JPS63273872A - Electrophotographic sensitive body - Google Patents

Abstract

PURPOSE:To enhance electrophotographic characteristics, such as electric chargeability, dark decay resistance, and photosensitivity, and resistance to environmental conditions by forming a photoconductive layer composed of a charge retaining layer and a charge generating layer each having superlattice structure. CONSTITUTION:The photoconductive layer 3 is composed of the charge generating layer 6 formed by alternately laminating thin films of 2 kinds of microcrystalline silicons different from each other in crystallization degree, and the charge retaining layer 5 formed by alternately laminating thin films of microcrystalline silicon and amorphous silicon containing at least one of C, O, and N, in a concentration distribution continuously changing near each interlayer of the thin films, thus permitting the obtained photosensitive body to be superior in chargeability, low in residual potential, high in photosensitivity in a wide wavelength region, and superior in environmental resistance.

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)
-3t: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, materials constituting the photoconductive layer of electrophotographic photoreceptors include inorganic materials such as CdS, ZnO, Se, or 5e-Te, or poly-N-vinylcarbazole (PVCz).
) or trinitrofluorenone (TNF).

However, compared to these inorganic or organic 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 and excellent wear resistance and impact resistance. Therefore, a-8i:H
is attracting attention as a photoreceptor for electrophotographic processes.

This a-3i: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-8i: Hydrogen is incorporated into the H film, and the electrical and optical characteristics vary greatly depending on the difference in the amount of hydrogen. That is, a-
As the amount of hydrogen that enters the 8i:H film increases, the optical bandgap increases and the resistance of a-8i:H increases, but as a result, the photosensitivity to long wavelength light decreases. For example, it is difficult to use it in a laser beam printer equipped with a semiconductor laser. Moreover, when the hydrogen content in the a-S i:H film increases,
Depending on the film forming conditions, materials having bonding structures such as (SiH2)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, a-3i:
Decreasing the amount of hydrogen incorporated into H reduces the optical bandgap and its resistance, but increases photosensitivity to long wavelength light. However, when the hydrogen content is low, there is less hydrogen to combine with and reduce silicon dangling bonds. For this reason, the mobility of the generated carriers decreases, the lifespan is shortened, and
The photoconductive properties deteriorate, 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 of only the i:H layer, there is a problem that the characteristics change greatly depending on the manufacturing conditions of the a-8j:H layer, and desired characteristics cannot be obtained.

-5 The present invention has been made in view of the above circumstances, and
To provide an electrophotographic photoreceptor that has 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. With the goal.

[Structure of the Invention (Means for Solving the Problems) As a result of various studies, the present inventors have discovered that the photoconductive layer of an electrophotographic photoreceptor is composed of a charge retention layer and a charge generation layer,
The inventors have also discovered that the above object can be achieved by stacking a plurality of semiconductor films, that is, by constructing a superlattice structure, and have 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 formed by alternately stacking two types of microcrystalline silicon thin films having different degrees of crystallization, and the charge retention layer is composed of a microcrystalline silicon thin film and at least one element selected from carbon, oxygen, and nitrogen. and amorphous silicon thin films containing amorphous silicon thin films are alternately stacked, and the element concentration continuously changes near the interface of the thin films.

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 crystallinity of the microcrystalline silicon thin film is preferably 60.
~90%, more preferably 60-80%.

The microcrystalline silicon (μC-8T) 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 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-S+ in which only a halo appears. Second, μc-8t
The dark resistance of can be adjusted to more than 1010Ω・mark,
It has a dark resistance of 105Ω, which is clearly distinguishable from polycrystalline silicon.

The optical bandgap (Eg') of the μc-8j used in the present invention is preferably L55eV, 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 bonds, balances dark resistance and bright resistance, and improves photoconductive properties.

(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 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 photoconductive layer increases,
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 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 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 pc-8i or a-3t:H, or a-BN:H (amorphous boron to which nitrogen and = 9 − hydrogen are added).

Furthermore, an insulating film may be used. For example, μc-3t
:H and a-8t:H contain one or more elements selected from carbon C1 nitrogen N and oxygen O, thereby making it possible to form a high-resistance insulating barrier layer. Barrier layer 2
The film thickness 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 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 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-3i:H
and a-3i: In order to make H type P,
It is preferable to dope with elements belonging to the group, such as boron B, aluminum A, gallium Ga1, indium In, and thallium T, 17, etc. Also, μc-3i:
H or a-3i: In order to make H type N,
It is preferable to dope with elements belonging to the group, such as nitrogen, phosphorus P1 arsenic As, antimony Sb1 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 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. The charge generation layer 6 is constructed by alternately laminating two types of microcrystalline silicon thin films having different degrees of crystallinity. , the element concentration in the charge retention layer 5 changes continuously near the interface of the thin film. The thickness of the thin film ranges from 30 to 500 mm.

Ideally, the superlattice structure constituting the charge retention layer 5 and the charge generation layer 6 should have, for example, thin films with different optical band gaps forming a discontinuous periodic potential, as shown in FIG.

However, in order to deposit such a superlattice structure, it is necessary to purge the gas in the reaction chamber after each thin film is deposited to prevent impurities from entering the thin film during the next deposition. However, there are disadvantages in that the film forming time is extremely long and mass productivity is poor. In addition, when forming a film by plasma CVD, ions constantly bombard the film forming surface (ion bombardment).
occurs, which causes impurities to diffuse into the thin film, making it impossible to form the discontinuous periodic potential shown in FIG.

On the other hand, in the superlattice structure according to the present invention, the = 12th
- As shown in Figure 3, the element concentration, that is, the optical band gap, near the interface of each amorphous silicon thin film of the charge retention layer 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, by adopting a superlattice structure in which the element concentration, and thus the optical band gap, are continuously changed near the interface of the thin film, the thin film can be deposited one after another without waiting for the deposition conditions to stabilize. Since film formation can be performed, the film formation 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 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 the thin film. 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 film 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-3i constituting the charge retention layer 5 and charge generation layer 6:
The hydrogen content in H and μc-8t: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 photoconductive properties.

a-3t: To form the H layer by glow discharge decomposition method, silane gases such as SiH4 and Si2H6 are introduced into the reaction chamber as raw materials, and H is added into the thin film by glow discharge using high frequency. Can be done. If necessary, hydrogen or helium gas can be used as a carrier gas for silanes. On the other hand, SiF4 gas and si
Silicon halides such as c and e4 gases can be used as the raw material gas. Further, a-3j:H containing H can be similarly formed by reacting with a mixed gas of a silane gas and a silicon halide gas. 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: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-3j:
The high frequency power is set higher than when forming H, and the high frequency power is also a-
If it is set higher than the case of 8t:H, μc-3t:H
becomes easier to form. Furthermore, by increasing the support temperature and high frequency power, the flow rate of source gas such as silane gas can be increased, and as a result, the film formation rate can be increased. In addition, SiH4 and Si of the raw material gas
By using a gas obtained by diluting a high-order silane gas such as 2H6 with hydrogen, μC-8i:H can be formed with higher efficiency.

In order to make μc-3i:H and a-8t:H p-type, elements belonging to group Ⅰ of the periodic table, such as boron B1
It is preferable to dope aluminum A, gallium Ga1, indium In, thallium T, fl', etc., and in order to make μc-8t:H and a-8j:H n-type, doping with group V of the periodic table is preferred. elements belonging to, for example, nitrogen N
1 Phosphorus P1 Arsenic As, Antimony Sb1 and Bismuth B
It is preferable to dope with i or the like. This p-type impurity or -16= is doped with an n-type impurity to prevent charges from moving from the support side to the photoconductive layer. On the other hand, μc-3
t:H and a-8t:H, carbon C1 nitrogen N and oxygen O
By containing at least one element selected from the following, 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 μc-8t:H 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. The material forming the surface layer is a-3iN:Hs.
These include inorganic compounds such as aS iO:H, and a-8iC:H, and organic materials such as polyvinyl chloride and polyamide.

= 17 = 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 toward the conductive support 1 side. 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. Furthermore, in the potential well layer, due to quantum effects, the lifetime of carriers is 5 to 10 times longer than in the case of a single layer without a superlattice structure. 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 tunnel effect, so the effective carrier mobility is equal to the bulk mobility. The carrier has excellent running performance.

Similarly, in the case of the charge retention layer 5, due to quantum effects, 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.

Furthermore, 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.
The effective mobility of the carrier is similar to that in the bulk, and the carrier has excellent mobility. As mentioned above,
A superlattice structure in which thin films with different optical band gaps are laminated can provide high photoconductivity and provide clearer images than conventional photoreceptors.

Referring to FIG. 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, St H4, B2 H6, H2, respectively.
, CH4, etc. (7) raw 14 gases are accommodated. The gas in these gas cylinders is supplied to the mixed volume 28 via a valve 26 and piping 27 for flow rate adjustment. A pressure gauge 25 is installed in each cylinder, and by adjusting the valve 26 while monitoring the pressure gauge 25, 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 two reaction vessels. At the bottom 31 of the reaction container 29, there is a rotating shaft 3.
0 is mounted rotatably 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 power source 36 is connected between the electrode 33 and the drum base 34, so that a high frequency current is supplied between the electrode 33 and the drum base 34. The rotating shaft 30 is rotationally driven by a motor 38. The pressure inside the reaction vessel 29 is monitored by a pressure gauge 37,
The reaction vessel 29 is connected via a gate valve 38 to a suitable exhaust means such as a vacuum pump.

When manufacturing a photoreceptor using the above 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, 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 vessels 29 is set so that the pressure within the two reaction vessels 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 current is supplied between the electrode 33 and the drum base 34 by the high frequency power supply 36 to form a glow discharge between them. As a result, a-8j:H is deposited on the drum base 34. Note that N20. NH3, No2. N2. CH4゜-21
= These elements can be contained in a-8i :H by using C2H4,02 gas or the like.

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

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

Test Example 1 A diameter of 80+n+n was subjected to acid treatment, alkali treatment, and sandblasting to prevent interference as necessary.
A 350 mm wide aluminum drum substrate was placed in the reaction vessel and the reaction vessel was evacuated to a vacuum of approximately 10-5 Torr. Heat the drum base to 250 °C and 10 rpm
5iH4 gas at 5008 CCM while rotating at B
2H6 gas was introduced into the reaction vessel at a flow rate ratio of 10-3 to 5iHa gas, and the pressure inside the reaction vessel was reduced to 1.
I adjusted it to the torque.

Then, a high frequency power of LL56 MHz is applied to generate plasma, and p-type a-1 is deposited on the drum base.
22-Sj:H barrier layer was formed.

Next, the flow rates of .5jH4 gas and N2 gas were set to 50 SCCM and 500 SCCM, respectively, and 1 kW of high frequency power was applied for 5 minutes. Next, CH4 gas was introduced at a flow rate of 15 SCCM for 2 minutes while high frequency power was applied. . By repeating such operations, μc-Sj:
H thin film and a- where the carbon concentration near the interface changes continuously.
8j C:H thin film (carbon concentration = 4 at%)
A charge retention layer of 0 μm was formed.

After that, 5jH4 gas is 208CCM, H2 gas is 5j
00 SC0M was introduced, 800 W of high frequency power was applied, and 100 μc-3t:H thin films were formed.

Then, 50 SCCM of SiH4 gas and 5 SCCM of N2 gas were added.
Introducing 009CCM and applying 800W of high frequency power,
100 μc-3i:H thin films were formed.

These operations were repeated to form a charge generation layer of 5 μm.

Finally, a surface layer of 0.5 μm consisting of a-3t:H was formed.

When the surface of the photoreceptor thus formed is positively charged at about 500 V and exposed to white light, this light is absorbed by the 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.

Test Example 2 Instead of the a-3iC:H thin film constituting the charge retention layer, a
An electrophotographic photoreceptor was manufactured in the same manner as in Test Example 1 except that a -5iN:H thin film was formed.

Note that the a-9iN: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 photoconductive layer is composed of two types of thin films, but the invention is not limited to this, and three or more types of thin films may be laminated.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 crystallinity near the interface of the thin film, making it excellent for mass production.
Because of the continuous film formation, 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. 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: charge retention layer, 6: charge generation layer.

Claims (7)

[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 has two types with different crystallinity. The charge retention layer is composed of alternating layers of microcrystalline silicon thin films and an amorphous silicon thin film containing at least one element selected from carbon, oxygen, and nitrogen. An electrophotographic photoreceptor comprising a laminated structure, wherein the element concentration continuously changes near an 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) 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. (5) The electrophotographic photoreceptor according to claim 4, wherein the barrier layer contains at least one element selected from elements belonging to Group III or V of the periodic table. (6) The electrophotographic photoreceptor according to claim 4, wherein the barrier layer contains at least one element selected from the group consisting of carbon, oxygen, and nitrogen. (7) The electrophotographic photoreceptor according to claim 1, further comprising a surface layer on the photoconductive layer.