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Micro-LED transfer via electrochemical etch
A team at the University of California Santa Barbara (UCSB) has demonstrated the first fully functional vertical micro-LEDs, down to 3μm in size, transferred via selective electrochemical etching and direct wafer bonding. The proof-of-concept, published in Applied Physics Letters (June 2026), offers a low-damage, high-throughput method for mass transfer of III-nitride devices, enabling scalable heterogeneous integration for micro-displays, optical communications, and sensing. Traditional methods like laser lift-off (LLO) cause thermal damage and cracking. The new approach uses an electrochemical etching release layer of heavily doped n-type GaN (10²⁰/cm³), combined with an AlGaN etch-stop. The lateral etch rate is 20μm/min, far faster than typical photoelectrochemical processes. Devices are grouped in uniform 160μm pads with thin tethers for anchoring; flip-chip bonding to a silicon carrier with Pd/Al/Ti/Au p-contacts and Au contacts ruptures the tethers. The etched surface roughness is 0.57nm RMS. Transferred devices show a turn-on voltage of 3.45V (0.5V higher than on-wafer, due to increased n-contact resistance on the etch-stop layer). Low reverse leakage current contrasts with LLO degradation. Output power is enhanced 2.2x, attributed to a thin-film flip-chip architecture with reflective metal contact. Electroluminescence shows blue-shift from the quantum-confined Stark effect and FWHM broadening. Arrays of micro-LEDs were fabricated with side lengths from 100μm down to 3μm. Leakage current density at -4V remains low for all sizes, comparable to state-of-the-art InGaN micro-LEDs. The method overcomes limitations of LLO, such as high interfacial temperatures and substrate transparency requirements, providing a scalable path for high-performance micro-LED integration on silicon platforms.