Structural and luminescence properties of heavily doped radio-frequency-sputtered ZnTe:Cu thin films

We report on the structural and luminescence properties of ZnTe:Cu films containing Cu concentrations up to 12 at. % and prepared using rf magnetron sputtering. The lattice parameters of the various crystalline phases prevailing at different Cu concentrations (cubic, hexagonal, and orthorhombic) are calculated and compared with literature results on films prepared using other techniques. Study of the steady state photoluminescence and excitation spectra revealed the presence of three donor impurities involved in the well-known band at ∼1.70 eV (peak L) attributed to self-activated transition. One of these donors is merging partially with the conduction band and the two others have mutually overlapping density of states with maxima at 0.29 eV and 0.45 eV below the conduction band edge. Another donor that is resonant with the conduction continuum is responsible for a higher energy emission band (peak H). The density of states of this donor has a maximum at 0.57 eV above the conduction band edge for a copper concentration of 8.2 at. %. The emission peak H undergoes a blue shift and its intensity increases sharply relative to the intensity of the L peak with the increase of Cu concentration. Moreover, the H emission extends to photon energies higher than the band gap. A possible interpretation of the behaviour of the peak H in terms of recombination involving the resonant states is suggested