Transferable Thru-Hole Epitaxy of GaN and ZnO, Respectively, over Graphene and MoS₂as a 2D Space Layer

It has been challenging to grow a readily-detachable crystalline film on a crystalline substrate. This is because (1) strong chemical bondings between the film material and the underlying substrate are typically a prerequisite for a crystalline film to be grown, and (2) it cannot be easily carried out to break down the chemical bondings over the entire or a large fraction of the interfacial region unless the substrate is readily wet-etchable. Alternatively, remote epitaxy was previously proposed to accomplish this task, but it requires an ultra-small thickness and state-of-the-art transfer of a 2D space layer. This challenging task can, however, be accomplished less stringently if the interfacial area, in which the grown material directly makes chemical bondings with the substrate, is made sufficiently small by covering the substrate with 2D materials with an inherent small opening. Here, we show that readily-detachable GaN and ZnO crystalline domains can be grown, respectively, on graphene/sapphire and MoS2/GaN/sapphire templates by carrying out thru-hole epitaxy, which is lateral growth over 2D materials with inherent small openings. We also demonstrate that the mechanism of the thru-hole epitaxy can be adopted for the fabrication of an array of transferrable microstructures over multilayer 2D materials. Moreover, our results suggest that thru-hole epitaxy is compatible with the bottom-up fabrication of an array of readily transferable inorganic microstructures, which can become basic building blocks for inorganic-material-based flexible devices.