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 delta layers in GaAs(001) grown by molecular beam epitaxy at low temperature (200 degrees C). This material, referred to as LT-GaAs, contains a high concentration (approximate to 10(20) cm(-3)) of point defects. It is established that when the material is delta-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 indium-containing 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 DIn-Ga = 5.1 x 10(-12) exp(-1.08 eV/kT) cm(2)/s, which is more than an order of magnitude larger than DIn-Ga for stoichiometric GaAs at 700 degrees C. (C) 1998 American Institute of Physics.