Production of acceptor complexes in sol-gel ZnO thin films by Sb doping

Abstract

Sb doped ZnO nanofilms were successfully deposited on glass substrates via economical sol-gel method. X-ray diffraction (XRD) patterns revealed the hexagonal wurtzite structure of the elaborated films and showed that the crystal growth of the doped samples is (002) preferentially oriented. X-ray photoelectron analysis suggested the successful substitution of antimony in Zn sites. According to XPS analysis, the presence of an important antimony ions states in fivefold coordination suggested the formation of the complex (SbZn−2VZn) level. It was found that low Sb doping (less than 1%) leads to slight broadening of the band gap and blue shift of the near band edge (NBE) emission of ZnO. It indicates the reduction of the intrinsic defects density for this doping regime. However, for Sb doping more than 1%, the optical results revealed the creation of an important defects density such as stacking faults and zinc vacancies (VZn) that lead to the formation of acceptors levels. From photoluminescence (PL) at low temperature, the presence of acceptor-bound exciton A0X (152meV) has been demonstrated. Stacking faults in ZnO seems to contribute particularly to the PL signal through the 3.316eV emission attributed to a free electron-to-neutral acceptor (e, A°) transition with binding energy of about 137meV. The p-type conductivity of ZnO thin films is confirmed by Hall measurement.