JPH0139964B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention uses photoconductive cadmium selenide (CdSe)
More specifically, the present invention aims to provide photoconductive CdSe with high output and high signal-to-noise ratio for use in imaging devices as a photoconductive material. Conventionally, CdS, CdSe, amorphous Si, etc. have been developed as photoconductive materials for imaging devices, but in order to be used for imaging devices, they require fast response speed and high output to ensure reliable reading. and high signal-to-noise ratio photoconductive materials are required. Currently used for these purposes
Photoconductive materials such as CdS, amorphous Si, or CdSe have been proposed, but CdS has extremely slow response speed, and amorphous Si does not have a sufficient signal-to-noise ratio. Although CdSe is a promising material, the methods for producing high-performance materials are extremely complicated. In other words, CdSe raw powder (hereinafter, unfired CdSe that is not doped with impurities is referred to as raw powder), which is the raw material for conventional photoconductive CdSe, is synthesized by a gas phase method and has very high crystallinity. Because the surface area of the body is small, it is extremely difficult to dope the dopant uniformly and easily, and if the dopant is forcibly doped sufficiently, dark current will flow excessively and a sufficient signal-to-noise ratio may not be obtained. This brings about a drawback. As a result of intensive research to solve the above-mentioned drawbacks of the prior art, the present inventor has found that the above-mentioned drawbacks of the prior art can be solved by using a specific CdSe raw powder as a raw material for producing photoconductive CdSe. Well-resolved and highly easily high-performance photoconductive CdSe
The present invention was completed based on the finding that the following could be obtained. That is, the present invention reduces selenium with a reducing agent in an aqueous medium to prepare a solution containing selenium anions, and adds a water-soluble cadmium salt to the solution.
Photoconductivity characterized by precipitating CdSe and then doping the obtained CdSe with a dopant
This is a method for producing CdSe. To explain the method of the present invention in detail, the first feature of the present invention is that CdSe raw powder, which is a raw material for photoconductive CdSe, is prepared by a wet method. The raw powder produced by this wet method is not exposed to high temperatures during production, so it is a fine powder that is almost amorphous, and the surface area of the powder is extremely large. It is done very easily and uniformly. The Se used in the present invention may be any form of selenium, but preferably has a purity of about 99.9%.
That's all. It is preferable to reduce such Se powder in an alkaline state in water, and the reducing agent can be Sn, Cl ₂ xH ₂ O, NaBH ₄ , LiAlH ₄ , as long as it can reduce Se.
Any reducing agent such as N ₂ H ₄ .xH ₂ O or liquid ammonia may be used, but N ₂ H ₄ .
It is a reducing agent that does not contain a compound like xH ₂ O. Such a preferred _N2H4.xH2O (x=1) reducing agent is preferably used in a proportion of 350 to ₁₅₀₀ g per 1 mole (about 79 g) of _selenium . Below the lower limit of this usage range, the reduction of selenium will be insufficient, resulting in a significant deterioration in the photoconductive properties of the final product. On the other hand, although a good product can be obtained even if an amount exceeding the above range is used, it is not preferable from an economic point of view. The reduction of selenium by such reducing agents must be carried out under alkaline conditions in an aqueous medium, preferably pure water, and may be carried out using hydroxides or carbonates of elements of group A of the periodic table, such as NaOH, LiOH,
KOH, Na ₂ CO ₃ , etc. can be used for alurination, but
Preferred is NaOH, such as
NaOH is preferably used in a proportion of about 5 to 30 parts by weight per 20 parts by weight of selenium. The medium used, for example pure water (ion-exchanged water), is preferably used in a proportion of about 400 to 4000 parts by weight per 100 parts by weight of selenium. The temperature of the reduction reaction may be room temperature, but it is usually better to carry out the reaction at about 90°C to the boiling point of water;
At 100°C, a reaction time of about 5 minutes to 2 hours is preferred. The reduction of selenium proceeds smoothly under these conditions, but the generated selenium anions are unstable in the air and easily oxidized, so the reaction atmosphere is N ₂
It is desirable to use an inert gas atmosphere such as an air current. It is also possible to perform the above reduction in advance in the presence of a water-soluble salt of cadmium to produce and precipitate CdSe at the same time as the reduction, but the preferred method is to add a water-soluble salt of cadmium after the reduction of selenium is complete. This is the way to do it. As the cadmium salt to be used, any water-soluble cadmium salt such as CdSO ₄ , CdCl ₂ , CdNO ₃ and the like can be used. These cadmium salts are about 1 mole of selenium.
It is preferred to use it in a proportion of 0.9 to 1.2 moles.
It may be added all at once or gradually as a solid salt, but in order to make the resulting CdSe precipitate uniform and fine, it is preferably added as an aqueous solution of about 10 to 50% by weight in pure water. 90~100℃
The selenium anion solution is preferably added dropwise to the selenium anion solution prepared above at a reaction temperature of about 30 minutes to 2 hours. Although CdSe is produced simultaneously with the dropwise addition, the produced suspension is preferably aged by stirring in an inert atmosphere at a temperature of about 90 to 100°C for about 30 minutes to 2 hours. The present invention is mainly characterized as described above.
CdSe raw powder is obtained, but since the CdSe raw powder is a uniform, fine, and easily dispersible powder, and its X-ray diffraction pattern shows almost no sharp peaks, almost no CdSe crystals grow. It can be seen that the shape is almost amorphous. On the other hand, CdSe raw powder prepared by the conventional gas phase method has very high crystallinity and therefore has a very small surface area, making the subsequent doping process extremely difficult. The CdSe raw powder according to the present invention as described above has low photoconductivity in this state, and by doping the CdSe raw powder with an activator, the photoconductivity of the present invention can be improved.
CdSe can be obtained. Such doping treatment is carried out using conventionally known methods, such as a first calcination step in which raw CdSe powder is mixed with an activator and a flux and treated at high temperature to diffuse the activator and crystallize CdSe, and co-activation. This can be carried out using a second firing step for diffusing the halogen agent, a third firing step if necessary, or various modification methods thereof. However, according to detailed research by the present inventor, the primary calcination involves adding an appropriate amount (e.g., about 100 to 3000 ppm) of an activator such as copper chloride to the CdSe raw powder and an appropriate amount (e.g., per 100 parts by weight of the raw powder). Approximately 0.1~10
After mixing a fluxing agent such as cadmium chloride (parts by weight) by an appropriate method, it is preferably carried out at a temperature of about 500 to 800°C for about 15 minutes to 2 hours in an inert atmosphere, and in this way the mixture is slightly sintered. A primary fired product that can be easily loosened is obtained. The purpose of secondary firing is to diffuse the halogen in the primary fired product and increase photoconductivity.
About 0.1 to 10 parts by weight of a fluxing agent such as cadmium chloride is mixed with 100 parts by weight of the primary fired product, and about 400
Heat treatment is performed at a temperature of ~600°C for approximately 15 minutes to 2 hours. Photoconductivity of the present invention obtained as described above
Compared to photoconductive CdSe obtained by conventional methods, CdSe has a somewhat improved response speed and a significant improvement in light output, as shown in the examples below.
Signal-to-noise ratio has been significantly improved. Therefore, the photoconductive CdSe of the present invention is extremely useful as an element for imaging devices, and is also useful as a photosensitive material for various devices to which these are applied, such as facsimile machines, laser printers, and input devices for computers. Next, the present invention will be specifically explained with reference to Examples and Comparative Examples. Note that "%" or "%" in the middle of the sentence is based on weight. Example 1 100.24 parts of powdered selenium (purity 99.9%), N ₂ H ₄ .
742 parts of H ₂ O and 101.5 parts of NaOH were added to 2500 parts of pure water, and after the atmosphere was sufficiently replaced with N ₂ , the mixture was stirred at about 100° C. for about 0.5 hour to obtain a solution containing selenium anions. Next, 752 parts of 26.46 parts of CdSO ₄ prepared in advance dissolved in 100 parts of pure water were added to about 60 parts of the selenium anion solution being stirred at a temperature of about 100°C.
It takes several minutes to drip. After the reaction is completed, further heat at 90℃ for 1.5
The CdSe was aged by stirring for hours. generated
CdSe raw powder was filtered, washed with water, and dried at 120°C.
Next, a solution of 1.3748 parts of CdCl ₂ and 0.3624 parts of CuCl _{2.2H 2} O dissolved in 150 parts of pure water was added to 150 parts of dry powder (purity 100%, average particle size 0.1 μ) and mixed thoroughly. Dry at °C. 150 parts of the obtained dry powder is placed in a quartz crucible and subjected to primary firing at approximately 600° C. for 30 minutes in an N ₂ atmosphere. The slightly sintered primary fired product is gently crushed, passed through a 500-mesh sieve to remove coarse particles, thoroughly washed with water, and dried. A solution of 1.3748 parts of CdCl ₂ dissolved in 150 parts of pure water is added to 150 parts of the primary fired product, thoroughly mixed, and dried at 120°C. The dry powder is placed in a quartz crucible and subjected to secondary firing at about 450° C. for 30 minutes in an N ₂ atmosphere with 0.15 parts of sulfur. Next, thoroughly thaw it in water using a homomixer, pass it through a 500 mesh filter, and wash thoroughly with water.
Dry at °C. The photoconductive CdSe of the present invention thus obtained was a fine powder that could be easily dispersed, but it was found to have a high degree of crystallinity according to X-ray diffraction. 10 parts of this photoconductive CdSe was mixed with 3 parts of a 5:1 mixture of styrene resin and toluene, coated on a comb-shaped aluminum evaporated electrode to a thickness of 45 μm, dried at 120°C, and then pulsed with a light intensity of 60 Lux and a wavelength of 695 nm. When the response speed, light output, dark output, and SN ratio were determined using light, they were as shown in Table 1 below. Comparative Example 1 Powder synthesized by gas phase method in place of raw CdSe powder in Example 1 (CdSe purity 99.9%, average particle size approximately 4μ)
The photoconductive
When CdSe was obtained and its properties were determined in the same manner as in Example 1, the results shown in Table 1 were obtained.

[Table] The response speed in Table 1 above is the time it takes for the output to reach 90% of the maximum value after light irradiation.
This is the time until the % output decreases. The output is
This is the measured value of the voltage applied to the load resistor of 10MΩ. As is clear from the results in Table 1 above, photoconductivity according to the present invention using raw CdSe powder obtained by wet method
CdSe has improved response speed and extremely improved light output compared to conventional CdSe, and therefore exhibits a significantly large signal-to-noise ratio.

Claims (1)

[Claims] 1. A solution containing selenium anions is prepared by reducing selenium with a reducing agent in an aqueous medium, and a water-soluble cadmium salt is added to the solution to precipitate cadmium selenide. A method for producing photoconductive cadmium selenide, which comprises doping cadmium chloride with an activator. 2. The manufacturing method according to claim 1, wherein the reducing agent is hydrazine.