Electron paramagnetic resonance and Coulomb gap in HgSe:Fe

The temperature and concentration dependence of the EPR absorption due to the Fe³⁺ state in HgSe is shown to be consistent with a Coulomb gap in the defect density of states. The latter is a consequence of inter-ion Coulomb interaction which renders a correlated ground state with short-range order of the partially ionised resonant donors. Possible mechanisms for a decrease of both the mobility and the EPR intensity for very high iron concentrations in this ordered, glass-like state are discussed.