Photogalvanic Etching of n-GaN for Three-Dimensional Electronics

Abstract

Etching in wide-bandgap semiconductors such as GaN aids applications including transistors, sensors, and radioisotope batteries. Plasma-based etching can induce surface damage and contamination that is detrimental to device performance. We present a photoelectrochemical approach to etching n-type GaN (n-GaN) that is low-cost, simple, and environmentally benign compared to plasma approaches, with the potential for highly anisotropic etching that avoids material damage. n-GaN was etched in a dilute KOH solution with K2S2O8 oxidizer, ultraviolet (UV) irradiation, and a catalytic metal mask which served as both photomask and counter electrode. Relatively smooth, highly anisotropic, non-defect-selective etching was achieved at rates in excess of 200 nm/min when etching at 65°C. The obstacle of bath acidification was circumvented using the addition of buffering salts to the etchant bath, substantially extending the etchant bath lifetime and etching depth achievable in a single, uninterrupted etch. These results represent a major step toward a scalable, device-ready electrochemical etch for vertical GaN structures and devices.