Fig. 1. (Color online) The STM images and topographic line profiles of (a, b) the GaSb buffer layer, (c, d) the 5 nm GaSbBi layer and (e, f) 10 nm GaSbBi layer, respectively.

Fig. 2. (Color online) (a) The STM image of the GaSb buffer with the indication of the positions of the STS measurements. The arrow designates the position of the I–V curve shown in (b), which is a typical I–V spectrum of GaSb indicating that the current plateau is approximately equal to the band gap of GaSb. (c) The bar graph on the energy distribution of band gaps based on all measured positions in (a).

Fig. 3. (Color online) (a) The STM image of the 5 nm GaSb_1–xBi_x layer with the positions of STS measurements marked and the arrows indicate the positions for the I–V curves shown in (b–d). (e) The bar graph on the distribution of energy band gaps measured with respect to the measurement positions in (a).

Fig. 4. (Color online) (a) The STM image of the 10 nm GaSb_1–xBi_x film with the positions of STS measurements indicated. (b) The bar graph on the distribution of energy band gaps measured.