JPH03198060A - Photosensitive body for electrophotographic recording - Google Patents

Abstract

PURPOSE:To obtain a photosensitive body capable of forming a record without being affected by the output energy of a light source by successively laminating a p-n-joined carrier generating layer and a carrier transfer layer on a conductive substrate and forming the p-n-junction to apply a reverse bias electric field at the time of electrically charging the photosensitive body. CONSTITUTION:This photosensitive body formed by successively laminating the carrier generating layer obtained by joining an n-type layer 2 with a p-type layer 3, and the carrier transfer layer 5, and the reverse electric field is applied when the surface of the photosensitive body is charged. This layer 4 is allowed to generate a large number of pairs of electrons and positive holes at the pn- junction by irradiation with light and further by the electron avalanche phenomenon, and one group of the generated pairs is drifted to the surface of the photosensitive body and the other group to the side of the substrate. Since the generation rate of the carriers are constant till the stop of the electron avalanche, the surface potential of the exposed area is kept almost constant irrespective of the intensity of the light, thus permitting the obtained photosensitive body to obtain stable record superior in edge sharpness without being affected by the output energy of a light source.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a photoreceptor used in electrophotographic recording devices such as copying machines, facsimiles, and optical printers.

[Prior art] Conventional photoreceptors include a-3i, 5e-Te, and OP.
There are many types such as c, etc., and due to the requirements for charging ability and spectral sensitivity, the structure is such that a carrier generation layer (CGL) b and a carrier transport layer (CTL) are placed on the top surface of a conductive substrate a, as shown in Figure 6. There is also a functionally separated type by laminating C and C.

[Question to be Solved 1fil] The relationship between exposure energy and surface potential of these conventional photoconductors is shown in FIG. 7, where the vertical axis is the photoconductor surface potential V.

If the horizontal axis is the exposure energy E, a gentle concave curve d
The sensitivity characteristics of the photoreceptor are expressed as: When an electrostatic latent image is formed on a photoreceptor having such sensitivity characteristics, variations in the light emission energy of the light source will cause variations in the surface potential of the exposed portion. That is, at low exposure energy EL, the surface potential becomes Vl, and at high exposure energy "I"
At t, the surface potential becomes Vu. If a laser is used as a light source to suppress this variation, the temperature of the laser must be controlled to suppress temperature fluctuations in the output, and the lens must be adjusted to keep the energy constant at the center and periphery of the scan. The design becomes complicated. When an LED array is used, chip selection and output correction must be performed based on the emission energy of the LED chips.

Therefore, the present invention has been developed so that even if the exposure energy of the light source changes, the surface potential of the photoreceptor at the light irradiation part remains constant, and as a result, it is not affected by the output energy of the light source and has a stable edge with good sharpness. It is an object of the present invention to provide a photoreceptor that allows recording with high quality.

[Means for Solving the Problems] In order to achieve the above object, the photoreceptor for electrophotographic recording of the present invention includes a conductive substrate, a carrier generation layer and a carrier transport layer which are pn-junctioned and stacked. has been formed,
The pn junction is formed so that a reverse bias electric field is applied when the surface of the photoreceptor is charged.

[Function] The pn-junctioned carrier generation layer generates electron-hole pairs at the junction by irradiation with light, and generates a large number of electron-hole pairs by an electron avalanche phenomenon. One of the generated electrons and holes drifts toward the surface of the photoreceptor, and the other drifts toward the substrate. Since the number of carriers generated until the electron avalanche phenomenon stops is constant, the surface potential of the exposed area is almost constant regardless of the intensity of light.

[Example] FIG. 1 shows an example of the structure of a photoreceptor according to the present invention.
A carrier generation layer 4 in which a type layer 2 and a p-type layer 3 are joined together, and a carrier transport layer 5 are laminated and formed, and this pn junction is formed by a reverse bias electric field when the surface of the photoreceptor is charged. When the surface of the photoreceptor is negatively charged as shown in the figure, n is formed on the conductive substrate 1 side.
The mold layer 2 will be laminated. Further, when the surface of the photoreceptor is positively charged, the p-type layer 3 is laminated on the conductive substrate 1 side.

FIG. 2 shows an energy unit diagram explaining carrier multiplication. When the reverse bias electric field of the pn junction is increased to a strength of 105V101 or more, electron avalanche multiplication occurs. This is explained like this. Electron-hole pairs "AlB" are generated by light absorption, and electrons B excited by the conductor are accelerated and acquire sufficient energy. The accelerated electron C generates a new electron-hole pair "E, F".

The generated electron-hole pairs "E, F" drift in opposite directions, and further electron-hole pairs are generated.

These phenomena progress in a chain sequence, resulting in electron avalanche multiplication.

FIG. 3 shows the voltage dependence of the current multiplication factor M by a curve e. This is M-1+p0p2+P3...-1/(1-P), where P is the probability that an electron-hole pair excited by light generates another electron-hole pair during drift.

Based on the above, the operating principle of the photoreceptor according to the present invention will be explained with reference to FIG. 4, which shows changes in energy level due to carrier generation.

In this example, as shown in the first diagram, the surface of the photoreceptor is negatively charged,
An n-type layer 2 is formed on the conductive substrate 1 side, and a reverse bias voltage is applied. The photoreceptor is 5e-T with low charging ability.
Even if it is an e-based photoreceptor, the film thickness is about 50 μm.
Since about 00OV will be charged, as shown in Fig. 4(a)
) is larger than 105 V/cm when not exposed to light.

Therefore, when the pn-junctioned carrier generation layer 4 is irradiated with light, electron-hole pairs are generated as described above, and a large number of electron-hole pairs are generated due to the electron avalanche phenomenon. Of the generated electron-hole pairs, the holes drift toward the surface of the photoreceptor, and the electrons drift toward the conductive substrate 1 side. Due to the drifted charges, the electric field at the junction becomes small, as shown in FIG. 4(b), and the carrier generation efficiency decreases rapidly.

Light irradiation is performed for a certain time t. At the initial stage of irradiation, an electron avalanche phenomenon is caused, but after the electric field at the junction drops below a certain value, carriers are only those directly generated by light absorption. When strong light is irradiated, the electron avalanche phenomenon stops in a short time, and when weak light is used, it continues for a relatively long time, but the electron avalanche phenomenon stops depending on the electric field at the junction, that is, the number of carriers generated. Therefore, the number of carriers generated until the electron avalanche phenomenon stops is constant regardless of the strength of the irradiation light.

Since the current multiplication factor M reaches as high as 104 in an ideal case, the number of carriers (due to light absorption) generated after the electron avalanche phenomenon stops is minute, and the low exposure energy EL
However, even with high exposure energy EII, the surface potential of the exposed area becomes VL''=v11, which is almost constant, regardless of the strength of the exposure energy, as shown by the curve f showing the photoreceptor sensitivity characteristics shown in Figure 5. .

In the embodiment shown in the first figure, the carrier transport layer 5 is formed on the carrier generation layer 4, but the carrier generation layer may be formed on the carrier transport layer conversely.

[Effect] In the present invention having such a configuration, even if the exposure energy of the light source varies, the surface potential of the photoreceptor at the light irradiation part remains constant, and as a result, it is not affected by the output energy of the light source. This results in a photoreceptor that provides stable recording with good edge cutting.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view showing an embodiment of the present invention, Fig. 2 is an energy level diagram explaining carrier multiplication, Fig. 3 is a graph showing the voltage dependence of avalanche multiplication, and Fig. 4 is a carrier Energy level diagram showing changes in energy levels due to generation,
FIG. 5 is a sensitivity characteristic diagram of a photoconductor according to the present invention, FIG. 6 is a sectional view showing a conventional function-separated type photoconductor, and FIG. 7 is a sensitivity characteristic diagram of a conventional photoconductor. 1. Conductive substrate, 2. N-type layer, 3. P-type layer, 4. Carrier generation layer, 5. Carrier transport layer. Applicant Seiko Co., Ltd. Attorney Kazuko Matsuda Figure 1 Figure 4 (a) NlE! (b) Dew p type N made Fig. 2 Fig. 3 Fig. 6 Reverse (Iasu 1 [S E

Claims (1)

[Claims] A carrier generation layer and a carrier transport layer are formed by stacking them on a conductive substrate, and the pn junction is formed so that a reverse bias electric field is applied when the surface of the photoreceptor is charged. A photoreceptor for electrophotographic recording, characterized in that: