(Invited) Epitaxial Lift-Off of GaN and Related Materials for Device Applications

Abstract

The unique material and transport properties of GaN and related III-N materials have led to their importance in both optoelectronic and RF/microwave power amplification applications, as well as to their promise for emerging applications including power control and conversion, harsh-environment and radiation-resistant sensing and signal processing, and biomedical applications. The use of epitaxial lift-off with III-N materials provides an approach that can improve the electrical and thermal performance of electronic and optoelectronic devices, while at the same time reducing cost and dramatically reducing device size and weight. However, in contrast to other III-V material systems, epitaxial lift-off of III-N materials is challenging due to the lack of high-selectivity, high-etch-rate wet etches in this material system. As an alternative, we have explored the use of band gap selective photoelectrochemical (PEC) wet etching to perform epitaxial lift-off of GaN-based materials and devices. By combining the use of a thin pseudomorphic InGaN release layer and KOH electrolyte with high-intensity filtered ultraviolet illumination tuned to generate electron-hole pairs only in the InGaN release layer (and not in the surrounding GaN material), sufficient selectivity and etch rate have been achieved to allow epitaxial lift-off of large-area films [1]. This process has been demonstrated to improve the electrical and thermal performance of Schottky diodes on non-native substrates [2, 3] and high-voltage, high-power pn junctions grown on low-dislocation-density bulk GaN substrates [4-6] without compromising material quality, while also resulting in ultra-thin devices with total thicknesses below 15 µm. The devices show no evidence of additional defects or recombination centers as a result of either the inclusion of the pseudomorphic InGaN release layer in the epitaxial layer structure or the epitaxial lift-off fabrication processing steps. In addition to device performance, device cost can be improved both through potential re-use of the substrate after lift-off [7] and reduction in die size due to improved thermal performance [8]. While demonstrated for power electronics applications, the ability to form high-quality, high-performance III-N based devices in an ultra-thin, flexible form factor may be an enabling technology for additional applications in flexible electronics, displays, wearable electronics, RF/microwave communication systems, and other fields.