Heteroepitaxial GaAs on aluminum oxide. I: Early growth studies

Abstract

The nucleation and initial growth of GaAs films prepared from trimethylgallium and arsine on (0001) Al₂O₃ substrates have been examined by means of electrical measurements and reflection electron diffraction and electron microscopy techniques. The early stage of growth of GaAs, under conditions which are consistent with epitaxial film formation, appears to be by the formation of many discrete nuclei which coalesce to form large islands and eventually produce complete surface coverage. Electron diffraction results provide evidence of a high density of defects near the interface with a considerable improvement in crystal quality as the film thickness increases. Electrical measurements show the film at the interface to bep type. The thickness of thep layer varies typically from ∼1 to ∼5 μm, depending on the concentration of donor impurities in the reactant gases. The films are found to convert ton type upon subsequent growth, suggesting that thep-type behavior may be related to the defect structure near the GaAs/Al₂O₃ interface.