Identification of deep centers in ZnSe

Abstract

Cu-doped, Mn-doped, and nominally undoped ZnSe crystals were prepared by vapor transport or sublimation. The presence of the dopants was established by photoluminescence EPR, atomic absorption, and radiotracer techniques, and their associated energy levels studied by photoluminescence. From measurements of photocurrent and photocapacitance, it was shown that Cu doping introduces an energy level at about 0.68 eV above the valence band. From the good agreement between the optical cross sections obtained from the measurement of photocapacitance and optical quenching of photoluminescence, it was concluded that this center is responsible for the red Cu-emission in photoluminescence. This conclusion was supported by the observation that the absolute concentration of this level agrees with the reduction of the free-carrier concentration caused by Cu doping. Owing, presumably, to residual copper contamination, the 0.68-eV center was sometimes detected in nonintentionally doped and Mn-doped material. Evidence is given that this center is identical to the M center reported previously in Mn-doped ZnSe is identical with the 0.68-eV energy level. Independent of dopant, another level at about 0.58 eV above the valence band was observed.