Electrochemical Etching for Seamless Micro-Transfer Printing of InGaN LEDs

The development of complex optoelectronic devices often necessitates efficient and high-quality visible light sources. The gallium nitride (GaN) material family, widely used in constructing light-emitting diodes for general lighting, is an obvious choice for this purpose, but the highest quality devices need to be obtained on native substrates. In this study, we demonstrate the fabrication of LEDs on bulk GaN substrates, which are compatible with microtransfer printing (μTP) technology, enabling integration onto foreign wafers. The structures are grown on a heavily doped n-type sacrificial underlayer realized through plasma-assisted molecular beam epitaxy. Fully processed LEDs are undercut by using electrochemical etching to selectively remove the underlayer, resulting in a thin-film structure with a smooth bottom surface. This smooth surface facilitates the easy integration with foreign wafers. A successful transfer using a micromanipulator and μTP setup was conducted, showing an electrical performance similar to that of the original devices. This work underscores the potential of GaN-based light emitters for advanced optoelectronic applications in integrated circuits and highlights the role that μTP plays in achieving heterogeneous integration.