Mechanical exfoliation was performed using (100) and (-201) oriented β-Ga2O3 wafers, grown by the edge-defined film fed (EFF) growth method . A film of medium-tack dicing saw tape was pressed and removed from freshly-cleaved facets of the wafers. The (-201) 2-inch wafer was cleaved in half in order to expose the (100) facet; thus, it was only possible to produce relatively narrow (~700 µm wide) flakes using this crystal orientation. However, the flakes obtained using this approach were more than 40 mm long and only the wafer size limited this dimension. They were also relatively thick (>500 µm) and thus could not be easily transferred onto another substrate. Using the (100) oriented wafer, on the other hand, allowed for ~5 mm wide, ~20 mm long flakes to be exfoliated as freestanding samples. Their yield decreased significantly upon transfer onto a substrate such as SiO2/Si. Nevertheless, about 4 mm long, 100 µm wide flakes were successfully transferred onto a diamond substrate. It was determined that the transfer area yield strongly depended on the force during transfer. While further controlled experiments are required to quantify this relationship, flakes of β-Ga2O3 were successfully transferred onto arbitrary substrates such as GaN, graphene/SiC, and single-crystal diamond, with various degrees of yield. The resulting transferred flakes were characterized by Raman spectroscopy, scanning electron microscopy, and other complementary techniques. Such a process could potentially open further avenues for novel device applications, for example thermally-managed Ga2O3 transistors on diamond.
Research at NRL was supported by the Office of Naval Research (ONR). A.K. acknowledges partial support by ONR Global (Dr. Ming-Jen Pan) under a NICOP contract. L.E.L. gratefully acknowledges postdoctoral fellowship support from the National Research Council.
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