Electrochemical etching for seamless microtransfer printing of InGaN LEDs

In this study, we demonstrate the fabrication of LEDs on bulk GaN substrates (Fig. 1a) that are compatible with micro-transfer printing (µTP) technology, enabling seamless integration onto foreign wafers. The structures are grown on a heavily doped n-type sacrificial underlayer, using plasma-assisted molecular beam epitaxy. Fully processed LEDs are undercut using electrochemical etching to selectively remove the underlayer. This results in a thin-film LED coupon that is 1.3 µm thick with a smooth bottom surface. Full removal of a sacrificial layer can be achieved by choosing an appropriately high doping level of a sacrificial layer and optimum etching bias for a given electrolyte. This smooth surface facilitates easy integration with foreign wafers. Additionally, since the source wafer is not destroyed in the process, such substrates can be recycled, substantially reducing the costs of their use in production