JPS61233751A - Electrophotographic sensitive layer - Google Patents

Abstract

PURPOSE:To obtain an electrophotographic sensitive layer for which a non- polluting material having high photoconductivity to light of a visible region, high dielectric strength and small dark current is used by forming a hetero junction of the 1st amorphous silicon layer and the 2nd amorphous semiconductor layer contg. carbon or silicon as an essential component element. CONSTITUTION:An a-Si layer 2 and an a-Si1-xCx layer 3 are provided on a conductive substrate 1. Pt, Au, In2O, SnO2, etc. can be used for the transparent conductive film 4. The hetero junction to provide the photosensitive function to the wide visible wavelength region to the 1st layer 2 and to provide the functions for high electric field resistance, high dielectric strength and implanted charge transfer to the 2nd layer 3 is formed, by which the photoconductive semiconductor element having the high sensitivity and high dielectric strength is constituted. The compsns. of both are different each other and have the hetero junction at the boundary thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses an amorphous silicon layer as a first layer and an amorphous semiconductor (hereinafter referred to as a S 11 x Cx *) whose main component is carbon or silicon as a second layer. O<X
It is written as ≦1. ) and relates to an electrophotographic photosensitive layer including a heterojunction between a first layer and a second layer.

Conventionally, S e , CdS, and the like have been known as substances that have high photoconductivity and high dark resistance, have long-term charge retention ability, and can further apply a high electric field.

However, these substances are toxic and belong to polluting substances, and there is a strong desire for an electrophotographic photosensitive layer using a non-polluting material instead.

In recent years, amorphous silicon (A-8
It is written as t. ) is attracting attention as having strong photoconductivity, but the room temperature dark specific resistance of this material is at most 1013Ω.
・The current and voltage characteristics are about α, the breakdown electric field is low, high voltages and high electric fields cannot be applied, the dark current is large, and the long-term charge retention ability is low. .

In recent years a-Si1, C! The manufacturing method and existence of is Ph11゜Ma
It is disclosed in G., Pl, Vol. 35 (197B), etc. that if the carbon concentration I is increased, the energy gap (Eq) increases up to a certain concentration, and at the same time, the room temperature dark resistivity also increases. Although this material has been disclosed, no report has been found that considers that this material has photoconductivity.

As a result of a detailed study of the characteristics of aSil, Cx, the present invention found that this carbon-containing material has a high room temperature dark specific resistance, excellent photoconductivity, and We are also thrilled to have discovered that it has the ability to transport. Further, by forming a heterojunction between the first amorphous silicon layer and the second amorphous semiconductor layer mainly composed of carbon or silicon, the first A good photosensitive layer for electrophotography is obtained, which has both the wide photosensitive wavelength range characteristics of the first layer and the high voltage resistance of the second layer.

The object of the present invention is to have high photoconductivity for light in the visible range,
It is an object of the present invention to provide a photosensitive layer for electrophotography using a material that has high voltage resistance, low dark current, and is non-polluting.

Another object of the present invention is to provide an electrophotographic photosensitive layer that is rich in mechanical strength and has excellent counterprinting properties.

Still another object of the present invention is to provide an electrophotographic photosensitive layer that can select a sensitive wavelength range and is easy to manufacture.

The object of the present invention described above is to form a first amorphous silicon layer and a second amorphous silicon layer.
This is achieved by forming a heterojunction with an amorphous semiconductor layer (a-3i 1-zC!, o<x≦1) whose main component element is carbon or silicon.

The present invention will be described in detail below with reference to the drawings. FIG. 1 is a diagram showing an example of the basic structure of a semiconductor element for confirming the photoconductive function of an electrophotographic photosensitive layer according to the present invention.

1 is a conductive substrate, 2 is a-3i layer is a-8i1-IC,
The two layers have different compositions, and there is a heterojunction at the interface between the two. 4 is a transparent conductive film made of Pt, Au, In2O, S
nO2 etc. may be used. 5.6 is an electrode for connecting the element to an external electric circuit. 7 is a power source, and 8 is a load resistor, which is connected to the power source 7 in the figure when the photoconductive element is used.

11 is incident light.

The layers 2 and 3 are selected to have a composition with a large X, and a first layer 2 that is sensitive to irradiation light in the visible range and easily generates photoexcited charge carriers. The second layer 3 has a relatively large energy gap (Ecr) and has high dark resistance and light transmission properties. By forming a heterojunction in which the first layer 2 has a photosensitive function over a wide visible wavelength range, and the second layer 3 has functions of high electric field resistance, high voltage resistance, and injection charge transport,
A photoconductive semiconductor element having high sensitivity and high voltage resistance is constructed. Note that either layer 2 or 3 in FIG. 1 may be the first layer or the second layer.

As described above, when the semiconductor device of the present invention is designed as a photoconductive device having high voltage resistance against externally applied voltage and high photosensitivity, the first layer (a-8t)
2nd layer (a Si1°Cx (0 x x 1))
It is sufficient to design the material by greatly changing the composition of the material and using a material with high resistance.

The semiconductor element of the present invention can be manufactured, for example, as follows. The substrate may be of any type as long as it has a smooth surface and can withstand the temperature at which the photoconductor layer is deposited, for example from 1600 to 400'C, and it does not matter whether it is crystalline or amorphous. For example, semiconductors such as St single crystals, metal disilica glass such as stainless steel and aluminum, ceramics, or insulators such as plastic films that can withstand the above temperatures are coated with a conductive film such as metal or metal oxide on the surface. can be used. After cleaning the surfaces of these substrates, they are placed in a glow discharge device and the substrate temperature is appropriately heated. Silicon compounds that exhibit a gaseous structure with a stable structure at room temperature, such as S I
A mixed gas having a first composition ratio and a mixed gas having a second composition ratio in which H4 and a carbon compound exhibiting a gaseous state with a stable structure at room temperature, such as C2H4, are mixed at a desired concentration ratio, respectively, with an inert gas such as an inert gas. diluted with argon, and sequentially guided these diluted mixed gases into the glow discharge device, 1
By sequentially decomposing glow discharge at a desired time under a pressure in the order of o-2 to 10 Torr, an a-5t layer and an aS layer each having a desired composition and film thickness are formed on the substrate.
A heterojunction consisting of a layer of l 1 x C is formed.

In particular, when it is necessary to deposit an a S ilx C8 layer doped with impurities, a gaseous compound of a Group I or Group V element, such as B2H6 or PH3, may be appropriately added to the diluted mixed gas.

The present invention will be explained in more detail below based on Examples.

[Element manufacturing example]

Substrate 1 includes SL single crystal (p-type 10Ω/crIL), stainless steel, and quartz glass.
) A material with a transparent conductive film was used. 13.5MHz
The substrate temperature is maintained at 260°C in a high frequency glow discharge device.
First, in order to form the first layer 2 with a thickness of approximately 1 μm, Ar gas containing a Si layer 4 of 2 ovOl-T was introduced, and the temperature was increased to 1 Torr.
It was decomposed by glow discharge at a pressure of . Here, an a-3t layer, which is the first layer 2, was formed. Note that layer 2 is a-8t containing hydrogen. Next, Ar gas containing a mixture of C2H4 and S I H4 at a concentration of 18vo and 11% was introduced, and the same (
The second layer 3 is formed by glow discharge decomposition at 0,1 Torr.
was deposited to a thickness of about 1 μm.

After that, Si single crystal was deposited on a stainless steel substrate.
Approximately 1,600 layers of ITO4 were formed on a film having a heterojunction of an S i layer, a Stl , and a C8 layer. As a result of measurement using the X-ray microanalysis method, the composition of the second layer
was about 35%.

The photoelectric characteristics of this device were measured using a tungsten lamp as a light source at an illuminance of 230 Lx.

[Example 1] Figure 2 shows an a-8i layer and an a-9i1-I layer on a p-type Si substrate.
Create a heterojunction of the Cx (o<x<, 1) layer, and further IT
○Characteristics of elements with transparent conductive films are shown. In the figure, curve 16 represents the dark current when the Si substrate is negatively biased.
Curve 16 shows the photocurrent. Curve 17 shows the dark current when the substrate is positively biased, and curve 19 shows the photocurrent.

The photoconductive element characteristics are approximately 1×103 at the above illuminance.
A double photocurrent/dark current ratio is obtained, and the dark current density is
The applied voltage exceeding X1O-10A and O- is approximately 10V, and the average electric field at this time is approximately 3 X 10 V/cI.
Get rL. For comparison, it is currently impossible to obtain a dark current density of I x 10''A/i or less using a layer of only a-3t.

[Example 2] A device on a stainless steel substrate with an ITO surface electrode was also prepared.
Both the dark current and charging current characteristics showed almost the same characteristics as in FIG. 2.

[Example 3] FIG. 3 shows the characteristics of a device on a Si substrate having approximately 1000 Au-8b alloy films as surface electrodes.

Curves 20 and 21 respectively show the dark current photocurrent when the substrate is negatively biased. Curves 22 and 23 show dark current and photocurrent when the substrate is positively biased. The charging current density is lower than in FIG. 3, but this is due to the use of a relatively "thick" semi-transparent conductive film. However, the dark current did not change particularly. Furthermore, since the Au-3b electrode was used, no photovoltaic force was generated and the result was very good in both the positive and negative bias directions, probably because the barrier at the interface between this electrode and the a-9t1-ECx (0<!<1) layer was reduced. Show similar characteristics.

Therefore, it is presumed that a good dissimilar bonding surface is formed.

[Example 4] A device on a stainless steel substrate having an AuSb alloy film of about 10 oo as a surface electrode as in Example 3 also exhibits almost the same characteristics as shown in FIG. 3.

[Example 6] a-5i1-EC! used in manufacturing the device of the above example. (
o<z<:1) layer and a conventional device having a photoconductive film of Ss, CdS, etc. were scratched with the tips of stainless steel tweezers, and their mechanical strengths were compared.

Conventional elements using Se and CdS were easily damaged, but
Although the element according to the invention was pressed with considerable force, no mechanical damage was observed.

FIG. 4 shows the spectral sensitivity distribution of the photoconductive characteristics of the device of the example described above. Curves 24 and 25 each contain Au as the surface electrode.
-5b, characteristics of an element made of ITO. curve 26
shows the spectral sensitivity distribution of an a-Si monolayer film (approximately 0.7 μm) as a relative value. Curve 24°25 is approximately 490 nm
It has the highest sensitivity at wavelengths longer than this, and exhibits a tendency almost similar to curve 26, with the sensitivity decreasing. As mentioned above, the composition of the second layer of the device of this example is X=0.35, and with this composition, the energy gap is about 2.3, which is V, so if only the second layer is used, There is no sensitivity on the long wavelength side. Since the overall sensitivity on the long wavelength side shows a similar tendency to the sensitivity distribution of the a-8L, this device shows that charge carriers photoexcited in the first layer, the a-5t layer, are injected into the second layer and transported. It is clear that this has been done. the other 490 nm
The reason why the sensitivity of the element decreases on the shorter wavelength side is considered to be because there is a second layer with a composition x=o and 3E5 on the light incident side, and the incident light is absorbed by this layer. This decrease in sensitivity at short wavelengths can be avoided by increasing the composition I of the second layer and increasing the energy gap. On the other hand, if the configuration is such that light is incident from the direction of the first layer, it becomes possible to guide the incident light to the first layer without being attenuated by the second layer.

The above-mentioned device can be used as an electrophotographic photosensitive layer for printing, etc. by applying an actual high-voltage surface charge and selectively discharging the surface charge by utilizing photoconductivity by selectively irradiating the device with light. For example, the device may be designed by removing the surface electrode 4 from the structure shown in FIG. 1 and increasing the voltage resistance of the device.

As described above in detail of the present invention, in the present invention, the composition
can be controlled continuously a5i1-eCx and a-3
The present invention provides an electrophotographic photosensitive layer using a heterojunction of t, in which the first layer has a photoexcited carrier generation function, and the second layer having a relatively large composition I has a light transmittance and electric field resistance. By sharing the functions and the transport function of photoexcited carriers, we were able to bring out the features of each layer. Therefore, the photosensitive layer of the present invention can provide a photosensitive layer that (1) has high sensitivity to light in the visible light range, is resistant to high electric fields and high voltages, and has a small dark current.

(2) It can provide a photosensitive layer with high mechanical strength, and is extremely useful for applications in the field of electrophotography, which requires abrasion resistance.

(3) The temperature for forming dissimilar junctions is low, no heat treatment is required after formation, and since it is amorphous, there is a wide range of selection of substrate materials and substrate shapes, and manufacturing is easy and flexible depending on the purpose of use. A photosensitive layer having the shape of can be provided.

(4) The basic constituent materials are non-toxic and non-polluting.

It has the following effects and has extremely great industrial value.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the basic structure of a semiconductor device for confirming the photoconductive function of a photosensitive layer according to an embodiment of the present invention, and FIGS. FIG. 4 is a diagram showing the relationship between applied voltage and dark current/photocurrent in one embodiment, and FIG. 4 is a diagram showing the relationship between photocurrent and incident light wavelength in one embodiment of the semiconductor element of the present invention. 1... Conductive substrate, 2... a-S
i layer, 3...a S il-e Cx layer, 4.
...Transparent conductive film, 5.6... Electrode, 7.
...Power source, 8...Load' appeal, 9...
···switch. Figure 1 Figure 2 - Kuiazu Den, L (v) Figure 3 No. 1? Viewing pressure (l/)

Claims (4)

[Claims] (1) having a multilayer structure of a first and second layer formed on a support, an amorphous silicon layer as the first layer;
The second layer is an amorphous semiconductor layer whose main component is carbon or silicon (a-Si_1_-_xC_x, 0<
x≦1), and includes a heterojunction between a first layer and a second layer. (2) The electrophotographic photosensitive layer according to claim 1, wherein the amorphous semiconductor layer is formed by glow discharge using a compound gas containing hydrogen. (3) The dark specific resistance value of the amorphous semiconductor layer at room temperature is 10^1
Claim 1 or 2 which is ^3Ω・cm or more
Electrophotographic photosensitive layer described in Section 1. (4) The photosensitive layer for electrophotography according to claim 1, 2, or 3, wherein the amorphous semiconductor layer has a larger optical band gap than the amorphous silicon layer.