JP4811890B2 - Method for producing photoconductive member - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to the production how the photoconductive member using a zinc oxide semiconductor.
[0002]
[Prior art]
In recent years, semiconductor light-emitting devices in the near-ultraviolet region have advanced from the research stage to practical use. As applications of semiconductor light-emitting elements in the near ultraviolet region, high-definition light sources for large-capacity optical disks and laser printers are expected. However, there are very few research reports on light receiving elements used in the same wavelength region as such light emitting elements.
[0003]
Among the II-VI group semiconductors expected to have near-ultraviolet light sensitivity with a band gap of 2.8 eV or more, the present inventors have a simple manufacturing process, are environmentally friendly, and are inexpensive materials such as zinc oxide ( The possibility of ZnO) as a light receiving element material has been studied. That is, zinc oxide is a material that has been used as a white pigment and catalyst since ancient times as zinc white, and its constituent components, zinc materials, are abundant in nature, and because zinc oxide is an oxide, there is a concern about environmental pollution. The safety has already been established.
[0004]
[Problems to be solved by the invention]
However, the zinc oxide thin film is an n-type semiconductor in which the composition ratio between Zn atoms and O atoms is difficult to be 1. Due to the conduction of electrons trapped in the unbonded hands of Zn, the resistivity is low, and furthermore, photocarriers generated by light incidence are captured by the unbonded hands and the photoresponse characteristics are deteriorated. There are many issues that must be addressed.
[0005]
As a solution to these problems, a method of controlling the composition ratio between Zn atoms and O atoms, or a method of compensating donor levels due to dangling hands with p-type impurities such as lithium (Li) and nitrogen (N ₂ ) (Katahira, Haga 1998 Electrical Engineering Society Tohoku Branch Joint Conference Preliminary Proceedings 2B17 p.80 (1998) ... Report 1) (1999) ... Report 2) has been proposed.
[0006]
In the example of Report 1, the photoresponsiveness is improved by forming a ZnO thin film to which Li is added using a high frequency (rf) sputtering method. More specifically, an rf sputtering method was used to form a ZnO thin film, and a p-type impurity was added by placing a small piece of Li ₂ O on a ZnO target (99.999% or more). The production conditions were Ar gas flow rate of 0.75 cc / min, O ₂ gas flow rate of 0.25 cc / min, high frequency power of 100 W, and a Pyrex glass substrate was used for depositing the ZnO thin film. The dark resistivity of the ZnO thin film prepared at room temperature was 10 ⁶ Ω · cm or less regardless of whether or not Li was added. However, the dark resistivity of the sample prepared at a substrate temperature of 100 ° C. without adding Li was Is about 3 digits lower. In addition, the dark resistivity increased in the sample to which Li was added at the substrate temperature of 100 ° C., and the same value as the sample prepared at room temperature was shown. Further, when the photoresponse characteristics of the sample prepared at room temperature were examined, it was confirmed that the photoresponse characteristics were greatly improved in the case of adding Li.
[0007]
In the example of report 2, the optical response characteristics are improved by subjecting the prepared ZnO thin film to surface treatment with N ₂ plasma. The method for producing the ZnO thin film and the conditions thereof are the same as in the case of Report 1. In the surface treatment, a ZnO thin film is deposited for 55 minutes at a high frequency power of 100 W, and then the N ₂ gas flow rate is set to 10 cc / min, and the N ₂ treatment is performed at a high frequency power of 100 to 250 W for 5 minutes. As a result of such surface treatment, it was confirmed that when light was incident from the thin film side, the photosensitivity was improved compared to the untreated sample, and both the rise and fall of photoresponse characteristics were improved. Yes.
[0008]
However, in the manufacturing method in which a ZnO thin film used as a photoconductive member is doped by sputtering a Group I metal compound (for example, LiO ₂ ) simultaneously with a ZnO target fired by a high-frequency sputtering method or the like, It is difficult to control a sufficient doping amount and carrier concentration, and the productivity is extremely poor.
[0009]
In view of this, the present invention provides a photosensitive member for electrophotography and an optical sensor having a photosensitivity up to the near-ultraviolet region having good photoresponse characteristics by doping a zinc oxide thin film with a Group I element as an impurity to control a predetermined carrier concentration. and to provide a manufacturing method suitable photoconductive member to equal.
[0010]
[Means for Solving the Problems]
Method for producing a photoconductive member of the invention of claim 1 wherein the zinc oxide by metal organic chemical vapor deposition and depositing a semiconductor thin film whose base material, during the step of depositing the semiconductor film, a source of zinc as the zinc acetylacetonate, one of O _2, O ₃ or H _{2 O} as the oxygen source, the N ₂ is used as a carrier gas, the β- diketone as a raw material of group I elements of the periodic table in the semiconductor thin film And a step of doping Li (DPM) , which is an organic metal of the system, as an impurity to bring the impurity concentration into a range of 10 ⁻⁵ to 10 [at ·%].
[0011]
Therefore, the use of Li (DPM) , which is a β-diketone-based organic metal , as a raw material for zinc acetylacetonate and Group I elements makes the material extremely stable and easy to handle in the atmosphere. In addition, the carrier concentration can be easily controlled and the productivity is improved.
[0014]
More specifically, in the metal organic chemical vapor deposition (MO-CVD) method, a raw material whose composition does not change is continuously supplied, and a thin film whose crystal orientation and composition are controlled has a large area. It has the advantage that a film can be formed. In addition, it has already been reported that a ZnO thin film having excellent orientation can be obtained with good reproducibility by adding oxygen gas from zinc acetylacetonate, which is a white powdery solid organometallic compound and stable in the atmosphere. In this process, Li (DPM) is added as a raw material for doping, so that the Li-doped ZnO thin film increases in resistivity and improves the light response characteristics under the condition that the doping amount and carrier concentration are easily controlled. Can be created.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described with reference to FIG. In the present embodiment, pyrex glass is formed by metal organic chemical vapor deposition (MO-CVD method) using zinc acetylacetonate, oxygen gas O ₂ , and Li (DPM) as raw materials and nitrogen gas N ₂ as a carrier gas. A Li-added ZnO thin film 2 as a photoconductive member was formed on 1. Further, an Al electrode 3 was formed thereon to produce an optical sensor 4. As a result, an optical sensor 4 capable of responding at a very high rise time and fall time and having photosensitivity up to the near ultraviolet region is obtained.
[0022]
【Example】
(experimental method)
This example clarifies a specific method for manufacturing the optical sensor 4 in the above-described embodiment. Zinc acetylacetonate (Zn (acac) ₂ ), a β-diketone organic metal that is stable in the atmosphere as the zinc feedstock, oxygen gas O _{2 with} a purity of 99.99% as the oxygen feedstock, As a raw material for lithium Li, which is a group I element, Dipivaloylmethanato Lithium (Li (DPM)), which is a β-diketone-based organic metal, is used (as the oxygen supply source, ozone (O ₃ ), water Similar results are obtained using (H ₂ O)). A nitrogen gas N ₂ having a purity of 99.99% is used as a carrier gas for transporting the sublimated raw material. The oxygen gas flow rate was 400 ml / min, and the carrier gas flow rates of the Zn raw material cylinder portion and the Li raw material cylinder portion were 400 ml / min and 100 ml / min, respectively. Pyrex glass 1 was used for the substrate, and the substrate temperature was 475 ° C. The Zn raw material cylinder temperature was constant at 122 ° C., which is the optimum sublimation temperature of zinc acetylacetonate (Zn (acac) ₂ ), and the Li raw material cylinder temperature was changed from 129 ° C. to 216 ° C.
[0023]
The resistivity was obtained by calculation from the resistance value and the film thickness between the electrodes by depositing an Al parallel plate electrode 3 on the surface of the Li-doped ZnO thin film 2. The light source used for the measurement of the optical response was selected from the bright line of the high-pressure mercury lamp with a filter in the wavelength range of 365 nm to 425 nm, and adjusted to the irradiation intensity of 3.8 mW / cm ² on the sample surface. An X-ray diffractometer was used to measure the crystal orientation, a stylus thickness meter to measure the film thickness, and an atomic force microscope (AFM) to observe the thin film surface.
[0024]
(Experimental results and discussion)
FIG. 2 shows the relationship between the Li raw material cylinder temperature (Tc) and the resistivity of the Li-added ZnO thin film 2. The resistivity does not change so much until Tc is around 160 ° C., indicating 10 ⁻² to 10 ⁻¹ [Ω · cm] which is close to the non-doped value. From the thermal analysis measurement, it was confirmed that the sublimation start temperature of Li (DPM) was around 155 ° C., and when Tc was around 160 ° C., the amount of Li added to the thin film was very small, which was almost the same resistance as the result of non-doping. It is thought that it showed the rate. Further, an increase in resistivity was observed from around 170 ° C. at which the sublimation amount of Li (DPM) increased, and the maximum value of 3.7 × 10 ⁶ [Ω · cm] was reached at Tc = 216 ° C. According to FIG. 2, the impurity concentration is suitably in the range of 10 ⁻⁵ [at ·%] at 130 ° C. to 10 [at ·%] at 220 ° C., and particularly 10 ⁻² [at ·%]. In the case of the impurity concentration, preferable results are obtained.
[0025]
FIGS. 3A, 3B, and 3C show AFM images of samples prepared by changing the Li raw material cylinder temperature Tc to 129 ° C., 183 ° C., and 216 ° C., respectively. As measurement conditions, the scanning range was 10 μm × 10 μm, and the maximum value in the height direction was unified to 0.35 μm. In the sample of FIG. 3A, small crystal grains are observed on the surface, but it can be confirmed from the figure that the sample is relatively flat. As the amount of Li added increases, the surface crystal grains increase, and in the sample of FIG. 3C, crystal grains having a grain size of about 0.6 μm and a height of about 0.19 μm are seen uniformly. Further, the results of X-ray diffraction of these samples all show uniaxial orientation of the (002) plane. However, the X-ray diffraction peak intensity decreases as the Li raw material cylinder temperature Tc increases, and it is considered that crystal growth occurs in a random direction when corresponding to the measurement result of AFM in which the crystal grain size increases. It is done.
[0026]
Regarding the photoelectric characteristics, it was confirmed that the photosensitivity was improved and the photoresponse characteristics were improved by optimizing the Li addition amount (impurity concentration). According to the experiment by the present inventor, good results were obtained when the impurity concentration of Li was in the range of 10 ⁻⁵ to 10 [at ·%] as described above.
[0027]
FIG. 4 shows a sample prepared by using the rf sputtering method with an addition amount of Li ₂ O of 2.4 mg, and a sample prepared by using the atmospheric pressure MO-CVD method and setting the Li raw material cylinder temperature Tc = 194 ° C. as in this example. The photoresponse characteristics are shown in comparison. The unit of the numbers shown in the figure is μm. From this characteristic diagram, it can be seen that the rise and fall characteristics of the photocurrent due to the turning on and off of light are greatly improved.
[0028]
As described above, according to this example, as a result of forming the Li-added ZnO thin film using the atmospheric pressure MO-CVD method using Zn (C ₅ H ₇ O ₂ ) ₂ ) and Li (DPM), the resistivity increased. It was confirmed that the photosensitivity and photoresponse characteristics were improved. However, from the results of the AFM image and X-ray diffraction measurement, although the crystal grains of the ZnO thin film increase with the increase of the Li addition amount (impurity concentration), the crystallinity is not improved, and the appropriate Li addition as described above It can be seen that there is an amount.
[0029]
In these embodiments and examples, application examples to the optical sensor 4 have been described. However, the present invention is similarly applied to an electrophotographic photoreceptor (not shown) having a Li-doped ZnO thin film in a photosensitive layer. obtain.
[0030]
【The invention's effect】
According to the method for producing a photoconductive member of the invention described in claim 1, by using Li (DPM) , which is a β-diketone organic metal , as a raw material for zinc acetylacetonate and Group I elements, Since the material is very stable and easy to handle, the doping amount and the carrier concentration can be easily controlled, and the productivity can be improved.
[0031]
Further, by depositing a semiconductor thin film by a metal organic chemical vapor deposition method, it becomes easy to control the film forming conditions of the thin film, and the productivity can be further improved.
[Brief description of the drawings]
FIG. 1 is a schematic perspective view of an optical sensor showing an embodiment of the present invention.
FIG. 2 is a characteristic diagram showing Li cylinder temperature dependence of resistivity in one embodiment of the present invention.
FIG. 3 is a photograph showing an AFM image according to the Li cylinder temperature of a Li-added ZnO thin film.
FIG. 4 is a characteristic diagram showing optical response characteristics according to a manufacturing method.
[Explanation of symbols]
2 Li-doped ZnO thin film = photoconductive member 4 optical sensor

Claims (1)

Depositing a semiconductor thin film using zinc oxide as a base material by metal organic chemical vapor deposition;
In the step of depositing the semiconductor thin film, zinc acetylacetonate is used as a zinc source, O _2, O ₃ or H ₂ O is used as an oxygen source , and N ₂ is used as a carrier gas. A step of doping Li (DPM) , which is a β-diketone-based organic metal , as an impurity as a raw material of the Group I element in the table so that the impurity concentration ranges from 10 ⁻⁵ to 10 [at ·%];
A method for producing a photoconductive member, comprising:

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