Diffusion of Cd vacancy and interstitials of Cd, Cu, Ag, Au and Mo in CdTe: A first principles investigation

Abstract

We present a first principles study of the diffusion profiles of native Cd, adatom and vacancy, and cationic non-native interstitial adatoms Cu, Ag, Au, and Mo in bulk CdTe. The high symmetry Wyckoff position 4(b) is the global minimum energy location for Cd and Ag interstitials and the 4(d) site for Mo interstitials. Adatoms of Cu and Au show an asymmetric shape of the energy diffusion barrier with two structurally equivalent minima and two energetically distinct maxima in the pathway. The others, Mo, Ag and Cd interstitial and vacancy, show a symmetric diffusion barrier with two structurally unique minima and a maximum. Diffusion for Cu and Au interstitials proceeds along the [110] channel in the crystal in a near straight line path, avoiding both high symmetry 4(b) and 4(d) sites. Diffusion for Cd and Ag proceeds along two nearly straight line paths along [111] and [11–1]. Diffusion for Mo is along the [110] channel however it deviates slightly from the straight line paths along [111] and [11–1] avoiding the 4(b) site. The rate-limiting diffusion barriers range from a low of 0.10eV for the symmetric diffusion path of a Ag interstitial to a high of 1.83eV for the symmetric diffusion path of a Cd vacancy. The rate-limiting barriers for the others are 0.27eV for Au, 0.30eV for Mo, 0.33eV for a Cd interstitial and 0.46eV for Cu. The symmetric or asymmetric nature of the diffusion path as well as the bond length and atomic coordination at the energetic-extrema positions influence the size of the diffusion energy barrier. In addition there exists two electronic signatures in the local density of states: one for the bond breaking in the symmetric diffusion barrier paths and the other in the difference in the energy of occupied states between the global minimum and global maximum energy positions.