Possible n-type carrier sources in In ₂O ₃(ZnO) _k

Homologous compounds with the formula In ₂O ₃(ZnO) _k, where k is an integer, have potential applications as transparent conducting oxides and high temperature thermoelectric materials. In this study, we focus on the defect properties. Using the k = 3 phase as a prototype, we calculate with the first-principles method the defect formation energies and transition levels of the most probable n-type carrier producers, which include oxygen vacancy (V _O), indium antisite on zinc (In _Zn), indium interstitial (In _i), and zinc interstitial (Zn _i). The site-preference of these defects has been explored by comparing the total energies of defects at different sites. Under the n-type environment, In _Zn has a low formation energy and meanwhile a transition energy level close to the conduction band minimum (CBM); V _O also has a lower formation energy, however a deep transition energy level in the band gap; the cation interstitials have high formation energies, although their defect transition energy levels are quite shallow. Besides, we find that V _O and In _Zn tend to form a defect complex when the two isolated defects take the nearest-neighboring atomic sites in the same ab-plane. We conclude that In _Zn and its related defect-complex are the possible n-type carrier sources in In ₂O ₃(ZnO) _k. Besides, we found that V _O has a significant site-preference, which can modify the site-preference of In _Zn by forming defect-complexes. This may lead to high anisotropy in relaxation time, and then the experimentally reported strong anisotropy in electrical conductivities in In ₂O ₃(ZnO) ₅.