Effects of Annealing on Bulk Properties of CdTe Detectors

The various crystal growing methods (Low Pressure Bridgman, High Pressure Bridgman, Horizontal Bridgman, Physical Vapor Transport, Travelling Heater Method-THM) and the subsequent bulk and surface treatments can greatly affect the performances of CdTe as well as CdZnTe based X-ray detectors. For this investigation THM was chosen as a low temperature growth process where the crystals have relatively low number of defects and less impurity incorporation from the crucible. Surface (i.e., electrode and electrode-bulk material interface) characteristics have been already investigated , , aiming at understanding the effects of annealing on the electrode deposition. Here bulk effects, including an analysis of the Te inclusion distribution, on CdTe wafers obtained starting from as-grown or subsequently annealed standard or large area ingots have been investigated by IR imaging, resistivity and electron mobility mappings as well as spectroscopic characterization. The results of these measurements are presented and correlated with the detector performances of hundreds of samples. The main observed effects of the annealing are a reduction of the large size (> 10 μm) Te inclusions and a peaking of the resistivity and electron mu-tau products, though in this last case around worse average values, over the entire wafers, that lead to a significant reduction of the spread in the electron transit times, and at the end to better spectroscopic performances.