Mobility and trapping time in HgI2: a comparison of measurement methods and results

The charge transport parameters of a solid-state nuclear radiation detector are of paramount importance in determining the spectrometric performance. The free drift lengths (lambda) for electrons and holes are given in terms of the products of mobility (μ) and trapping time (tau) for electrons and holes. For good spectrometric performance the carrier free drift lengths should be much greater than the thickness of the detector. The μ tau product is so important in this regard that different solid-state detector materials are compared on the basis of their μ tau values, and for a given material progress is gauged by the current value of μ tau which it is possible to achieve. Workers in the field are fond of plotting μ tau versus time (in years, usually) to show how the state-of-the-art is advancing, often towards some asymptotic value. Different methods of measuring the charge transport parameters of mercuric iodide (HGI2) are discussed and experimental values are presented