Ab initio studies on segregation of n-type dopants and vacancies near beta-Ga2O3(010) surface

Beta-Ga2O3 is a wide-bandgap semiconductor with important electronic and optoelectronic applications. It has been observed that upon extended period of thermal annealing, certain types of n-type dopants such as Sn show strong tendency of segregation towards Ga2O3 surfaces, even forming a secondary SnO2 phase. Using density functional theory, we conducted a comprehensive study on the thermodynamic preferrence of common n-type dopants (Si_Ga, Ge_Ga, Sn_Ga) and intrinsic defects (V_Ga, V_O) both near the (010)-surface and in the bulk of Ga2O3. The key findings are: (1) in bulk Ga2O3, Si prefers to occupy tetrahedral over octahedral Ga site (by -0.60 eV), Sn shows the opposite preference (by -0.90 eV), and Ge have almost equal preferrence on either Ga site; (2) Si and Ge shows weaker likelihood of segregation towards Ga2O3(010) surface (-0.14 eV for Si, -0.11 eV for Ge) than Sn (-0.25 eV), while both V_Ga and V_O assume strong tendency of segregation (< -0.4 eV); (3) all dopant species (Si, Ge, Sn) show significantly decreased (increased) segregation energy with the presence of surface V_Ga (V_O); (4) co-doping with Si or Ge in the second-nearest-neighbor configuration can raise the segregation energy of Sn. The implications for experimental processing conditions will be discussed.