MECHANISMS OF ATOMIC LAYER EPITAXY OF GAAS

We have studied the surface chemistry of trimethylgallium and diethylgallium chloride on GaAs(100) surfaces as related to the atomic layer epitaxy (ALE) of GaAs. We have observed that during the Ga deposition, the reaction pathway of trimethylgallium changes such that there is significant CH3Ga emission at high Ga coverages. An examination of the Ga coverage dependence reveals that this stoichiometry dependent CH3Ga desorption can lead to self-limiting Ga deposition which is a prerequisite for ALE. Numerical simulation of the reaction shows reasonable agreement with low-pressure ALE growth data. Diethylgallium chloride was found to deposit GaCl on the GaAs surfaces, but with residence time decreasing rapidly with increasing Ga coverage. Again a numerical examination of this stoichiometry dependent phenomenon indicates that it can significantly contribute to the self-limiting Ga deposition. Both systems showed that stoichiometry dependent reactions can be important mechanisms for the atomic layer epitaxy process.