Single-crystal silicon is the industry standard for electronic devices because of its high crystalline order and abundance. However, the brittle nature of bulk silicon precludes its use in flexible electronics. Here, we show a simple and inexpensive procedure for epitaxial lift-off of wafer-size flexible and transparent foils of single-crystal Au using Si(111) as a template. Lateral electrochemical undergrowth of a sacrificial SiO_x layer was achieved by photoelectrochemically oxidizing n-Si(111) under light irradiation. The processing scheme is shown in Fig. 1. Cu₂O as an inorganic semiconductor was epitaxially electrodeposited onto the Au foils, which showed a more ideal diode quality factor of 1.6 (where n=1 is ideal) than the value of 3.1 observed for a polycrystalline deposit. ZnO nanowires electrodeposited epitaxially on a Au foil showed flexibility with the nanowires intact up to 500 bending cycles. A 28 nm Au foil with a sheet resistance of 7 Ω.sq^-1 showed only a 4% increase in resistance after 4000 bending cycles. A flexible organic light-emitting diode based on tris(bipyridyl)ruthenium(II) was spin-coated on a foil to exploit the transmittance and flexibility of the gold foil. The simple epitaxial lift-off procedure produces single-crystal Au foils that offer the order of traditional semiconductors such as Si wafers without the constraint of a rigid substrate.

Reference

[1] N. K. Mahenderkar, Q. Chen, Y.–C. Liu, A. R. Duchild, S. Hofheins, E. Chason, and J. A. Switzer, “Epitaxial lift-off of electrodeposited single-crystal gold foils for flexible electronics,” Science 355, 1203 (2017).

Fig. 1. Schematic for epitaxial lift-off of single-crystal Au foils [1].