Mass spectrometry during molecular-beam epitaxy: An alternative to reflection high-energy electron diffraction

Abstract

A quadrupole mass spectrometer has been positioned in a commercial molecular-beam epitaxy system so that the desorption of atomic and molecular species, from GaAs substrates, can be monitored at various stages in the growth process. The sharply peaked Ga2O154 thermal desorption spectrum, from the surface oxides, is found to provide a useful temperature calibration, and its width is a measure of the substrate temperature distribution. Gallium desorption from GaAs surfaces, as a function of temperature, can be used to calculate growth rate curves, whereas the desorption flux from GaAlAs surfaces enables the alloy composition to be determined directly. Interfacial transients between layers can be monitored, and results are described which suggest that GaAs/AlAs interfaces are not atomically abrupt. Unlike the reflection high-energy electron diffraction technique, these measurements can all be carried out on rotating, large size, substrates.