Surface reaction mechanisms in GaAs atomic layer epitaxy

Abstract

The reactions of trimethyl gallium (TMG) on a gallium-rich surface (Ga surface) and an arsenic-rich surface (As surface) of (001)GaAs were studied using quadrupole mass spectrometry (QMS) by temperature programmed desorption (TPD) and the response of desorbed species from the surfaces during the exposure of TMG under a constant temperature. It has been found that TMG is adsorbed and decomposed on both the As and the Ga surfaces in the temperature region where atomic layer epitaxy (ALE) growth can occur. It has also been found that even the decomposed species, i.e. MenGa(n=1, 2), can be desorbed from the Ga surface together with TMG molecules, but not from the As surface. The results are inconsistent with the prevalent model based on selective adsorption on the As surface, and so a new selective desorption model is instead proposed for the self-limiting deposition of Ga for ALE growth. This model emphasizes that even Ga-containing decomposition products, i.e. MenGa(n=1, 2), are desorbed selectively from the Ga surface.