Direct Observation of GaAs Atomic Layer Epitaxy by Reflection High Energy Electron Diffraction.

Atomic layer epitaxy (ALE) of GaAs using trimethylgallium (TMG) and triethylgallium (TEG) by chemical beam epitaxy (CBE) is reported. Reflection high energy electron diffraction (RHEED) is employed to monitor the formation of each individual monolayer directly. A new (4X8) surface reconstruction, characteristic of an ordered chemisorbed molecular Ga monolayer is observed for the first time. Each Ga atom in this transitional layer has at least one alkyl radical cleaved away. The stability of this transitional stage varies depending on the alkyl group involved and the temperature. Dynamical evolution of this adsorbed layer is described. The chemical properties of this overlayer dictate the GaAs ALE growth conditions.