The Thermal Stability of Heavily Carbon-Doped GaAs Grown by Metalorganic Molecular Beam Epitaxy

Heavily carbon-doped GaAs thin films with a hole concentration of 5.8 × 10 20 cm -3 , grown by metalorganic molecular beam epitaxy (MOMBE), were annealed at 900°C for 30 minutes. The microstructural changes due to annealing were investigated by transmission electron microscopy. Electron diffraction study showed some evidence of carbon clustering on {111} in as-grown samples. A high density of precipitates was found in the annealed sample, together with a decrease of the lattice contraction and hole concentration. In the as-grown layer, misfit dislocations with only one type of Burgers vector were observed, while misfit dislocations with the several Burgers vectors were observed in [110] direction after annealing. The density of misfit dislocations in both directions increased significantly even though the lattice contraction in carbon-doped GaAs decreased after annealing. A model is proposed to explain the change of misfit dislocation density in heavily carbon-doped GaAs layer.