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=2.2×1019cm−3 is investigated in the temperature interval 1.4–100K at a frequency of 53MHz. For the slow transverse mode an absorption peak at 7.3K and a decrease of the phase velocity below 40K 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.