Fabricating high-quality GaN-based nanobelts by strain-controlled cracking of thin solid films for application in piezotronics

Abstract

High-quality, dopants controlled and heterostructure engineered GaN-based nanobelts are highly desirable for fabricating nanogenerators and piezotronic devices with high-output and stable performance, but such structures cannot be easily fabricated using the well established techniques such as the vapor-phase deposition method. We describe a new approach for fabricating high-quality GaN-based nanobelts via strain-controlled cracking of thin solid films. By epitaxially growing InGaN/GaN bilayer film along its [112¯0] crystal axis on an r-plane sapphire substrate with ZnO serving as a sacrificial buffer template, the in-plane elastic stress can be asymmetrically stored in the bilayer film with the component along [11¯00] axis much larger than that along [0001] axis. A lateral wet-chemical etching of the ZnO template causes the InGaN/GaN bilayer film to peel off with a rational cracking in parallel to [112¯0] while perpendicular to [11¯00] and [0001]. The cracking-fronts proceed along the [0001] axis with the increase in etching time, forming parallel allied nanobelt arrays. Such structures can be the fundamental materials for studying piezotronic and piezo-phototronic devices.