BACKGROUND OF THE INVENTION
[0001] This invention relates to an electrophotographic photosensitive member, and particularly
to an electrophotographic photosensitive member with excellent electrostatic charge
acceptance for laser printers.
[0002] The conventional electrophotographic photosensitive member has a basic structure
of a photoconductive layer and a surface protective layer, successively laid one upon
another on an electroconductive support, where inorganic photoconductive materials
such as Se, CdS, As₂Se₃, etc. or organic photoconductive materials such as PVC
z-TNF, etc. have been used in the photoconductive layer. These inorganic and organic
photoconductive materials are not always satisfactory in heat resistance and durability.
Heretofore, amorphous Si containing hydrogen, which will be hereinafter abbreviated
to a-Si:H, has been proposed as a photoconductive material and has excellent heat
resistance and a high hardness, and thus has excellent durability, but the volume
resistivity of ordinary a-Si:H film is as low as about 10¹⁰ Ω·cm, which is too low
to obtain a satisfactory electrostatic charge acceptance. Thus, it has been proposed
to dope the a-Si:H film with boron or to add carbon, nitrogen or oxygen to the a-Si:H
film in order to increase the volume resistivity, or it has been proposed to add an
element of Group III or V of the Periodic Table to the a-Si:H film in order to control
the conduction type and increase the electrostatic charge acceptance [Japanese Patent
Application Kokai (Laid-open) No. 58-88115]. In case of a photosensitive member for
positive electrostatic charging, it has been proposed to locally increase the boron
doping concentration in the photoconductive layer, that is, to make the boron doping
concentration higher in the region near the substrate in order to suppress the charge
injection from the substrate.
[0003] On the other hand, the surface protective layer provided on the surface of the photoconductive
layer is a layer of high volume resistivity, which is directed to an increase in the
moisture resistance and corona resistance as well as to a prevention of charge injection
from the surface of the photosensitive member. When the thickness of the surface protective
layer is increased to improve the electrostatic charging characteristics of the photosensitive
member such as an electrostatic charge acceptance, dark decay, etc., the residual
potential after light exposure will be increased. Thus, the thickness of the surface
protective layer must take such a value as to satisfy the electrostatic charge acceptance
and the dark decay as well as the residual potential.
[0004] It has been also proposed that the surface protective layer is in a double layer
structure, that is, a moisture and corona-resistant layer as an upper layer and a
charge injection blocking layer as a lower layer in order to increase the moisture
resistance and corona resistance of the surface protective layer. The electrostatic
charge acceptance and the dark decay, and the residual potential cannot be readily
balanced owing to the influence of the charge injection blocking layer.
[0005] An electrophotographic photosensitive member comprising a photoconductive layer of
a-Si:H:B (4 ppm) of intrinsic conduction, a charge injection blocking layer of a-Si:H:B
(100 ppm) of p-type conduction, and a moisture and corona-resistant layer of a-SiN,
laid one upon another on an aluminum support is disclosed in J. Appl. Phys. Vol. 55,
No. 8, 3197-3198 (1984), where the conduction type of the charge injection blocking
layer is different from that of the photoconductive layer, but the optical band gap
of the charge injection blocking layer is equal to that of the photoconductive layer,
and the blocking ability of the charge injection blocking layer is small because of
the equal optical band gaps, and thus the quantity of light into the photoconductive
layer is smaller and the photosensitivity of the photosensitive member is lowered.
SUMMARY OF THE INVENTION
[0006] An object of the present invention is to provide an electrophotographic photosensitive
member with excellent electrostatic charging characteristics, where the electrostatic
charge acceptance and dark decay are increased, while suppressing a residual potential
increase.
[0007] The present invention provides an electrophotographic photosensitive member, which
comprises an electroconductive support, a photoconductive layer made from hydrogen-containing
amorphous silicon as a matrix, a charge injection blocking layer having a different
conduction type from that of the photoconductive layer and having a broader optical
band gap than that of the photoconductive layer, and a moisture and corona-resistant
layer, laid one upon another successively on the electroconductive support.
[0008] Different conduction type of the charge injection blocking layer from that of the
photoconductive layer means that when the photoconductive layer is of p-type, the
charge injection blocking layer is of n-type or intrinsic type, and when the photoconductive
layer is of n-type, the charge injection blocking layer is of p-type or intrinsic
type.
[0009] In order to improve the electrostatic charge acceptance and dark decay without increasing
the residual potential, it is necessary to transfer the charges generated in the photoconductive
layer by irradiation of light to the region near the surface of the photosensitive
member. Thus, it is necessary that the charge injection blocking layer provided on
the photoconductive layer has a high mobility of charges with a reversed polarity
to the polarity of the charges on the surface of the photosensitive member. On the
other hand, when the charges are injected from the surface of the photosensitive member,
it is desirable that the charge injection blocking layer has a low mobility of such
charges. That is, the charge injection blocking layer has a function to block the
charges with the same polarity as that of charges on the surface of the photosensitive
member.
[0010] For example, when the surface of the photosensitive member is plus (+) charged,
the charge injection blocking layer on the photoconductive layer must be of n-type,
whereas, when the surface of the photosensitive member is minus (-) charged, the charge
injection blocking layer must be of p-type.
[0011] It is desirable that the photoconductive layer is of p-type in case of plus (+) charging,
and of n-type in case of minus (-) charging, and thus the charge injection blocking
layer provided on the photoconductive layer must have a different conductivity type
from that of the photoconductive layer. That is, when the photoconductive layer is
of p-type, the charge injection blocking layer provided thereon must have a conductivity
type of n-type or intrinsic type, and when the photoconductive layer is of n-type,
the charge injection blocking layer provided thereon must have a conductivity type
of p-type or intrinsic type. When the photoconductive layer is of intrinsic conduction
type, that is, when both plus (+) and minus (-) carriers have a high mobility, the
charge injection blocking layer provided on the photoconductive layer must be of n-type
in case of plus (+) charging and of p-type in case of minus (-) charging.
[0012] In order to allow light to go into the photocnductive layer, the charge injection
blocking layer provided on the photoconductive layer must have a broader optical band
gap than that of the photoconductive layer.
[0013] Thus, the charge injection blocking layer provided on the photoconductive layer must
be a film capable of controlling the p-n conduction type and having a broader optical
band gap.
[0014] As a result of extensive studies, the present inventors have found that a film of
hydrogen-containing amorphous SiC (a-SiC:H) is preferable as the charge injection
blocking layer. The a-SiC:H film has a broader band gap, i.e. 1.9 eV - 2.0 eV, than
those of a-Si:H (optical band gap: 1.8 eV) or a-SiGe:H (hydrogen-containing amorphous
SiGe; optical band gap: 1.5 eV), used as the photoconductive layer. The a-SiC:H film
is of n-type, when not doped with an impurity such as B, and has a high electron mobility,
but the hole mobility is not so high. The film, when doped with a small amount of
boron, has a high hole mobility, but the electron mobility is decreased, and the conduction
type of the film turns from n-type to p-type through the intrinsic type. That is,
the conduction type of the electron injection blocking layer can be changed from the
n-type to the p-type through the intrinsic type by doping with B.
[0015] On the other hand, when the film is doped with a small amount of phosphorus, the
electron mobility of the film is increased; i.e. the n-type conduction of the film
increases.
[0016] As the charge injection blocking layer provided on the electroconductive layer, a-SiC:X:H
film where X is a halogen atom, (halogen and hydrogen containing amorphous SiC; optical
band gap: 1.9 eV - 2.0 eV) or a-SiN:X:H film, where X is a halogen atom (halogen and
hydrogen containing amorphous SiN; optical band gap: 1.9 eV or more) can be used in
place of the a-SiC:H film as the charge injection blocking layer provided on the photoconductive
layer. The effect of halogen atom is an increase in the durability, that is, less
susceptibility to optical fatigue.
[0017] By providing a charge injection blocking layer having a different conduction type
from that of a photoconductive layer on the photoconductive layer, injection of charges
from the surface of the photosensitive member can be suppressed, and the charges can
be readily transferred from the photo conductive layer, and thus an electrophotographic
photosensitive member with a lower residual potential and better dark decay and charge
acceptance can be obtained. By using a charge injection blocking layer having a broader
optical band gap than that of the photoconductive layer, the photoconductive layer
can be thoroughly irradiated with light, and a higher photosensitivity can be obtained.
[0018] In order to improve the moisture and corona resistance of an electrophotographic
layer, an a-SiC:H film having a higher carbon content or an a-C film is desirably
provided as a moisture and corona-resistant layer on the surface of the charge injection
blocking layer.
[0019] Furthermore, a charge blocking layer can be provided between the support and the
photoconductive layer. The charge blocking layer can be made of the same material
as used in the charge injection blocking layer.
[0020] Films of the charge blocking layer, photoconductive layer, charge injection blocking
layers and the moisture and corona blocking layer can be formed on the electroconductive
support one upon another successively by CVD including plasma CVD, photo CVD, thermal
CVD and ECR microwave CVD, by sputtering or by vapor deposition, and the individual
films can be also formed by any combination of these forming procedures.
[0021] The individual layers desirably have a thickness as given below:
The charge blocking layer : 0.5 - 3µm
The photoconductive layer : 20 - 50 µm
The charge injection blocking layer: 0.5 - 3 µm
The moisture and corona-resistant layer: 0.2 - 1 µm
[0022] Furthermore, the photoconductive layer can be of a double structure of different
materials, i.e. a lower photoconductive layer of e.g. a-Si:H film and an upper photoconductive
layer of e.g. a-SiGe:H film.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023]
Figs. 1, 4 and 7 are cross-sectional profiles of the present electrophotographic photosensitive
members.
Figs. 2 and 5 are diagrams showing a relationship between the thickness of charge
injection blocking layer and dark decay of the photosensitive member.
Figs. 3 and 6 are diagrams showing a relationship between the thickness of charge
injection blocking layer, and the electrostatic charge acceptance or the residual
potential of the photosensitive member.
PREFERRED EMBODIMENTS OF THE INVENTION
[0024] The present invention will be described in detail below, referring to Examples and
the drawings, which are not limitative of the present invention.
Example 1
[0025] An electrophotographic photosensitive member having a cross-sectional profile as
shown in Fig. 1 was prepared.
[0026] As aluminum drum whose outer surface was polished to the mirror surface degree was
fixed as an electroconductive support
1 in a vacuum chamber, which was evacuated to about 1x10⁻⁶ Torr. Then, a gas mixture
of monosilane (SiH₄), ethylene (C₂H₄) and hydrogen (H₂) was introduced at a pressure
of 0.5 Torr into the vacuum chamber in a gas ratio, (SiH₄ + C₂H₄)/(H₂ + SiH₄ + C₂H₄),
of 0.6 and a gas ratio, C₂H₄/(SiH₄ + C₂H₄), of 0.05. Diborane (B₂H₆) was introduced
thereto to make a gas ratio, B₂H₆/(SiH₄ + C₂H₄), of 1x10⁻⁴. The aluminum drum
1 was kept at 250°C and an a-SiC:H film was formed to a thickness of 1 µm as a charge
blocking layer
2 on the aluminum drum
1 by high frequency glow discharge at 13.56 MHz and a power of 300 W.
[0027] Successively, a gas mixture of SiH₄, H₂ and B₂H₆ was introduced at a pressure of
0.5 Torr into the vacuum chamber in a gas ratio, SiH₄/(SiH₄ + H₂), of 0.6 and a gas
ratio, B₂H₆/SiH₄, of 3x10⁻⁶. The aluminum drum
1 was kept at 250°C, and an a-Si:H film was formed to a thickness of 20 µm as a lower
photoconductive layer
3 on the charge blocking layer
2 by high frequency glow discharge at 13.56 MHz and a power of 300 W.
[0028] Then, a gas mixture of SiH₄, GeH₄ and H₂ was introduced at a pressure of 0.5 Torr
into the vacuum chamber in a gas ratio, (SiH₄ + GeH₄)/(H₂ + SiH₄ + GeH₄), of 0.6 and
a gas ratio, GeH₄/(SiH₄ + GeH₄), of 0.2. Furthermore, B₂H₆ was introduced thereto
to make a gas ratio, B₂H₆/(SiH₄ + GeH₂), of 1x10⁻⁶. The aluminum drum
1 was kept at 250°C, and an a-SiGe:H film was formed to a thickness of 1 µm as an upper
photoconductive layer
4 on the lower photoconductive layer
3 by high frequency glow discharge at 13.56 MHz and a power of 300 W (optical band
gap: 1.5 eV; conduction type: p-type).
[0029] Then, a gas mixture of SiH₄, C₂H₄ and H₂ was introduced at a pressure of 0.5 Torr
into the vacuum chamber in a gas ratio, (SiH₄ + C₂H₄)/(H₂ + SiH₄ + C₂H₄), of 0.6 and
a gas ratio, C₂H₄/(SiH₄ + C₂H₄), of 0.05, and an a-SiC:H film was formed to a thickness
of 0 to 3 µm as a charge injection blocking layer
5 on the upper photoconductive layer
4 by high frequency glow discharge at 13.56 MHz and a power of 300 W (optical band
gap: 1.9 eV; conduction type: n-type).
[0030] Then, the same gas mixture as used in forming the charge injection blocking layer
5 was introduced at a pressure of 0.5 Torr into the vacuum chamber in a gas ratio,
(SiH₄ + C₂H₄)/(H₂ + SiH₄ + C₂H₄), of 0.6 and a gas ratio, C₂H₄/(SiH₄ + C₂H₄), of 0.6,
and an a-SiC:H film was formed to a thickness of 0.4 µm as a moisture and corona-resistant
layer
6 on the charge injection blocking layer
5 by high frequency glow discharge at 13.56 MHz and a power of 300 W.
[0031] In Fig. 2, a relationship between the thickness of the charge injection blocking
layer
5 (µm) on the abscissa and the dark decay (3-second value) of the photosensitive member
on the ordinate is shown. By providing the charge injection blocking layer
5 in the electrophotographic photosensitive member, the dark decay can be improved.
Better electrostatic charge acceptance and the residual potential of the photosensitive
member can be also obtained thereby, as shown in Fig. 3.
Example 2
[0032] An electrophotographic photosensitive member having a cross-sectional profile as
shown in Fig. 4 was prepared.
[0033] An aluminum drum whose outer surface was polished to the mirror surface degree was
fixed as an electroconductive support
1 in a vacuum chamber, which was evacuated to about 1x10⁻⁶ Torr. Then, a gas mixture
of monosilane (SiH₄), ethylene (C₂H₄) and hydrogen (H₂) was introduced at a pressure
of 0.5 Torr into the vacuum chamber in a gas ratio, (SiH₄ + C₂H₄)/(H₂ + SiH₄ + C₂H₄),
of 0.6 and a gas ratio, C₂H₄/ (SiH₄ + C₂H₄), of 0.05. Diborane (B₂H₆) was introduced
thereto to make a gas ratio, B₂H₆/(SiH₄ + C₂H₄), of 1x10⁻⁴. The aluminum drum
1 was kept at 250°C and an a-SiC:H film was formed to a thickness of 1 µm as a charge
blocking layer
2 on the aluminum drum
1 by high frequency glow discharge at 13.56 MHz and a power of 300 W.
[0034] Successively, the gas ratio, B₂H₆/(SiH₄ + C₂H₄), was changed to 3 x 10⁻⁶, and an
a-SiC:H film was formed to a thickness of 20 µm as a lower photoconductive layer
7 on the charge blocking layer
2 under the same high frequency glow discharge conditions as above.
[0035] Then, a gas mixture of SiH₄, GeH₄ and H₂ was introduced at a pressure of 0.5 Torr
into the vacuum chamber in a gas ratio, (SiH₄ + GeH₄)/(H₂ + SiH₄ +GeH₄), of 0.6 and
a gas ratio, GeH₄/(SiH₄ + GeH₄), of 0.2. B₂H₆ was introduced thereto to make a gas
ratio, B₂H₆/(SiH₄ + GeH₄), of 1x10⁻⁶. The aluminum drum
1 was kept at 250°C, and an a-SiGe:H film was formed to a thickness of 1 µm as an upper
photoconductive layer
4 on the lower photoconductive layer
7 by high frequency glow discharge at 13.56 MHz and a power of 300 W (optical band
gap: 1.5 eV; conduction type: p-type).
[0036] Then, a gas mixture of SiH₄, C₂H₄ and H₂ was introduced at a pressure of 0.5 Torr
into the vacuum chamber in a gas ratio, (SiH₄ + C₂H₄)/ (H₂ + SiH₄ + C₂H₄), of 0.6
and a gas ratio, C₂H₄/(SiH₄ + C₂H₄) of 0.05, and an a-SiC:H film was formed to a
thickness of 0 to 3 µm as a charge injection blocking layer
5 on the upper photoconductive layer
4 by high frequency glow discharge at 13.56 MHz and a power of 300 W (optical band
gap: 1.9 eV; conduction type: n-type).
[0037] Then, the same gas mixture as used in forming the charge injection blocking layer
5 was introduced at a pressure of 0.5 Torr into the vacuum chamber in a gas ratio,
(SiH₄ + C₂H₄)/(H2 + SiH₄ + C₂H₄), of 0.6 and a gas ratio, C₂H₄/(SiH₄ + C₂H₄), of 0.6
and an a-SiC:H film was formed to a thickness of 0.4 µm as a moisture and corona-resistant
layer
6 on the charge injection blocking layer
5 by high frequency glow discharge at 13.56 MHz and a power of 300 W.
[0038] In Fig. 5, a relationship between the thickness of the charge injection blocking
layer
5 (µm) on the abscissa and the dark decay (3-second value) of the photosensitive member
on the ordinate is shown. By providing the charge injection blocking layer
5 in the electrophotographic photosensitive member, the dark decay can be improved.
Better electrostatic charge acceptance and the residual potential of the photosensitive
member can be also obtained thereby, as shown in Fig. 6.
Example 3
[0039] An electrophotographic photosensitive member having a cross-sectional profile as
shown in Fig. 7 was prepared.
[0040] An aluminum drum whose outer surface was polished to the mirror surface degree was
fixed as an electroconductive support
1 in a vacuum chamber, which was evacuated to about 1x10⁻⁶ Torr. Then, a gas mixture
of monosilane (SiH₄), ethylene (C₂H₄) and hydrogen (H₂) was introduced at a pressure
of 0.5 Torr into the vacuum chamber in a gas ratio, (SiH₄ + C₂H₄)/(H₂ + SiH₄ + C₂H₄),
of 0.6 and a gas ratio, C₂H₄/(SiH₄ + C₂H₄), of 0.05. Diborane (B₂H₆) was introduced
thereto to make a gas ratio, B₂H₆/(SiH₄ + C₂H₄) of 1x10⁻⁴. The aluminum drum
1 was kept at 250°C and and a-SiC:H film was formed to a thickness of 1 µm as a charge
blocking layer
2 on the aluminum drum
1 by high frequency glow discharge at 13.56 MHz and a power of 300 W.
[0041] Successively, a gas mixture of SiH₄, H₂ and B₂H₆ was introduced at a pressure of
0.5 Torr into the vacuum chamber in a gas ratio, SiH₄/(SiH₄ + H₂), of 0.6 and a gas
ratio, B₂H₆/SiH₄, of 3x10⁻⁶. The aluminum drum
1 was kept at 250°C, and an a-Si:H film was formed to a thickness of 20 µm as a photoconductive
layer
3 on the charge blocking layer
2 by high frequency glow discharge at 13.56 MHz and a power of 300 W. (optical band
gap: 1.8 eV; conduction type: p-type).
[0042] Then, a gas mixture of SiH₄, C₂H₄ and H₂ was introduced at a pressure of 0.5 Torr
into the vacuum chamber in a gas ratio, (SiH₄ + C₂H₄)/(H₂ + SiH₄ + C₂H₄), of 0.6 and
a gas ratio, C₂H₄/(SiH₄ + C₂H₄), of 0.05, and an a-Sic:H film was formed to a thickness
of 0.5 to 2 µm as a charge injection blocking layer
5 on the photoconductive layer
3 by high frequency glow discharge at 13.56 MHz and a power of 300 W (optical band
gap: 1.9 eV; conduction type: n-type)
[0043] Then, the same gas mixture as used in forming the charge injection blocking layer
5 was introduced at a pressure of 0.5 Torr into the vacuum chamber in a gas ratio,
(SiH₄ + C₂H₄)/(H₂ + SiH₄ + C₂H₄), of 0.6 and a gas ratio, C₂H₄/(SiH₄ + C₂H₄), of 0.6,
and an a-SiC:H film was formed to a thickness of 0.4 µm as a moisture and corona-resistant
layer
6 on the charge injection blocking layer
5 by high frequency glow discharge at 13.56 MHz and a power of 300 W.
[0044] The thus prepared photosensitive member has a good electrostatic charge acceptance
as in Examples 1 and 2.
Example 4
[0045] An electrophotographic photosensitive member having a cross-sectional profile as
shown in Fig. 7 was prepared.
[0046] An aluminum drum whose outer surface was polished to the mirror surface degree was
fixed as an electroconductive support
1 in a vacuum chamber, which was evacuated to about 1x10⁻⁶ Torr. Then, a gas mixture
of monosilane (SiH₄), ethylene (C₂H₄) and hydrogen (H₂) was introduced at a pressure
of 0.5 Torr into the vacuum chamber in a gas ratio, (SiH₄ + C₂H₄)/(H₂ + SiH₄ + C₂H₄),
of 0.6 and a gas ratio, C₂H₄/(SiH₄ + C₂H₄), of 0.05. Phosphine (PH₃) was introduced
thereto to make a gas ratio, PH₃/(SiH₄ + C₂H₄) of 1x10⁻⁴. The aluminum drum
1 was kept at 250°C and an a-SiC:H film was formed to a thickness of 1 µm as a charge
blocking layer
2 on the aluminum drum
1 by high frequency glow discharge at 13.56 MHz and a power of 300 W.
[0047] Successively, a gas mixture of SiH₄, H₂ and B₂H₆ was introduced at a pressure of
0.5 Torr into the vacuum chamber in a gas ratio, SiH₄/(SiH₄ + H₂), of 0.6 and a gas
ratio, B₂H₆/SiH₄, of 0.5x10⁻⁶. The aluminum drum
1 was kept at 250°C, and an a-Si:H film was formed to a thickness of 20 µm as a photoconductive
layer
3 on the charge blocking layer
2 by high frequency glow discharge at 13.56 MHz and a power of 300 W. (optical band
gap; 1.8 eV; conduction type: n-type).
[0048] Then, a gas mixture of SiH₄ + C₂H₄ and H₂ was introduced at a pressure of 0.5 Torr
into the vacuum chamber in a gas ratio, (SiH₄ + C₂H₄)/(H₂ + SiH₄ + C₂H₄), of 0.6
and a gas ratio, C₂H₄/ (SiH₄ + C₂H₄), of 0.05. Diborane (B₂H₆) was introduced thereto
to make a gas ratio, B₂H₆/(SiH₄ + C₂H₄), of 3 x 10⁻⁶, and an a-SiC:H film was formed
to a thickness of 0.5 to 2 µm as a charge injection blocking layer
5 on the photoconductive layer
3 by high frequency glow discharge at 13.56 MHz and a power of 300 W (optical band
gap: 1.9 eV; conduction type: p-type).
[0049] Then, the same gas mixture as used in forming the charge injection blocking layer
5 was introduced at a pressure of 0.5 Torr into the vacuum chamber in a gas ratio,
(SiH₄ + C₂H₄)/(H₂ + SiH₄ + C₂H₄), of 0.6 and a gas ratio, C₂H₄/(SiH₄ + C₂H₄), of 0.6,
and an a-SiC:H film was formed to a thickness of 0.4 µm as a moisture and corona-resistant
layer
6 on the charge injection blocking layer
5 by high frequency glow discharge at 13.56 MHz and a power of 300 W.
[0050] The thus prepared photosensitive member has a good electrostatic charge acceptance
as in Examples 1 and 2.
Example 5
[0051] An electrophotographic photosensitive member having a cross-sectional profile as
shown in Fig. 1 was prepared.
[0052] An aluminum drum whose outer surface was polished to the nirror surface degree was
fixed as an electroconductive support
1 in a vacuum chamber, which was evacuated to about 1x10⁻⁶ Torr. Then, a gas mixture
of monosilane (SiH₄), ethylene (C₂H₄) and hydrogen (H₂) was introduced at a pressure
of 0.5 Torr into the vacuum chamber in a gas ratio, (SiH₄ + C₂H₄)/(H₂ + SiH₄ + C₂H₄),
of 0.6 and a gas ratio, C₂H₄/(SiH₄ + C₂H₄), of 0.05. Phosphine (PH₃) was introduced
thereto to make a gas ratio, PH₃/(SiH₄ + C₂H₄) of 1x10⁻⁴. The aluminum drum
1 was kept at 250°C and an a-SiC:H film was formed to a thickness of 1 µm as a charge
blocking layer
2 on the aluminum drum
1 by high frequency glow discharge at 13.56 MHz and a power of 300 W.
[0053] Successively, a gas mixture of SiH₄, H₂ and B₂H₆ was introduced at a pressure of
0.5 Torr into the vacuum chamber in a gas ratio, SiH₄/(SiH₄ + H₂), of 0.6 and a gas
ratio, B₂H₆/SiH₄, of 0.5x10⁻⁶. The aluminum drum
1 was kept at 250°C, and an a-Si:H film was formed to a thickness of 20 µm as a lower
photoconductive layer
3 on the charge blocking layer
2 by high frequency glow discharge at 13.56 MHz and a power of 300 W.
[0054] Then, a gas mixture of SiH₄, GeH₄ and H₂ was introduced at a pressure of 0.5 Torr
into the vacuum chamber in a gas ratio, (SiH₄ + GeH₄)/(H₂ + SiH₄ + GeH₄), of 0.6 and
a gas ratio, GeH₄/(SiH₄ + GeH₄), of 0.2. The aluminum drum
1 was kept at 250°C, and an a-SiGe:H film was formed to a thickness of 1 µm as an upper
photoconductive layer
4 on the lower photoconductive layer
3 by high frequency glow discharge at 13.56 MHz and a power of 300 W (optical band
gap: 1.5 eV; conduction type: n-type).
[0055] Then, a gas mixture of SiH₄, C₂H₄ and H₂ was introduced at a pressure of 0.5 Torr
into the vacuum chamber in a gas ratio, (SiH₄ + C₂H₄)/(H₂ + SiH₄ + C₂H₄), of 0.6 and
a gas ratio, C₂H₄/(SiH₄ + C₂H₄), of 0.05. Diborane (B₂H₆) was introduced thereto to
make a gas ratio, B₂H₆/(SiH₄ + C₂H₄) of 3 x 10⁻⁶, and an a-SiC:H film was formed to
a thickness of 0.5 to 2 µm as a charge injection blocking layer
5 on the upper photoconductive layer
4 by high frequency glow discharge at 13.56 MHz and a power of 300 W (optical band
gap: 1.9 eV; conduction type: p-type).
[0056] Then, the same gas mixture as used in forming the charge injection blocking layer
5 was introduced at a pressure of 0.5 Torr into the vacuum chamber in a gas ratio,
(SiH₄ + C₂H₄)/(H₂ + SiH₄ + C₂H₄), of 0.6 and a gas ratio, C₂H₄/(SiH₄ + C₂H₄), of 0.6,
and an a-SiC:H film was formed to a thickness of 0.4 µm as a moisture and corona-resistant
layer
6 on the charge injection blocking layer
5 by high frequency glow discharge at 13.56 MHz and a power of 300 W.
[0057] The thus prepared photosensitive member had a good electrostatic charge acceptance
as in Example 1.
[0058] According to the present invention, an electrophotographic photosensitive member
with excellent electrostatic charge acceptance and photosensitivity can be provided
by providing on a photoconductive layer a charge injection blocking layer having a
different conduction type and a broader band gap from and than those of the photoconductive
layer.
1. An electrophotographic photosensitive member, which comprises an electroconductive
support, a photoconductive layer made from hydrogen-containing amorphous silicon
as a matrix, a charge injection blocking layer having a different conduction type
from that of the photoconductive layer and a broader optical band gap than that of
the photoconductive layer and a moisture and corona-resistant layer, laid one upon
another successively on the electroconductive support.
2. An electrophotographic photosensitive member, which comprise an electroconductive
support, a charge blocking layer, a photoconductive layer made from hydrogen-containing
amorphous silicon as a matrix, a charge injection blocking layer having a different
conduction type from that of the photoconductive layer and a broader optical band
gap than that of the photoconductive layer and a moisture and corona-resistant layer,
laid one upon another successively on the electroconductive support.
3. An electrophotographic photosensitive member according to Claim 1 or 2, wherein
the photoconductive layer is of p-type, and the charge injection blocking layer is
of n-type or intrinsic type.
4.An electrophotographic photosensitive member according to Claim 1 or 2, wherein
the photoconductive layer is of n-type and the charge injection blocking layer is
of p-type or intrinsic type.
5. An electrophotographic photosensitive member according to any one of claims 1 to
4 wherein the charge injection blocking layer is made from a film of a-SiC:H, a-SiC:X:H,
or a-SiN:X:H wherein X represents an halogen atom.
6. An electrophotographic photosensitive member according to any one of claims 1 to
5 wherein the photoconductive layer is made of a single film of a-Si:H or a-SiGe,
or a double film of a-Si:H or a-SiC:H and a SiGe:H.
7. An electrophotographic photosensitive member according to any one of claims 1 to
6 wherein the photoconductive layer has an optical band gap of 1.5 to 1,8 eV and the
charge injection blocking layer has an optical band gap of 1.9 to 2.9 eV.
8. An electrophotographic photosensitive member according to any one of claims 1 to
7 wherein the moisture and corona-resistant layer is made from a film of a-SiC:H having
a high carbon content.
9. An electrophotographic photosensitive member according to Claim 2, wherein the
charge blocking layer is made from the same film as that for the charge injection
blocking layer.
10. An electrophotographic photosensitive member according to Claim 1, wherein the
photoconductive layer has a thickness of 20 to 50 µm, the charge injection blocking
layer has a thickness of 0.5 to 3 µm, and the moisture and corona-resistant layer
has a thickness of 0.2 to 1 µm.
11.An electrophotographic photosensitive member according to Claim 2, wherein the
charge blocking layer has a thickness of 0.5 to 3 µm, the photoconductive layer has
a thickness of 20 to 50 µm, the charge injection blocking layer has a thickness of
0.5 to 3 µm, and the moisture and corona-resistant layer has a thickness of 0.2 to
1 µm.
12. An electrophotographic photosensitive member according to any one of claims 1
to 11 wherein the individual layers are formed by CVD, sputtering or vapor deposition
alone or in their combination.
13. An electrophotographic photsensitive member according to any one of claims 1 to
12 wherein the conduction type of the photoconductive layer and the charge injection
blocking layer is controlled by doping with boron or phosphorus.