. The layer 6 is made of amorphous Si or microcrystalline Si. A barrier layer 2 of an amorphous material or at least partially microcrystallized semiconductor material and a surface layer 4 are preferably formed between the electrically conductive 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) 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, Zn0,3e, or Kuha5e-Te, or poly-N-vinylcarbazole (PVCz) have been used as materials constituting the photoconductive layer of electrophotographic photoreceptors.
Alternatively, organic materials such as trinitrofluorenone (TNF) have been used.

However, compared to these inorganic materials or specific materials, a-8i: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, excellent M abrasion resistance and impact resistance. Therefore, a-8i:H
1 is attracting attention as a photoreceptor for electrophotographic processes.

This a-s+:H is being studied as a photoreceptor material based on the Karun system, but in this case, the photoreceptor is required to have high resistance and photosensitivity.

However, since it is difficult to satisfy both of these characteristics with a single photoreceptor, a barrier layer is provided between the leading 'R layer and the conductive support, and the light guide l! These requirements are satisfied by forming a layered structure in which a surface charge retention layer is provided on top of the layers.

(Problems to be Solved by the Invention) By the way, a-3i:H is usually formed by a glow discharge decomposition method using a silane gas, but at this time,
a-8i: Hydrogen is incorporated into Hl, and the electrical and optical properties vary greatly depending on the difference in the amount of hydrogen. That is,
a-8i: HI! When the amount of hydrogen that enters into l increases, the optical bandgap increases and the resistance of a-8iH increases, but as a result, the photosensitivity to long wavelength light decreases. Difficult to use with mounted laser beam printer. Furthermore, when the hydrogen content in the a-8i H film increases, depending on the film formation conditions, (SiH2)n and SiH2
In some cases, a bond structure such as occupies 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. On the contrary, a-
As the amount of hydrogen incorporated into 8i:H decreases, the optical band gap decreases and its resistance decreases, but the photosensitivity to long wavelength light increases. However, when the hydrogen content is low, there is less hydrogen to combine with and reduce silicon dangling bonds. As a result, the mobility of the generated carriers decreases, the life span becomes short, and the photoconductive properties deteriorate, 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 the layer is composed only of i:HIH, 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 photosensitivity over a wide wavelength fEi region 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 inventors have constructed a photoconductive layer of an electrophotographic photoreceptor including a charge retention layer and a charge generation layer,
A charge retention layer? ! The inventors have discovered that the above object can be achieved by continuously changing the concentration of carbon, etc. in the vicinity of the interface of these semiconductor films, and have completed the present invention. This is what we have come to.

That is, the electrophotographic photoreceptor of the present invention is an electrophotographic photoreceptor comprising a conductive support and a photoconductive layer, the photoconductive layer having a charge generation layer and a charge retention layer, ! The charge generation layer is made of amorphous silicon or microcrystalline silicon, and the charge retention layer is made of an amorphous silicon thin film containing microcrystalline silicon FiJR and at least one element selected from carbon, oxygen, and nitrogen. The thin film is characterized in that it is configured by alternately laminating layers, and the concentration of the element changes continuously near the interface of the thin film.

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

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 approximately several tens of angstroms, and has the following physical properties. It has the following 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-3i
The dark resistance of can be adjusted to 1010Ω・1 or more,
It can also be clearly distinguished from polycrystalline silicon, which has a dark resistance of 10+30·α.

The optical band gap (Ey") of the μc-8i used in the present invention is preferably set to, for example, 1.55 e V. However, it can be set arbitrarily within a certain range. In order to obtain the desired E9" It is preferable to add a predetermined amount of hydrogen to each of them and use them as μc-8i: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 superlattice structure is provided in the charge retention layer, 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 charge retention layer is increased, and the lifetime of the carriers is improved, thereby significantly improving the sensitivity of the electrophotographic photoreceptor.

Moreover, in the present invention, a-8iiiil! Since it contains at least one of carbon, oxygen, and nitrogen, it not only adjusts the band gap as described above, but also
By increasing the resistance of the photoconductive layer, the ability of the surface to retain the 'R' charge can be increased.

(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 the charge retention layer 5 has 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.

Barrier M2G, tuc-S i and a-8t
:H may be used, or 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
-3i: ) (and a-8h: carbon C1 nitrogen N in H
By containing one or more elements selected from 110 and 110, a high resistance insulating barrier WIWJ can be formed. 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 charge generation layer 5, thereby increasing the charge retention function of the surface of the photoreceptor and increasing the charging ability of the photoreceptor. It is something. Therefore, when constructing a Carlson type photoreceptor using a semiconductor layer as a barrier layer, in order not to reduce the ability to retain charges on the surface, a ¥8 wall layer 2 is required.
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, if the surface is to be negatively charged, the barrier H2 should be 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 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:H
and a-8i: In order to make H type P,
It is preferable to dope with an element that belongs to the group B1 aluminum 82, gallium Qa, indium In, thallium TR, etc. Also, μc-3i:
In order to make H or a-3i:@ 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 Sb1, and bismuth Bi.

The charge generation layer 6 generates carriers when light enters the layer, and carriers of one polarity neutralize the charges on the surface of the photoreceptor, and the other carriers travel within the charge retention wJ5 and become conductive. The support 1 is reached.

The charge retention layer 5 is constructed by alternately laminating microcrystalline silicon thin films and amorphous silicon thin films.

The amorphous silicon thin film contains at least one selected from carbon, oxygen, and nitrogen, and its concentration continuously changes near the interface. 'The thickness of the 4 legs is 30~5
It is in the range of 00 people.

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 purge the gas in the reaction chamber after each thin film is formed to prevent impurities from entering i'1l13 during the next film formation. Therefore, the film formation time is extremely long, and the at-product 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, in the vicinity of the interface of each thin film is continuously changed. Such a superlattice structure can be created by lowering the radio frequency power slightly to weaken ion bombardment, introducing a large amount of H2 gas, and changing the flow rate of gas containing impurities while keeping the radio frequency power constant; or This 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, carbon, etc.! By adopting a superlattice structure in which the optical bandgap is changed continuously, it is possible to deposit films one after another without stabilizing the film-forming conditions. The membrane time can be shortened considerably, resulting in excellent productivity. Moreover, since the film formation is continuous, the adhesion between each 'aWA becomes good.

As explained above, by stacking thin films with different optical bandgaps, the optical bandgap becomes larger than the film with a small optical bandgap, regardless of the size of the optical bandgap itself. A superlattice structure having periodic potential barriers is formed in which the film serves as a barrier. In this superlattice structure, since the barrier thin film is extremely thin, carriers pass through the barrier and travel within the superlattice structure due to the carrier tunneling effect in [. 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 Ill thickness of the thin film having the superlattice structure, the apparent bandgap of the layer having the heterojunction superlattice structure can be freely adjusted.

a-s+ constituting the charge retention layer 5 and the charge generation layer 6
The hydrogen content in :H and μc-8i :H is preferably 0.01 to 30 at%, and 1 to 25 at%
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 a film of a-s+:tuii by the glow discharge decomposition method, SiH+ and silane gases such as 3i2Hs are introduced into the reaction chamber as raw materials, and H is added into the thin film by glow discharge using high frequency. can. If necessary, hydrogen or helium gas can be used as a carrier gas for silanes. On the other hand, silicon halides such as S:F4 gas and 5iCffi4 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,
Similarly, a-3i:@ containing 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-8i:@, μc-8iIiii can also be formed into a film by the high-frequency glow discharge decomposition method using silane gas as a raw material. In this case, the humidity of the support is a-8
If it is set higher than when forming i:H and the high frequency power is also set higher than when forming a-8i:H, μc-3i
: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, by using a raw material gas of SiH+ and a gas obtained by diluting a high-order silane gas such as 5i2Hs with hydrogen, μC-8i:H can be formed with higher efficiency.

In order to make μC-8t:H and a-8i:@ n-type, elements belonging to Group Ⅰ of the periodic table, such as boron B, aluminum A°C, and gallium Ga are used.

It is preferable to dope with indium In, thallium TI2, etc., μc-8t:H and a-8i:H
In order to make it n-type, elements belonging to face V of the periodic table, such as nitrogen N1 phosphorus P1 arsenic AS, antimony Sb
, bismuth 3i, etc. are preferably doped. By doping with this n-type impurity or n-type impurity,
Charge migration from the support side to the leading N layer is prevented. On the other hand, by incorporating at least one element selected from carbon C nitrogen N and oxygen O into uc-8t: ) (and a-8t:@), high resistance can be achieved and the surface charge retention ability can be increased. Can be done.

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 proportion of light m absorbed by the charge generation layer decreases, and light loss increases. For this reason, it is preferable to provide a surface 14 to prevent reflections. Further, by providing the surface 114, charge generation [1
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-8iN:
There are non-corrosive compounds such as H, a-8i O:H, and a-8iC:H, as well as corrosive 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 at charge generation Fm6. Electrons in the conduction band are accelerated toward the surface layer 4 side by the electric field in the photoreceptor, and holes are
accelerated towards the side. In this case, in the charge retention layer, the carrier lifetime 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 quantum effects. Furthermore, in the superlattice structure, periodic barriers Fm are formed due to discontinuities in the band gap, but carriers easily pass through the bias layer due to the tunnel effect, so the effective mobility of carriers is equal to that in the bulk. The carrier has excellent running performance. As described above, the superlattice structure in which thin films with different optical band gaps are laminated can provide photoconductive properties and provide clearer images than conventional photoreceptors.

Referring to FIG. 4, 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 controlled by a valve 26 and piping 2 for regulating the flow.
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 N pole 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 'a36 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 reaction vessel 29 is connected via a gate valve 38 to an appropriate 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 approximately 0.1 Torr 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 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 electrode 33 and the drum base 34. A glow discharge is formed between the two. As a result, a-8i:H is placed on the drum base 34.
is deposited. In addition, N20. NH3, NO
2, N2.

By using CH4, C2H4,02 gas, etc.
These elements can be contained in a-3i:@.

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 m and a width of 350 m was treated as necessary to prevent interference. An aluminum drum substrate of 1.5 mm was placed in the reaction vessel, and the reaction vessel was evacuated to a vacuum level of approximately 10 −5 Torr. While heating the drum base to 250 °C and rotating it at 10 rpm, SiH + gas was introduced into the reaction vessel at a flow rate of 500 SCCM and 82 Hs gas was introduced into the reaction vessel at a flow rate of 10-3 at the maximum flow ratio to SiH + gas, and the pressure inside the reaction vessel was decreased. Adjusted to 1 torr. Then, a high frequency power of 13.56 M@z was applied to generate plasma to form a p-type a-8i:H barrier layer on the drum base.

Next, the flow rates of SiH+ gas and H2 gas were each set to 5
08 CCM and 750 SCCM, and a high frequency power of 600 W was applied for 4 minutes. Next, while applying the high frequency power, flow J! 1 liter, 105 cc of CH4 gas was introduced for 4 minutes. By repeating such operations, the carbon concentration near the interface changes continuously.a-3i H1l! (carbon concentration: 3 atomic%) and a 20 μm film consisting of μc-5i:H thin film
A charge retention layer of m was formed.

After that, add 500SCCM of SiH+ gas and 300SCCM of H2 gas.
00 SCCM, B2 Ha gas was introduced at a flow ratio of 10-6 to the SiH+ gas flow rate, and a high frequency power of 400 W was applied to form a 65 μm charge generation layer of a-8t:H.

Finally, a surface layer of 0.5 μm consisting of a-3i:H 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 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, the photoreceptor manufactured in this test example was repeatedly tested at W! When subjected to electricity, it was demonstrated that the reproducibility and stability of the transferred image were extremely good, and furthermore, the durability such as corona resistance, moisture resistance, and abrasion resistance was excellent.

Test Example 2 a-S+C constituting the charge retention layer: + a instead of a thin film
An electrophotographic photoreceptor was produced in the same manner as in Test Example 1, except that a -8iN:)l film (nitrogen concentration: 3 at %) was formed. Note that the a-8iN:HFa antinode was obtained by introducing 158 CCM of N2 gas for 4 minutes 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 test example in which the charge retention layer is composed of two types of thin films has been described above, but the invention is not limited thereto, and three or more types of thin films may be laminated.In short, a 1 liter boundary with different optical band gaps is formed. Just do it.

[Effects of the Invention] According to the present invention, since the charge retention layer uses a superlattice structure formed by laminating 'a films having mutually different optical band gaps, carrier mobility is high, and An electrophotographic photoreceptor with high resistance and excellent charging characteristics can be obtained. In particular, the concentration of carbon etc. near the interface of the thin film is
Since it adopts a structure that changes in the @ direction, it is excellent in mass production, and because the film formation is continuous, the adhesion between each thin film is good. Furthermore, in the electrophotographic photoreceptor of the present invention,
By appropriately combining materials forming the thin film, there is an advantage that a photoreceptor having optimal photoconductive properties for light in any wavelength band can be obtained.

[Brief explanation of drawings]

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. 1 is a diagram showing an apparatus for manufacturing a photographic photoreceptor. 1: Conductive support, 2: Barrier layer, 3: Photoconductive layer, 4: Surface layer, 5: Ti charge retention layer, 6: Charge generation layer. Applicant's representative Patent attorney Takehiko Suzue Figure 1 Thin film Figure 2 Figure 3

Claims (8)

[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 made of amorphous silicon or microcrystalline silicon. The charge retention layer is made of silicon, and is configured by alternately laminating microcrystalline silicon thin films and amorphous silicon thin films containing at least one of the elements selected from carbon, oxygen, and nitrogen, and An electrophotographic photoreceptor, wherein the concentration of the thin film changes continuously near the interface of the 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 photoreceptor 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. . (4) The microcrystalline silicon regions of the charge generation layer and the charge retention layer contain at least one element selected from carbon, oxygen, and nitrogen. The electrophotographic photoreceptor according to any one of the above. (5) 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. (6) The electrophotographic photoreceptor according to claim 5, wherein the barrier layer contains at least one element selected from elements belonging to Group III or V of the periodic table. (7) The electrophotographic photoreceptor according to claim 5, wherein the barrier layer contains at least one element selected from the group consisting of carbon, oxygen, and nitrogen. (8) The electrophotographic photoreceptor according to claim 1, further comprising a surface layer on the photoconductive layer.