Insight into the Growth and Control of Single-Crystal Layers of Ge-Sb-Te Phase-Change Material

Employed for a long time in optical disks, Ge2Sb2Te5 is nowadays considered the most promising material also for phase-change nonvolatile memories. In the current paper, Ge-Sb-Te phase-change material thin films with a nominal composition of Ge2Sb2Te5 were grown by molecular beam epitaxy on slightly mismatched GaSb and InAs substrates with (001) and(111) orientations. In situ quadrupole mass spectrometry and reflection high-energy electron diffraction allowed tight control of the growth parameters, revealing that Ge2Sb2Te5 grows in epitaxial fashion-only within a narrow window of substrate temperatures around 200 degrees C. Smooth surfaces were, achieved solely on (111)-oriented substrates. Rough surfaces and interfaces, were observed by transmission electron microscopy for films grown on (001)-oriented substrates. Whereas Erns deposited (001) substrates possess two different vertical epitaxial orientations, single-crystalline layers exclusively (111) oriented were achieved-on (111) siiliVraies, as shown by synchrotron radiation X-ray diffraction. All the results point to the superior crystalline quality and morphology of Ge2Sb2Te5 layers grown on (111) surfaces, independent of the substrate material.