CdSe Detector Wafer Surface Treatment And Passivation Study

CdSe is a kind ofⅡ-Ⅵcompound semi-conductive material with higher average atomic number, higher density (5.74g/cm3), longer carrier migration life (7.2×10-4 cm2v-1), and wider forbidden band gap (1.73eV). It has strong ability to stop x andγ.rays and can be used under normal temperature. With these properties, CdSe nuclear detectors have relatively higher energy resolution and efficiency under normal temperature. Compared with HgI2, CdTe, CdSe has better chemical stability and mechanical processing property. All these features above enable CdSe to be a suitable photoelectricity material for normal temperature detectors, LED, sensicon target and photoelectric cells. While the affected layers, kerfs and structure faults on the surfaces of CdSe wafers widely affect the performance of the detectors. So wafer surface treatment technology becomes an important factor to affect the ultimate performance of detectors. But there is no report about the CdSe wafer surface treatment process. So, we carried out research on the CdSe wafer surface process.CdSe single crystals grown by previous methods have very lower quality specifies in crystal integrity, Chemical deviation and low electrical resistance, thus these crystals can not reach the requirement of normal temperature nuclear detector. In this paper, based on our research work, we use VUVG method to grow CdSe crystals which have high crystal integrity, high component uniformity and up to 107?·cm electrical resistance. CdSe crystals grown by VUVG method can provide insurance for the quality of normal temperature nuclear detectors.CdSe crystals are brittle and forms cracks easily under external force. Combined with XRD and crystal cleavage plane, we find out an optimal process to use excircle slicing equipment to get CdSe wafers. The detail of this process is as the following: blade rotating rate around 1000 rpm; blade dropping speed around 1mm/min; cut the crystals along cleavage plane into 2mm thick wafers.For the first time, we introduce CMP (Chemical Mechanical Polishing) technology into CdSe wafer surface treatment process. We use CMP solution whose main ingredient is mixed sapphire powder (w0.5, 10% concentration) and weak acid or wick base (NaOH, PH≈8). CMP technology heavily improves polishing speed, reduces kerfs on the surfaces and flaws in structure. Then we can thus get the proper wafer thickness and surface states for making detectors.Surface passivation technology is adopted to improve CdSe wafer electrical resistance which provides an optimal foundation for making detectors. The research results show us: CdSe wafers treated by H2O2 for 40 minutes have smoothest surfaces and highest electrical resistance up to 7.3×108?·cm and are suitable to make normal temperature nuclear detectors.