Characterization of low temperature GaAs buffer

A study of the electrical and physical characteristics of GaAs buffer layers grown at low temperatures as a function of substrate temperature, T_S, is discussed. Three approximate temperature ranges with different electrical properties were identified: high (T_S⩾460°C), intermediate (280°C⩽T_S⩽420°C), and low (T_S⩽250°C). In the high range, the lattice parameter of the epilayer is the same as that of GaAs. In the intermediate range, the perpendicular lattice parameter of the epilayer is larger than and the in-plane lattice parameter is equal to that of GaAs. In the low range, the epilayer appears to be polycrystalline or amorphous. For the high and intermediate ranges, the epilayers are the color of ordinary GaAs. However, for the low range, the epilayers have a gold tint. Hall measurements were performed on the as-grown samples and annealed samples. Samples of the high and intermediate ranges remained highly resistive after annealing while usually high carrier concentrations were observed for 850°C-annealed low range samples, 8.8×10¹⁷ to 1.5×10¹⁸ cm³, with mobilities of 490 to 920 cm² V^-1 s^-1