Extension of Meyer-Neldel rule using chemical diffusion experiments in CdTe

Abstract

The chemical diffusion coefficient D˜ in chlorine-doped CdTe with Cl concentration [Cl]≈4.3×1016cm−3 was determined by means of the high-temperature in-situ measurement of the relaxation of electrical conductivity after step-like changes of ambient Cd pressure for temperatures 600 °C, 700 °C and 800 °C. Weak dependence of D˜ on the ambient Cd pressure was found. Both D˜ and equilibrium conductivity for different Cl doping were calculated based on the defect model in which monovalent chlorine donors (ClTe) are compensated by divalent acceptors Cd vacancies (VCd) and monovalent acceptor-like complexes (ClTeVCd). It was shown that experimental D˜ can fit well for [Cl]=4×1016cm−3 assuming different diffusion coefficients for singly and doubly charged VCd. The temperature dependence of D˜ in the temperature interval 600–800 °C near Cd saturation was properly approximated by D˜(cm2s−1)=68exp(−1.38eV/kBT). Linear dependence of the pre-exponential term D0 on activation energy EA known as a Meyer-Neldel rule (MNR) was discussed in detail and its limited validity was proven based on experimental data and numerical simulations. It was shown that the standard MNR may be conveniently extended to a ”triangle Meyer-Neldel rule”, which conforms with theory and relevant experiment.