Carrier compensation in semi-insulating CdTe: First-principles calculations

Carrier compensation in semi-insulating CdTe has been attributed to the compensation of surplus shallow acceptors by deep donors, usually assumed to be Te antisites. However, our first-principles calculations show that intrinsic defects may not have a significant effect on the carrier compensation due either to lack of deep levels near midgap or to low defect concentration. We demonstrate that an extrinsic defect, ${\mathrm{O}}_{\mathrm{Te}}\text{−}\mathrm{H}$ complex, may play an important role in the carrier compensation in CdTe because of its amphoteric character and reasonably high concentration.

Figure 1

(Color online) Calculated formation energies for various intrinsic defects in CdTe as a function of electron Fermi energy at (a) Te-rich and (b) Cd-rich limits. The slope of an energy line indicates the charge state of the defect, as selectively shown. The transition levels are given by the Fermi energy at which the slope changes.

Figure 2

(Color online) Calculated lowest hydrogenation energies for ${\mathrm{O}}_{\mathrm{Te}}\text{−}\mathrm{H}$ complexes at (+), neutral, and (−) charge states as a function of electron Fermi energy. The transition levels are given by the Fermi energy at which two energy lines cross. Insets show the structures of (a) ${\mathrm{O}}_{\mathrm{Te}}\text{−}{\mathrm{H}}^{+}$ $\left(BC\right)$ and (b) ${\mathrm{O}}_{\mathrm{Te}}\text{−}{\mathrm{H}}^{-}$ $\left(AB\right)$ complexes.