An electrophotographic photosensitive member

0001This invention relates to an electrophotographic photosensitive member comprising a photoconductive layer made of amorphous silicon which is formed by an electron cyclotron resonance method.

0002In recent years, as an electrophotographic photosensitive member which is used, for example, in an apparatus for forming images based on electrophotography, there has been proposed a photosensitive member in which a photoconductive layer made of amorphous silicon (referred to as a-Si hereinafter) is formed on a conductive substrate. This a-Si type photosensitive member has numerous advantages such as its long working life, high photosensitivity, high degree of hardness (Hv:1500-2000 kg/mm²), and harmlessness to human bodies. Thus, many attempts have been made to put it into practical use as a desirable photosensitive material.

0003U.K. Patent Application GB 2,077,451A relates to a photoconductive member comprising a substrate, a a-Si photoconductive layer, and a barrier layer between the substrate and the photoconductive layer. U.S. Patent No. 4,532,199 corresponding to DE-A-3 407 643 relates to a method of forming an amorphous silicon film including the steps of bringing a gas which is pre-excited by electron cyclotron resonance generated by an alternating electric field and a magnetic field into contact with a raw material gas containing silicone atoms in a reaction chamber in which a substrate is placed, so that the raw material gas is converted to radicals, and forming an amorphous silicon film on a surface of the substrate by the reaction of radicals therewith. U.S. Patent No. 4,698,288 relates to a photoresponsive imaging member comprising a supporting substrate, a ground plane of hydrogenated silicon having incorporated therein dopants; and a photoconductive layer comprising hydrogenated amorphous silicon.

0004Conventional a-Si type photosensitive members have usually been produced by plasma CVD, sputtering, or other techniques. In the plasma CVD method, a source gas such as monosilane or disilane is first introduced into a vacuum chamber in which a conductive substrate made of aluminum or the like is disposed. The introduction of the source gas into the vacuum chamber is followed by glow discharge with the application of high-frequency power, so that the source gas in the vacuum chamber is decomposed and an a-Si layer containing hydrogen is grown on the substrate. In the sputtering method, which employs a Si wafer as a target, both H₂ gas and a rare gas such as Ar, He, or the like are first introduced into a chamber, and then glow discharge is caused by the application of high-frequency power, so that the target is sputtered and an a-Si layer containing hydrogen is grown on a substrate.

0005However, to confer sufficient photosensitivity to the a-Si type photosensitive member in the production processes mentioned above, the conductive substrate must be heated to form the a-Si layer thereon. Consequently, the amount of hydrogen contained in the a-Si layer is increased. The excessive amount of hydrogen contained in the a-Si layer makes its electric conductivity as high as 10^-10s/cm, so that the electric-charge retaining property of the a-Si layer is deteriorated.

0006The electric conductivity of the a-Si layer can be increased by the addition of boron thereto with the use of, for example, B₂H₆ gas. In this case, however, the degree of increase is relatively small and there can only be obtained the electric conductivity of at most about 10^-11-10^-12s/cm.

0007The conventional production processes are also disadvantageous in that the deposition rate is very low; the availability of source gas is low; and plenty of powdered polymer such as (SiH₂)_n is produced as a by-product and deposited on the surface of the conductive substrate during the growth of a-Si layer, so that many defects can be generated in the a-Si layer, resulting in reduced production yield of a-Si type photosensitive members.

0008For the conventional a-Si type photosensitive members, the amount of hydrogen contained in the a-Si layer is strictly limited to the range of 10-40 atomic %. (See Japanese Patent Publication No. 60-35059 and U.S. Patent No. 4,265,991.) Moreover, Japanese Laid-open Patent Publication No. 57-158650 discloses an a-Si layer containing 10-40 atomic % of hydrogen, in which the ratio of the absorption coefficient α(SiH₂) at around 2100 cm^-1 to the absorption coefficient α(SiH) at around 2000 cm^-1 in the infrared spectrum of the a-Si layer is in the range of about 0.2-1.7. The absorption coefficient α(SiH₂) at around 2100 cm^-1 is due to Si-H₂ bonds, and the absorption coefficient α(SiH) at around 2000 cm^-1 is due to Si-H bonds. To ensure sufficient photosensitivity for the electrophotographic photosensitive members comprising an a-Si photoconductive layer, their resistivity becomes as small as 10⁹Ω·cm, and even when boron (B) is doped in the a-Si layer, their resistivity is still as small as 10¹¹Ω·cm, so that the electric-charge retaining property of the a-Si type photosensitive members is inferior to that of conventional selenium or organic photosensitive members.

0009To improve the electric-charge retaining property of the conventional a-Si photosensitive members, it is necessary to increase the absorption coefficient ratio α(SiH₂)/ α(SiH). However, in the processes by plasma CVD or sputtering, the reaction of the source gas becomes more active with the increase in high-frequency power in forming each layer, so that a lot of powdered polymer such as (SiH₂)_n is produced. The resulting powdered polymer is deposited on the surface of the substrate of the photosensitive member, which impairs the quality of the photosensitive member obtained.

0010It is an object of the present invention to provide an electrophotographic photosensitive member which overcomes the above-discussed and other disadvantages and deficiencies of the prior art.

0011In accordance with the present invention there is provided, an electrophotographic photosensitive member comprising an electrically conductive substrate, an intermediate layer formed on said substrate, a photoconductive layer formed on said intermediate layer and an outer coating layer formed on said photoconductive layer, wherein said photoconductive layer is made of amorphous silicon containing 40 or more atomic % of hydrogen and/or halogen, and which is obtainable by the electron cyclotron resonance method without heating the substrate and using a gas pressure in the range from 0.373 to 0.453 Pa (2.8x10^-3 to 3.4x10^-3 Torr), and wherein the ratio of the adsorption coefficient at around 2,100 cm^-1 of SiH₂ to the absorption coefficient at around 2,000 cm^-1 of SiH in the infrared spectrum of said amorphous silicon is in a range from 1.3 to 2.5, and the ratio of the integrated absorption intensity at around 840 cm^-1 to the integrated absorption intensity at around 880 cm^-1 in the infrared spectrum of said amorphous silicon is in a range from 0.2 to 0.6.

0012In a preferred embodiment, the photosensitive layer is made of amorphous silicon containing 40 to 60 atomic % of hydrogen and/or halogen.

0013In a more preferred embodiment, the photosensitive layer is made of amorphous silicon containing 40 to 50 atomic % of hydrogen and/or halogen.

0014In a preferred embodiment, the photoconductive layer is doped with an element of Group IIIA of the Periodic Table as an impurity.

0015In a preferred embodiment, the photoconductive layer is doped with an element of Group VA or Group VIA of the Periodic Table as an impurity.

0016Thus, the invention described herein makes possible the provision of (1) an electrophotographic photosensitive member which has high photosensitivity and extremely high dark resistivity, so that its excellent electric-charge retaining property can be attained, resulting in an image of high quality; (2) an electrophotographic photosensitive member which has improved electric conductivity and electric-charge retaining property, so that an image of high quality can be obtained; (3) an electrophotographic photosensitive member which is produced by the electron cyclotron resonance method, so that the deposition rate and gas availability can be improved, resulting in reduced production cost; and (4) an electrophotographic photosensitive member which is produced by the electron cyclotron resonance method, so that the production of powdered polymer such as (SiH₂)_n can be prevented, resulting in improved production yield.

0017The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings, in which: <ul id="ul0001" list-style="none"><li>Figure 1 is a cross sectional view showing the structure of an electrophotographic photosensitive member of this invention;</li><li>Figure 2 is a cross sectional view showing an apparatus for the production of the electrophotographic photosensitive member of this invention by an electron cyclotron resonance method;</li><li>Figure 3 shows the relationship between the pressure of gas and the hydrogen content in the a-Si layers of various electrophotographic photosensitive members;</li><li>Figure 4 shows the relationship between the pressure of gas and the absorption coefficient ratio α(SiH₂)/α(SiH) of the a-Si layers of various electrophotographic photosensitive members;</li><li>Figure 5 shows the relationship between the pressure of gas and the photo conductivity (η·µ·τ) of the a-Si layers of various electrophotographic photosensitive members;</li><li>Figure 6 shows the relationship between the pressure of gas and the dark resistivity (ρd) of the a-Si layers of various electrophotographic photosensitive members; and</li><li>Figure 7 shows the relationship between the integrated absorption intensity ratio (I₂/I₁) and the electric conductivity and the relationship between the integrated absorption intensity ratio (I₂/I₁) and the photo conductivity (η·µ·τ) of the a-Si layers of various electrophotographic photosensitive members.</li></ul>

0018In Figure 2, the apparatus comprises a plasma formation chamber <b>11</b> in which hydrogen plasma is formed and a deposition chamber <b>12</b> in which each layer is formed. The plasma formation chamber <b>11</b> and the deposition chamber <b>12</b>, which communicate with each other via a plasma inlet <b>13</b>, are evacuated with an exhaust system (not shown) comprising an oil diffusion pump and an oil rotary pump.

0019The plasma formation chamber <b>11</b> serves as a cavity resonator into which 2.45-GHz microwaves are introduced through a waveguide <b>14</b>. A microwave supply window <b>15</b> is made of a quartz glass plate which can transmit the microwaves. The plasma formation chamber <b>11</b> is provided with a gas supply pipe <b>19</b> through which hydrogen gas can be introduced thereinto. Magnetic coils <b>16</b> and <b>17</b> are disposed around the plasma formation chamber <b>11</b>. The magnetic coil <b>16</b> generates a magnetic field (875G) for the formation of plasma and the magnetic coil <b>17</b> generates a magnetic field by which the plasma formed in the plasma formation chamber <b>11</b> is introduced into the deposition chamber <b>12</b>.

0020The electrophotographic photosensitive member of this invention is produced with this apparatus as follows: First, a conductive substrate <b>18</b> is positioned nearly in the central portion of the deposition chamber <b>12</b>. The conductive substrate <b>18</b> can be, for example, a drum made of aluminum. The plasma formation chamber <b>11</b> and the deposition chamber <b>12</b> are evacuated with the exhaust system. Then, hydrogen gas and, if required, additional gas are introduced into the plasma formation chamber <b>11</b> through the gas supply pipe <b>19</b>, while source gas is introduced into the deposition chamber <b>12</b> through gas supply pipes <b>20</b>. The source gas can be a gas of silicon compounds such as SiH₄, Si₂H₆, SiF₄, SiCl₄, SiHCl₃, and SiH₂Cl₂, or a mixture thereof. When an a-SiC or a-SiN layer is formed, for example, CH₄ or NO gas is added to the source gas. In this case the pressure of gas is controlled to be in the order of 0.133 to 0.013 Pa (10^-3-10^-4 Torr). Then the microwaves generated from a microwave oscillator (not shown) are introduced into the plasma formation chamber <b>11</b>, while the magnetic field is being formed. The hydrogen gas is converted into plasma in the plasma formation chamber <b>11</b>, and the resulting hydrogen plasma is introduced into the deposition chamber <b>12</b> through the plasma inlet <b>13</b>, to convert the source gas into plasma there. The resulting plasma of the source gas is then brought onto the conductive substrate <b>18</b> by the magnetic field for the introduction of plasma, and a-Si is deposited on the surface of the conductive substrate <b>18</b>. Because the conductive substrate <b>18</b> is being rotated by a supporting member, a layer (e.g., an a-Si layer) having a uniform thickness can be formed on the surface of the conductive substrate <b>18</b>. The uniformity of the thickness of the layer can be further improved by regulating the position and size of the plasma inlet <b>13</b>.

0021As is similar to the case of the conventional plasma CVD, the conductivity type of the a-Si layer formed can be determined by the sort of additional gas to be introduced. When the additional gas of a compound containing an element of Group IIIA of the Periodic Table such as B₂H₆ or BH₃ is used, the a-Si layer of p-type is obtained. On the contrary, when the additional gas of a compound containing an element of Group VA or Group VIA of the Periodic Table such as PH₃, PCl₃, or PCl₅ is used, the a-Si layer of n-type is obtained.

0022With this apparatus, a series of experiments for forming a-Si layers were conducted using the source gas of SiH₄ under the different pressures of gas. The dependences of the hydrogen content, absorption coefficient ratio α(SiH₂)/ α(SiH), photo conductivity (η·µ·τ), and dark resistivity (ρd) of these a-Si layers upon the pressure of gas are respectively shown in Figures 3, 4, 5, and 6.

0023As can be seen from these figures, when 40 atomic % or more of hydrogen was contained in the a-Si layer and the absorption coefficient ratio α(SiH₂)/ α(SiH) was in the range of 1.3-2.5, the a-Si layer having dark resistivity of 10¹²Ω·cm or more and high photo conductivity (i.e., high photosensitivity) was obtained. It is noted that the conventional a-Si layers containing 40 atomic % or less of hydrogen and having the ratio α(SiH₂)/ α(SiH) in the range of 0.2-1.7 could not have attained dark resistivity of 10¹²Ω·cm or more and high photo conductivity (i.e., high photosensitivity). Preferably, the amount of hydrogen contained in the a-Si layer is 40-60 atomic %, and more preferably 40-50 atomic %. When the amount of hydrogen contained in the a-Si layer is greater than 60 atomic %, the optical band gap of the a-Si layer becomes excessively large, so that the layer is not suitable for the photoconductive layer of the electrophotographic photosensitive member which must have photosensitivity to visible light.

0024In general, the absorption peak due to Si-H bonds is observed at around 2000 cm^-1 and the absorption peak due to Si-H₂ bonds is observed at around 800-900 cm^-1 in the infrared spectrum of a-Si. When SiH₂ is present in the form of a monomer, its absorption peak is observed only at around 880 cm^-1 and when SiH₂ is present in the form of a polymer such as (SiH₂)_n, its absorption peaks are observed both at around 880 cm^-1 and at around 840 cm^-1 in the infrared spectrum of a-Si.

0025As for the a-Si layer of the electrophotographic photosensitive member, SiH₂ and (SiH₂)_n are present as a mixture, and it is well known that the properties of the photosensitive member such as electric conductivity can vary depending on the ratio of (SiH₂)_n to SiH₂. The inventors have found that the ratio of (SiH₂)_n to SiH₂ can be estimated on the basis of the I₂ (the integrated absorption intensity at around 840 cm^-1)/I₁ (the integrated absorption intensity at around 880 cm^-1) ratio in the infrared spectrum of a-Si. The integrated absorption intensity is expressed by the integral ∫ α (w)/w·dw where α (w) is the absorption coefficient at the wave number of w. If the ratio is nearly set to satisfy the inequality 0.2&lt;(I₂/I₁)&lt;0.6, it is possible to improve the properties of the a-Si type photosensitive member such as electric conductivity.

0026Figure 7 shows the relationship between the integrated absorption intensity ratio (I₂/I₁) and the electric conductivity and the relationship between the integrated absorption intensity ratio (I₂/I₁) and photo conductivity. When the integrated absorption intensity ratio (I₂/I₁) is in the range of about 0.2-0.6, the electric conductivity is about 10^-12s/cm and the photo conductivity is about 10^-6cm²/V, both of which are satisfactory.

0027The a-Si layer formed by the electron cyclotron resonance method is advantageous in that: (1) Stable plasma can be produced under relatively low pressure of gas 0.001 to 0.013 Pa (10^-5-10^-3 Torr) and the production of powdered polymer such as (SiH₂)_n be avoided by preventing the secondary reaction between the reactants, so that the a-Si layer which is satisfactory can be formed; (2) Because of the high energy of electrons, the efficiencies of decomposition, excitation, and ionization of the introduced gas are remarkably improved. As a result, both the deposition rate and gas availability are increased by 6-10 times. For example, it is possible to attain the deposition rate of about 23 µm/hr and the gas availability of about 49%; and (3) Because of the appropriate degree of ion impingement, it is possible to form the a-Si layer without heating the conductive substrate, so that the amount of (SiH₂)_n contained in the a-Si layer can be reduced, resulting in a high-quality a-Si layer with high photosensitivity.

0028The a-Si layer of this invention is suitable for the photosensitive element of a device by which optical information from outside can be converted into electrical signals, so that it can serve as the photoconductive layer of an electrophotographic photosensitive member, the photosensitive element of an image sensor, or the photosensitive element of a liquid crystal or multilayer display device. Moreover, the a-Si layer of this invention can also be applied to various devices such as solar batteries and thin film transistors.

Example 1

0029In this example, an electrophotographic photosensitive member <b>1</b> to be positively charged as shown in Figure 1 was produced as follows: On a conductive substrate 2, an intermediate layer <b>3</b> made of a-Si in which a large amount of boron was doped, a photoconductive layer <b>4</b> made of a-Si in which a small amount of boron was doped, and an outer coating layer <b>5</b> made of a-SiC were successively formed in that order by the electron cyclotron resonance method. As an additional gas for doping boron in the a-Si layers, a compound of boron with hydrogen or halogen such as B₂H₆ is preferred. In place of boron, an element of Group IIIA of the Periodic Table such as aluminum, gallium, indium, or the like can be used. The conditions for the production of respective layers are shown in Table 1 below. <tables id="tabl0001" num="0001"><table frame="all"><title>Table 1</title><tgroup cols="6" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="26.25mm" /><colspec colnum="2" colname="col2" colwidth="26.25mm" /><colspec colnum="3" colname="col3" colwidth="26.25mm" /><colspec colnum="4" colname="col4" colwidth="26.25mm" /><colspec colnum="5" colname="col5" colwidth="26.25mm" /><colspec colnum="6" colname="col6" colwidth="26.25mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" rowsep="0" align="left">Layer</entry><entry namest="col2" nameend="col2" rowsep="0" align="left">MW power (kW)</entry><entry namest="col3" nameend="col5" align="center">Flow rate</entry><entry namest="col6" nameend="col6" rowsep="0" align="center">Gas pressure Pa</entry></row><row><entry namest="col1" nameend="col1" /><entry namest="col2" nameend="col2" /><entry namest="col3" nameend="col3" align="left">SiH₄ (SCCM)</entry><entry namest="col4" nameend="col4" align="left">B₂H₆ (SCCM)</entry><entry namest="col5" nameend="col5" align="left">CH₄ (SLM)</entry><entry namest="col6" nameend="col6" /></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">Intermediate</entry><entry namest="col2" nameend="col2" align="char" char=".">2.5</entry><entry namest="col3" nameend="col3" align="right">120</entry><entry namest="col4" nameend="col4" align="right">30 ^*1</entry><entry namest="col5" nameend="col5" align="char" char=".">--</entry><entry namest="col6" nameend="col6" align="char" char=".">0.373</entry></row><row><entry namest="col1" nameend="col1" align="left">Photoconductive</entry><entry namest="col2" nameend="col2" align="char" char=".">2.5</entry><entry namest="col3" nameend="col3" align="right">120</entry><entry namest="col4" nameend="col4" align="right">5 ^*2</entry><entry namest="col5" nameend="col5" align="char" char=".">--</entry><entry namest="col6" nameend="col6" align="char" char=".">0.373</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">Outer coating</entry><entry namest="col2" nameend="col2" align="char" char=".">2.5</entry><entry namest="col3" nameend="col3" align="right">30</entry><entry namest="col4" nameend="col4" align="right">--</entry><entry namest="col5" nameend="col5" align="char" char=".">2.0</entry><entry namest="col6" nameend="col6" align="char" char=".">0.373</entry></row></tbody></tgroup><tgroup cols="6" colsep="0" rowsep="0"><colspec colnum="1" colname="col1" colwidth="26.25mm" /><colspec colnum="2" colname="col2" colwidth="26.25mm" /><colspec colnum="3" colname="col3" colwidth="26.25mm" /><colspec colnum="4" colname="col4" colwidth="26.25mm" /><colspec colnum="5" colname="col5" colwidth="26.25mm" /><colspec colnum="6" colname="col6" colwidth="26.25mm" /><tbody valign="top"><row><entry namest="col1" nameend="col6" align="justify">*1: 3000 ppm in H₂.</entry></row><row><entry namest="col1" nameend="col6" align="justify">*2: 30 ppm in H₂.</entry></row></tbody></tgroup></table></tables>

0030The a-Si photoconductive layer 4 contained 48 atomic % of hydrogen, and its absorption coefficient ratio α(SiH₂)/α(SiH) in the infrared spectrum was 2.15.

0031In this example, powdered polymer such as (SiH₂)_n was not produced, and both the deposition rate and the gas availability were increased 6-10 times compared with that of the conventional processes. Moreover, when the resulting a-Si type photosensitive member was examined for its properties, its electric-charge retaining property was particularly excellent compared with the conventional a-Si type photosensitive members. When the a-Si type photosensitive member was used in a commercial copying machine to carry out copying, images of high quality were obtained.

0032When an a-SiN layer or a-SiO layer formed by the electron cyclotron resonance method was used as the outer coating layer <b>5</b> instead of the a-SiC layer, the results obtained were also satisfactory.

Example 2

0033An electrophotographic photosensitive member <b>1</b> as shown in Figure 1 was produced in a similar manner to that of Example 1, except that different gas pressures were used to form the photoconductive layer <b>4</b>. The resulting photosensitive members were examined for their electric charge retaining property and photosensitivity. The results obtained are shown in Table <b>2</b>. <tables id="tabl0002" num="0002"><table frame="all"><title>Table 2</title><tgroup cols="6" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="26.25mm" /><colspec colnum="2" colname="col2" colwidth="26.25mm" /><colspec colnum="3" colname="col3" colwidth="26.25mm" /><colspec colnum="4" colname="col4" colwidth="26.25mm" /><colspec colnum="5" colname="col5" colwidth="26.25mm" /><colspec colnum="6" colname="col6" colwidth="26.25mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" align="center">Sample No.</entry><entry namest="col2" nameend="col2" align="center">1</entry><entry namest="col3" nameend="col3" align="center">2</entry><entry namest="col4" nameend="col4" align="center">3</entry><entry namest="col5" nameend="col5" align="center">4</entry><entry namest="col6" nameend="col6" align="center">5</entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">Gas pressure Pa</entry><entry namest="col2" nameend="col2" align="center">0.373</entry><entry namest="col3" nameend="col3" align="center">0.453</entry><entry namest="col4" nameend="col4" align="center">0.506</entry><entry namest="col5" nameend="col5" align="center">0.586</entry><entry namest="col6" nameend="col6" align="center">0.666</entry></row><row><entry namest="col1" nameend="col1" align="left">Electric charge retaining property*</entry><entry namest="col2" nameend="col2" align="center">ⓞ</entry><entry namest="col3" nameend="col3" align="center">ⓞ</entry><entry namest="col4" nameend="col4" align="center">○</entry><entry namest="col5" nameend="col5" align="center">Δ</entry><entry namest="col6" nameend="col6" align="center">Δ</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">Photosensitivity*</entry><entry namest="col2" nameend="col2" align="center">ⓞ</entry><entry namest="col3" nameend="col3" align="center">ⓞ</entry><entry namest="col4" nameend="col4" align="center">×</entry><entry namest="col5" nameend="col5" align="center">×</entry><entry namest="col6" nameend="col6" align="center">×</entry></row></tbody></tgroup><tgroup cols="6" colsep="0" rowsep="0"><colspec colnum="1" colname="col1" colwidth="26.25mm" /><colspec colnum="2" colname="col2" colwidth="26.25mm" /><colspec colnum="3" colname="col3" colwidth="26.25mm" /><colspec colnum="4" colname="col4" colwidth="26.25mm" /><colspec colnum="5" colname="col5" colwidth="26.25mm" /><colspec colnum="6" colname="col6" colwidth="26.25mm" /><tbody valign="top"><row><entry namest="col1" nameend="col6" align="justify">* ⓞ Very good ○ Good Δ Acceptable for practical use × Poor</entry></row></tbody></tgroup></table></tables>

0034As can be seen from Table 2 above, satisfactory results were obtained when the ratio α(SiH₂)/α(SiH) was set to 1.3-2.5 by controlling the gas pressure to 0.373 to 0.453 Pa (2.8 x 10^-3-3.4 x10^-3 Torr) according to the relationship shown in Figure 4.

0035The amount of hydrogen contained in the photoconductive layer was measured for each photosensitive member. The results were that when the gas pressure to 0.373 to 0.453 Pa (2.8 x 10^-3-3.4 x 10^-3 Torr) 45-52 atomic % of hydrogen was contained in the photoconductive layer and when the gas pressure was 0.506 to 0.666 Pa (3.8 x 10^-3-5.0 x 10^-3 Torr), 20-30 atomic % of hydrogen was contained in the photosensitive layer.

Example 3

0036A photosensitive member to be negatively charged as shown in Figure 1 was produced in a similar manner to that of Example 1, except that an a-Si layer doped with a small amount of phosphorus was used as the photoconductive layer 4 and an a-Si layer doped with a great amount of phosphorus was used as the intermediate layer 3. As an additional gas for doping phosphorus in the a-Si layers, a gas of a compound of phosphorus with hydrogen or halogen such as PH₃, PCl₃, or PCl₅ is preferred. In place of phosphorus, an element of Group VA or Group VIA of the Periodic Table such as nitrogen, antimony, oxygen or the like can be used. The conditions for the production of respective layers are shown in Table 3 below. <tables id="tabl0003" num="0003"><table frame="all"><title>Table 3</title><tgroup cols="6" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="26.25mm" /><colspec colnum="2" colname="col2" colwidth="26.25mm" /><colspec colnum="3" colname="col3" colwidth="26.25mm" /><colspec colnum="4" colname="col4" colwidth="26.25mm" /><colspec colnum="5" colname="col5" colwidth="26.25mm" /><colspec colnum="6" colname="col6" colwidth="26.25mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" rowsep="0" align="left">Layer</entry><entry namest="col2" nameend="col2" rowsep="0" align="left">MW power (kW)</entry><entry namest="col3" nameend="col5" align="center">Flow rate</entry><entry namest="col6" nameend="col6" rowsep="0" align="center">Gas pressure Pa</entry></row><row><entry namest="col1" nameend="col1" /><entry namest="col2" nameend="col2" /><entry namest="col3" nameend="col3" align="center">SiH₄ (SCCM)</entry><entry namest="col4" nameend="col4" align="center">PH₃ (SCCM)</entry><entry namest="col5" nameend="col5" align="center">CH₄ (SLM)</entry><entry namest="col6" nameend="col6" /></row></thead><tbody valign="top"><row rowsep="0"><entry namest="col1" nameend="col1" /><entry namest="col2" nameend="col2" /><entry namest="col3" nameend="col3" /><entry namest="col4" nameend="col4" align="center">*1</entry><entry namest="col5" nameend="col5" /><entry namest="col6" nameend="col6" /></row><row><entry namest="col1" nameend="col1" align="left">Intermediate</entry><entry namest="col2" nameend="col2" align="char" char=".">2.5</entry><entry namest="col3" nameend="col3" align="right">120</entry><entry namest="col4" nameend="col4" align="center">10</entry><entry namest="col5" nameend="col5" align="char" char=".">--</entry><entry namest="col6" nameend="col6" align="char" char=".">0.373</entry></row><row rowsep="0"><entry namest="col1" nameend="col1" /><entry namest="col2" nameend="col2" /><entry namest="col3" nameend="col3" /><entry namest="col4" nameend="col4" align="center">*2</entry><entry namest="col5" nameend="col5" /><entry namest="col6" nameend="col6" /></row><row><entry namest="col1" nameend="col1" align="left">Photoconductive</entry><entry namest="col2" nameend="col2" align="char" char=".">2.5</entry><entry namest="col3" nameend="col3" align="right">120</entry><entry namest="col4" nameend="col4" align="center">1</entry><entry namest="col5" nameend="col5" align="char" char=".">--</entry><entry namest="col6" nameend="col6" align="char" char=".">0.373</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">Outer coating</entry><entry namest="col2" nameend="col2" align="char" char=".">2.5</entry><entry namest="col3" nameend="col3" align="right">30</entry><entry namest="col4" nameend="col4" align="center">--</entry><entry namest="col5" nameend="col5" align="char" char=".">2.0</entry><entry namest="col6" nameend="col6" align="char" char=".">0.373</entry></row></tbody></tgroup><tgroup cols="6" colsep="0" rowsep="0"><colspec colnum="1" colname="col1" colwidth="26.25mm" /><colspec colnum="2" colname="col2" colwidth="26.25mm" /><colspec colnum="3" colname="col3" colwidth="26.25mm" /><colspec colnum="4" colname="col4" colwidth="26.25mm" /><colspec colnum="5" colname="col5" colwidth="26.25mm" /><colspec colnum="6" colname="col6" colwidth="26.25mm" /><tbody valign="top"><row><entry namest="col1" nameend="col6" align="justify">*1: 3000 ppm in H₂.</entry></row><row><entry namest="col1" nameend="col6" align="justify">*2: 30 ppm in H₂.</entry></row></tbody></tgroup></table></tables>

0037In this example, powdered polymer such as (SiH₂)_n was not produced, and both the deposition rate and the gas availability were much higher than those obtained following the conventional processes. Furthermore, when the resulting a-Si type photosensitive member was examined for its properties, its electric-charge retaining property was particularly excellent. When the a-Si type photosensitive member was used in a commercial copying machine to carry out copying, images of high quality were obtained.

0038When an a-SiN layer or a-SiO layer formed by the electron cyclotron resonance method was used as the outer coating layer <b>5</b> instead of the a-SiC layer, the results obtained were also satisfactory.

Example 4

0039In this example, an electrophotographic photosensitive member <b>1</b> as shown in Figure 1 was produced as follows: On a conductive substrate <b>2</b> an intermediate layer <b>3</b> made of a-SiN in which a large amount of boron was doped, a photoconductive layer <b>4</b> made of a-Si in which a small amount of boron was doped, and an outer coating layer <b>5</b> made of a-SiC were successively formed in that order by the electron cyclotron resonance method. The a-Si layer of the resulting photosensitive member <b>1</b> was of p-type. The conditions for the production of respective layers are shown in Table 4 below. <tables id="tabl0004" num="0004"><table frame="all"><title>Table 4</title><tgroup cols="7" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="22.50mm" /><colspec colnum="2" colname="col2" colwidth="22.50mm" /><colspec colnum="3" colname="col3" colwidth="22.50mm" /><colspec colnum="4" colname="col4" colwidth="22.50mm" /><colspec colnum="5" colname="col5" colwidth="22.50mm" /><colspec colnum="6" colname="col6" colwidth="22.50mm" /><colspec colnum="7" colname="col7" colwidth="22.50mm" /><thead valign="top"><row rowsep="1"><entry namest="col1" nameend="col1" rowsep="0" align="center">Layer*1</entry><entry namest="col2" nameend="col2" rowsep="0" align="center">MW power (kW)</entry><entry namest="col3" nameend="col6" align="center"><u>Flow rate</u></entry><entry namest="col7" nameend="col7" rowsep="0" align="center">Gas pressure Pa</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" /><entry namest="col2" nameend="col2" /><entry namest="col3" nameend="col3" align="center">SiH₄ (SCCM)</entry><entry namest="col4" nameend="col4" align="center">B₂H₆ (SCCM)</entry><entry namest="col5" nameend="col5" align="center">NO (SCCM)</entry><entry namest="col6" nameend="col6" align="center">CH₄ (SCCM)</entry><entry namest="col7" nameend="col7" /></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" /><entry namest="col2" nameend="col2" /><entry namest="col3" nameend="col3" /><entry namest="col4" nameend="col4" align="right">*2</entry><entry namest="col5" nameend="col5" /><entry namest="col6" nameend="col6" /><entry namest="col7" nameend="col7" /></row><row><entry namest="col1" nameend="col1" align="left">Intermediate</entry><entry namest="col2" nameend="col2" align="char" char=".">2.5</entry><entry namest="col3" nameend="col3" align="right">120</entry><entry namest="col4" nameend="col4" align="right">22</entry><entry namest="col5" nameend="col5" align="right">12</entry><entry namest="col6" nameend="col6" align="right">--</entry><entry namest="col7" nameend="col7" align="char" char=".">0.359</entry></row><row><entry namest="col1" nameend="col1" /><entry namest="col2" nameend="col2" /><entry namest="col3" nameend="col3" /><entry namest="col4" nameend="col4" align="right">*3</entry><entry namest="col5" nameend="col5" /><entry namest="col6" nameend="col6" /><entry namest="col7" nameend="col7" /></row><row><entry namest="col1" nameend="col1" align="left">Photosensitive</entry><entry namest="col2" nameend="col2" align="char" char=".">2.5</entry><entry namest="col3" nameend="col3" align="right">120</entry><entry namest="col4" nameend="col4" align="right">6</entry><entry namest="col5" nameend="col5" align="right">--</entry><entry namest="col6" nameend="col6" align="right">--</entry><entry namest="col7" nameend="col7" align="char" char=".">0.359</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">Outer coating</entry><entry namest="col2" nameend="col2" align="char" char=".">1.5</entry><entry namest="col3" nameend="col3" align="right">120</entry><entry namest="col4" nameend="col4" align="right">--</entry><entry namest="col5" nameend="col5" align="right">--</entry><entry namest="col6" nameend="col6" align="right">18</entry><entry namest="col7" nameend="col7" align="char" char=".">0.106</entry></row></tbody></tgroup><tgroup cols="7" colsep="0" rowsep="0"><colspec colnum="1" colname="col1" colwidth="22.50mm" /><colspec colnum="2" colname="col2" colwidth="22.50mm" /><colspec colnum="3" colname="col3" colwidth="22.50mm" /><colspec colnum="4" colname="col4" colwidth="22.50mm" /><colspec colnum="5" colname="col5" colwidth="22.50mm" /><colspec colnum="6" colname="col6" colwidth="22.50mm" /><colspec colnum="7" colname="col7" colwidth="22.50mm" /><tbody valign="top"><row><entry namest="col1" nameend="col7" align="justify">*1: The substrate was at room temperature.</entry></row><row><entry namest="col1" nameend="col7" align="justify">*2: 3000 ppm in H₂.</entry></row><row><entry namest="col1" nameend="col7" align="justify">*3: 30 ppm in H₂.</entry></row></tbody></tgroup></table></tables>

0040In this example, electrophotographic photosensitive members with different integrated intensity ratios (I₂/I₁) in the infrared spectra were also produced in the same way as above. Figure 7 shows the relationship between the integrated absorption intensity ratio (I₂/I₁) and the electric conductivity, and the relationship between the integrated absorption intensity ratio (I₂/I₁) and the photo conductivity. Table 5 shows four other properties of the a-Si type photosensitive members <b>A-D</b> with different integrated absorption intensity ratios and the conventional a-Si type photosensitive member <b>E</b> produced by plasma CVD method. <tables id="tabl0005" num="0005"><table frame="all"><title>Table 5</title><tgroup cols="6" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="26.25mm" /><colspec colnum="2" colname="col2" colwidth="26.25mm" /><colspec colnum="3" colname="col3" colwidth="26.25mm" /><colspec colnum="4" colname="col4" colwidth="26.25mm" /><colspec colnum="5" colname="col5" colwidth="26.25mm" /><colspec colnum="6" colname="col6" colwidth="26.25mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" align="left">Sample</entry><entry namest="col2" nameend="col2" align="center">A</entry><entry namest="col3" nameend="col3" align="center">B</entry><entry namest="col4" nameend="col4" align="center">C</entry><entry namest="col5" nameend="col5" align="center">D</entry><entry namest="col6" nameend="col6" align="center">E</entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">Surface potential(V)</entry><entry namest="col2" nameend="col2" align="char" char=".">870</entry><entry namest="col3" nameend="col3" align="char" char=".">860</entry><entry namest="col4" nameend="col4" align="char" char=".">860</entry><entry namest="col5" nameend="col5" align="char" char=".">800</entry><entry namest="col6" nameend="col6" align="char" char=".">820</entry></row><row><entry namest="col1" nameend="col1" align="left">Percentage of electric charge remaining <b>1</b> second after charging (%)</entry><entry namest="col2" nameend="col2" align="char" char=".">89</entry><entry namest="col3" nameend="col3" align="char" char=".">89</entry><entry namest="col4" nameend="col4" align="char" char=".">88</entry><entry namest="col5" nameend="col5" align="char" char=".">83</entry><entry namest="col6" nameend="col6" align="char" char=".">79</entry></row><row><entry namest="col1" nameend="col1" align="left">Sensitivity (cm²/erg)</entry><entry namest="col2" nameend="col2" align="char" char=".">0.1</entry><entry namest="col3" nameend="col3" align="char" char=".">0.42</entry><entry namest="col4" nameend="col4" align="char" char=".">0.44</entry><entry namest="col5" nameend="col5" align="char" char=".">0.23</entry><entry namest="col6" nameend="col6" align="char" char=".">0.45</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">Residual Potential (V)</entry><entry namest="col2" nameend="col2" align="char" char=".">210</entry><entry namest="col3" nameend="col3" align="char" char=".">50</entry><entry namest="col4" nameend="col4" align="char" char=".">45</entry><entry namest="col5" nameend="col5" align="char" char=".">105</entry><entry namest="col6" nameend="col6" align="char" char=".">35</entry></row></tbody></tgroup></table></tables>

0041The a-Si type photosensitive members <b>B</b> and <b>C</b> with the integrated absorption intensity ratios in the range of 0.2-0.6 have excellent sensitivities and the improved electric-charge retaining property compared with the conventional a-Si type photosensitive member E. The image formation was conducted by use of these a-Si type photosensitive members <b>B</b> and <b>C</b>, so that images of high quality free from fog were obtained. Table 5 also indicates that, although the a-Si type photosensitive members <b>A</b> and <b>D</b> with the integrated absorption intensity ratios outside the range of 0.2-0.6 have the improved electric-charge retaining property, their sensitivities and residual potentials are unsatisfactory, so that these photosensitive members are not suitable for practical use.

0042The a-Si layers with the integrated absorption intensity ratio in the range of 0.2-0.3 were quantitatively analyzed, and it was found that the amounts of hydrogen contained in the a-Si layers were 40-50 atomic %. When the a-Si layer contained hydrogen at a percentage in this range, the dark resistivity and photo conductivity of the photosensitive member were particularly satisfactory.

0043It is understood that various other modifications will be apparent to and can be readily made by those skilled in the art without departing from the scope of this invention as defined by the appended claims.