In this paper the three dimensional Laplace equation was solved for a three layer photoreceptor with ti (i=1,2,3) thicknesses and dielectric εj(j =1,2,3) under suitable boundary conditions and the vertical component of electric field was obtained over the photoreceptor's photoconductive layer. Then, the behavior of the above equation was studied for different photoconductive layer's thicknesses and four thicknesses were chosen. For making the samples, the deposition of Al and formation Al2O3 in 2x10-5 - 5x10-7 mbar pressure, and coating of Se in 2x10-7 mbar pressure, 250 °C boat temperature and 95 °C substrate temperature in 120 min were carried out after the design and manufacture all of subsystems. In this way four samples were made by different photoconductive layer's thicknesses. Electrical measurements showed a resistance above 1012Ω in dark and about zero in light which these values suitable for development of electrostatic latent image. To consider the development field of made photoreceptors, the samples were mounted in Xerox machine and the operation of them observed. The sample with 60 μm photoconductive layer's thickness showed the best development and less background effects.