CdSe - - A Broadband Nuclear Detector Material

CdSe, a wide bandgap semiconductor, combining high resistivity, good carrier trans-port properties, and large average Z number is ideal for use as a room-temperature x-ray and y-ray detector. In the x-ray regime, the large bandgap (-1.7 eV) of GdSe eliminates the need to cool the crystal in order to reduce thermal noise. Si and Ge detectors must be cryogenically cooled, which precludes their use in portable systems. CdSe is a promising alternative to CdTe and HgI2 y-ray detectors. CdSe detectors exhibit no polari-zation under bias in contrast to the high resistivity Cl-doped CdTe; they are also superior to HgI2 in terms of carrier mobilities as well as thermal. chemical, and mechanical stability. However, the presence of electron traps in CdSe due to Cu and Ag impurities is the limiting factor responsible for preventing its use as a room-temperature nuclear radiation detector. During Phase I, improved purity and resistivity CdSe would be grown. The goal would be at least two orders of magnitude improvement in these properties. The resistivity, mobility-lifetime products, and impurity levels of the material would be characterized for use in nuclear radiation detectors. Detectors would be fabricated and evaluated in terms of energy resolution and counting efficiency. Phase II would target continued material improvements along with contacting and fabrication issues unique to CdSe.