Electrochemical epitaxial lift-off and transfer of InGaN/GaN heterostructure films for vertical micro-LED arrays

Abstract

Although electrochemical epitaxial lift-off (EELO) has recently been developed to successfully obtain freestanding nitride membranes and fabricate various novel optoelectronic devices, controllability of the electrochemical reaction and subsequent device fabrication strategies are yet to be explored. In this study, the analysis using Tafel extrapolation reveals that the lift-off rate of EELO with nitric acid as the electrolyte is high and the freestanding 3 × 3 micro-LED array membranes obtained have low n-GaN surface roughness, which facilitates the subsequent deposition of electrode materials and bonding. The reaction dynamics suggests that NO₂ is generated during the EELO process, and NO₂ is readily soluble in the nitric acid electrolyte, thus promoting the complete corrosion of the sacrificial layer. The turn-on voltage of a single micro-LED device is 2.38 V, with an ideality factor of n = 1.16, indicating low contact resistance and good current spreading. At a reverse bias of −5 V, the leakage current of the device remains on the order of 10⁻¹¹ A. This results from the optimization of the EELO process and the availability of devices with low surface roughness. This low-cost and efficient substrate stripping method can be employed to integrate various III-nitride device elements.