| Ternary and more complicated polynary oxide semiconductors could be applied in many fileds because of its high gas sensitivity, catalytic activity and conductivity. Moreover, nanomateirals based on polynary oxides have interesting dimension-related properties including multi-ferroelectricity, ferroelectricity, superconductivity, giand magnetoresistivity. Nevertheless, compared with methods of fabricating binary oxide semiconductors, those of ternary materials are limited and unsystematic. For example, Zn-Sn-O materials prepared with different processes would have various structures. Further, present researches focus mostly on the performance rather than on the influence of fabrication on structures or of doping on properties. In this paper, undoped, Ti-doped and Mg-doped Zn-Sn-O thin films were spin-coated on silicon wafer and silica glass to study the influence of fabrication on structures, surface morphologies and optical properties, and then electronic states were studied via first principle calculation to predict the semiconductivity and functional properties.Results show that high temperature is essential to prepare ternary oxides. Then thin films made from stannate precursor were annealed in the range of 300-1000?. Zn2SnO4 is produced in the range of 400-700?, and ZnSnO3 in the range of 900-1000?, according to which controllable growth could be realized. Based on these findings, fabricating parameters were optimized for Zn-Sn-O thin films, and results show that the best films are grown with tin sol of stannate salt, molar ratio Zn:Sn of 2:1, annealing temperature of 700? for Zn2SnO4 and 900? for ZnSnO3, annealing time of 3 h, heating rate of 12.5?/min. Films prepared using these parameters have grain size of about 80 nm, low inner stress, small lattice deformation, flat and tense surface, bandgap of 4.2 eV, and transmittance of 95% for visible light. At last, first principle calculation results propose the possibility of materials modifying by Ti and Mg doping.Ti and Mg doped samples annealed with 700? have the same composition but higher bandgaps and better visible light transmittace than the undoped films. The films fabricated with 2 at% Ti and 6 at% Mg have the best crystallinity and thus compressive strain. However, in the Ti and Mg doped samples annealed with 900?, Zn2SnO4 and ZnSnO3 are detected, Ti doping makes the surface morphology worse, and Mg doping makes the visible light transmittalce lower than that of the undoped films, implying that further optimizing of processing parameters is needed.Compared with undoped Zn2SnO4, electronic states study shows that the valence band top and the conduction band (CB) bottom are at different points in Ti doped sample, and the bandgap is narrowed while the denstity of states in CB top is inhenced. The discrepancy between results of experiments and calculation is caused by the influence of calculation accuracy and experiment processing error. Mg doped Zn2SnO4 has higher Mg-2p and Mg-3s states, which introduce impurity levels in the band gap and improve the opto-electrical properties. For doped ZnSnO3, Mg and Ti atoms have no influence on the band gap and energy levels among the gap, but they reduce the CB energy range and intensify the density of states in CB, thus increase the carrier mobility. In conclusion, Ti and Mg doping can effectively modify the electronic states of Zn-Sn-O ternary materials, which offer various options when chosing materials for different application areas. |
PDF Full Text Request