Water-assisted exfoliation of epitaxial CdTe film from mica analyzed with azimuthal RHEED

Highlights: • A simple method to release epitaxial films from its substrates is presented. • Electron diffraction reveals complicated near-surface structures. • Atomically smooth and flat semiconductor films can be grown on mica substrates for flexible device applications. Semiconductor thin films grown on weakly interacting substrates have recently attracted much attention due to the fact that one can peel/release the film from its substrate for flexible electronic and optoelectronic applications. In this work we report separable CdTe(1 1 1) epitaxial films grown on mica substrate via vapor transport deposition. The CdTe films were separated from the mica substrate using double-sided Cu tape, exposing the CdTe interface-surface. Azimuthal reflection high-energy electron diffraction (ARHEED) was used to characterize the fresh CdTe interface-surface and the original CdTe surface. Dramatic differences between these two surfaces were observed. (1) Diffraction streaks were observed from the interface-surface, indicating a smooth surface. Diffraction spots were observed from the surface, indicating a rough surface. (2) The rough CdTe surface has twin and secondary twin structures, which are difficult to be observed with conventional X-ray diffraction. (3) The full-width-at-half maximum (FWHM) analysis of the streaks and spots in RHEED patterns reveals that despite the smoothness of the interface-surface, there is a lower degree of lateral long-range order as compared with the rough surface. This etchant-free method to create smooth interface-surface and ARHEED characterization may be applicable to other films that are detachable from weakly interacting substrates.