Abstract

Atomic layer epitaxy (ALE) is a technique which, in principle, yields unparalleled deposition uniformity with precise (i.e. monolayer) thickness control. The technique has been used to deposit compound semiconductors, e.g. GaAs, although the success has not been universally good. In many examples the ALE operating “window” is very small or non-existent. Unintentional carbon doping is another problem which has limited the utility of this technique. In order to address the problems limiting GaAs ALE, we have investigated the surface chemical properties of the standard deposition precursors on GaAs(100) using a variety of surface science diagnostics. Results of these experiments have shed light on the mechanisms of precursor decomposition which lead to film growth and carbon doping. For instance, the kinetics of trimethylgallium (TMGa) decomposition on the Ga-rich and As-rich surfaces, measured by TPD, are in semiquantitative agreement with ALE results. This indicates that the dominant growth mechanism during ALE is heterogeneous in nature. We have also investigated the mechanism of carbon incorporation when using TMGa. Normally, a small fraction of adsorbed methyl (CH3) groups dehydrogenate into methylene (CH2) groups, which are a likely precursor to carbon incorporation. This adsorbate was characterized with vibrational spectroscopies and static SIMS. The rate of CH₃ dehydrogenation is consistent with the carbon doping levels obtained during ALE and MOMBE.

© 1995 Optical Society of America