Electrical and Optical Studies of Semiconducting CdF₂:In Crystals

Optical absorption and electrical conductivity of In‐doped CdF 2 crystals have been measured at various temperatures. The results confirm the assumption of Trautweiler et al. [12] that the In 3+ centers offer two localization possibilities t o the electrons introduced by annealing the crystals in Cd vapour: an atomic ground state (In 2+ ) and a hydrogenic ground state (In 3+ :e − ). From an analysis of the results 0.055 eV is obtained for the energy distance between the two ground states and approximate values for their positions below the bottom of the conduction band. The latter depend on the degree of conversion. At temperatures below 50 K the occupation ratio between the two ground states can be strongly altered permanently in favour of the In 3+ : e − donor states by irradiation with visible or UV light producing a photo‐induced conductivity and absorption. From measurements of the dependence of the photo‐induced conductivity below 50 K on temperature, irradiation time, and intensity, some properties of the In 3+ :e − donors are deduced.