Self-Compensation and Interaction of Li with Thermal- and Radiation-Induced Defects in CdTe

Lithium was introduced into CdTe by diffusion at three different temperatures (600, 680, and 750 °C) under the corresponding cadmium overpressures. Resistivity and Hall-effect measurements were the main experimental methods used in monitoring the stability and modification of various defects connected with the presence of lithium immediately after diffusion as well as after aging for more than a year at room temperature. Two levels at $E_v+0.14\mathrm{}$ eV and $E_v+0.27\mathrm{}$ eV were found in lithium-doped $p$-type CdTe. Several samples were also irradiated by ${\mathrm{Co}}^{60}$ $\gamma$ rays and the results compared with those obtained by annealing at higher temperatures. A model of self-compensation by amphoteric action of lithium was proposed in CdTe containing lithium in higher concentrations. The apparently inconsistent results of various authors on the observed energy levels attributed to lithium in CdTe were explained by a tendency of lithium to modify only ionization energies of defects present in the lattice.