Wafer-scale all-epitaxial GeSn-on-insulator on Si(111) by molecular beam epitaxy

Abstract

All epitaxial GeSn-on-insulator (GeSnOI) heterostructures have been realized by conventional molecular beam epitaxy of both GeSn and a thin Gd2O3 insulating layer, on Si(111) substrates. Analysis of the crystal and surface quality by high-resolution transmission electron microscopy (HRTEM), high-resolution X-ray diffraction (HRXRD), and atomic force microscopy (AFM) revealed the formation of a continuous and fully-relaxed single-crystalline GeSn epilayer, however with a surface roughness of 3.5 nm. Stacking faults and reflection microtwins were also observed in cross-sectional HRTEM images. From Hall measurement, the concentration and mobility of holes, introduced by un-intentional p-type doping of the GeSn epilayers, were estimated to 8x10^16 cm-3 and 176 cm-2V-1s-1, respectively. In metal-semiconductor-metal (MSM) Schottky diodes, fabricated with these GeSnOI heterostructures, the dark current was observed to be lower by a decade, when compared to similar diodes fabricated with GeSn/Ge/Si(001) heterostructures. The results presented here are encouraging for the development of these engineered substrates for (opto)electronic applications.