COMPARATIVE-STUDY OF SELF-LIMITING GROWTH OF GAAS USING DIFFERENT GA-ALKYL COMPOUNDS - (CH3)3GA, C2H5(CH3)2GA, AND (C2H5)3GA

We studied the self-limiting growth of GaAs using three kinds of Ga-alkyl compounds-trimethylgallium (TMGa), ethyldimethylgallium, and triethylgallium-as atomic layer epitaxy (ALE) sources. Perfect self-limiting behavior was found only for TMGa. The self-limiting mechanism could be explained by the surface site selectivity of the metalorganic molecules in the adsorption, desorption, and decomposition processes. We found that the degree of the site selectivity declined as methyl groups attached to a Ga atom were replaced by ethyl groups. We believe that the TMGa molecule is adsorbed without decomposition in the first step, and then fully decomposed into Ga. Three methyl groups of the adsorbed TMGa play an important role in the site selectivity and make the growth self-limited. We studied the evolution of the chemical state of the TMGa-exposed (001) GaAs surface by changing the length of the interruption following a TMGa pulse. There was no change in the surface chemical conditions and in the degree of self-limiting during the H2 purge after TMGa pulse. These results provide a detailed understanding of the surface chemistry and self-limiting growth involved in ALE.