Growth Of CdSe Single Crystals And Room Temperature Nuclear Radiation Detectors

Cadmium Selenide (CdSe) single crystal is regarded as one of the most promising materials for room temperature nuclear radiation detectors,but CdSe detectors have not been studied in detail because of the lack of high quality CdSe single crystals and suitable technology for this semiconductor and the devices. In this paper,the growth technique of CdSe single crystals and preparation of CdSe detectors were investigated. CdSe single crystals with the resistivity of 107 Qcm magnitude and sizes of 4> 10mmx30mm were obtained successfully from the starting materials with proper stoichiometry. CdSe room temperature nuclear radiation detectors with the energyresolution of 10% (FWHM) for 241Am 59.5KeV line have also been prepared successfully.In experimental studies,a new type quartz ampoule was designed for purification and crystal growth to avoid the pollution of purified materials effectively. Multi-steps purified CdSe polycrystalline starting materials were transported into the growth ampoule directly,so high purity starting materials with proper stoichiometry can be obtained. With this high purity materials,CdSe single crystals with the resistivity of 107 cm magnitude and sizes of 10mmx30mm were obtained successfully by using the vertical unseeded vapor growth (VUVG) method. With the high quality CdSe crystals,the processing of CdSe wafers and the preparation of electrodes of CdSe detectors were investigated. Two kinds of CdSe detectors were obtained. One has metal-semiconductor-metal (MSM) structure with better working stability and large leakage current and poor energy resolution. The other has two metal-insulator-semiconductor (MS) contacts with lower leakage current (less than 4 pA ,300V) and better energy resolution (about 10% FWHM for 241Am 59.5KeV line) and poor working stability.In theoretical studies,the analysis on the phase equilibrium in the vapor growth of CdSe single crystals shows that the stoichiometry of CdSe crystals can be controlled effectively by controlling the stoichiometry of starting materials and the vapor growth temperature. Besides,the investigation of the transporting properties of charge carries in CdSe detectors indicates that the noise in energy spectrum detected by using the detectors with MSM structure is caused by the hole injection,which is induced by electron injection and the light injection. While in detectors with MIS contacts,polarization effect is caused by the further ionization of deep donors. To avoid the noise and the polarization effect,the most suitable structure for CdSe detectors made up of perfect crystal wafers should be that:IT-N contact as anode,MIS contact as cathode.