First Principle Study of Zn-based Transition Metal (TM) doped II-VI Ferromagnetic Semiconductors

Abstract

The present study involves a comprehensive theoretical investigation of the structural, mechanical, electronic, magnetic and optical properties of Zn1- xTMxS/Se/Te (TM = Mn, Fe, Co, Ni), Ti doped ZnS/Se and V doped ZnS compounds with different dopant concentrations (TM = 0.00, 0.0625, 0.125, 0.25, 0.50, 0.75, 1.00). The first principle approach has been applied in the frame work of density functional theory (DFT) by using full potential linearized augmented plane wave (FP- LAPW) method. The optimized structures have been employed to depict the thermodynamic stability of ferromagnetic state from the calculated values of the enthalpy of formation (ΔH) and the cohesive energy. More recently developed modified Becke and Johnson (mBJ) potential, which calculates the most accurate band gap, has been employed to achieve a realistic set of the calculated properties. The origin and the nature of the ferromagnetism is elucidated from the calculated band structures (BS) and density of states (DOS), by analyzing the calculated exchange constants (N0α and N0β) and the magnetic moments. The negative and large values of N0β depict large splitting of 3d-states of TMs, due to the crystal field, indicating that the ferromagnetism is induced by the strong p-d hybridization. Moreover, it has been observed that Mn and Co doped ZnS/Se/Te compounds are ferromagnetic semiconductors, while Ti, V, Fe and Ni doped ZnS/Se/Te alloys are half-metallic ferromagnetic semiconductors. The estimated Curie temperatures (Tc) have shown that the studied compounds exhibit above room temperature ferromagnetism (RTFM), indicating potential spintronic device applications. The potential of the compounds for various optical applications has also been explored. The calculated real part of the static dielectric constant ε1(0) and optical band gap, Eg have depicted an inverse relation, in agreement with the Penn’s model, which confirm the accuracy of the presented calculations. A blue shift in the absorption region has been found for TM = Mn, Fe, Co, Ni doped ZnS/Se and V doped ZnS, while TM = Mn, Fe, Co, Ni doped ZnTe and Ti doped ZnS/Se have demonstrated a red shifted absorption. The decreasing trend of band gap and high value of absorption in the visible region, due to the magnetic ions doping, indicate