Structural transformations in low-temperature grown GaAs:Sb

Sb-doped and Sb-free GaAs films were grown by molecular beam epitaxy (MBE) at low temperature (LT) and were annealed in the MBE set-up at various temperatures within the range of 500-900°C. The concentrations of arsenic antisites in as-grown samples obtained using near-infra-red optical absorption were found to be as high as 6 × 10¹⁹ and 7 × 10¹⁹ cm^-3 in Sb-doped and Sb-free samples, respectively. Samples were studied by high-resolution x-ray diffractometry (HRXRD) and transmission electron microscopy (TEM). Despite the high concentration of intrinsic point defects, x-ray rocking curves demonstrated perfect crystalline quality in as-grown samples. After annealing at temperatures of 500-700°C, the lattice mismatch decreased in both Sb-doped and Sb-free samples, but in Sb-doped samples the reduction was much higher than would be expected for the antisite defect concentration determined from optical measurements. The segregation of isovalent Sb impurity into the As clusters was suggested. Upon annealing at temperatures higher than 700°C, Sb-doped samples manifested a strong broadening of the diffraction maximum related to the LT GaAs:Sb layer. The TEM and HRXRD studies revealed that high-temperature annealing resulted in formation of dislocation loops attached to the large As clusters.