Ultrasonic investigations of the Jahn-Teller effect in a ZnSe: Fe2+ crystal

Abstract

The temperature dependence of the absorption and velocity of transverse ultrasonic waves propagating in the [110] direction in a ZnSe: Fe2+ crystal with the iron impurity of n=2.2× 1019 cm-3 is investigated in the temperature interval 1.4-100 K at a frequency of 53 MHz. For the slow transverse mode an absorption peak at 7.3 K and a decrease of the phase velocity below 40 K are found, while no such features are observed for the fast mode. The anomalies are interpreted as manifestations of the Jahn-Teller effect. The softening of the elastic modulus (C11 - C12) 2 indicates that the local distortions in ZnSe: Fe2+ are tetragonal. Under the assumption that the absorption maximum is of a relaxational nature, the temperature dependence of the relaxation time is recovered from the data, and the values of the potential barrier height and vibronic frequency are obtained. © 2009 American Institute of Physics.