Reversible conductivity modulation by tuning surface band bending in Sn-doped <i>β</i>-Ga2O3 single crystal

Developing methods for modulating the band structure of semiconductor material is crucial for the application. In this work, the electron concentration of heavy Sn doped β-Ga2O3 crystals showed an interesting partially reversible phenomenon after multiple annealings under different atmospheres. The carrier concentration of Sn-doped β-Ga2O3 is significantly enhanced from 1.89 × 1018 to 8.90 × 1018 cm−3 through N2 annealing with a mobility of 70.12 cm2/V s, nearly double the theoretical limit. The increase in electron concentration is caused by the reduction in VGa concentration. A large amount of VO generated after N2 annealing combines with VGa to form VGa–VO complexes, compensating for the acceptor effect of VGa and leading to a decrease in VGa concentration. The reduction in VGa concentration shortens the space charge region and strengthens the downward band bending, ultimately resulting in the accumulation of electrons at the surface. After air annealing under identical conditions, the increased VGa caused a significant reduction in electron concentration, leading to an upward surface band bending of 0.88 eV. Furthermore, this process is reversible. The conductive crystal becomes insulating when annealed in air, but its conductivity can be restored after annealing in N2. Combined with different annealing processes, the modulation of the electron concentration and surface band structures can be effectively achieved by transforming the concentrations of VGa and VO. This study provides a convenient and efficient route to modulate the band structure via manipulating surface defects of β-Ga2O3.