Physics.Crystal Structure of Heavily Doped GaAs and In GaAs

点击翻译按钮获取中文摘要

Heavily carbon-doped GaAs (C-GaAs) was grown by metalorganic molecular beam epitaxy (MOMBE), and the material properties of the as-grown and annealed C-GaAs were mainly studied by transmission electron microscopy (TEM), photoluminescence (PL), electroluminescence (EL), X-ray diffraction, and Hall measurements. In the as-grown sample, carbon is electrically active as an acceptor, and the hole concentration as high as 10^<21>cm^<-3> was obtained. Because of a small size of a carbon atom, heavy carbon doping decreases the lattice constant and results in a misfit with that of a GaAs substrate. The tensile strain in a plane is found to be incompletely relaxd even with formation of misfit dislocations.Annealing of C-GaAs at high temperature was found to reduce the hole concentration and increases the lattice constant. The detailed TEM analysis revealed carbon precipitates and an increased number of misfit dislocations. We proposed a model to explain a decrease of the hole concentration as fo … More llows. In the early stage of annealing, the residual strain is further relaxd by formation of misfit dislocations. In the later stage, the carbon atoms at arsenic slowly move to the interstitial sites and form precipitates. Since the diffusivity of carbon in GaAs is extremely small, this process is slow. The movement of carbon atoms from the arsenic sites results in a decrease of the hole concentration. It also increases the lattice constant. However, the formed misfit dislocations have already relaxd the tensile strain which resulted from the lattice mismatch between C-GaAs and GaAs substrate. Therefore, the already-formed misfit dislocations must be canceled. For this purpose, more misfit dislocations with the Burgers vector opposite to those of the already-formed misfit dislocations are formed.The above model well explains the TEM and XRD results. Electrominescence was observed from C-GaAs before and after the anneal, and the origin of EL was attributed to the misfit dislocations. This study helps us understand thermal instability of heavily C-doped GaAs. Less