Phase transition, structural stability and electrical properties of V or Mn doped ZnSe composites under high pressure.

The structural parameters and enthalpies of pure ZnSe and different concentrations of V/Mn:ZnSe at high pressures were calculated using the first principles calculation method based on density functional theory. The lattice constants and bond lengths of all the systems decrease under pressure, and the respective phase transition pressures are obtained from the enthalpy-pressure relationship curves, which show that V/Mn elemental doping reduces the phase transition pressure of ZnSe, and the phase transition pressure further decreases with the increase of the doping concentration. The doping formation energies and the elastic constant criterion at atmospheric and high pressures confirm the structural stability of all the systems within the pressures of this study, and the pugh ratio confirms that they are all ductile structures.The results of electrical properties study show that at atmospheric pressure, all V:ZnSe systems have metallic properties, and a metal to semiconductor transition occurs at high pressure when the doping concentration is 12.5%. However, the Mn:ZnSe systems are semiconductors at both atmospheric and high pressures. Pressure significantly influences the degeneracy and position of the impurity bands: the impurity bands of V:ZnSe move toward higher energy under pressure, while the impurity bands of the Mn:ZnSe system shift toward lower energy. The element doping concentration also affects the d orbital degeneracy of V/Mn:ZnSe under atmospheric pressure, the degeneracy of V/Mn-d orbital decreases with the increase in doping concentration. Under high pressure, the degeneracy of the V/Mn-d orbital decreases further when the doping concentration is 3.13%, but the degeneracy is enhanced when the doping concentration is 6.25 and 12.5%. Doping can effectively change the phase transition pressure of ZnSe, and the pressure can effectively modulate the properties of this material.