Use of Raman spectroscopy to examine the effects of growth stops on the interfaces of superlattices grown by molecular beam epitaxy

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Abstract
Raman spectroscopy of confined longitudinal optical phonons is used to examine the abruptness of the interfaces in a sequence of (GaAs)7(AlAs)7 superlattice samples grown by molecular beam epitaxy. The duration and stoichiometry of growth stops at each heterointerface was varied throughout the sequence. Arsenic rich, group III rich, and approximately stoichiometric growth stops were investigated. It was found that, when the arsenic beam remains on during the growth stops, the surfaces continuously become smoother, resulting in more abrupt interfaces. However, when growth is stopped under group III rich or stoichiometric conditions, an initial roughening of the surface occurs, followed by gradual smoothing.