“…1(a). First, oxide on semiinsulating GaAs (0 0 1) substrate was removed by As-free high-temperature surface cleaning method [6][7][8] in an annealing chamber of molecular beam epitaxy (MBE) system. Next, the substrate was transferred into a growth chamber (Riber MBE 32P), GaAs buffer layer of 300 nm was grown at 620 1C by the solid source MBE with the following conditions: As 4 /Ga flux ratio was 5, growth rate was 1 mm/h.…”