The scanning tunneling microscopy and spectroscopy of GaSb 1– x Bi x films of a few-nanometer thickness grown by molecular beam epitaxy

The ultrahigh vacuum scanning tunneling microscope (STM) was used to characterize the GaSb1–xBix films of a few nanometers thickness grown by the molecular beam epitaxy (MBE) on the GaSb buffer layer of 100 nm with the GaSb (100) substrates. The thickness of the GaSb1–xBix layers of the samples are 5 and 10 nm, respectively. For comparison, the GaSb buffer was also characterized and its STM image displays terraces whose surfaces are basically atomically flat and their roughness is generally less than 1 monolayer (ML). The surface of 5 nm GaSb1–xBix film reserves the same terraced morphology as the buffer layer. In contrast, the morphology of the 10 nm GaSb1–xBix film changes to the mound-like island structures with a height of a few MLs. The result implies the growth mode transition from the two-dimensional mode as displayed by the 5 nm film to the Stranski–Krastinov mode as displayed by the 10 nm film. The statistical analysis with the scanning tunneling spectroscopy (STS) measurements indicates that both the incorporation and the inhomogeneity of Bi atoms increase with the thickness of the GaSb1–xBix layer.