Fabrication And Performance Research Of X-ray Detector Based On Amorphous Selenium Film

Amorphous selenium?a-Se?can be applied for preparing the direct conversion X-ray detector,due to its nature of directly converting X-ray energy to electrical energy.However,there are lots of disadvantages existing in current a-Se X-ray detector,such as high vacuum degree(10^-3-10^-4 Pa)for a-Se material prepared by thermal evaporation method,being easy to be crystallized in terms of material?crystallization temperature is generally 40-50?C?,and a requirement of large voltage value to drive a-Se X-ray detector?voltage is as high as tens of volts per micron?.In this work,the process parameters for preparing amorphous selenium?a-Se?films by thermal evaporation technology at low vacuum degree(10^-2 Pa)were found.The a-Se films with three different thicknesses have been fabricated,and based on a-Se films,X-ray detectors with metal-semiconductor-metal?MSM?structure were obtained.In order to explore the crystallization temperature of a-Se,each sample was divided into several parts to be annealed at different temperature in air,and the structural and optical properties of all final samples were investigated by X-ray diffraction?XRD?patterns,atomic force microscope?AFM?images and ultraviolet-visible?UV-VIS?transmittance curves.It was found that the crystallization temperature of samples was higher than that of the previous reports,meanwhile,the deposition quality of a-Se increased with the rising films thickness,and the crystallization temperature of the thicker samples decreased.Specifically speaking,the sample with evaporation of 30 min crystallized slightly at annealing 65?C.However,for sample with evaporation of 45 min,the complete crystallization had occurred at annealing 65?C.With the evaporation time rose to 60 min,sample had begun to crystallize at annealing 60?C,suggesting a lower crystallization temperature.I-V curves of devices were firstly characterized and shown the good ohmic contact quality for all devices.Further,the dark current of samples was measured at voltages of1 V,3 V and 5 V.Comparing these samples at the same measure voltage,the dark conductivity of the thinner samples was lower(for voltage of 1 V,as example,dark conductivity is 5×10^-5?^-1?cm^-1 for 30 min,1.05×10^-6?^-1?cm^-1 for 45 min,and 8×10^-8?^-1?cm^-1 for 60 min.The X-ray photoresponse characterization of a-Se films shown that there relatively were the fast photoresponse speeds that were 0.4 s-0.8 s,and which required only a tiny driving voltage?1 V-5 V?.Besides,at the same radiation intensity of X-ray,the samples with the longer evaporation time had the larger sensitivity values that are⁰.52,¹.53 and².11 in turn.Overall,this work provided the experimental and theoretical references for preparing the a-Se films X-ray detector with the low cost,resistant to the higher temperature,quick photoresponse and low dark current.