ORIENTATION OF THE ELECTRIC-FIELD GRADIENT ARISING FROM A VACANCY IN HG0.79CD0.21TE

We have used the perturbed angular correlation technique to measure th e orientation of the electric-field gradients (EFGs) due to vacancy tr apping by substitutional indium donors in the II-VI semiconductor Hg0. 79Cd0.2Te. Previously, two hyperfine interaction frequencies were meas ured and were attributed to the trapping of a metal vacancy at a next nearest-neighbor site to the indium atom in bulk solid-state recrystal lized materials. In the present experiments, measurements are done on thin-film samples to find the principal axes of the EFGs. Both EFGs ar e found to have principal axes parallel to a [111] crystal axis, despi te the fact that a simple point charge model supports a [110] EFG for this [110]-oriented In-V(Hg) complex. A similar situation exists for i ndium-vacancy pairing in other II-VI semiconductors. We propose that t he [111] EFG orientation arises from the electric dipole moments of th e highly polarized Te ions in the region of the vacancy.