Investigation Of X-ray Detector Based On CdSe Single Crystals

Cadmium selenide?CdSe?is one kind of the widely used II–VI compounds semiconductor materials with its excellent photoelectric properties,large average atomic number,high resistivity,large carrier lifetime product and strong blocking ability for high-energy ray.Therefore,as a kind of materials for room temperature X-ray detector,CdSe is promising.However,the preparation of high-quality CdSe single crystal has been difficult.The CdSe single crystal with a natural exposed surface was grow by the unconstrained gas phase transport method combined with the in-situ annealing process.The X-ray diffractometer?XRD?was used to scan the crystal.The results show that the crystals are wurtzite-type and two exposed planes are?001?plane and?100?plane,respectively.Furthermore,the photoluminescence of the obtained crystal was studied,to analyses the defect concentration of crystal.The results show that the CdSe single crystal prepared by the unconstrained gas phase transport method has more less defects than obtained by traditional method.Further,the CdSe wafer of?001?plane and?100?plane are obtained through the process of cutting,grinding,polishing,and passivation.Two types?001-type,100-type?of X-ray detector chips with metal-semiconductor-metal configuration were fabricated,the electrode material was gold?Au?.The chip is hermetically mounted on a Teflon substrate using transparent insulating silicone rubber,and finally encapsulated in a TO8 metal case with an aluminum foil window.In this paper,the dark current characteristics,photocurrent response time,signal-to-noise ratio and sensitivity of X-ray detector are systematically studied.The research results as follows:The dark current density of detector is low?<0.2 nA/cm²?at electric fields of0.1V/?m.According to dark current the resistivity of CdSe crystal is calculated,which reach to 10¹²¹0¹³?·cm.The dark current is stably maintained at a low level after a relaxation time about 40s.The dark current density under positive bias is one-eighth of that under negative bias.The photocurrent response of detectors was measured under positive bias.The results show that the rectangular wave image of photocurrent changes with X-ray switch is clear,demonstrating the detector responds well to low dose X-rays,and the rise time and decay time are about 0.2s?the experimental test sampling interval is 0.1s?.Based on the photocurrent response,the signal-to-noise ratio of the detector was studied.While the detector was irradiated by X-ray with dose rate of 0.085?Gyair/s,the signal-to-noise ratio remains above 15.The sensitivity of the detector was also studied.The results show that the sensitivity of the detector can be up to 1.77×10⁵?CGy^-1air·cm^-2?bias of 0.2V/?m?.Comparing the performance parameters of two types?001-type,100-type?of X-ray detectors,we found that the 001-type detector based on the?001?plane is superior to the?100?plane 100-type detector.