JPH0715585B2 - Photoconductor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a photoconductor composed of germanium nitride and an amorphous material containing silicon atoms or germanium atoms as main components.

(Prior Art) Amorphous hydrogen silicon (hereinafter abbreviated as a-SiH) is photoconductive,
Since it has excellent heat resistance and is non-polluting, development research on its use in imaging devices and electrophotographic photoreceptors is active.
As a method for realizing the high sensitivity and low dark current required for these image pickup devices, a blocking structure in which a charge injection blocking layer is formed at the interface of the photoconductive layer is effective. For example,
In the case of a hole blocking layer that blocks the inflow of holes into the photoconductive layer, oxides such as Al ₂ O ₃ and SiOx and organic polymer SiNx such as polycarbonate have been conventionally proposed.
(References: JP-A-56-24356 and JP-A-57-58161) (Problems to be solved by the invention) The conventional hole blocking layer is SiNx, SiOx, Al ₂ O ₃ and organic polymer. If such a structure is used, a barrier is also formed for electrons in the photoconductive layer, and there is a problem in reducing the operating voltage (reducing the afterimage in the image pickup device and the electrophotographic photoreceptor).

An object of the present invention is to solve the conventional drawbacks, to use a layer containing germanium nitride as a main component as a hole blocking layer, to realize a low dark current and a low operating voltage, and to reduce loss due to absorption and reflection of an incident hole. To provide a photoconductor that does not.

(Means for Solving the Problems) The photoconductor of the present invention comprises a film of amorphous silicon containing hydrogen atoms or halogen atoms as a main component and a film of amorphous silicon germanium as a main component on a conductive substrate. Forming a first layer made of any one of them or a combination thereof, and further forming at least a second layer containing germanium nitride as a main component on the first layer. is there.

Further, the first layer contains any one of oxygen atom, nitrogen atom, carbon atom or a combination thereof, and the first layer contains at least one kind of boron atom or phosphorus atom. The second layer, germanium nitride, contains either one or both of an oxygen atom and a carbon atom, and further contains boron between the conductive substrate and the first layer, In addition, any one of amorphous silicon and amorphous silicon germanium containing at least a hydrogen atom or a halogen atom is formed.

(Function) Since germanium nitride exhibits n-type conduction regardless of the composition ratio of nitrogen, it blocks the inflow of holes into the amorphous silicon that is the photoconductive layer, and prevents the electrons in the amorphous silicon from being affected. Since no barrier is formed, the dark current is reduced and the operating voltage is reduced. Also when the photoconductive layer is made of amorphous silicon germanium with a narrow band gap,
By reducing the nitrogen composition ratio x of germanium nitride, it is easy to reduce the bandgap of germanium nitride. It works effectively as a blocking layer, and it is possible to obtain the same effect as when the photoconductive layer is amorphous silicon. Furthermore, germanium nitride, which has a large nitrogen composition ratio, is transparent to visible light and has a smaller refractive index than the photoconductive layer.Therefore, when light is irradiated from the germanium nitride side, absorption loss and reflection of incident light It is possible to significantly reduce loss. Further, when the photoconductor of the present invention is used as an electrophotographic photoreceptor, germanium nitride has a large surface tension with respect to water, so that dew does not easily condense even in a high humidity atmosphere, and image deletion and blurring can be suppressed.

(Embodiment) An embodiment of the present invention will be described with reference to FIGS. 1 to 4.

Ge is used to form a germanium nitride (hereinafter abbreviated as GeNx) film.
_{H 4, Ge 2 H 6,} Ge 3 H 8, GeF 4, GeHF 3, GeH 2 F 2, GeH 3 F, GeCl
Source gas of Ge atom such as ₄ , GeHCl ₃ , GeH ₂ Cl ₂ , GeH ₃ Cl, GeF ₂ , GeCl ₂ and N ₂ , NH ₃ , H ₂ NNH ₂ , HN ₃ , NH ₄ N ₃ , F
Plasma CVD using N atom source gas such as ₃ N and F ₄ N ₂
Method, the target is Ge or Ge ₃ N _4, and Ar, H ₂ , N ₂ , N
H ₃ reactive sputtering method or a vapor deposition method in is employed.
Amorphous silicon in the photoconductive layer is composed of SiH ₄ , Si ₂ H ₆ , and Si _{3
H 8, SiF 4, SiHF 3} , SiH 2 F 2, SiH 3 F, SiCl 4, SiHCl 3, SiH
₂ Cl ₂ , SiH ₃ Cl or other source gas of Si atom or plasma CVD method using these gases diluted with gas such as H ₂ , Ar or He, or targeting Si in Ar, H ₂ Can be formed by the reactive sputtering method or the vapor deposition method. In the case of amorphous silicon germanium, the source gas of Ge atoms and
The mixed gas of Si atom source gas, or this mixed gas
Plasma using a gas diluted with a gas such as H ₂ , Ar, or He
CVD method or mixed target of Si and Ge or Si
It can be formed by a reactive sputtering method or an evaporation method in Ar and H ₂ using two targets of Ge and Ge.

An example using the reactive sputtering method will be described in Example 1, and an example using the plasma CVD method will be described in Examples 2 and 3.

Example 1 FIG. 1 is a sectional view of a photoconductor of the present invention. In the figure, the glass substrate 6 on which the ITO transparent electrode 4 is formed is placed in a magnetron sputtering apparatus, and after evacuation to 2 × 10 ⁻⁸ Torr or less, the substrate temperature is raised to 250 ° C. Using a polycrystal of Si as a target, Ar: 1 to 10 mTorr and H ₂ : 0.3 to 4 mTorr are introduced into the apparatus, and an a-Si: H layer 3 of 8 μm is formed by a high frequency power of 200 to 800 W at a frequency of 13.56 MHz. Subsequently, Ar: 1 to 3 mTorr, N ₂ :: 2 to 6 mTorr were introduced, the target was Ge polycrystal, and the discharge power was 300 to 5
A GeNx layer 2 of 0.2 μm is formed with 00W. Further, the Al electrode 1 is formed by the sputtering method or the vacuum evaporation method.

As shown in FIG. 1, when the voltage is applied so that the Al electrode 1 is positive and the ITO transparent electrode 4 on the substrate side is negative, the dark current and the voltage dependence of the photocurrent with respect to the light of the wavelength of 435 nm are shown in FIG. Shown in. As a conventional example for comparison, as shown in FIG.
SiNx layer 5 with Ar: 2 to 4 mTorr and N ₂ : 1 to 2 mTorr, targeting Si polycrystal and discharge power of 300 to 500 W
FIG. 3 shows the voltage-current characteristics in the structure using 0.2 μm of the above as a blocking layer. As is clear from the figure,
The embodiment of the present invention has low voltage operation, high sensitivity, and low dark current.

Like GeNx, SiNx acts as a hole blocking layer, but it acts as a barrier to electrons in a-Si: H, and the operating voltage is higher than GeNx that does not create a barrier. There is.

In addition, the photoconductor shown in FIG.
When the electrode 1 and the external circuit were removed and used positively, the saturated surface potential was 440V and the residual potential was 5V or less. It can be seen that the examples of the present invention provide electrophotographic photoreceptors having a large amount of charge acceptance and a small residual potential.

Embodiment 2 FIG. 4 is a sectional view of a photoconductor according to the second embodiment of the present invention. In the figure, the mirror-polished Al drum 20 is placed in a capacitively coupled plasma CVD apparatus, the reaction vessel is evacuated to 5 × 10 ⁻⁶ Torr or less, and then the Al drum 20 is heated to 150 to 250 ° C. . SiH ₄ : 5 to 10 sccm, NH ₃ : 100 to 200 sccm were introduced, and the pressure in the reaction vessel was also 0.2 to 1.
After adjusting to 0 Torr, SiNx layer 24 with high frequency power of 150 to 600 W
1000 to 2000Å formed, SiH ₄ : 100 to 200 sccm, pressure 0.2 to 1.0 Torr, high frequency power 150 to 500 W, and a-Si: H layer 23 formed 10 to 15 μm.
F _4: 0.5 to 10 sccm, SiH _4: 100 to 200 sccm, PH of 10ppm concentrations of hydrogen diluted _3: 5 to to 10 sccm introduced, pressure 0.2
Or 1.0 Torr and high frequency power: 150 to 500 W to form a phosphorus-doped amorphous silicon germanium layer 22 of 1 to 3 μm. In addition, GeF ₄ : 1 to 5 sccm, NH ₃ : 190 to 20
A GeNx layer 21 of 0.2 to 1 μm is formed with a pressure of 0.2 to 1.0 Torr and a high frequency power of 300 to 800 W to obtain a photoconductor.

The spectral sensitivity of this photoconductor for positive charging is 400 to 850.
It was highly sensitive over the wavelength range of nm, and it was confirmed that the amorphous silicon germanium layer 22 was added to the a-Si: H layer 23 as a photoconductive layer to improve the photosensitivity in the infrared region.
This photoconductor was mounted on a laser beam printer using an 800 nm semiconductor laser as a light source, and clear printing was confirmed.
In this case, the GeNx layer 21 increases the composition ratio x of nitrogen to widen the bandgap, and functions not only as a hole blocking layer but also as a window layer that does not absorb light for exposure. Is playing.

Further, in order to stabilize the photosensitive member and increase the resistance, carbon atoms, oxygen atoms or nitrogen atoms may be added to the amorphous silicon germanium layer 22 and the a-Si: H layer 23, and the GeNx layer Oxygen atoms or carbon atoms may be added to 21 in order to effectively widen the band gap and increase the surface hardness.

(Embodiment 3) As in Embodiment 2, the plasma CVD method is used to obtain 150 to 250
SiH ₄ : 100 to 200 sccm, hydrogen diluted 40 ppm, concentration BF ₃ : 100 to 200 sccm, gas pressure 0.2 to 1.0 Torr, p-type a-Si boron added with discharge power 100 to 400 W on Al drum heated to ℃. H film 0.2 to 1.0μm thick, SiH ₄ : 100 to 200sccm, diluted with hydrogen 40ppm, concentration BF
₃ : 1 to 10 sccm, gas pressure 0.2 to 1.0 Torr, discharge power 100 to 400 W, boron-doped a-Si: H film 10 to 2
0 μm is formed. Furthermore, GeH ₄ : 0.5 to 1.0 sccm, N ₂ : 1
A GeNx layer 1000 to 5000Å is formed at 50 to 200 sccm, a gas pressure of 0.2 to 1.0 Torr, and a discharge power of 300 to 600 W to obtain an electrophotographic photoreceptor.

It was confirmed that when this electrophotographic photosensitive member was mounted on a commercially available copying machine, it was possible to obtain a printing durability of 500,000 sheets and a good image by positive charging.

(Effect of the Invention) The photoconductor according to the present invention has a low dark current and a low operating voltage and can be used as an electrophotographic photoreceptor, an imaging device or a photodiode. In particular, when light is irradiated from the a-GeNx side, by using an a-GeNx film having a high nitrogen content, there is no reflection loss or absorption loss of incident light and high photosensitivity is obtained. Further, when used as an electrophotographic photosensitive member, image deletion and blurring can be suppressed even in a high-humidity atmosphere, so that the element structure is effective for actual use.

[Brief description of drawings]

FIG. 1 is a sectional view of a photoconductor according to an embodiment of the present invention,
FIG. 2 is a cross-sectional view of a conventional photoconductor, FIG. 3 is a chart showing the voltage dependence of dark current and photocurrent, and FIG. 4 is a photoconductor of the present invention for an electrophotographic photoreceptor. It is sectional drawing of one application example. 1 …… Al electrode, 2,21 …… GeNx layer, 3,23 …… a-Si: H layer, 4
...... ITO transparent electrode, 5,24 …… SiNx layer, 6,11 …… Glass substrate, 22 …… Amorphous silicon germanium layer.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Masanori Watanabe 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) Reference JP-A-60-75841 (JP, A) JP-A-61-48866 (JP, A) JP-A-61-288076 (JP, A)

Claims (5)

[Claims] 1. A film containing hydrogen atoms or halogen atoms as a main component of amorphous silicon and a film containing amorphous silicon germanium as a main component, or one of them, on a conductive substrate. And a second layer containing germanium nitride as a main component is further formed on the first layer. 2. The light according to claim 1, wherein the first layer contains any one of an oxygen atom, a nitrogen atom, a carbon atom or a combination thereof. conductor. 3. The photoconductor according to claim 1, wherein the first layer contains at least one type of boron atom or phosphorus atom. 4. The second layer, germanium nitride, contains either one or both of an oxygen atom and a carbon atom, and the germanium nitride according to claim 1 is used. The photoconductor according to any one of claims. 5. Forming, between the support and the first layer, any one of amorphous silicon and amorphous silicon germanium containing boron and containing at least hydrogen atoms or halogen atoms. The photoconductor according to any one of claims (1) to (4).