Effects of substrate preparation conditions on GaAs oval defects grown by molecular beam epitaxy

Effects of substrate preparation conditions, i.e., wet chemical and ultrahigh vacuum cleaning preparations, on GaAs oval defects grown by molecular beam epitaxy (MBE) were investigated. It is found that, with our MBE system, the presence of the smaller (<10 μm) ovally shaped defects without macroscopic core particulates can be ascribed to surface microscopic contaminations. Most of the other remaining larger (>10 μm) oval defects with core particulates observed on 1-μm-thick GaAs MBE layers are attributed to surface macroscopic contaminations. The total density is reduced to 300 cm−2 without significantly modifying the growth cell parameters.