Development of Cadmium Magnesium Telluride (Cd1−xMgxTe) for room temperature X- and gamma-ray detectors

Abstract

Cadmium Magnesium Telluride (Cd1−xMgxTe/CMgT) offers several pronounced potential advantages over the well-studied CdZnTe and CdMnTe, possibly making it a good alternative for room-temperature X- and gamma-ray detectors. It possesses high crystallinity due to the near-similar lattice structure of CdTe (6.48Å) and MgTe (6.42Å). Its displays good homogeneity as the Mg segregation coefficient in CdTe is nearly 1. Furthermore, inhomogeneities in the crystal due to alloying effects can be minimized, because the optimal energy band-gap can be achieved using less Mg in CdMgTe compared to Zn and Mn needed in CdZnTe and CdMnTe. We recently grew an undoped- and a doped-ingot of CdMgTe, characterized its material properties, and tested its detection performance. We obtained some exciting results that demonstrated some of its potential advantages over the other materials. The band-gap was measured as 1.61eV at room temperature and 1.73eV at 4K. The yield was predominantly single crystals with about two orders-of-magnitude fewer Te inclusions and other growth defects compared to CdZnTe and CdMnTe crystals. The measured resistivity of the undoped annealed crystal was about ∼107Ω-cm; after doping in a second growth trial, it increased by 2–3 orders-of-magnitude (109–1010Ω-cm). We examined the doped as-grown crystal as a radiation detector and acquired reasonably good spectral response to an Am-241 source. The estimated mu-tau value was as high as 7×10−4cm2/V, which is an extraordinarily high value for such an early-phase investigation. We also analyzed point and extended defects using various techniques that will be discussed in this manuscript.