Positron trapping at the charged vacancies, VHg0, VHg-, VHg2-, in Hg0.8Cd0.2Te was investigated. The use of Doppler methods revealed a temperature dependence of the trapping rates and provided evidence for the predicted existence of Rydberg precursor states. A first direct observation of the vacancy charge states indicated energies of 0.018 and 0.041eV for the singly and doubly ionized states, respectively.

C.D.Smith, P.Rice-Evans, N.Shaw: Physical Review Letters, 1994, 72[7], 1108-11