JPH06194856A - Electrophotographic photoreceptor - Google Patents

Abstract

PURPOSE:To obtain an electrophotographic photoreceptor having high sensitivity by forming a charge injection preventing layer on a conductive supporting body and forming a carrier multiplying layer to multiply the carrier thereon. CONSTITUTION:The photoreceptor has a diode structure consisting of a charge injection preventing layer 12, (photoconductive layer 13), carrier multiplying layer 14, and charge preventing layer 15 formed on a conductive supporting body 11. This diode element is in a reverse bias state according to the polarity to form an electrostatic latent image. When the photoreceptor is irradiated with light in a reversed bias state, photocarriers move to the carrier multiplying layer 14. If the energy difference between the layer of wider forbidden band width and the layer of narrow forbidden band width is equal or larger than the ionization energy of the carrier, traveling carriers are ionized and multiplied. The multiplied carriers reach to the surface of the photoreceptor and neutralize the charges. Thereby, the obtd. photoreceptor has high sensitivity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic photosensitive member, and more particularly to a novel constitution of a high-sensitivity electrophotographic photosensitive member made of a material mainly containing silicon.

[0002]

2. Description of the Related Art Conventionally, as an electrophotographic photosensitive member, for example,
Known are a photoconductor in which amorphous Se is doped with impurities such as As, Te, Sb and Bi, and a photoconductor in which CdS is dispersed in a resin binder. However, these photoreceptors have problems in environmental pollution, thermal stability, and mechanical strength.

On the other hand, amorphous Si (hereinafter abbreviated as a-Si)
Recently, the practical application of the electrophotographic photosensitive member made of a material has been progressing. a-Si has a so-called dangling bond in which Si-Si bonds are broken, and due to this defect, many localized levels exist in the forbidden band. Therefore, due to hopping conduction, the dark resistance is small, and due to defects,
Since a-Si has a low photoconductivity, a-Si alone is not suitable as an electrophotographic photosensitive material. On the other hand, hydrogenated amorphous Si having dangling bonds terminated by hydrogen atoms
(Hereinafter abbreviated as a-Si: H) has a slightly higher dark resistance than a-Si and is 10 ⁹ to 10 ¹¹ Ω · cm. However, the photoconductivity with respect to visible light and infrared light has excellent characteristics as an electrophotographic photosensitive material.

As an example of an electrophotographic photosensitive member which makes use of such photoelectric properties of a-Si: H and has a high dark resistance,
A is a photoconductive layer on the charge injection blocking layer made of SiC.
-Si: H laminated structure (for example, Japanese Patent Laid-Open No. 57-17
952), and O in a-Si: H which is a photoconductive layer,
Examples in which C, N, etc. are added (for example, JP-A-56-6434).
7 etc.) and the like.

[0005]

However, in the above-mentioned conventional hydrogenated amorphous Si, as described above,
Since the dark resistance is rather small, it has been attempted to add impurities such as O, C, and N to further increase the dark resistance, but the presence of the impurities lowers the photoconductivity and realizes high sensitivity. Is difficult. Further, even in the case where a-Si: H is used as an optical transmission layer, higher sensitivity is desired. An object of the present invention is to provide a high-sensitivity electrophotographic photosensitive member, in which the disadvantages of the above-mentioned conventional techniques are improved.

[0006]

In order to achieve the above object, the present invention provides a charge injection blocking layer on a conductive support, and a carrier multiplication for multiplying at least carriers on the charge injection blocking layer. And an electrophotographic photosensitive member formed by stacking layers.

Further, the present invention is an electrophotographic photosensitive member comprising a photoconductive layer provided between the charge injection blocking layer and the carrier multiplication layer of the above photosensitive member.

The present invention is also an electrophotographic photosensitive member comprising a charge multiplication block layer provided on the carrier multiplication layer of the above photosensitive member.

Further, in the present invention, at least one or more of the above-mentioned carrier multiplication layers generate an energy step E on the conduction band side after continuously changing from the minimum forbidden band width Eg1 to the maximum forbidden band width Eg2. It is configured to have an energy level composed of a step-back structure.

Further, the energy step E is equal to or more than the ionization energy of carriers in the layer having the minimum forbidden band width Eg1 and larger than the minimum forbidden band width Eg1.

The layer structure of the electrophotographic photosensitive member of the present invention is a so-called charge injection blocking layer- (photoconductive layer)-(layer for multiplying carriers) -charge injection blocking layer or charge injection blocking layer-.
(Layer that multiplies carriers) -It is a structure of a diode element of a charge injection blocking layer, and this diode element is formed according to the polarity of charge +/- when an electrostatic latent image is formed on an electrophotographic photoreceptor. Reverse bias is applied. The charge injection blocking layer is
The purpose of this is to prevent injection of charged charges on the surface of the photoconductor into the photoconductive layer. When light irradiation is performed in this reverse bias state, the photocarriers generated in the photoconductive layer travel to the carrier multiplication layer that multiplies the carriers. The carrier multiplication layer has a composition change portion that changes from a narrow forbidden band width to a wide forbidden band width, the wide forbidden band maximum, and the narrow forbidden band minimum after the wide forbidden band width. It consists of an energy step with a layer having a forbidden band and a layer having a step-back structure. This energy step, or the substantial energy step including the reverse bias electric field is equal to the ionization energy of carriers,
Alternatively, when it is larger than that, the traveling carriers are ionized and multiplied. The multiplication factor can be changed depending on the number of multiplication layers. The multiplied carriers reach the surface of the photoconductor and neutralize the charge. Therefore, the provision of the high-sensitivity electrophotographic photosensitive member which is the object of the present invention is achieved by the novel constitution of the present invention.

The present invention will be described in more detail below with reference to the drawings.

FIG. 1 shows an example of the constitution of the electrophotographic photosensitive member of the present invention. The figure shows the charge injection blocking layer 1 on the conductive support 11.
2, an example of a case where the photoconductive layer 13, the carrier multiplication layer 14, and the charge injection blocking layer 15 are sequentially laminated.
A structure without the light transmission layer 13 may be used. In this case, by increasing the layer thickness of the carrier multiplication layer 14, the layer is made to have optical conductivity. In FIG. 1, the carrier multiplication layer 14 has a four-layer structure, but the number of layers or the layer thickness of each layer is further increased to increase the layer thickness of the carrier multiplication layer.

The materials constituting each layer will be described below.

A drum-shaped support is preferably used as the conductive support, and aluminum, NiCr, stainless steel, Cr,
Mo etc. can be used.

As the charge injection blocking layer, SiO₂ , Si
O, Al₂ O₃ , ZrO₂ , TiO ₂ , MgF₂ , Zn
S, a-Si_x C_1-x : Insulator such as Hand / orX or half
A conductor material or the like can be used.

Of these, a-Si _x C _{1 -X} : H is particularly preferable.

As the photoconductive layer, a-Si: Hand / orX
(X is halogen), a-SiGe: Hand / orX, a-S
i _x C _1-x Hand / or X or the like can be used.

As the carrier multiplication layer, a-SiH:
_{a-Si 1-x C x} : Hand / orX like can be used.

The electrophotographic photosensitive member of the present invention can be prepared by glow discharge decomposition method, sputtering method or the like.

The method for producing a photosensitive member by the glow discharge decomposition method will be described below, but the present invention is not limited to this.

FIG. 3 is a conceptual diagram showing the structure of a capacitively coupled glow discharge decomposition apparatus. This device is in the vacuum chamber 31,
The anode electrode 32 and the cathode electrode 33 are installed in predetermined places. Further, a heater for heating the substrate is installed below the anode electrode 32, and the substrate 30 is installed on the anode electrode. A high frequency power supply 35 is connected to the cathode electrode 33, and the anode electrode 32 and the cathode electrode 3 are connected.
The space between 3 becomes a glow discharge space. In the vacuum chamber 31,
It is connected a gas introduction pipe 36-1,36-2,36-3,36-4, respectively _{SiH 4, H 2, CH 4} , C 2 H 2
Will be introduced. Further, an exhaust device 37 is connected to the vacuum chamber 31. Further, in particular, the carrier multiplication layer 14 is a
_{-Si: H~a-Si 1-x} C x: Since the composition of the H is _{modulated, SiH 4 36-1, H 2 36-2} , C 2 H 2 36
At -4, a flow rate control device (not shown) is precisely and automatically controlled to obtain a desired composition. The carbon source gas species such as C ₂ H ₂ or CH ₄ may be appropriately selected according to the desired band gap.

First, the substrate 30 made of the above material is placed on the anode electrode 32, and is usually heated by the heater 34 to a substrate temperature of 250 to 350.degree. Next, for example, Si
H ₄ , H ₂ and C ₂ H ₂ were introduced, a high frequency of 13.56 MHz was applied to cause glow discharge, and a film thickness of 200 was formed on the substrate.
A-Si _x C _1-x : H of 10,000 angstroms
A charge injection blocking layer made of (x = 0 to 0.9) is formed. This layer may contain group III atoms such as B or group V atoms such as P.

Next, after the gas in the vacuum chamber is exhausted by the exhaust device 37, for example, SiH ₄ and H ₂ are introduced, and 1
Applying high frequency of 3.56MHz, film thickness 1-100μm
A non-doped photoconductive layer of 1 is laminated on the charge injection blocking layer.

After evacuating the vacuum chamber 31, for example, SiH
₄ , H ₂ and C ₂ H ₂ are introduced, and a high frequency of 13.56 MHz is applied to laminate a carrier multiplication layer having a film thickness of 2000 angstrom to 20 μm on the photoconductive layer.

If necessary, a plurality of carrier multiplication layers may be formed. In this case, it is necessary to consider the difference in band gap from the photoconductive layer. For example, a-Si _1-x C _x :
The composition is changed within the range of H (however, x = 0 to 0.5). Therefore, its composition is changed depending on the flow rate of the C ₂ H ₂ gas.

Next, after the inside of the vacuum chamber 31 is evacuated, SiH ₄ , H ₂ and CH ₄ are introduced, and a high frequency of 13.56 MHz is applied to apply a high film thickness of 30 Å to 1 μm.
-Si _x C _1-x: the H (x = 0.1~0.9) charge injection blocking layer is a surface layer made of forming the carrier multiplication layer.

In the above manufacturing method, the apparatus having one film forming chamber has been described, but a plurality of film forming chambers may be provided in order to prevent contamination in the vacuum chamber due to mixing of each gas.

FIG. 2 shows a band diagram when the surface 15 side of the electrophotographic photosensitive member having the structure shown in FIG. 1 is not charged. 22 is a charge injection blocking layer, 23 is a photoconductive layer having a forbidden band width E _g O, 24 is a carrier multiplication layer, and has a minimum forbidden band width E.
This is a step-back structure in which the energy gap E is generated on the conduction band side after the forbidden band width is continuously changed from _g 1 to the maximum forbidden band width E _g 2, and a plurality of layers of this one cycle are repeated. For each energy step,
If the ionization energy of the electron is equal to or larger than the ionization energy of the electron, the electron is ionized to generate an electron-hole pair and a multiplication effect occurs. In the photoreceptor shown in FIG. 2, the carrier multiplication layer is
This is the case when there are four layers. It should be noted that, on the valence band side, by selecting the material configuration, a large energy step, unlike the conduction band side, is prevented from occurring. Reference numeral 25 is a charge injection blocking layer.

Using the electrophotographic photosensitive plate according to the present invention, the surface of the photosensitive member was positively charged by corona discharge or the like, and the dark decay of the surface potential was observed. As a result, the electron using the conventional a-Si: H was used. It exhibits the same characteristics as a photographic photoreceptor. FIG. 4 shows a band diagram when the surface is positively charged. As shown in FIG. 4, a band diagram equivalent to a so-called charge injection blocking layer-i-carrier multiplication layer-charge injection blocking layer in a reverse bias state is obtained. Light enters from the charge injection blocking layer 25 side, and a part of the incident light is
Although the light is absorbed according to the light absorption coefficient of each of the charge injection blocking layer 25 and the carrier multiplication layer 24, most of the incident light is absorbed by the photoconductive layer 23. The light absorbed in the photoconductive layer 23 generates electron-hole pairs, and the holes travel to the charge injection blocking layer 22 and the conductive support 11 such as Al by the electric field. On the other hand, the electrons travel to the carrier multiplication layer 24,
After traveling through the band slope portion, after reaching the energy step, that is, the step back portion, the energy step and the electric field give energy equal to or larger than the ionization energy, and impact ionization occurs, resulting in electron-hole pairing. To occur. This process is repeated as many times as the number of step backs, and the electrons are multiplied. As a result,
In the first embodiment, are ideally 2 ⁴ fold magnification. Note that holes do not have sufficient multiplication effect because they do not have enough energy to be ionized. After this, ideally 2
^The electron multiplied by ⁴ moves to the surface side, neutralizes the surface charge, and the surface potential is photo-attenuated. From the above, in this case, compared to the conventional electrophotographic photosensitive member having no multiplication effect,
^With the incident light of ⁴ , the same optical attenuation of the surface potential as before is expected. That is, the sensitivity is equivalent to 2 ⁴ times.

[0031]

EXAMPLES The present invention will be described in more detail below with reference to examples.

Example 1 First, a drum-shaped Al substrate was set at a predetermined position in a vacuum chamber of a glow discharge decomposition apparatus. The substrate was heated with a heater until the substrate temperature reached 300 ° C. At this time, the degree of vacuum in the vacuum chamber was 0.4 Torr.

Then, SiH ₄ 25 sccm and H ₂ 30
Sccm and 60 sccm of C ₂ H ₂ were introduced to form a charge injection blocking layer having a film thickness of 500 Å and a high frequency power density of 0.2 W / cm ² . The forbidden band width of the layer is 3.
It was 2 eV.

After exhausting the vacuum chamber, SiH ₄ 60sc
cm, H _{2 of} 20 sccm was introduced to form an optical transmission layer having a film thickness of 10 μm at a high frequency power density of 0.1 W / cm ² and a substrate temperature of 300 ° C. The forbidden band width of the layer was 1.6 eV. Further, the dark specific resistance was 10 ¹⁰ Ω · cm or more, indicating sufficient photoconductivity.

Next, after exhausting the inside of the vacuum chamber, SiH ₄ 2
5 sccm, H ₂ 30 sccm and C ₂ H ₂ 40 sccm
m was introduced to form a carrier multiplication layer at a high frequency power density of 0.2 W / cm ² and a substrate temperature of 300 ° C. Similarly C ₂
By appropriately changing the flow rate of H ₂ , a-Si _1-X C _X : H
A carrier multiplication layer having a composition of (x = 0 to 0.4) was formed. As a result, the forbidden band width is 1.6eV to 3.5e
Change to V and the energy difference on the conductor side is 1.7e
It was V. The thickness of each carrier multiplication layer is 5
It was 00 angstrom.

Next, after exhausting the inside of the vacuum chamber, SiH_Four 25
sccm, H₂ 30 sccm and C ₂ H₂ 60 sccm
Introduced, high frequency power density 0.2W / cm² , Substrate temperature
At a temperature of 300 ° C, a film thickness of 500 Å is blocked.
A stop layer was formed to complete the electrophotographic photoreceptor of the present invention.

Next, the surface of the photoconductor was positively charged by corona discharge, and the dark decay characteristics were examined. Further, the surface was irradiated with halogen lamp light, and the light attenuation characteristics of the surface potential were measured. As a result, as compared with the conventional electrophotographic photosensitive member using a-Si, the dark attenuation characteristics were equivalent, and the half-exposure amount was about 1/5. In this example, the multiplication of 1.7 times was performed per one carrier multiplication layer. However, although four carrier multiplication layers were laminated in this example, the fourth layer has a small energy step and is not considered to be involved in multiplication.

Example 2 An electrophotographic photosensitive member was produced in the same manner as in Example 1 except that the optical transmission layer was not provided. However, as the carrier multiplication layer, 15 layers having a thickness of 4000 angstroms were laminated in order to have photoconductivity. Each layer is a-Si _1-x C
_The composition was appropriately changed within the range of _X : H, (x = 0 to 0.3).

The dark decay characteristics and light decay characteristics of the above-mentioned photosensitive member were measured in the same manner as in Example 1. As a result, conventional a-Si:
Compared with the photoreceptor using H, the dark attenuation characteristic was equivalent, and the half-exposure amount showing the light attenuation characteristic was about 1/15. In this example, the carrier multiplication factor per carrier multiplication layer was 1.2 times.

Although the present invention according to the two embodiments has been described in detail above, according to the idea of the present invention, the charging polarity of the electrostatic latent image is
It can also be applied to the case of negative charging. In this case, the same structure as the above may be adopted from the side of the conductive support. The carrier multiplication layer may have a band structure having an energy step required for ionization on the valence band side and a small energy step on the conduction band side so that holes are multiplied.

In the embodiment of the present invention, a-Si: H
And a-Si _x C _{1-x and the} like, the materials are not limited to these materials.

[0042]

According to the present invention, a novel structure in which a charge injection blocking layer, a photoconductive layer and a layer for multiplying photocarriers generated in the photoconductive layer are provided on a conductive support, that is, The charge injection blocking layer-photoconductive layer-carrier multiplication layer-charge injection blocking layer can provide a highly sensitive electrophotographic photoreceptor.

Further, as another effect of the present invention, by increasing the sensitivity, the thickness of the photoconductor layer can be reduced, and not only production problems such as film peeling are alleviated but also cost reduction is achieved. You can expect an effect.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of a layer structure of an electrophotographic photosensitive member of the present invention.

FIG. 2 is a band diagram showing an example of energy levels when the electrophotographic photosensitive member of the present invention is not charged.

FIG. 3 is a conceptual diagram showing a configuration of a glow discharge decomposition device.

FIG. 4 is a band diagram showing an example of energy levels during charging of the electrophotographic photosensitive member of the present invention.

FIG. 5 is a band diagram showing another example of energy levels of the electrophotographic photosensitive member of the present invention when it is not charged.

[Explanation of symbols]

 11 conductive support 12 charge injection blocking layer 13 photoconductive layer 14 carrier multiplication layer 15 charge injection blocking layer 22 charge injection blocking layer 23 photoconductive layer 24 carrier multiplication layer 25 charge injection blocking layer 30 substrate 31 vacuum chamber 32 Anode electrode 33 Cathode electrode 34 Heater 35 High frequency power supply 36 Gas introduction tube 37 Exhaust device 52 Charge injection blocking layer 53 Photoconductive layer 54 Carrier multiplication layer 55 Charge injection blocking layer

Claims (6)

[Claims] 1. An electrophotographic photosensitive member comprising: a charge injection blocking layer on a conductive support; and a carrier multiplication layer multiplying at least carriers on the charge injection blocking layer. body. 2. An electrophotographic photoreceptor comprising a photoconductive layer between the charge injection blocking layer and the carrier multiplication layer of the electrophotographic photoreceptor according to claim 1. 3. An electrophotographic photoreceptor having a charge injection blocking layer provided on the carrier multiplication layer of the electrophotographic photoreceptor according to claim 1. 4. The carrier multiplication layer has a minimum forbidden band width Eg1.
4. The structure according to claim 1, further comprising an energy level having at least one step-back structure that causes an energy step E on the conduction band side after continuously changing from the maximum band gap Eg2 to Eg2. The electrophotographic photosensitive member described. 5. The energy step E is a minimum forbidden band width Eg.
The electrophotographic photosensitive member according to claim 4, which has an ionization energy of carrier or more in the layer having 1. 6. The energy step E is a minimum forbidden band width Eg.
The electrophotographic photosensitive member according to claim 4, wherein the electrophotographic photosensitive member is larger than 1.