Indium layers in low-temperature gallium arsenide: Structure and how it changes under annealing in the temperature range 500-700°C

Transmission electron microscopy is used to study the microstructure of indium δ layers in GaAs(001) grown by molecular beam epitaxy at low temperature (200°C). This material, referred to as LT-GaAs, contains a high concentration (≈10²⁰ cm^-3) of point defects. It is established that when the material is δ-doped with indium to levels equivalent to 0.5 or 1 monolayer (ML), the roughness of the growth surface leads to the formation of InAs islands with characteristic lateral dimensions < 10 nm, which are distributed primarily within four adjacent atomic layers, i.e., the thickness of the indium-containing layer is 1.12 nm. Subsequent annealing, even at relatively low temperatures, leads to significant broadening of the indiumcontaining layers due to the interdiffusion of In and Ga, which is enhanced by the presence of a high concentration of point defects, particularly V_Ga, in LT-GaAs. By measuring the thickness of indium-containing layers annealed at various temperatures, the interdiffusion coefficient is determined to be D_In-Ga=5.1×10^-12 exp(-1.08 eV/kT) cm2/s, which is more than an order of magnitude larger than D_In-Ga for stoichiometric GaAs at 700°C.