JPH0652428B2 - Photoconductor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Purpose of the invention Industrial field of application The present invention provides a photoconductive layer comprising a photoconductive layer made of amorphous silicon hydride containing a Group Va element of the periodic table on a conductive substrate. The present invention relates to a conductor that can be used as a one-dimensional or two-dimensional image sensor or an electrophotographic photosensitive member.

2. Description of the Related Art In recent years, a photoconductor having a photoconductive layer made of amorphous hydrogenated silicon on a conductive substrate is pollution-free, has good photosensitivity, excellent heat resistance, and spectral sensitivity of all visible light. It is high in the area and has excellent wear resistance, so it is a camera tube target,
It is being increasingly researched as an image sensor for a solid-state imaging device or an electrophotographic photosensitive member.

As a method of forming a photoconductive layer made of amorphous silicon hydride on a conductive substrate, (1) plasma CVD method by decomposing silane gas in plasma, (2) targeting silicon, inert gas In addition, there are a reactive sputtering method by introducing hydrogen gas, and (3) an ion plating method by reacting silicon vapor in hydrogen plasma.

Among these methods, the photoconductive layer made of amorphous silicon hydride formed by the plasma CVD method and the ion plating method has a low resistance of the photoconductive layer and has a dark current for use as an image sensor or electrophotography. It has the drawback of being large. Therefore, when a photoconductive layer made of amorphous hydrogenated silicon is formed by the plasma CVD method, a blocking layer is provided between the photoconductive layer and the conductive substrate,
High resistance is achieved by introducing oxygen or nitrogen into the photoconductive layer.

On the other hand, when the amorphous silicon hydride layer is formed by the reactive sputtering method, a photoconductive layer having a higher resistance than that of the amorphous silicon photoconductive layer formed by the plasma CVD method is obtained, Although it is expected to be applied as an image sensor or an electrophotographic photosensitive member, in this case, it has a drawback that the photosensitivity is poor, and there are not many studies.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The present invention improves the conventional photoconductive layer so that it can be applied as an image sensor and an electrophotographic photoreceptor, and further satisfies the characteristics of high resistance and high photosensitivity a-Si. : H is to obtain a photoconductor.

In particular, as for the electrophotographic photosensitive member, the charging potential per unit film thickness, that is, the charging ability is 40 V / μm by any of the above-mentioned methods, and it is possible to further increase the withstand voltage, reduce the film thickness, and reduce the manufacturing cost. There is an urgent need for commercialization.

(2) Structure of the Invention Means for Solving the Problems In order to achieve the above object, the present invention is as a first invention.
In a photoconductor in which a photoconductive layer made of amorphous silicon hydride containing a Va group element of the periodic table is provided on a conductive substrate, the content of the Va element group and hydrogen in the photoconductive layer is set to the above. In the cross section of the photoconductive layer, in the vicinity of the interface with the conductive substrate or in the vicinity of the surface of the photoconductor, the photoconductor was made larger than in other portions.

Further, as a second invention, the periodic table Va is formed on the conductive substrate.
In a photoconductor provided with a photoconductive layer made of amorphous silicon hydride containing a group element, from the interface of the conductive substrate (or the surface of the photoconductor) to the surface of the photoconductor (or the interface of the conductive substrate) , Amorphous hydrogenated silicon containing a large amount of Va group element and hydrogen, amorphous silicon containing a small amount of Va group element and hydrogen, and a photoconductor provided with an electron blocking layer.

Action Va group elements such as N, P, As and Sb act as donor impurities in the photoconductive layer made of amorphous silicon hydride. Therefore, as described above, the concentration distribution of the Va group element in the photoconductive layer is increased near the interface with the conductive substrate or near the surface opposite thereto in the concentration as compared with other portions to provide a difference. Since that portion is made more n-type, it is considered that the n-i type diode is configured only by making the distribution concentration of the Va group element have a difference. In addition, the introduction of a small amount of Va group element into the i layer increases the mobility of electrons, thereby lowering the operating voltage.

Further, if the hydrogen content in the photoconductive layer of amorphous silicon hydride having a large content of the above-mentioned Va group element is made larger than that in other portions, the band gap becomes larger than that in the inside, and the hole blocking layer becomes more effective. And can have a higher breakdown voltage. Therefore, compared with the case where the Va group element and hydrogen are uniformly distributed in the photoconductive layer, the breakdown voltage is higher and the photosensitivity is higher.

Example The above description will be specifically described with reference to the drawings. First
2 and FIG. 2 each show the structure of a photoconductor in which a photoconductive layer 2 of amorphous silicon hydride is provided on a conductive substrate 1 (for example, an aluminum plate). In the first embodiment shown in FIG. 1, the photoconductive layer 3 of amorphous hydrogenated silicon having a high Va group element and hydrogen content, that is, a high concentration, is provided near the interface with the conductive substrate 1. In the second embodiment shown in FIG. 2, contrary to the case shown in FIG. 1, the amorphous silicon hydride photoconductive layer 3 is formed near the surface of the amorphous hydrogenated silicon layer 2.
Is provided. By doing so, as described above, the photoconductor has an n-i type diode structure having a different forbidden band width, which is the first structure when used as an electrophotographic photoreceptor.
In the case of FIG. 2, the negative charging voltage can be increased, and in the case of FIG. 2, the positive charging voltage can be increased.

In the present invention, it is not necessary to divide the difference in the concentration distributions of the Va group element and hydrogen into two layers that are distinct in stages as described above, and from one (from the photoconductive layer 3) to the other (light The concentration may be changed by gradually increasing the concentration of the Va group element and the hydrogen concentration toward the side opposite to the conductive layer 3).

In addition, in FIGS. 1 and 2, when a very small amount of a Va group element is introduced into the photoconductive layer 4 of amorphous hydrogenated silicon having a low Va group element concentration, the electron mobility becomes large, but there is an advantage. It does not contradict the intention of the present invention even when the group element is not contained.

The above-described Va group element and hydrogen concentration distribution do not necessarily have to match.

In FIGS. 1 and 2, since the amorphous silicon hydride photoconductive layer 3 having a high Va group element content acts as a hole blocking layer, the amorphous hydrogenation having a low Va group element content is performed. The silicon photoconductive layer 4 is sandwiched between the photoconductive layer 3 and the opposite side, that is, on the photoconductive layer 4 in FIG.
Further, in FIG. 2, if an electron blocking layer is provided on the side of the conductive substrate, an n-ip type diode can be constructed and the breakdown voltage can be further increased. As the electron blocking layer at this time, a p-type amorphous hydrogenated silicon layer, an amorphous silicon carbide layer, or an insulating layer such as silicon nitride, silicon oxide, or alumina oxide can be used. Also Va
IIIa was added to an amorphous hydrogenated silicon layer containing a small amount of group elements.
Group B, such as B, Al, Ga, In, etc., and Group IIb, such as Zn, C
When an acceptor impurity such as d or Hg is added, the above layer becomes more intrinsic and the breakdown voltage can be further increased.

The present invention will be described below with reference to examples.

Example 1 This example shows an example of the photoconductor shown in FIG.

After placing the phosphorus (P) -doped Si single crystal in the magnetron sputtering device and evacuating the device to 2 × 10 ⁻⁶ Torr or less,
The conductive substrate 5 formed with Mo on the Si wafer is set to 250 ° C.
Held in, and then 4.5 × 10 ^-3 Torr and Ar in the device, H ₂ and 5 × 10 ^-4 Torr, 1% of of H ₂ containing P ₂ H ₆ 5 × 10 ^-4
Introduced so that the partial pressure ratio of Torr, discharge power 200W
Then, a photoconductive layer 6 of amorphous hydrogenated silicon containing P having a thickness of 0.2 μm was formed. After that, only the introduction of H ₂ containing P ₂ H ₆ was stopped, and the other conditions were the same and the photoconductive layer 7 of amorphous silicon hydride having a thickness of 2 μm was continuously formed at a discharge power of 200 W. Thus, the photoconductive layer 6 containing a large amount of P was provided at the interface with the conductive substrate 5. 1mm square transparent electrode 1
After forming to a thickness of 000Å, in vacuum at 300 ℃ 20
Heat treatment was performed for a minute. The resistance before heat treatment is 5 × 10 ¹² Ωcm
However, it became 1 × 10 ¹³ Ωcm after the heat treatment. Photocurrent is 400 ~ before and after heat treatment when -5V is applied to the transparent electrode.
It had a high quantum efficiency of 0.98 in the visible light region of 600 nm. When this photoconductive film was formed on a CCD as a laminated solid-state image pickup element, a solid-state image pickup device having characteristics such that dark current, photosensitivity, optical response, and resolution were sufficiently satisfied was obtained. The effect of this trace impurity P was the same for As and Sb. If N,
The operating voltage was higher than that of other elements.

Example 2 Next, as shown in FIG. 4, the Al substrate 8 was kept at 250 ° C., and the inside of the apparatus was evacuated to 2 × 10 ⁻⁶ Torr or less. Next, Ar in the apparatus was 4 × 10 ^-3 Torr, and H ₂ containing 5% of P ₂ H ₆ was 1 × 1.
It is introduced so that it becomes 0 ^-3 Torr, and the first with discharge power of 100W.
0.2 μm of the photoconductive layer 9 of amorphous silicon hydride containing Se
Formed with a thickness of. Next, Ar is 4.5 × 10 ^-3 Torr, 50p
H ₂ containing pm of P ₂ H ₆ was changed to 0.5 × 10 ⁻³ Torr and the discharge power was set to 300 W to form the second Se-containing amorphous hydrogenated silicon photoconductive layer 10 with a thickness of 6 to 7 μm. did. Photoconductive layer 10
The P / Si of was measured by an atomic absorption method and found to be 2 × 10 ⁻³ . The average value of P / Si of the photoconductive layer 9 was 5 × 10 ⁻⁵ .

According to the measurement by infrared absorption, the photoconductive layer 9 is the photoconductive layer.
It has been confirmed that the hydrogen content is higher than 10.

The composition distribution of each element of Si, H, and P in the cross-sectional direction of the photoconductive layer of amorphous hydrogenated silicon as a whole thus formed was analyzed by SIMS.

The photoconductive layers 6 and 9 of amorphous hydrogenated silicon adjacent to the conductive substrate contain a large amount of P and a large amount of hydrogen. In the photoconductive layers 7 and 10, the P concentration and the hydrogen concentration decrease toward the surface. In this case, the photoconductive layer serves as a hole blocking layer having a large forbidden band and has a higher breakdown voltage.

When the photoconductive layer of amorphous silicon hydride was charged with a corotron, it was charged to -350 V, and the half decay time in the dark was 15 seconds. Irradiation with a tungsten lamp 3 lux reduced the surface potential to 0 in less than 1 second.

Example 3 This example is an example in which an electron blocking layer 14 is provided on the surface of the amorphous silicon hydride layers 12 and 13 having the P concentration distribution shown in Examples 1 and 2, and is shown in FIG.

On the amorphous hydrogenated silicon layers 12 and 13 of the photoconductors manufactured in Examples 1 and 2, the temperature of the Al substrate 11 is set to 150 ° C., and Ar is set to 1 × 10 ⁻³ Torr, N _{2 in the apparatus.} Was introduced to obtain 2 × 10 ⁻³ Torr, and a discharge power of 400 W was applied to produce Si with a thickness of 600 Å.
An electron blocking layer 14 made of Nx was formed. This SiNx
According to ESCA analysis, is the stoichiometric ratio of SiNx, that is, Si ₃ N
It was very close to ₄ .

The initial charge potential of the photoconductor thus prepared is -400V,
Half-decay time in the dark is 30 seconds, residual potential is -5V
Became.

In the case of the present embodiment, since the electron blocking layer SiNx layer is formed on the surface, it becomes similar to the nip type diode and the resistance at the time of reverse bias becomes large, so that the charging potential rises and the half decay time is reduced. It is considered that the increase occurred.

The same effect can be obtained by forming a p-type amorphous hydrogenated silicon layer, an amorphous SixC _1-x layer, or an insulating layer such as SiOx instead of the SiNx layer.

Example 4 The electrophotographic photosensitive member having the SiNx surface layer as shown in Example 3 was heat-treated at 250 to 350 ° C. for 5 to 100 minutes in vacuum. The initial charging potential reached -480V. Also, the photosensitivity is not deteriorated by the heat treatment.

Comparative example in which the photoconductive layer 12 has the same H concentration and P concentration as the photoconductive layer 13 in the film structure of the photoconductor, that is, has a uniform distribution.
(1), the photoconductive layer 12 has a higher H concentration than the photoconductive layer 13, and the H concentration is the same. (2), the photoconductive layer 12 is the photoconductive layer 1
Only the P concentration is larger than 3, and the H concentration is shown in the table by comparing the initial charging potentials after the heat treatment of the same Comparative Example (3).

The initial charging potential increases with the P concentration distribution and the H concentration distribution. Further, although the initial charging potential of the comparative example and the example of the present invention was improved even if the heat treatment was carried out in vacuum, the comparative example of the present invention, that is, the example in which the P concentration and the H concentration were changed at the same time, was relatively good. is good. The effect of heat treatment in vacuum is SiCx, SiOx
Other surface layers such as the above also improved the characteristics.

Example 5 The sample before heat treatment used in Example 3 was heated to 250-4 in air.
Heat treatment was performed at 00 ° C. for 5 to 200 minutes. It can be seen that although the initial charging potential is lower than that in the heat treatment in vacuum, the characteristics of the examples of the present invention are good.

Example 6 The sample before the heat treatment used in Example 5 was treated with an inert gas atmosphere,
5-2 at 250-400 ° C in hydrogen atmosphere or nitrogen atmosphere
When the heat treatment was performed for 00 minutes, the initial charging potential was obtained almost similarly to the heat treatment in vacuum.

Example 7 This example shows an example in which impurities of a Va group element are not intentionally introduced into the photoconductive layer of amorphous hydrogenated silicon having a low hydrogen content shown in FIG.

The mirror-polished stainless steel plate 15 is placed in an RF magnetron sputtering apparatus, the apparatus is evacuated to 1 × 10 ⁻⁶ Torr or less, and the substrate temperature is raised to 210 ° C. Next, H ₂ containing Ar 3.5 × 10 ⁻³ TorrP ₂ H ₆ 3% was placed in the apparatus at 1.5 × 10 ⁻³ To.
rr was introduced and 0.4 μm was formed at a discharge power of 800 W to form a first amorphous silicon hydride photoconductive layer 16. Then Ar 4.0
× 10 ^-3 Torr H ₂ and H ₂ containing no Se 1.0 × introduced 10 ^-3 Torr, 8.0 .mu.m in discharge power 800 W, thereby forming a second amorphous silicon hydride of the photoconductive layer 17. Continue to Ar 1
Introducing 3 × 10 ⁻³ Torr of × 10 ⁻³ Torr and N ₂ to form a SiNx layer 18 of 1000 Å at 400 W. The discharge was stopped and the substrate temperature was raised to 300 ° C. and kept for 30 minutes. When the temperature was lowered, the photoconductor was taken out of the apparatus and its characteristics were measured.
Could be formed in time.

Example 8 Example 7 is an example in which the hydrogen partial pressure is changed so that the hydrogen concentration of the amorphous silicon hydride photoconductive layer 16 in the vicinity of the substrate 15 is made larger than that of the internal amorphous silicon hydride photoconductive layer 17. Is. The hydrogen concentration in the film width can also be changed by changing the discharge power while keeping the hydrogen partial pressure constant. That is, it is utilized that the hydrogen concentration in the amorphous hydrogenated silicon increases as the discharge power decreases when the hydrogen partial pressure is constant.

After evacuation, the substrate temperature is maintained at 210 ° C. as in the sixth embodiment.
Ar containing 4.0 × 10 ^-3 Torr P ₂ H ₆ containing 3% H ₂ at 1.0
A first amorphous silicon hydride photoconductive layer 16 of 0.4 μm was formed by introducing × 10 ⁻³ Torr and discharging power of 550 W. Then, in the same manner as in Example 6, with Ar pressure kept constant, H ₂ containing no H ₂ P ₂ H ₆ was switched to introduce H ₂ at 1.0 × 10 ⁻³ Torr, and the discharge power was set to 800.
The second photoconductive layer 17 of amorphous hydrogenated silicon is formed with W, and the formation and heat treatment of the SiNx layer 18 are the same as in the sixth embodiment.
The electrophotographic photosensitive member thus formed had substantially the same characteristics as in Example 6.

Example 9 This example shows an example of the electrophotographic photosensitive member shown in the second example.
The cross-sectional view is shown in the figure. In addition, a case where a chalcogen element and an acceptor impurity (boron) are simultaneously introduced into the layer 20 having a small chalcogen element content is shown. When a chalcogen element acting as a donor and an acceptor impurity are introduced at the same time, the amorphous hydrogenated silicon layer becomes more intrinsic, has a high resistance, and facilitates the movement of electrons and holes.

After evacuation of the inside of the magnetron sputtering device, the mirror-polished stainless steel substrate 19 is kept at 200 ° C. and Ar is 4.0 × 1.
0 ^-3 Torr, 5 x 10 ^-4 Torr of H ₂ containing 50 ppm of P ₂ H ₆
Introduced into the equipment, 5 × 1 of H ₂ containing 50 ppm of B ₂ H ₆
A total pressure of 5 × 10 ⁻³ Torr was introduced by introducing 0 ⁻⁴ Torr. Target thickness of Si single crystal and discharge power of 400W and thickness of 20μ
m amorphous silicon hydride photoconductive layer 20 was formed.

Next, the introduction of H ₂ containing B ₂ H ₆ was stopped and the content of 1% P ₂ H ₆ was reduced.
A photoconductive layer 21 of amorphous hydrogenated silicon was formed to a thickness of 1 μm at a total pressure of 5 × 10 ⁻³ Torr with H ₂ at 2 × 10 ⁻³ Torr. The concentration of P and H on the surface of this photoconductive layer 21 is higher than that of the inside, and since the photoconductive layer 20 of amorphous hydrogenated silicon inside contains P and B at the same time, it can be charged both positively and negatively. An electrophotographic photosensitive member was formed.

In the embodiments described above, an example of amorphous hydrogenated silicon is shown, but a layer containing amorphous hydrogenated silicon as a main component, for example, a layer containing Ge, Sn, C or the like can also be used.

The photoconductor according to the present invention can also be manufactured by the plasma CVD method and the ion plating method, and similarly, the breakdown voltage can be increased. However, the use of the reactive sputtering method is advantageous in that a photoconductor having a high breakdown voltage can be obtained as compared with the other two methods described above.

Generally, if the withstand voltage of the photoconductor becomes high, the thickness of the layer required to obtain the same surface potential can be made thin, which has the advantage that the manufacturing time can be shortened. Further, the layer formed by the reactive sputtering method has a high hardness and is strongly attached to the substrate, so that an electrophotographic photoreceptor having a long life can be obtained.

EFFECTS OF THE INVENTION As described above, according to the present invention, by introducing a group Va element of the periodic table and hydrogen into the photoconductor containing amorphous silicon hydride as a main component while changing the concentration distribution in its cross section, Provide a photoconductor having excellent withstand voltage and photosensitivity. Further, when the photoconductor of the present invention is used as an electrophotographic photoreceptor, it has a high charging ability per unit film thickness, and the film thickness necessary for obtaining the same surface potential can be reduced.

[Brief description of drawings]

1 and 2 are schematic sectional views of the photoconductor of the present invention, FIG. 3 is a sectional view showing Embodiment 1 of the present invention, FIG. 4 is a sectional view showing Embodiment 2 and FIG. 6 is a sectional view showing Examples 3, 4, 5, and 6, FIG. 6 is a sectional view showing Examples 7 and 8, and FIG. 7 is a sectional view showing Example 9. 1, 5, 8, 11, 15, 19 ... Conductive substrate 2 ... Amorphous hydrogenated silicon photoconductive layer 3, 6, 9, 12, 16, 21 ... Va group element and hydrogen content Amorphous silicon hydride layer 4, 7, 10, 13, 17, 20, ... Amorphous silicon hydride layer 14, 18 ... Electron blocking layer containing a small amount of Va group element or element and hydrogen

 ─────────────────────────────────────────────────── --Continued from the front page (56) References JP-A-57-105745 (JP, A) JP-A-58-115442 (JP, A) JP-A-56-65142 (JP, A) Actual development Sho-56- 153946 (JP, U)

Claims (5)

[Claims] 1. A photoconductor in which a photoconductive layer made of amorphous silicon hydride containing a Va group element of the periodic table is provided on a conductive substrate, wherein the Va element group and hydrogen in the photoconductive layer are provided. In the cross section of the photoconductive layer in the vicinity of the interface with the conductive substrate or in the vicinity of the surface of the photoconductor, which is larger than in other portions. 2. The photoconductor according to claim 1, wherein a Group IIb group element or a IIIa group element of the periodic table is added to the Va group element and other portions having a low hydrogen content. 3. A photoconductor in which a photoconductive layer made of amorphous silicon hydride containing a group Va element of the periodic table is provided on a conductive substrate, from the interface of the conductive substrate (or the surface of the photoconductor). Amorphous silicon hydride having a large content of Va group elements and hydrogen, amorphous hydrogenated silicon having a small content of Va group elements and hydrogen, and electrons toward the surface of the photoconductor (or the interface of the conductive substrate) A photoconductor provided with a blocking layer. 4. The photoconductor according to claim 3, wherein the electron blocking layer is an insulating layer. 5. The photoconductor according to claim 3, wherein the electron blocking layer is any one of silicon oxide, silicon nitride and silicon carbide.