In situ composition control of III-As1-xSbx alloys during molecular beam epitaxy using line-of-sight mass spectrometry

The interaction of a Sb-2 molecular beam with the film surface during molecular beam epitaxy (MBE) of GaAs1-xSbx layers was monitored by a quadrupole mass spectrometer (QMS) positioned in line-of-sight of the substrate. It was observed that the QMS signal from the monomeric Sb-species (mass/q = 121 or 123 amu/e) is proportional to the total Sb-flux leaving the film surface within a wide range of temperatures and surface composition. This enabled the accurate determination of the antimony incorporation coefficient, sigma(Sb), and consequently the Sb-mole fraction during growth. Due to its applicability in growth conditions where sigma(Sb) is less than unity, this compositional monitoring technique expands the practical range of MBE growth parameters for III-As1-xSbx alloy growth. Real-time in situ control of alloy composition was demonstrated by implementing a feedback control scheme based on the QMS Sb signal. GaAs1-xSbx alloys in which the Sb-fraction varied in a controlled manner in the direction of growth were deposited.