JPH0425533B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in electrophotographic photoreceptors.

A conventional amorphous silicon (hereinafter abbreviated as a-Si) electrophotographic photoreceptor will be described with reference to FIG. In FIG. 1, 1 is a conductive support formed by depositing NiCr or indium tin oxide (ITO) on an aluminum alloy or glass substrate, and 2 is a p-type or n-type conductive support formed on this support 1. A charge injection blocking layer 3 is made of type a-Si, silicon nitride, silicon oxide, aluminum oxide, and a-Si carbide. This is a photosensitive layer consisting of an added layer.

In order for the electrophotographic photoreceptor constructed as described above to have sufficient charging ability, the charge injection blocking layer sufficiently prevents charge injection from the support side during corona charging and dark decay, and prevents the surface of the photoreceptor from being charged. The applied charge must be retained.

On the other hand, even if the charge injection blocking layer is sufficient, if the dark resistivity of the photosensitive layer 3 is small, carriers due to thermal excitation within the photosensitive layer 3 will flow to neutralize the surface charge, resulting in insufficient charging ability. I can't get it.

In the case of the a-Si mentioned above, by adding a small amount of boron of several tens of ppm, its dark resistivity can be reduced.
Since it can be set to 10 ¹¹ to 10 ¹² Ωcm, an electrophotographic photoreceptor having a sufficient charging ability of 20 to 40 V/μm can be obtained with the structure shown in FIG.

Here, in the electrophotographic photoreceptor described above, the surface potential increases approximately in proportion to the thickness of the a-Si layer. In other words, the photosensitive layer 3 is a charging layer in the sense that it determines the charging ability of the electrophotographic photoreceptor, and it is also a photosensitive layer in the sense that photocarriers are generated within this layer by light irradiation and erase the charges on the surface. It is also called a photosensitive layer and a charging layer.

However, the electrophotographic photoreceptor in which the above-mentioned a-Si is used as the photosensitive layer and charging layer 3 has a photosensitivity peak of 630~
The wavelength is 700 nm, and photosensitivity decreases rapidly at wavelengths longer than this range.

In recent years, there has been a demand for electrophotographic photoreceptors that have good photosensitivity to long wavelengths up to around 800 nm as photoreceptors for laser beam printers using semiconductor lasers as light sources.

When germanium (Ge) is added to a-Si, a-Si germanium (a-Si _1-x Ge _x ) can be easily obtained, and the optical band gap of this can be changed by increasing the amount of Ge added. It can be reduced from 1.7eV to about 1.1eV for Ge. Therefore, a
If an electrophotographic photoreceptor using -Si _1-x Ge _x8 as the photosensitive layer and charging layer 3 can be realized, it will be possible to increase the photosensitivity to a longer wavelength.

However, when an electrophotographic photoreceptor is formed with the structure shown in FIG. 1 in which a-Si _1-x G _x is used as the photosensitive layer/charged layer 3, the following problem occurs.

Generally, the dark resistivity of a-Si _1-x Ge _x decreases as the amount of Ge added increases. For this reason, neutralization is likely to occur after the surface charge due to thermally excited carriers.
As the amount of Ge increases, the charging ability decreases.

Moreover, the photoconductivity of a-Si _1-x G _x also decreases with an increase in the amount of Ge. An important factor that determines the photosensitivity of a photoreceptor is the travel distance of the optical carrier. The traveling distance L is expressed as L=μτV/d. Here, μ
is the mobility of the optical carrier, τ is its lifetime, V is the voltage applied to the photosensitive and charged layer, and d is the thickness of the photosensitive and charged layer. Unless the above formula L>d, good photosensitivity cannot be obtained. The μτ value of holes determined from the optical attenuation characteristics of a positively charging photoreceptor with a-Si as the photosensitive layer and charging layer is approximately 10 ⁻⁸ cm ² /V, and this value is determined from the photoconductivity. This is two orders of magnitude smaller than the μτ value of about 10 ⁻⁶ cm ² /V. On the other hand, a-Si _1-x
When about 50% Ge is added to Ge _x , the photoconductivity decreases by one to two orders of magnitude compared to a-Si. At this time,
The μτ value of a hole is considered to be about 10 ^-9 to 10 ^-10 cm ² /V, and when V = 600 V and d = 200 μm, L is 3 to 3.
It is approximately 0.3 μm. Therefore, in the case of a positively charging photoreceptor with a-Si _{1-x Ge}
Therefore, the structure shown in FIG. 1 cannot realize a practical photoreceptor.

Furthermore, in order to obtain a practical charging voltage of 600V or more as a photoreceptor, the thickness of the photosensitive layer and charging layer must be 20μ.
If a glow discharge method is used to form this photosensitive layer/charged layer, GeH ₄ which is the raw material gas for Ge is replaced with SiH ⁴ which is the raw material gas for Si.
The price is approximately 60 times higher than that of a-Si _{1-x Ge} .

That is, in these conventional examples, when the a-Si layer is used as a photosensitive layer and a charging layer, sensitivity at long wavelengths cannot be obtained, and the a-Si _1-x Ge _x layer is used as a photosensitive layer and a charging layer. In some cases, although sensitivity at long wavelengths can be obtained, a sufficient surface potential cannot be obtained and the device is expensive. These drawbacks are caused by the fact that one layer has two functions: photosensitive and charging.

The present invention aims to eliminate such conventional drawbacks, and aims to provide a-Si as another charged layer between the charge injection blocking layer and the a-Si _1-x G _x which is the photosensitive layer.
Another object of the present invention is to provide an electrophotographic photoreceptor that has excellent durability and high sensitivity up to a long wavelength region by providing an a-Si layer doped with boron.

With this structure, the charging ability is determined by the charging layer made of a-Si or an a-Si layer with added boron, and the wavelength range to be exposed to light is determined by the photosensitive layer made of a-Si _1-x Ge _x . A decomposable electrophotographic photoreceptor is realized.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 shows an embodiment of the invention. In FIG. 2, 4 is a support made of aluminum alloy;
5 is a charge injection blocking layer formed on the surface of the support 4 and made of p-type a-Si; 6 is a charging layer formed on the surface of the charge injection layer 5 and made of boron-doped a-Si; 7 is a charge injection blocking layer made of a-Si doped with boron; a- formed on the charged layer 6
It is a photosensitive layer made of Si _1-x Ge _x .

Further, FIG. 3 shows an apparatus used for manufacturing the electrophotographic photoreceptor having the structure shown in FIG. 2 described above. In FIG. 3, 8 is a vacuum pump, which is communicated with a reaction chamber 10 via a stop valve 9. In FIG. Reference numeral 11 denotes a high frequency power source, which is connected to a cathode electrode 12 provided in the reaction chamber 10 , and an anode electrode 13 and a heater 14 provided in the reaction chamber 10 opposite to this electrode 12 . Further, the reaction chamber 10 is communicated with three gas flow rate controllers 16, 17, 18 via a stop valve 15, and these are communicated via pressure reducing valves 19, 20, 21.
SiH ₄ gas cylinder 22, GeH ₄ gas cylinder 23, B ₂
Each of them is in communication with an H ₆ gas cylinder 24 .
25 is an aluminum substrate which is a support placed on the anode electrode 13.

The case where an electrophotographic photoreceptor having the structure shown in FIG. 2 is manufactured using the apparatus shown in FIG. 3 will be described.
First, the inside of the reaction chamber 10 is heated to 10 ^-3 to 10 ^-6 using the vacuum pump 8.
After evacuation to torr, SiH ₄ and B ₂ H ₆ are extracted from these gas cylinders 22 and 24 with a ratio of B ₂ H ₆ /SiH ₄ of several
Gas controller 16 to make it 100ppm,
Gas controller 16,1 to make it 100ppm
8 and introduce the gas into the reaction chamber 10. Then, applying high frequency power between the electrodes 12 and 13,
Then, by applying high frequency power between the electrodes 12 and 13 to generate glow discharge, the substrate 25 is heated in advance to 200 to 300°C by the heater 14.
A p-type a-Si film doped with boron is formed thereon as a charge injection blocking layer. This film thickness is several thousand Å
When the required value is reached, the glow discharge is temporarily stopped.
Then, to form a charged layer, B ₂ H ₆ /SiH ₄
After adjusting the gas flow rate so that the ratio of . Next, a photosensitive layer made of a-Si _1-x Ge _x is formed by adjusting the flow rate ratio of SiH ₄ and GeH ₆ to a predetermined value.

The operation of the electrophotographic photoreceptor manufactured in this way will be explained. A photoreceptor having this structure is used for positive charging. During charging, the junction formed by the charge injection blocking layer 5 and the charging layer 6 is in a reverse bias state, and neutralization of the surface charge due to charge injection from the support 4 side is prevented. In addition, the dark resistivity of boron-doped a-Si, which is the charged layer 6, can be increased to 10 ¹¹ to ^{10 13} Ωcm by adjusting the amount of boron doped, so that the carrier generated by thermal excitation in the charged layer 6 can be increased. The effect of neutralizing the surface charge is small. For this reason, a photoreceptor with this structure has a voltage of 20 to 40V/
It has a sufficient charging ability of about μm, and a dark decay half-life time of about 10 to 20 seconds, which is long enough for practical use.

Next, consider a case where a photoreceptor charged to a sufficient surface potential is irradiated with light. Even without the photosensitive layer 7, the photoreceptor of this example has good photosensitivity characteristics with a photosensitivity peak at about 650 nm. a
The optical bandgap of -Si is 1.8 to 1.7eV, and if the optical energy of the peak photosensitivity and the value of the optical bandgap are proportional, a-Si _1-x G _x is used as a photosensitive layer and its optical bandgap is 1.5eV
If this is the case, the peak of photosensitivity will be approximately 780 nm, indicating a wide range of photosensitivity and long-wavelength sensitization. In order to set the optical band gap to 1.5 eV, the amount of Ge added must be 40 to 50%. Generally, in a-Si _1-x Ge _x , when the amount of Ge added increases,
There is a possibility that the μτ value decreases significantly, and the traveling distance of light carriers, especially holes, becomes several μm or less. However, in the structure of the photoreceptor of this example, a-Si _1-x Ge _x
The photosensitive layer can be kept to a few micrometers or less, and the photo-excited holes travel through the photosensitive layer without any hindrance and are injected into the charged layer. The hole μτ value in the boron-doped a-Si, which is the charged layer, is sufficiently large, and the injected holes travel without hindrance and reach the support.
Therefore, the photoreceptor of this example exhibits good photosensitivity even at long wavelengths.

According to this invention, a photoreceptor having the structure shown in FIG. 2 was manufactured. The support is aluminum, the charge injection blocking layer is an a-Si film with a thickness of about 1000 Å formed with a B ₂ H ₆ /SiH ₄ ratio of 200 ppm, and the charging layer is B ₂ H ₆ /SiH 4 .
Thickness of a-Si formed with a SiH ₄ ratio of 10 ppm
The photosensitive layer was a 2-μm-thick film of a-Si _1-x Ge _x (x about 0.5) formed with a SiH ₄ /(GeH ₄ +Si ₄ ) ratio of 0.85. When this photoreceptor was charged with a corona voltage of +7KV, the charging ability was approximately
30V/μm, half-reduced exposure amount at optical attenuation is 450~
Approximately 0.5μW/ ^cm2 for 750nm light, and 800nm light
It also showed a good photosensitivity of 0.8 μW/cm ² to light of

As explained above, in this example, the photosensitive layer and the charged layer are separated, and the charged layer has a large μτ value.
In addition, since the structure uses boron-doped a-Si with high dark resistivity and a-Si _1-x G _x with a small optical energy gap as the photosensitive layer, the charging ability and photosensitive wavelength range can be controlled independently. This has the advantage that it is possible to realize an electrophotographic photoreceptor having photosensitive band characteristics with high charging ability and good photosensitivity in a long wavelength region.

In the present invention, p-type a-Si was used as the charge injection blocking layer in the above embodiment, but if n-type a-Si was used instead, a negatively charged photoreceptor could be realized, and silicon By using a nitride film, a silicon oxide film, an aluminum oxide film, or an a-Si carbide film, a photoreceptor for positive or negative charging can be realized, and the same effects as in the above embodiments can be obtained.

Further, in the present invention, the charged layer may be an a-Si film.

The present invention also provides a-Si or boron-doped a-Si on the surface of the photoreceptor having the structure of the above-described embodiment.
may be formed. A photoreceptor having this structure will be explained below.

In the above embodiment, the photosensitive layer made of a-Si _1-x Ge _x is as thin as a few micrometers, so when the photoreceptor is used repeatedly, the thickness of the photosensitive layer decreases due to wear, resulting in a decrease in photosensitivity. There is a possibility that this may occur. Therefore, by forming a-Si or boron-doped a-Si as a surface protective layer on the surface of the photosensitive layer, the life of the photosensitive member can be extended. a-Si itself has good photosensitivity at short wavelengths of 700 nm or less, and does not inhibit the movement of photoexcited electrons and holes, so the thickness of the surface protective layer can be reduced.
Even if the thickness is about 10 μm, there will be no problem with the photosensitivity of the photoreceptor. Further, in this embodiment, the same effect can be obtained when the charge injection blocking layer is made of n-type a-Si, silicon nitride film, silicon oxide film, aluminum oxide film, or a-Si carbide.

Furthermore, the present invention provides a photoreceptor with a longer lifespan by providing an a-Si carbide layer on the surface of the surface protective layer described above, since a-Si carbide is more resistant to mechanical wear than a-Si. can be realized.

As mentioned above, the electrophotographic photoreceptor of the present invention separates the photosensitive layer and the charged layer, and uses a-Si _1-x Ge _x that is sensitive to long wavelengths as the photosensitive layer, so it has a long life and a large size. It has the effect of having charging ability and high photosensitivity at long wavelengths, and can be used as a photoreceptor for laser printers using semiconductor lasers.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of a conventional electrophotographic photoreceptor;
FIG. 3 is a sectional view of an electrophotographic photoreceptor according to an embodiment of the present invention, and FIG. 3 is a schematic structural explanatory diagram showing an apparatus for manufacturing an electrophotographic photoreceptor according to an embodiment of the invention. 1...Support, 2...Charge injection blocking layer, 3...
Photosensitive layer/charged layer, 4...Support, 5...p-type a
-Si conductive layer, 6... boron-doped a-Si layer, 7...
...A photosensitive layer consisting of a-Si _1-x Ge _x .

Claims (1)

[Claims] 1 Support and n formed on the surface of this support
type or p-type amorphous silicon, amorphous silicon carbide, silicon nitride film,
A charge injection blocking layer made of a silicon oxide film or an aluminum oxide film, and a charged layer with a dark resistivity of 10 ¹¹ Ωcm or more made of amorphous silicon or boron-doped amorphous silicon formed on the surface of this charge injection blocking layer. and an a-Si _1-x Ge _x (0.4<X) photosensitive layer formed on this layer and made of amorphous silicon germanium.