Temperature-induced charge transfer in Fe-doped ZnSe single crystal: mechanism and features

We have collected the EPR spectra for Fe ions of zinc selenide single crystals in the temperature range from 5 to 300 K. The samples under test were grown by the Bridgman method and had a homogeneous structure of the ZnSe:Fe solid solution. Temperature-induced charge transfer from Fe 3+ into Fe 2+ on cooling is detected. The EPR spectrum formation mechanism is studied using a complex theoretical approach that combines the semi-empirical Modified Crystal Field Theory and structure optimizations using the DFT-based band-periodic plane-wave pseudopotential method. A theoretical model of the EPR spectrum formation due to two alternative paramagnetic sub-systems related to Fe 2+ and Fe 3+ ions is developed. The manifestation of structural defects occurring in the doping process in the EPR spectrum formation is analyzed. Graphical abstract