Atomically resolved silicon donor states of β-Ga2O3

The electronic states of silicon donors in a wide gap semiconductor, β-Ga2O3(100), have been studied using low-temperature scanning tunneling microscopy. We observe one-dimensional rows along [010], as expected from the crystal structure. In addition, substitutional Si donors are identified up to the fourth subsurface layer with clear spectroscopic features at the bottom of the conduction band. The decay length of each subsurface Si donor is systematically measured, and reasonably agrees with a picture of the Si donor in bulk β-Ga2O3. These results strongly suggest that Si impurities are shallow donors and responsible for the high electrical conductivity of β-Ga2O3.