Growth control of epitaxial GeTe–Sb2Te3 films using a line-of-sight quadrupole mass spectrometer

• Epitaxy of Ge–Sb–Te (GST) and the film composition is shown to be highly sensitive to the growth temperature.
• For the same supplied flux, the composition of the film is shown to vary along the technologically relevant GeTe–Sb2Te3 pseudobinary line with change in growth temperature.
• We report on the successful use of desorption as a feedback to control the surface temperature and hence, the composition of epitaxial phase-change Ge–Sb–Te alloys.
• The out-of-plane lattice constant of the epitaxially grown GST films are shown to increase with an increase in the Ge content.

A narrow growth window combined with highly temperature dependent compositional variations poses a serious problem for the growth of epitaxial GeTe–Sb2Te3 (GST) thin films. The problems are further aggravated by the weak coupling of the radiatively heated non-contact thermocouples to the substrate. An increase in surface temperature during growth as inferred from the increase in desorption of GeTe heteromolecules and the resulting change in alloy composition are studied. Using the desorption signal as a feedback to control the surface temperature, the thermocouple temperature was varied over the duration of the growth to maintain a constant desorption and hence constant surface temperature. Interestingly, the composition of the grown films varies along the GeTe–Sb2Te3 pseudobinary line just by varying the desorption without changing the supplied flux. The out-of-plane lattice constant of the epitaxially grown GST thin film increases with an increase in Ge concentration.