Suppression of three-dimensional pit formation of InAs on GaSb(001) by Sb-free two-step molecular beam epitaxy

•InAs on GaSb heteroepitaxial growth by molecular beam epitaxy was investigated.•Pits are easily formed on InAs surface at low growth temperatures.•Pits are suppressed by irradiation of trace Sb due to surfactant effect.•Without Sb irradiation, two step InAs growth sequence can suppress pits.•Extremely flat surface was obtained by initial at 400 °C and subsequent at 520 °C.