Properties of aluminum epitaxial growth on GaAs

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Abstract
The structural perfection and epitaxial growth process of Al films deposited by molecular beam epitaxy (MBE) on (100) GaAs substrates have been analyzed by transmission electron microscopy (TEM) and Rutherford backscattering analysis (RBS). Two epitaxial relationships between the Al film and (100) GaAs are observed. In general, deposition on As-rich surfaces at room temperature and low deposition rates (200–750 Å/h) lead to 〈110〉 oriented Al films. Higher deposition rates at room temperature yield a mixture of 〈110〉 and 〈100〉 oriented films or completely 〈100〉 oriented films at the higher deposition rates. On Ga-rich surfaces, only 〈100〉 oriented Al films are observed. For both epitaxial orientations the misfit elastic strain at the interface is accommodated by misfit dislocations localized in the Al film for film thicknesses of ⩾ 600 Å. Under these conditions the GaAs substrate at the interface is strain free and dislocation free. The presence of surface steps associated with surface reconstruction at the start of the epitaxial process is invoked to account for the existence of 〈110〉 oriented film growth on 〈100〉 substrates.