EP0211421B1 - Electrophotographic photoreceptor - Google Patents

Description

• The present invention relates generally to an electrophotographic photoreceptor, and more particularly to a photoreceptor for an electrophotographic copy machine or a light beam printer.
• Amorphous silicon (hereinafter is referred to as a-Si:H) which contains 10 to 40 atm % of hydrogen as modifying materials for reducing the concentration of localized states and has a high photosensitivity, does not give rise to environmental pollution and has a high hardness, is utilized as the photoconductive material of an electrophotographic photoreceptor.
  A piled layer construction comprising such an a-Si:H layer has, however, in practice many drawbacks, like a too high corona charge current and a still not satisfactorily high sensitivity.
• Many amendments have been proposed in the prior art in order to remedy those deficiencies.
• DE-A1-3304198 p.e. envisages two layers which separate the photoconductive layer from the substrate and both contain Si as an essential element. The lower layer shall improve adhesiveness to the substrate whereas the upper layer shall have rectifying characteristics.
• The embodiments characterized bysubclaims 2 to 5 of this prior art comprise an additional top layer which again contains silicon. It is obvious that such silicon comprising layers cannot act as carrier transport layer but are used according to the explanations given on page 26, lines 7 to 12, of this prior art as a stabilizing surface layer. Besides, in order to improve the photosensitivity in visible light and near-infrared light, an electrophotographic photoreceptor having a piled layer constitution of a-Si:H and hydrogenerated amorphous germanium (hereinafrer is referred to as a-Ge:H) (the Japanese published unexamined patent application Sho 56-150753), a piled layer constitution of a-Si:H and hydrogenerated amorphous silicon germanium (hereinafter is referred to as a-Si_1-xGe_x:H(0<x<1)) (the Japanese published patent application Sho 57-115552), a single layer constitution of a-Si_1-xGe_x:H with addition of boron and oxygen (the Japanese published patent application Sho 57-172344), or the like is proposed. However, the above-mentioned electrophotographic photoreceptorsmade from a-Si:H have many problems yet to be solved.
• A first problems, for example, is that the a-Si:H requires a very large corona charge current when its surface is charged, because the a-Si:H has a higher dielectric constant of about eleven, compared with a value of about three in an organic photosemiconductor, or about six in Se and a larger capacitance compared with other photoreceptor materials such as an organic photosemiconductor (hereinafter is referred to as OPC).
• Furthermore, a second problem is that the surface charge concentration of a-Si:H is higher and more light energies are required for light erase. Therefore, actual effective sensitivity is not sufficiently high.
• A third problem is that a plasma chemical vapor deposition method (hereinafter referred to as a plasma CVD method) using silane gas (SiH₄) and germane (GeH₄) is generally adopted to form the a-Si:H and a-Si_1-xGe_x:H (0<x<1) layer, but the deposition rate of such layers is low and is less than 10 micron per hour. Furthermore reduction of manufacturing costs is difficult since silane gas and germane gas used therein is expensive.
• Furthermore, a fourth problem is that the thickness of the actually used layer is less than 30 micron and the actual surface potential is less than 500 V and is lower than the surface potential of 800 V of a photoreceptor using Se. Therefore, there is still another problem in that a sufficient optical image concentration is not realized in a conventional two components development system.
• A fifth problem is that pinholes are liable to be formed on the layer of a-Si:H, a-Si_1-xGe_x:H or a-Ge:H produced by the plasma CVD method, thereby presenting white stains.
• In order to solve the above-mentioned problems, a function-separated photoreceptor using an organic semiconductor material is disclosed in the Japanese published unexamined patent application Sho 56-116930, and a function-separated photoreceptor using an inorganic semiconductor material is also disclosed in the Japanese published unexamined patent application Sho 55-127561.
• In case that the organic semiconductor material is adopted, the corona charge potential increases due to reduction of the dielectric constant. However, a long life photoreceptor such as a-Si:H layer which has higher hardness is not realized, since the organic semiconductor material has a low hardness.
• On the other hand, in case that the inorganic semiconductor material is adopted, there are problems that, for example, chalcogens of the inorganic semiconductor material are liable to form polycrystals and temperature characteristics become inferior. When SiC with a higher dielectric constant is used, the increase of the corona charge potential can not be prevented.
• An object of the present invention is to provide an electrophotographic photoreceptor which has a high sensitivity to visible light and a small corona charge current.
• The electrophotographic photoreceptor in accordance with the present invention is based on the novel concept of combining an inorganic photoconductive layer for issuing movable carriers by light excitation and a carrier transport layer containing amorphous carbon as main component, whereby the above-mentioned carriers are efficiently injected into the amorphous carbon layer and can move effectively.
• Amorphous carbon has a small dielectric constant and a high hardness. Hence, when the function-separated photoreceptor is formed by the amorphous carbon layer as a carrier transport layer and an a-Si:H layer as a photoconductive layer, the dielectric constant of the photoreceptor decreases by combination of both the layers, and the corona charge current decreases. As a result, surface charge concentration decrease and the sensitivity can be improved.
• The electrophotographic photoreceptor according to the invention comprises:
  a carrier transport layer containing amorphous carbon as main component and at least one element selected from the group consisting of hydrogen and halogen elements, the dielectric constant of said amorphous carbon layer being in the range of 2.3 - 6 and the thickness of said amorphous carbon layer being in the range of 5 to 50 µm, an inorganic photoconductive layer of 0.2 to 10 µm thickness for issuing movable carriers by light excitation, and a substrate for bearing said photoconductive layer and said carrier transport layer.
• The amorphous carbon layer is containing hydrogen or halogen in a suitable concentration and thereby the carrier injection efficiency of the carriers generated in the inorganic photoconductive layer can be improved. Moreover, carrier injection from a substrate is prevented, and therefore a stable operation in the electrophotographic process is obtained.
• The amorphous layer including 5--60 atm %, preferably 5--40 atm % of hydrogen has a small dielectric constant such as 2.3--6, and the carrier injection efficiency from the photoconductive layer is high. Hence, an electrophotographic characteristic similar to the a-Si:H layer is realized by the layer of half or one third thickness compared to the photoreceptor which is formed only by the a-Si:H layer.
• In case that the plasma CVD method is adopted to form the amorphous carbon layer, gases such as CH₄, C₂H₄, C₂H₆, C₂H₂, C₃H₈ or C₆H₆ are usable as a base gas. The fabrication costs of the photoreceptor are greatly reduced, since the above-mentioned gases are inexpensive in comparison with SiH₄ gas which is used in the conventional process for forming the photoreceptor by a single layer of a-Si:H.
• Furthermore, pinholes are not formed on the amorphous carbon layer which is formed by the plasma CVD method, and a fine printing without the white stains is achieved.
• FIG.1 is a cross-sectional view of a first embodiment of an electrophotographic photoreceptor in accordance with the present invention.
• FIG.2 is a cross-sectional view of a second embodiment of an electrophotographic photoreceptor in accordance with the present invention.
• A cross-sectional view of a fundamental embodiment of an electrophotographic photoreceptor in accordance with the present invention is shown in FIG.1.
• The electrophotographic photoreceptor has acarrier transport layer 2 of amorphous carbon including at least hydrogen or halogen (hereinafter referred to as a-C(:H:X), wherein X refers F, Cl, Br or I) and aphotoconductive layer 3 including silicon, both formed on asubstrate 1, thephotoconductive layer 3 having a free surface 4.
• In the present invention, the inorganicphotoconductive layer 3 including at least one element of the group comprising hydrogen and halogen and at least one of the elements silicone and germanium as a main component is formed by a material selected from the following group:
     a single layer of a-Si(:H:X), a single layer of a-Ge(:H:X), a single layer of a-Si_1-xGe_x(:H:X), a multilayer of a-Si(:H:X) and a-Ge(:H:X), a multilayer of a-Ge(:H:X) and a-Si_1-xGe_x(:H:X), a multilayer of a-Si(:H:X) and a-Si_1-xGe_x(:H:X), a multilayer of plural a-Si_1-xGe_x(:H:X) with different values of suffix x and a multilayer of a-Si(:H:X), a-Ge(:H:X) and a-Si_1-xGe_x(:H:X).
• Thephotoconductive layer 3 including silicon in the present invention is formed by a single layer of a-Si(:H:X), a-Si_1-yC_y(:H:X)(0<y<1), a-Si_1-yO_y(:H:X)(O<y<1) or a-Si_1-yN_y(:H:X)(0<y<1), or by piled layers of the combination of the above-mentioned materials. In the above-mentioned materials, the suffix "y" in the above-mentioned representation can take various values between zero and one, and the elements with the suffix "y" are contained in the materials with the ratio shown by the value of "y". These various materials are also usable to form thephotoconductive layer 3.
• Other usable material for the inorganicphotoconductive layer 3 is chalcogenide glass which is made of a material consisting of Se, Te or S, or two or more kinds thereof, which is added with Ge, for example, Ge-S, Ge-Se, Ge-Te, Ge-P-S, Ge-P-Se, Ge-P-Te, Ge-As-S, Ge-As-Se, Ge-As-Te, Ge-Sb-S, Ge-Sb-Se, Ge-Sb-Te, Ge-Si-As-Se, Ge-Si-As-Te, Ge-As-Te-Se, Ge-As-S-Te, K-Ca-Ge-S, and Ge-Te-Sb-S.
• The thickness of thecarrier transport layer 2 is 5--50 micron (micrometer) and preferably is 10--25 micron. The thickness of thephotoconductive layer 3 is 0.2--10 micron and preferably is 1--5 micron.
• At least one element selected from oxygen, sulfur and nitrogen may be incorporated into the layer of a-C(:H:X) forming thecarrier transport layer 2 in order to reduce defects in the layer of a-C(:H:X) and improve a change with the passage of time.
• It is recommended that abarrier layer 10 is formed between thesubstrate 1 and thecarrier transport layer 2 for effective interception of carriers which are injected from thesubstrate 1 into thecarrier transport layer 2 in order to improve the characteristics of the electrophotography of the present invention as shown in FIG.2.
• Thebarrier layer 10 is formed by metal oxides such as Al₂O₃ , BaO, BaO₂ , BeO, Bi₂O₃ , CaO, CeO₂ , Ce₂O₃, La₂O₃ , Dy₂O₃ , Lu₂O₃ , Cr₂O₃ ,CuO, Cu₂O, FeO, PbO, MgO, SrO, Ta₂O₃ , ThO₂ , ZrO₂ , HfO₂ , TiO₂ , TiO, SiO₂ , GeO₂ , SiO, GeO or the like, metal nitrides such as TiN, AlN, SnN, NbN, TaN, GaN or the like, metal carbides such as WC, SnC, TiC or the like, insulators such as SiC, SiN, GeC, GeN, BC, BN or the like, or organic components such as polyethylene, polycarbonate, polyurethane, polyparaxylene or the like. In case that the free surface 4 is made to be charged with positive electricity, a P-type semiconductor, such as a-Si(:H:X), a-Si_1-xGe_x(:H:X), a-Ge(:H:X), a-C(:H:X), a-Si_1-xC_x(:H:X) or a-Ge_1-xC_x(:H:X), to which is added an element of group III of the periodic table, such as B, Al or Ga, is usable. On the other hand, in case that the free surface 4 is made to be charged with negative electricity, an N-type semiconductor as the barrier layer such as a-Si(:H:X), a-Si_1-xGe_x(:H:X), a-Ge(:H:X), a-C(:H:X), a-Si_1-xC_x(:H:X) or a-Ge_1-xC_x(:H:X), which is added an element such as N, P or As of V of the periodic table, is recommended to be used.
• Furthermore, a surface covering layer may be formed on the free surface 4 in order to improve abrasion resistive characteristics and stable corona charging characteristics as shown in FIG.1 and FIG.2. Suitable materials for the surface covering layer are inorganic materials such as Si_xO_1-x , Si_xC_1-x , Si_xN_1-x , Ge_xO_1-x , Ge_xC_1-x , Ge_xN_1-x , B_xN_1-x , B_xC_1-x , Al_xN_1-x (0<x<1), or the like or plastics such as polyethyleneterephthalate, polycarbonate, polypropylene, polyamide, polytetrafluoroethylene, polytrifluoroethylene, polyvinylidenefluoride, polyurethane, or the like.
• In order to form the a-C(:H:X) layer, a plasma CVD method using a base gas comprising the element carbon, e.g. hydrocarbons such as CH₄ , C₂H₆ , C₃H₈ , C₄H₁₀ , C₂H₄ , C₃H₆ , C₄H₈ , C₂H₂ , C₃H₄ , C₄H₆ , C₆H₆ , or the like, allyl halide such as CH₃F, CH₃CI, C₂H₅Cl, C₂H₅Br, or the like, a fluorine-compound gas such as CClF₃ , CF₄ , CHF₃ , C₂H₆, C₃F₈ or the like, or a benzene derivative such as C₆H_6-mF_m (m=1--6) is adopted. A reactive sputtering method in the gas atmosphere of Ar, H₂ , F₂ , Cl₂ , C₂H₄ or C₂H₂ is also adopted by using graphite as a target.
• In order to add oxygen, sulfur or nitrogen to a-C(:H:X), a gas such as O₂ , O₃ , CO, CO₂ , NO, NO₂ , N₂O , N₂O₃ , N₂O₄ , N₂O₅ , NO₃ , or the like as a source of oxygen, a gas such as CS₂ , H₂S , S₂O . SO₂ , SO₃ or the like as a source of sulfur, and a gas such as N₂ , NH₃ , H₂NNH₂ , HN₃ , NH₄N₃ , F₃N₂ , F₄N₂ , NO, N₂O, NO₂, N₂O₃ , N₂O₄ , N₂O₅ , NO₃ or the like as a source of nitrogen are used; and these source gas is mixed with the gas of a-C(:H:X) in case of the plasma CVD method, and is mixed with a gas such as Ar, H₂ , F₂ , Cl₂ , CH₄ , C₂H₄ , C₂H₂ or the like in case of the reactive sputtering method.
• The plasma CVD method using as base gas a silicon component such as SiH₄ , Si₂H₆ , Si₃H₈ , SiF₄ , SiCl₄ , SiHF₃ , SiH₂F₂ , SiH₃F, SiHCl₃ , SiH₂Cl₂ , SiH₃Cl or the like is used to form a photoconductive layer comprising silicon represented by a-Si(:H:X), a-Si_1-yC_y(:H:X)(0<y<1), a-Si_1-yO_y(:H:X)(0<y<1) or a-Si_1-yN_y(:H:X)(0<y<1). The reactive sputtering method in the mixed gas atmosphere of Ar and H₂ (F₂ or Cl₂ can be added to the mixed gas of Ar and H₂.) is also adopted by using polycrystalline silicon as a target. Furthermore, in order to form the component represented by a-Si_1-yC_y(:H:X)(0<y<1), a-Si_1-yO_y(:H:X)(0<y<1),
  a-Si_1-yN_y(:H:X)(0<y<1), hydrocarbons such as CH₄, C₂H₆ , C₃H₈ , C₄H₁₀ , C₂H₄ , C₃H₆ , C₄H₈ , C₂H₂ , C₃H₄ , C₄H₆ , C₆H₆ or the like, an allyl halide such as CH₃F, CH₃Cl, CH₃I, C₂H₅Cl, C₂H₅Br or the like,a fluorine compound gas, such as CClF₃ , CF₄, CHF₃ , C₂F₆ , C₃F₈ or the like, or a benzene fluoride of the formula C₆H_6-mF_m(m=1--6) are added to the silicon base gas in the plasma CVD method, or are added to the sputtering gas such as Ar or the like in the reactive sputtering method. Moreover, O₂ , CO, CO₂ , NO, NO₂ or the like are added as oxygen source, and N₂ , NH₃ , NO or the like are added as nitrogen source.
• In case of adding Ge to a-Si(:H:X), or in case of forming a layer of a-Ge(:H:X) or a-Si_1-xGe_x (:H:X), only one of the compounds GeH₄ , Ge₂H₆ , Ge₃H₈ , GeF₄ , GeCl₄ , GeHF₃ , GeH₂F₂ , GeH₃F , GeHCl₃ , GeH₂Cl₂ , GeH₃Cl or the like is generally used, or one of the above-mentioned gases is mixed with the above-mentioned source gas comprising Si, and the layer can be formed by the plasma CVD method. As another method, the reactive sputtering method is adopted with the mixed gas of Ar and H₂ (furthermore, F₂ or Cl₂ may be added) by using polycrystalline germanium as a target.
• Furthermore, in the present invention, the conductivity of the layer can be controlled by addition of an impurity in the above-mentioned a-Si(:H:X), a-Si_1-yC_y(:H:X) (0<y<1), a-Si_1-yO_y(:H:X)(0<y<1), a-Si_1-yN_y(:H:X)(0<y<1), or in the materials containing Ge, and in that way a preferable characteristic in the electrophotography is realized. As p-type impurities for making p-type conductivity B, Al, Ga, In or the like one in the group of IIb of the periodic table, are suitable and B, Al or Ga is preferable for use as the impurity. As n-type impurities for n-type conductivity N, P, As, Sb or the like one in the group of Vb of the periodic table is used, and among them P or As is preferable for use as the impurity.
• The plasma CVD method is adopted for addition of these impurities, wherein one of the gases of B₂H₆ , B₄H₁₀ , B₅H₉ , B₅H₁₁ , B₆H₁₂ , B₆H₁₄ , BF₃ , BCl₃ , BBr₃ , AlCl₃ , (CH₃)₃Al, (C₂H₅)₃Al, (iC₄H₉)₃Al, (CH₃)₃Ga, (C₂H₅)₃Ga, InCl₃, (C₂H₅)₃In or the like is added as a p-type impurity to the base gas comprising C or Si and one of the gases of PH₃, P₂H₄, PH₄I, PF₃, PF₅, PCl₃, PCl₅, PBr₃, PBr₅, PI₃, AsH₃, AsF₃, AsCl₃, AsBr₃, SbH₃, SbF₃, SbF₅, SbCl₃, SbCl₅ or the like is added as an n-type impurity to the base gas comprising C or Si during the respective layer forming processes. The above-mentioned gases are diluted with H₂ gas, Ar gas or He gas in the actual process. The reactive sputtering method is also adopted and one of the above-mentioned gases is mixed to the gas of Ar, H₂, F₂ or Cl₂.
Example 1
• A mirror-finished aluminum substrate (1) was disposed in a capacitive coupling plasma CVD reactor wherein an electrode was 15.24 cm in diameter. After evacuation of air of the plasma CVD reactor to lower than 6.7 x 10⁻⁴Pa the substrate was heated to 150--300°C, preferably 200--250°C, and 10--80 sccm of C₂H₄ and 0.5--20 sccm of B₂H₆ , which were diluted to one percent with He, were introduced into the plasma CVD reactor. The pressure of the plasma CVD reactor was adjusted to 13.3 --133 Pa . An a-C:H layer having a thickness of 25 micron into which was incorporated B was formed as thecarrier transport layer 2 by a high frequency glow discharging of 20--150 W power and 13.56 MHz. Secondly, 10--40 sccm of SiH₄ were injected in the reactor, and the pressure was adjusted to 16.7 - 133 Pa. A non-doped a-Si:H layer having a thickness of 0.5--2 micron was formed as aphotoconductive layer 3 by a high frequency glow discharging of 20--100 W power. Furthermore, 10--30 sccm of SiH₄ and 20--40 sccm of C₂H₄ were introduced and the pressure was adjusted to 16.7 - 133 Pa and Si_1-xC_x:H(0<x<1) having a thickness of 0.08--0.3 micron was formed as asurface covering layer 5 by a high frequency glow discharging of 50--150 W power; thus an electrophotographic photoreceptor was completed.
• When the electrophotographic photoreceptor was charged with a corona charge voltage of +6.3 KV, the surface potential reached to +3000 V and the residual potential was less than +30 V after exposure by white light. An exposure for half decay was less than 1 lux·sec and a high sensitivity was realized. When the electrophotographic layer was charged to +800 V and was exposed by the white light, the exposure for half decay was less than 0.3 lux·sec and a very high sensitivity was realized. The sensitivity was as large as twice that of the conventional electrophotographic photoreceptor wherein the a-Si:H layer having a thickness of 20 micron was charged by +400 V and was exposed with the same white light. Furthermore, when it was exposed by a visible light, the sensitivity was improved to a value as large as two and half times of the conventional electrophotographic photoreceptor. When the above-mentioned embodiments of an electrophotographic photoreceptor and an electrophotographic photoreceptor formed by a-Si:H only were both charged by the same corona charge voltage, the corona charged potential of the former was as large as three times of that of the latter, and a higher sensitivity was realized by a small corona charge current. The reason is that a boron-added a-C:H layer acts as a carrier transport layer for holes and the dielectric constant of the electrophotographic photoreceptor decreases.
• In case that a photoconductive layer having a thickness of 0.2--2 micron is formed by a-Si:H containing 200--3000 ppm oxygen or 0.5--5 ppm boron, an electrophotographic photoreceptor which was similar to the above-mentioned photoreceptor was realized.
• When the a-C(:H:X) layer was formed in the C₂H₄ gas including 1 % of CF₄ , a characteristic which was similar to the above-mentioned photoreceptor was realized.
Example 2
• A mirror-finished aluminum drum was disposed in a cylindrical electrode of the capacitive coupling plasma CVD reactor wherein the size of the cylindrical electrode was of 45 cm length and of 16 cm inner diameter. After evacuation of the air of the plasma CVD reactor to a pressure lower than 6.7 x 10⁻⁴Pa,the aluminum drum was heated to 150--300°C, preferably 200--250°C. Then, 50--150 sccm of SiH₄ and 50--150 sccm of B₂H₆ which was diluted with H₂ and had a concentration of 400 ppm were introduced. Then, the pressure was adjusted to 16.7-133 Pa and a p-type a-Si:H layer having a thickness of 0.3--1.5 micron was formed as abarrier layer 10 on thesubstrate 1 by a high frequency glow discharging with a power of 100--250 W. Secondly, 50--150 sccm of SiH₄ was introduced and the pressure was adjusted to 16.7 - 133 Pa and an un-doped a-Si:H layer 3 having a thickness of 5--1 micron was formed on the barrier layer. Subsequently, 20--50 sccm of SiH₄ were added together with CH₄ and an a-Si_1-xC_x layer having a thickness of 0.5--1 micron was formed. Then, the introduction of SiH₄ was stopped and CH₄ only was introduced, and a carrier transport layer having a thickness of 5--10 micron was formed.
• The photoreceptor of this example was mounted in an optical printer wherein a LED having a wavelength of 670 nm was used as its light source. And when the surface voltage was a positive charge of +500--800 V, a clear print was obtained. When an a-Si:H(:F) layer was formed instead of the a-Si:H layer as the photoconductive layer or when an a-Si_1-xO_x layer or a-Si_1-xN_x layer was formed instead of the a-Si_1-xC_x layer, an electrophotographic photoreceptor which was similar in its characteristics to the above-mentioned embodiment was realized.
• When a-Si_1-yGe_y:H, which is a-Si:H added with Ge, or a-Si_1-yGe_y(:H:F), which is a-Si:H(:F) added with Ge, is used, the sensitivity of the respective photoreceptors are further improved. In this example, thebarrier layer 10, the twophotoconductive layers 3 and thecarrier transport layer 2 are formed on thesubstrate 1 in the named order as shown in FIG.2.
Example 3
• In this example, asurface covering layer 5 of a-Ge_1-xC_x (0<x<1) having a thickness of 0.1--0.5 micron was formed on the surface of the electrophotographic photoreceptor which was made by the process of Example 2 by the plasma CVD method.
• This photoreceptor was superior in heat and humidity resisting property. When it was mounted in the optical printer elucidated in the Example 2, the photoreceptor could print 800,000 sheets.
Example 4
• A polycarbonate resin layer having a dried thickness of 1 micron was coated on the electrophotographic photoreceptor which was made in the process of the example 2. This electrophotographic photoreceptor was superior in humidity resisting property. When it was mounted in the optical printer elucidated in the Example 2, the photoreceptor could print 50,000 sheets.
Example 5
• An a-Ge:H layer or a-Si_1-xGe_x:H layer having a thickness of 0.1--1 micron, both including boron, was formed on a glass substrate on the surface whereof Al was deposited, by plasma CVD method as a barrier layer. And further thereon, an a-C:H layer having a thickness of 10 micron including oxygen and boron respectively with concentration proportions of F atoms to C atoms of 0.5--20 atm % and a H atom concentration of 10--35 atm %, and further an a-Si:H layer having a thickness of 0.5--2 micron and as a surface coating layer a phosphorous-added a-Si_1-xC_x layer having a thickness of 0.1--0.5 micron were piled in the named order, and thereby an electrophotographic photoreceptor was made. When the photoreceptor was charged by a corona charge voltage of +6.3 KV and was exposed to white light, the charged potential was high and a high photosensitivity was realized.
• When the same volume of S was added instead of oxygen, the identical electrophotographic characteristic was achieved.
Example 6
• An a-C:H layer having a thickness of 6 micron including 500--1000 atom ppm of P, an a-Si:H layer having a thickness of 0.5--2 micron including 0.5--50 atom ppm of P and a-Si_1-xN_x:H layer having a thickness of 0.1--0.2 micron were piled in the named order on a substrate wherein Mo was deposited on the surface by the plasma CVD method. When the photoreceptor was charged by a corona charge voltage of -6.0 KV, the surface potential reached was -800 V. When it was exposed to white light, an exposure for half decay reached to 0.71 lux·sec and the residual potential was less than -15 V, and the sensitivity was higher. In this example, the a-C:H layer containing P acts as a carrier transport layer of electrons.
Example 7
• An aluminum deposited glass substrate was disposed in a magnetron sputtering apparatus with a target having a diameter of 15.24 cm. The substrate temperature was maintained in the range of 150--300°C, and a Dy₂O₃ layer having a thickness of 0.1--0.5 micron was formed in an atmosphere of Ar having a pressure of 0.4 - 2.7 Pa and O₂ having a pressure of 1.3 - 5.3 Pa using a sinter of Dy₂O₃ as a target by a high frequency glow discharging of a power of 100--300 W. Subsequently, an a-C:H layer having a thickness of 5 micron was formed in an atmosphere of Ar having a pressure of 0.13 - 1.3Pa and H₂ having a pressure of 1.2 - 12 Pa, using graphite as a target by a high frequency glow discharging of a power of 100--600 W. Moreover, a photoconductive a-Si:H layer having a thickness of 0.5--2 micron was formed in an atmosphere of Ar having a pressure of 0.7 - 1.3Pa and H₂ having a pressure of 0.04-0.5 Pa using polycrystal silicon as a target, by a high frequency glow discharging of a power of 200--800 W. Furthermore, a-Si_1-xN_x (0<x<1) layer having a thickness of 0.08--0.2 micron was formed as a surface covering layer by exchanging H₂ to N₂.
• When a corona charge voltage of -6.0 KV was applied to this photoreceptor, the surface charge potential reached to -650 V. When it was exposed to white light, an exposure for half decay reached to 1.2 lux·sec.
Example 8
• A non-doped a-C:H layer having an optical band gap of 1.7--1.9 eV, a layer thickness of 10--15 micron and a dielectric constant of 4--5 was formed on analuminum substrate 1, by plasma CVD method using C₂H₂ gas. Subsequently, an a-Si:H:F layer having a thickness of 1--3 micron was formed for the photoconductive layer in an atmosphere of a mixture of SiH₄ and SiF₄. Furthermore, after replacing the SiF₄ gas by N₂ gas, an a-Si_1-xN_x (0<x<1) layer having a thickness of 0.08--0.2 micron was formed as a surface covering layer. A corona charging process was applied to the electrophotographic photoreceptor which was obtained by the above-mentioned process under the corona charge voltage of -6.0 KV. As a result, a higher surface voltage potential such as -1500 V was realized, and an exposure for half decay reached to 0.5 lux·sec using white light. The above-mentioned result shows that the non-doped a-C:H layer acts as a carrier transport layer which has higher electron efficiency in the above-mentioned range of dielectric constant.
Example 9
• A mirror-finished aluminum drum was set in the capacitive coupling plasma CVD reactor. After evacuation of the air of the plasma CVD reactor to a pressure lower than 6.7x10⁻⁴ Pa, the aluminum drum was heated to 150--250°C. Then 5--30 sccm of GeH₄ and 50--200 sccm of N₂ were introduced. The pressure was adjusted to 13.3 - 133 Pa, and a Ge_1-xN_x layer having a thickness of 0.1--2 micron was formed as a barrier layer by a high frequency glow discharging with a power of 100--400 W. Subsequently, 1--5 sccm of GeF₄ , 100--200 sccm of SiH₄ and 1--5 sccm of PH₃ having a concentration of 20 ppm which was diluted with H₂ were introduced. The pressure was adjusted to 16.7 - 133 Pa and an a-Si_1-xGe_x:H:F layer having a thickness of 0.5--1 micron and including phosphorus was formed by a high frequency glow discharging with a power of 100--300 W. After that the introduction of GeF₄ was stopped and 5--20 sccm of CH₄ was introduced. An a-Si_1-xC_x:H layer having a thickness of 0.5--1 micron and including phosphorus was formed. Subsequently, 70--150 sccm of CH₄ and 1--5 sccm of N₂ were introduced. The pressure was adjusted to 13.3 - 133 Pa, and an a-C:H layer having a thickness of 3--10 micron and including nitrogen was piled by a high frequency glow discharging with a power of 100--500 W (wherein, the range of the concentration proportion of H atoms to C atoms was 10--50 atm %). Furthermore, a Ge_1-xC_x layer having a thickness of 0.1--0.8 micron was formed in a gas atmosphere of 5--10 sccm of GeH₄ and 50--100 sccm of C₂H₄ under a pressure of 13.3 - 133 Pa by a high frequency glow discharging with a power of 100--500 W and the electrophotographic photoreceptor was made. The photoreceptor of this example was mounted in a laser beam printer wherein a semiconductor laser source having a wavelength of 800 nm was used. A clear and fine printing without white stains was obtained in a negative charge. Furthermore, the photoreceptor could print 800,000 sheets and blurring of printing did not arise in a high humidity atmosphere (40°C, 90 Rh %). The photosensitivity of this photoreceptor was sensitive to white light.
• In case that one layer selected from a single layer of a-Ge:H(:F), a single layer of a-Ge_1-xC_x:H(:F), a single layer of a-Si_1-xGe_x:H(:F), and a piled layer of a-Ge:H(:F) and a-Si:H(:F), a piled layer of a-Ge:H(:F) and a-Ge_1-xC_x:H(:F), a piled layer of a-Ge:H(:F) and a-Si:H(:F), a piled layer of a-Ge_1-xC_x:H(:F) and a-Si_1-xC_x:H(:F), a piled layer of a-Ge_1-xC_x:H(:F) and a-Si:H(:F), a piled layer of a-Ge:H(:F) and a-Ge_1-xC_x:H(:F), and a piled layer of a-Ge_1-xC_x:H(:F) and a-Si_1-xGe_x:H:(F), which was piled on the surface of Al drum in the named order, was used instead of a photoconductive layer of an a-Si_1-xGe_x:H:F layer including phosphorus and an a-Si_1-xC_x:H:F layer including phosphorus, an electrophotographic receptor having a characteristic similar to the above-mentioned example was obtained.
Example 10
• A glass substrate wherein Al was deposited on the surface was set in a magnetron sputtering apparatus and was heated to 150°C--300°C. A Dy₂O₃ layer having a thickness of 0.1--0.5 micron was formed in an atmosphere of Ar having a pressure of 0.4 -2.7 Pa and of O₂ having a pressure of 1.3 - 5.3 Pa using a sinter of Dy₂O₃ as a target by a high frequency glow discharging of a power of 100--300 W. Subsequently, an a-C:H layer having a thickness of 5 micron was formed in an atmosphere of Ar having a pressure of 0.13 - 5.3Pa and of H₂ having a pressure of 1.2 - 12 Pa using graphite as the target by the high frequency glow discharging of a power of 100--600 W. Furthermore, an As-Se-Ge layer having a thickness of 1--2 micron was formed by vapour deposition, and an uniform polycarbonate layer having a dried thickness of 10 micron was formed on the As-Se-Ge layer as a surface covering layer. Thus the electrophotographic photoreceptor was made. After a corona charging process of the electrophotographic photoreceptor under the corona charge voltage of +6.3 KV, it was exposed to white light, a high charging potential and high sensitivity were achieved.

Claims (11)

1. An electrophotographic photoreceptor comprising:
   a carrier transport layer containing amorphous carbon as main component and at least one element selected from the group consisting of hydrogen and halogen elements, the dielectric constant of said amorphous carbon layer being in the range of 2.3 - 6 and the thickness of said amorphous carbon layer being in the range of 5 to 50 µm, an inorganic photoconductive layer of 0.2 to 10 µm thickness, preferably of 1 to 5 µm thickness, for issuing movable carriers by light excitation, and a substrate for bearing said photoconductive layer and said carrier transport layer.
2. An electrophotographic photoreceptor in accordance with claim 1 further comprising
   a surface covering layer formed on a free surface of said electrophotographic photoreceptor.
3. An electrophotographic photoreceptor in accordance with claim 1 or 2, wherein
   said inorganic photoconductive layer contains at least one element selected from the group consisting of amorphous silicon and germanium.
4. An electrophotographic photoreceptor in accordance with claim 1 or 2, wherein
   a barrier layer is formed between said substrate and said inorganic photoconductive layer or between said substrate and said carrier transport layer.
5. An electrophotographic photoreceptor in accordance with claim 1, 2 or 3, wherein
   said inorganic photoconductive layer contains at least one element selected from the group consisting of hydrogen and halogen elements.
6. An electrophotographic photoreceptor in accordance with claim 1 or 2, wherein
   said amorphous carbon layer contains at least one element selected from the groups of IIIB and Vb of the Periodic Table.
7. An electrophotographic photoreceptor in accordance with claim 1 or 2, wherein
   said inorganic photoconductive layer contains at least one element selected from the group consisting of carbon, oxygen and nitrogen.
8. An electrophotographic photoreceptor in accordance with claim 1 or 2, wherein
   said amorphous carbon layer contains at least one element selected from the group consisting of oxygen, sulfur and nitrogen.
9. An electrophotographic photoreceptor in accordance with claim 1 or 2, wherein
   said inorganic photoconductive layer contains at least one element selected from the groups of IIIb and Vb of the Periodic Table.
10. An electrophotographic photoreceptor in accordance with claim 1 or 2, wherein
    said inorganic photoconductive layer contains at least one element selected from the group of VI of the Periodic Table.
11. An electrophotographic photoreceptor in accordance with claim 1, 2 or 10, wherein
    said inorganic photoconductive layer contains chalcogens.

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