JPH0572780A - Electrophotographic sensitive body - Google Patents

Abstract

PURPOSE:To enhance sensitivity by forming a carrier multiplying layer between a first conductive electric charge injection barrier layer and a second barrier layer. CONSTITUTION:The first conductive charge injection barrier layer 14, a photoconductive layer 12, and the second barrier layer 15 are successively laminated on a conductive substrate 11, and when this laminate is irradiated with light, light carriers generated in the photoconductive layer 12 transfer toward the layer 14. This layer 14 comprises a layer changing from a narrow forbidden band to a wide forbidden band, and a layer having energy level difference between the widest forbidden band in the wide forbidden bands and the following the narrowest forbidden band in the narrow forbidden bands, and stepback structure. When this energy level difference is equal to the ionization energy of the carriers or higher than this, transferred carriers are ionized and multiplied, and arrived at the surface of the photosensitive body to neutralize charge.

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,
There are known a photosensitive body in which amorphous Se is doped with impurities such as As, Te, Sb and Bi, and a photosensitive body 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 photoconductor using the above-mentioned material has been advanced. 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, the dark resistance is small due to hopping conduction, and the photoconductivity is small due to defects.
Not suitable as an electrophotographic photosensitive material. On the other hand, hydrogenated amorphous Si (hereinafter abbreviated as a-Si: H) whose dangling bonds are terminated by hydrogen atoms has a dark resistance
It is slightly larger 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 that makes use of such photoelectric properties of a-Si: H and has high dark resistance, a-Si: H, which is a photoconductive layer, is laminated on a charge injection blocking layer made of a-SiC. Configuration (for example, JP-A-57-17952),
Examples thereof include O-, C-, N-, etc. added to a-Si: H, which is a photoconductive layer (for example, JP-A-56-64347).

[0004]

However, in the above-mentioned conventional hydrogenated amorphous Si, since the dark resistance is slightly small as described above, the impurities such as O, C and N are contained, Attempts have been made to further increase the dark resistance, but the presence of impurities reduces the photoconductivity, making it difficult to achieve high sensitivity. 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 by improving the above-mentioned disadvantages of the prior art.

[0005]

SUMMARY OF THE INVENTION To achieve the above object, the present invention provides a first charge injection blocking layer having a first conductivity type on a conductive support, and a first conductivity type. A second charge injection blocking layer having a second conductivity type different from that, and a carrier multiplication layer for multiplying carriers between the first charge injection blocking layer and the second charge injection blocking layer. Further, the electrophotographic photosensitive member is provided with an optical transmission layer if necessary.

Here, the carrier multiplication layer continuously changes from the minimum forbidden band width E _g 1 to the maximum forbidden band width E _g 2,
It is configured to have an energy level formed of at least one step-back structure that causes an energy step E on the conduction band side.

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 E _g 1 and is equal to or more than the minimum forbidden band width E _g 1. It constitutes the multiplication layer.

The layer structure of the electrophotographic photosensitive member of the present invention is so-called p- (photoconductive layer)-(layer for multiplying carriers) -n.
Alternatively, n- (photoconductive layer)-(layer for multiplying carriers)
-P is a diode element structure. The stacking order is selected so that the diode element is in a reverse bias state according to the polarities of charging +/- when an electrostatic latent image is formed on the electrophotographic photosensitive member. The p and n layers are charge injection blocking layers that prevent injection of charged charges on the surface of the photoconductor into the photoconductive layer. When light is irradiated in this reverse bias state, the photocarriers generated in the photoconductive layer travel to the carrier multiplication layer that multiplies the carriers, and the carrier multiplication layer changes from a narrow bandgap to a wide bandgap. And a layer having a step back structure, which is an energy step between the composition change part that changes and the maximum forbidden band width of the wide forbidden band width and the layer of the narrowest forbidden band width of the narrowest forbidden band width. However, this energy level difference or the actual energy level difference including the reverse bias electric field is
Equal to the ionization energy of the carrier, or
When it is larger than that, the traveling carriers are ionized and multiplied. The multiplication factor can be changed by 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.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings. Example 1 FIG. 1 shows a sectional view of an electrophotographic photosensitive member according to a first example of the present invention. Reference numeral 11 is a drum-shaped conductive support such as Al, and 12 is charge injection having a first conductivity type of a-Si: H doped with a group IIIa (for example, B) of the periodic table. The blocking layer 13 is a non-doped a-Si: H and is an optical transmission layer. 14 is a multiplication layer of the carrier, a-Si: H~a-Si 1-x C x: a plurality of layers that have changed the composition of the H. Reference numeral 15 is a charge injection blocking layer having a second conductivity type and made of a-Si: H doped with Va of the periodic table (for example, P).

Of the electrophotographic photosensitive member having the structure shown in FIG.
A band diagram when the surface 15 side is not charged is shown in FIG. 22 is a first charge injection blocking layer, and 23 is a forbidden band E
An optical transmission layer 24 having _g 0, and 24 is a carrier multiplication layer, and after the forbidden band width is continuously changed from the minimum forbidden band width E _g 1 to the maximum forbidden band width E _g 2, energy is transferred to the conduction band side. The step-back structure has a step E, and a plurality of layers each having one cycle are repeated. For each energy step, if the energy step is equal to or greater than the ionization energy of the electron, the electron is ionized and
Generates hole pairs and causes a multiplication effect. The photoconductor shown in FIG. 2 has three carrier multiplication layers. It should be noted that the valence band side does not have a large energy step, unlike the conduction band side, by selecting the material configuration. Two
Reference numeral 5 is a second charge injection blocking layer.

FIG. 3 is a conceptual diagram of an apparatus for producing an electrophotographic photosensitive member according to the first embodiment, here, a glow discharge decomposition apparatus. Capacitively coupled glow discharge decomposition device 3
An anode electrode 32 and a cathode electrode 33 are installed in a vacuum chamber 31 of 0 at a predetermined distance between electrodes, a heater 34 for heating a substrate is installed in the anode electrode 32, and the substrate is on the anode electrode 32 side. Is installed in. Further, the cathode electrode 33 is connected to a high frequency power source 35, and the space between the anode electrode 32 and the cathode electrode 33 becomes a glow discharge space. The vacuum tank 31 includes gas introduction pipes 36-1, 36-
2,36-3,36-4,36-5 are connected, _{respectively, SiH 4, H 2, PH} 3, B 2 H 6, C 2 H 2 is 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 3
In 6-5, a flow rate control device (not shown) is precisely and automatically controlled so as to obtain a desired composition. Although FIG. 3 shows one film forming chamber, when forming a plurality of layers as shown in FIG. 1, a plurality of film forming chambers are provided in order to prevent contamination by each gas. May be.

The electrophotographic photosensitive member of the present invention was produced as follows using the glow discharge decomposition apparatus described above.

SiH ₄ 25 sccm, H ₂ 30 sccm
And B ₂ H _{6 2} sccm were respectively introduced into the film forming chamber, and the high frequency power density was 0.2 W / cm ² , and the substrate temperature was 300 ° C.
00Å was deposited to form a p-type first charge injection blocking layer. Next, the non-doped layer 13, which is an optical transmission layer, is covered with SiH ₄
A film having a film thickness of 10 μm was formed at 25 sccm, H ₂ 30 sccm, high frequency power density 0.2 W / cm ² , and substrate temperature 300 ° C. The forbidden band width of the formed photoconductive layer is 1.6 eV.
The dark specific resistance was 10 ¹⁰ Ω · cm or more, and sufficient photoconductivity was obtained. Next, a method for forming the carrier multiplication layer 14 will be described. SiH ₄ 25sccm, H ₂ 30scc
m, C ₂ H _{2 0 to} 100 sccm, high frequency power density 0.2 W / cm ² , and substrate temperature 300 ° C. At this time, a-Si: H~a-Si 1-x C x: to alter the composition of the H, was appropriately changed the flow rate of C ₂ H _2. As a result, the forbidden band width is the minimum forbidden band width E _g 1 = 1.
The change was from 6 eV to the maximum forbidden band width E _g 2 = 3.5 eV, and the energy level difference on the conduction band side was 1.7 eV. The number of layers in which the forbidden band width changes continuously is 500 Å per layer, and in the first embodiment, in the same manner as the three layers,
Laminated. Next, SiH ₄ 25sccm, H ₂ 30s
ccm and PH ₃ 1sccm, high frequency power density 0.2
An n-type second charge injection blocking layer of 500Å was formed under the conditions of W / cm ² and substrate temperature of 300 ° C. to complete an electrophotographic photosensitive member composed of p-i-carrier multiplication layer-n.

The electrophotographic photosensitive member prepared as described above is
When the surface of the photoconductor was positively charged by corona discharge and the dark decay of the surface potential was observed, the same characteristics as those of the conventional electrophotographic photoconductor using a-Si: H were shown. FIG. 4 shows a band diagram when the surface is positively charged. As shown in FIG. 4, a band diagram equivalent to the so-called reverse bias state of the p-i-carrier multiplication layer-n is obtained. Light enters from the second charge injection blocking layer 25 side, and a part of the incident light is absorbed according to the light absorption coefficient of each of the second 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 generates electron-hole pairs, and the electric field causes the holes to travel to the first charge injection blocking layer 22 and the conductive support 11 such as Al (not shown). On the other hand, the electron travels through the band slope portion toward the carrier multiplication layer 24 and then reaches an energy step, that is, a step back portion, and thereafter, due to the energy step and the electric field, the energy is equal to or larger than the ionization energy. Are given, and impact ionization is performed to generate electron-hole pairs. This process is repeated for the number of step backs, and the electrons are multiplied. As a result, in the first embodiment, it is ideally multiplied by 2 ³ times. still,
Holes have no multiplication effect because they do not give enough energy to be ionized. After this, ideally 2 ³
The doubled electrons move to the surface side, neutralize the surface charge, and the surface potential is photo-attenuated. From the above, in this case, compared with the conventional electrophotographic photosensitive member having no multiplication effect,
^With the incident light of ³ , the same optical attenuation of the surface potential as before is expected. That is, the sensitivity is equivalent to 2 ³ times.

Then, the positively charged surface of the photosensitive member was irradiated with halogen lamp light, and the light attenuation characteristic of the surface potential was measured. The half-exposure amount was compared with the conventional electrophotographic photosensitive member using a-Si. And it became about 1/5. That is,
This means that the carrier multiplication layer has been multiplied by 1.7 times per layer. Example 2 The second example of the present invention is an example in which the short wavelength spectral sensitivity of the electrophotographic photosensitive member is increased. As in the first embodiment, the structure is a p-i-carrier multiplication layer-n from the conductive support side, and the charging polarity when forming an electrostatic latent image on the photoconductor is positive.
Therefore, the layer structure is similar to that shown in FIG. FIG. 5 shows a band diagram when the second embodiment of the present invention is not charged. The first charge injection blocking layer 52 is made of a-Si _x.
C _1-x : H is a p-layer in which B ₂ H ₆ is doped, the photoconductive layer 53 is also a-Si _x C _1-x : H, and the first charge injection blocking layer 52 and the photoconductive layer are The forbidden band width of 53 was set to the same 2.2 eV. The carrier multiplication layer 54 is made of the same material as in the first embodiment. The second charge injection blocking layer 55 is also an n layer obtained by doping a-Si _x C _1-x : H with PH ₃ and has a forbidden band width of the first charge injection blocking layer 52 and the photoconductive layer 53. Almost the same. The photoconductor was prepared in the same manner as in Example 1 except that the flow rate of C ₂ H ₂ was changed to 1 part. When the dark decay characteristics and the light decay characteristics of this electrophotographic photosensitive member were measured in the same manner as in Example 1, the dark decay characteristics were excellent as compared with Example 1, and the half-exposure amount of the light decay characteristics was Example 1
Similarly, the carrier multiplication factor per layer is about ⅕ compared to the conventional one, and the multiplication factor is about 1.7 times. Further, the spectral sensitivity was shifted to the shorter wavelength side of 100 to 200 nm as compared with Example 1. Regarding the dark decay characteristics, it is assumed that the above-mentioned difference in characteristics is due to the improvement of the blocking characteristics due to the increase of the forbidden band width of the charge injection blocking layer and the increase of the dark resistance due to the increase of the forbidden band width of the optical transmission layer. ..

The present invention has been described above with reference to the two embodiments for the case where the charging polarity of the electrophotographic photosensitive member is made positive when the latent image is formed. However, the present invention is also realized when the charging polarity is negative. Of course. When the charging polarity at the time of latent image formation is made negative, the structure is such that the n-i-carrier multiplication layer-p layer is laminated in this order from the conductive support side. Further, 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.

Further, in the embodiment of the present invention, the i layer which is the optical propagation layer is provided. However, in order to have a function as the optical propagation layer in the carrier multiplication layer, the film thickness of each layer of the carrier multiplication layer is increased. May be increased and the total film thickness may be increased so that the i layer is not formed.

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.

[0019]

According to the present invention, the first member is provided on the conductive support.
A first charge injection blocking layer having a second conductivity type, a second charge injection blocking layer having a second conductivity type, and a first charge injection blocking layer and a second charge injection blocking layer. A novel structure in which a photoconductive layer and a carrier multiplication layer for multiplying photocarriers generated in the photoconductive layer are provided between the two layers, that is, a p-i-carrier multiplication layer-n provides a high-sensitivity electrophotographic photosensitivity. Can provide the body.

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 can be alleviated but also cost reduction effect can be obtained. Can be expected.

[Brief description of drawings]

FIG. 1 is a 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 First Charge Injection Blocking Layer 13 Photoconductive Layer 14 Carrier Multiplying Layer 15 Second Charge Injection Blocking Layer 22 First Charge Injection Blocking Layer 23 Photoconductive Layer 24 Carrier Multiplying Layer 25 Second charge injection blocking layer 31 Vacuum chamber 32 Anode electrode 33 Cathode electrode 34 Heater 35 High frequency power supply 36 Gas introduction tube 37 Exhaust device 52 First charge injection blocking layer 53 Photoconductive layer 54 Carrier multiplication layer 55 Second charge Injection blocking layer

Claims (5)

[Claims] 1. A first charge injection blocking layer having a first conductivity type on a conductive support, and a second charge injection blocking layer different from the first conductivity type.
A second charge injection blocking layer having a conductivity type of
2. An electrophotographic photosensitive member comprising a carrier multiplication layer for multiplying carriers at least between the charge injection blocking layer and the second charge injection blocking layer. 2. The electrophotographic photosensitive member according to claim 1, wherein a photoconductive layer and a carrier generated in the photoconductive layer are multiplied between the first charge injection blocking layer and the second charge injection blocking layer. An electrophotographic photosensitive member, which is provided with a carrier multiplication layer. 3. The carrier multiplication layer has a minimum forbidden band width E._g 1
To maximum forbidden band width E _g After continuously changing to 2, the conduction band
Energy step E on the side, at least one or more
Have an energy level consisting of a step-back structure
The electrophotographic photosensitive member according to claim 1 or 2, wherein the electrophotographic photosensitive member is configured according to claim 1. 4. The energy step E has a minimum forbidden band width E _g.
The electrophotographic photosensitive member according to claim 3, which has an ionization energy of carrier or more in the layer having 1. 5. The energy step E has a minimum forbidden band width E _g.
The electrophotographic photosensitive member according to claim 3, wherein the electrophotographic photosensitive member is larger than 1.