JPS61126559A - Photoconductive material - Google Patents

Abstract

PURPOSE:To prevent residual potential on the surface of a photosensitive body and dielectric breakdown due to developing bias by laminating the first charge injection preventive layer made of an amorphous silicon carbide on a conductive substrate, on this layer the second charge injection preventive layer made of an amorphous silicon nitride, and on this layer a photoconductive layer made of an amorphous silicon. CONSTITUTION:The photoconductive material 1 is composed of the conductive substrate 2, the charge injection preventive layer 3 made of an amorphous silicon carbide contg. an element of group IIIa or Va of the periodic table in an amt. of 1X10<-4>-1.0 atomic % formed on the substrate 2, the 5-40mum thick second charge injection preventive layer 4 made of an amorphous silicon nitride contg. said element in an amt. of 1X10<-4> atomic % formed on the layer 3, the first photoconductive layer 5 made of an amorphous silicon contg. said element in an amt. of 1X10<-8>-1X10<-4> atomic % formed on the layer 4, and a 500Angstrom -5mum thick surface coat layer 6 made of an amorphous silicon carbide, silicon nitride, or silicon oxide formed o the layer 5 for enhancing chemical stability.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a photoconductive member that is sensitive to light (electromagnetic waves ranging from ultraviolet to visible, infrared, X-rays, gamma rays, etc.).

[Technical background of the invention and its problems]

Photoconductive materials constituting photoconductive layers in solid-state imaging devices, electrophotographic photoreceptors, etc. have a high specific resistance in the dark (usually 1013Ω1 or more) due to the purpose of use, and have a low specific resistance when irradiated with light. It must have the following characteristics.

Here, taking electrophotography as an example, its principle and conditions necessary for a photoreceptor will be briefly explained. In electrophotography, the surface of a photoreceptor is charged by spreading electric charge through corona discharge. Next, when the photoreceptor is irradiated with light, pairs of electrons and holes are created, and one of them neutralizes the surface charge. For example, if it is positively charged.

Among the pairs created by the light irradiation, the electrons are neutralized and a positively charged latent image is formed on the surface of the photoreceptor. Visualization is achieved by attracting black powder called toner, which is charged with the opposite sign to the charge on the surface of the photoreceptor, to the surface of the photoreceptor using Coulomb force. At this time, even if there is no charge on the surface of the photoreceptor, an electric field is generated between the photoreceptor and the developer in the opposite direction to the electric field due to the charges in order to avoid toner being attracted to the photoreceptor due to the toner's charge. - Processing is done to increase the potential of the developing device. This is called developing bias.

The above is the principle, but next we will describe the conditions necessary for a photoreceptor: firstly, the charge charged by corona discharge is retained until light irradiation, and secondly, the electrons and holes generated by light irradiation must be maintained until light irradiation. For example, one of the pairs neutralizes the surface charge without recombining, and the other one reaches the support of the photosensitive layer in a short time.

Conventionally, amorphous chalcogenide materials have been used to form photoconductive layers in photoconductive members. Amorphous chalcogenide materials are excellent photoconductive materials that can easily be made into large-area materials, but the edges of the light absorption region range from the visible region to near the ultraviolet region, so they are practically limited to the visible region. Due to its low photosensitivity and low hardness, it has several problems when applied to electrophotographic photoreceptors, including short life.

Amorphous silicon is a photoconductive material that has recently attracted attention due to these problems (hereinafter referred to as a-5i).
), a-5i has a wide absorption wavelength range and is fully colorimetric (Pa
nchromatic) and has high photosensitivity.

Furthermore, a-5i has high hardness, and when applied to electrophotographic photoreceptors, it is expected to have a lifespan 10 times longer than conventional ones. Furthermore, a-5i has many advantages such as being harmless to the human body and being inexpensive and easily large-sized when compared with single-crystal silicon.

However, a-5i has a specific resistance of less than C in the dark.

Since the dark resistance (referred to as dark resistance) is usually as low as about 10@Ωc11 to 10 IOΩ, an electrophotographic photoreceptor that forms an electrostatic latent image cannot retain charges on its surface. Therefore, in an example where a-5i is applied to electrophotography, between the amorphous silicon photosensitive layer and the support,
Attempts have been made to prevent carrier injection from the support by interposing silicon nitride, silicon carbide, silicon oxide, or the like.

However, if this attempt was made to increase the thickness of the a-5i layer with high resistivity, it would block the passage of carriers flowing from the overlying a-5i layer to the support, resulting in a higher residual potential. This problem arises. Further, if the thickness of the a-5i layer having a high specific resistance is made small, it becomes impossible to provide sufficient potential holding ability, and there are also disadvantages in that dielectric breakdown occurs due to development bias.

On the other hand, there is also a method of providing a semiconductor film having P-type or n-type conductivity between the conductive substrate and the photoconductive layer. Usually, P-type or n-type amorphous silicon heavily doped with boron (8) or phosphorus (P) is used. Such a layer is called a charge injection prevention layer. The ability to prevent charge injection in this layer can be improved by doping a large amount of B or P, but such a film has a large internal strain, and if a film with a different strain is stacked on top of it, the film will peel off. It has a defect. Furthermore, light absorption in amorphous silicon occurs over a wide wavelength range, and the absorption gradually decreases even near the light absorption edge. That is, from 700n+m to 8
In the wavelength range of 00 nm, absorption decreases but does not become zero.
It absorbs a small amount.

When a photoconductive layer is made of such a material, if the photoconductive layer is thick as in an electrophotographic photoreceptor, long-wavelength light is absorbed even in areas close to the base of the photoconductive layer. Since the mobility of amorphous silicon, along with electrons and holes, is not very high, carriers generated at a distance from the surface of the photoreceptor due to exposure tend to remain. Electrophotographic equipment has a process called static elimination that removes the charge remaining on the surface of the photoreceptor after forming an image, but when this is done by light irradiation, the carriers in the film that remain are removed due to the above-mentioned reasons. This neutralizes the surface charge caused by charging the surface of the photoreceptor to obtain the next image. Therefore, a problem arises in that the charging ability immediately after exposure is much lower than the charging ability after being left in the dark.

[Purpose of the invention]

The present invention has been made based on the above circumstances, and does not generate residual potential on the surface of the photoreceptor.

It is an object of the present invention to provide a photoconductive member that has high potential holding ability and charging ability and does not cause dielectric breakdown due to development bias.

[Summary of the invention]

In order to achieve the above object, the present invention provides a photoconductive member in which a charge injection prevention layer, a photoconductive layer and a surface coating layer are formed on a conductive support in this order. In between, either one of the Ma group element or the Va group element is added from 1xio-4 to 1. Oato■ic
A first charge injection prevention layer made of amorphous silicon carbide containing % is laminated, and further on this first charge injection prevention layer, the film thickness is 5μl to 40μ−, and the periodic table ma
1×10 of either group element or Va group element
A second charge injection prevention layer made of amorphous silicon nitride containing 1.times.-" to 1.times.108 atomic percent is stacked.

It is characterized in that a second charge injection prevention layer made of amorphous silicon nitride is laminated.

[Embodiments of the invention]

The present invention will be described below based on an embodiment shown in the drawings. In the figure, (1) is a photoconductive member used, for example, as an electrophotographic photoreceptor. This photoconductive member (1) is laminated on a flat plate-shaped or drum-shaped conductive support (2), and contains elements of group Ma or group Va of the periodic table.
1. A first charge injection prevention layer (3) made of amorphous silicon carbide containing Oatoi + ic%, and a group IIIa element or V
Any one of the group a elements I X 10-8 ~ L X
A second charge injection prevention layer (4) having a thickness of 5 μm to 40 μm and made of amorphous silicon nitride containing 10-' atomic%.
and laminated on this second charge injection prevention layer (4),
Group 111a element or Va group element of the periodic table at 1×10−
A photoconductive layer (5 μm) with a film thickness of 0.5 μm to 5 μ− made of amorphous silicon containing 1×10′″’ atomic%
), and a surface coating layer (6) in which amorphous silicon carbide, silicon nitride, or silicon oxide with a thickness of 500 A to 5 μm is laminated on the photoconductive layer (5) to further improve chemical stability. It consists of

Next, each layer will be explained. First, the thickness of the first charge injection prevention layer (3) may be 5 μm;
) When used with a charged surface, the film thickness is set to vary depending on how much surface potential is to be obtained. Also,
The amorphous silicon laminated as the photoconductive layer (5) has a high absorption coefficient over a wide wavelength range, and sufficient sensitivity can be obtained with the above film thickness.

Further, the surface coating layer (6) is preferably doped with an element of group 1a of the synchronous table in order to increase the mobility of electrons.

On the other hand, the second charge injection prevention layer (4) plays a supplementary role to the first charge injection prevention layer (3).

It is amorphous silicon nitride, which has an optical bandgap slightly wider than that of the first charge injection prevention layer (3) and also has a high specific resistance.

Next, a method for forming a photoconductive member of the present invention based on the above structure will be explained. First, the conductive support (2) is attached to a vacuum reaction chamber (not shown), and a mechanical booster pump (not shown) and an oil rotary pump (not shown)
A vacuum state of ~10 −4 Torr is established. At this time, the support (2) is maintained at a temperature of 100°C to 400°C.

Next, a gas containing Si atoms, for example 5iF, is added to one reaction chamber.
14. A gas such as SiH6 or SiF4 is introduced, but in order to form a film of amorphous silicon carbide used for the first charge injection prevention layer (3), CO4. Mix hydrocarbons such as cna. In addition, N2. N.H.
It is sufficient to mix 3 grade gases. At this time, the optical bandgap can be changed by changing the gas mixture ratio.

Furthermore, periodic table T used as one surface coating layer (6)
For doping with Group IIa or Va elements, [32
H6+ BF3. Alternatively, this can be achieved by mixing gases such as PH3 and PFs.

Such a gas is introduced into the reaction chamber based on the composition of each layer, and the exhaust speed is adjusted so that the pressure is approximately 0.1 to 3 Torr.

Next, a film can be formed on the support (2) by applying high frequency power between electrodes installed so that plasma is generated around the support (2).

Therefore, an example will be described in which the film is laminated onto, for example, an A1 cylindrical support using the above-mentioned film forming method to form an electrophotographic photoreceptor. First, boron (B) is placed on the conductive support (2) at I x 10
A first charge injection prevention layer (3) made of amorphous silicon carbide doped with -3at, owic% is laminated to a thickness of 0.5 μm. This first charge injection prevention layer (3) is doped with a large amount of boron (B), has a low specific resistance, and has an optical band gap of about 1.7 eV.

Next, the second charge injection prevention layer (4) is made by adding boron (B) to I
Amorphous silicon nitride doped with X 10-6at and omic% is laminated to a thickness of 25 μm. This second charge injection prevention layer (4) can be obtained close to the intrinsic region by doping with a small amount of boron (B), has a high specific resistance of 1013 Ωcm or more, and has an optical band gap of 1.
, about 75 eV, the first charge injection prevention layer (3)
It becomes wider.

Next, photoconductive material M(5) is formed by laminating amorphous silicon to a thickness of about 5 μm. This photoconductive layer (5) may not be doped, but may be doped with boron (B) at 1×10-' atoms.
By doping to about ic%, the mobility of holes increases, and a more preferable result can be obtained.

Further, this layer has an optical band gap of about 1.55 eV and can absorb light over a wide wavelength range.

Furthermore, the surface coating layer (6) has an optical band gap of 2.
．． Amorphous silicon carbide having a resistivity of 2 eV and a specific resistance of about 1014 Ωcm is laminated to a thickness of 1 μm. This surface coating layer (6
) may be about 0.1 μm, but if it is thicker than 5 μI, the residual potential will only increase a little, and the charging ability in the dark will be improved and it will be chemically stable. It has the advantage of

Also, boron (B) is I X I O-'aton+ic
% doping increases the mobility of electrons, so doping is also effective.

When the photoconductive member treated in this manner is used as an electrophotographic photoreceptor, a surface potential of 700 V or more can be obtained under the condition that the inflow current from the corona charger to the photoreceptor is 0.4 μc/cal, and charging takes 15 seconds. The potential retention rate after is 8
It has good electrostatic properties of 0%.

Although the photoconductive member described above is applied to a positively charged electrophotographic photoreceptor, a negatively charged electrophotographic photoreceptor can be obtained by replacing the doped boron (B) with phosphorus (P). In other words, the gases mixed during film formation are changed from B2 IIIa to PH
3, and the other conditions are the same as above. The photoconductive member thus prepared has charging ability and potential holding ability under the same conditions as above except that the polarity of the voltage applied to the corona charger is changed.

〔Effect of the invention〕

As explained above, according to the present invention, no residual potential is generated on the surface of the photoconductive member, and the photoconductive member has excellent potential holding ability and charging ability, and does not cause dielectric breakdown due to development bias. It is effective.

[Brief explanation of the drawing]

The drawing is a schematic diagram of a photoconductive member showing an embodiment of the present invention.

Claims (3)

[Claims] (1) In a photoconductive member formed by laminating a first charge injection prevention layer, a second charge injection prevention layer, a photoconductive layer, and a surface coating layer on a conductive support, the first charge injection prevention layer described above is provided. The layer contains 1 x 10 ^-^ of group IIIa elements or group Va elements of the periodic table.
The second charge injection prevention layer is made of amorphous silicon carbide containing 4 to 1.0 atomic%, and has a thickness of 5 to 40 μm.
μm, Group IIIa element or Va group element of the periodic table is 1×
It is made of amorphous silicon nitride containing 10^-^4 to 1 x 10^-^8 atomic%, and the photoconductive layer is an amorphous silicon layer with a film thickness of 0.5 μm to 5 μm. A photoconductive member. (2) The photoconductive member contains Group IIIa elements of the periodic table or Va.
The photoconductive member according to claim 1, characterized in that it contains a group element. (3) The light according to claim 1, wherein the surface coating layer is made of amorphous silicon carbide having a thickness of 0.05 μm to 5 μm and a specific resistance of 10^1^3 Ωcm or more. conductive member.