Optoelectronic properties and doping of magnetron sputtered highly mismatched ZnO_1-xTe_x alloy thin films

Highly mismatched alloys (HMAs) provide a unique venue for controlling electronic band structures and consequently the optoelectronic properties of materials for specific device applications. In this paper, we synthesize the ZnO_1-xTe_x HMA thin films over the entire composition range by magnetron co-sputtering. We find that the alloys with x<0.15 and x>0.9 are wurtzite and zinc blende structures, respectively, while alloys with composition in between (0.15<x < 0.9) are amorphous. The dielectric functions of the ZnO_1-xTe_x alloy thin films were determined by using spectroscopic ellipsometry. Electrically, we find that Al and H doping in crystalline ZnO-rich ZnO_1-xTe_x alloys results in n-type materials, with both their electron density and mobility decrease with increasing x. This can be understood as the effect of upward shift of the valence band which favors the formation of native acceptors compensating the donors. Interestingly, while Sb substituting O in ZnO is expected to be a deep acceptor, Sb doped ZnO-rich ZnO_1-xTe_x alloys also exhibit n-type conductivity, attributed to the formation substitutional Sb in Zn (Sb_Zn) that are confirmed by x-ray photoelectron spectroscopy measurements. In addition, other Sb related acceptors are also present in the materials and at elevated temperature these acceptors dominate the conductivity and the alloy becomes p-type.