Role of substrate temperature and tellurium flux on the electrical and optical properties of MBE grown GeTe and Sb₂Te₃ thin films on GaAs (100)

Van der Waals layered GeTe/Sb₂Te₃ chalcogenide superlattices have demonstrated outstanding performance for use in dynamic resistive memories in what is known as interfacial phase change memory devices due to their low power requirement and fast switching. These devices are made from the periodic stacking of nanometer thick crystalline layers of chalcogenide phase change materials. The mechanism for this transition is still debated, though it varies from that of traditional phase change melt-quench transition observed in singular layers of GeTe and Sb₂Te₃. In order to better understand the mechanism and behavior of this transition, a thorough study on each constituent layer and the parameters for growth via molecular beam epitaxy was performed. In this work, the authors show the effect of tellurium overpressure and substrate temperature on the growth of thin film GeTe and Sb₂Te₃ on (100) GaAs. The authors demonstrate the significant role during growth that tellurium overpressure plays in the transport properties of both GeTe and Sb₂Te_3, as well as the negligible impact this has on both the structural and optical properties. The highest mobility recorded was 466 cm²/V s with a p-type bulk carrier concentration of 1.5 × 10¹⁹ cm⁻³ in Sb₂Te₃. For GeTe, the highest achieved was 55 cm²/V s at a p-type bulk carrier concentration of 8.6 × 10²⁰ cm⁻³. The authors discuss transport properties, orientation, and crystal structure and the parameters needed to achieve high mobility chalcogenide thin films.