The behaviour of selected impurities in CdxHg1−xTe

Abstract Although Cd x Hg 1−x Te is generally considered to be a defect semiconductor, whose electrical properties are controlled by adjusting the balance of metal vacancies to metal interstitial atoms, electrically active impurities present at the 0.1 ppma level, or below, can dominate the electrical properties. The main tool used to study the behaviour of impurties is Hall effect measurements, however, this should be supported by measurements of minority carrier lifetime in the bulk material. Crystals doped deliberately with Li, Cu, Ag, Ay, Al, In, Si, P, As, Sb, Cl and Fe have been grown. Mass Spectrometry and Atomic Absorption Spectrometry have been used to determine segregation coefficients for these and other elements. Combining Hall effect measurements with these chemical data enables the electrical behaviour of each impurity to be determined at a known level. In these crystals Li, Ag, Cu, P, As and Sb are found to be acceptors, Si, In, Al and Cl are donors while Au and Fe are electrically inactive. In the deliberately doped crystals both acceptor and donor impurities are found to drastically reduce the bulk lifetime at the high concentrations added, as expected. Iron also acts as a lifetime killer, despite its electrical inactivity, but gold does not. For crystals doped with donor impurities lifetime measurements down to low temperatures have been carried out to study the recombination mechanisms and the results of this work suggest that Shockley-Read centres exist even in undoped CMT crystals.