Wet chemical etching induced stress relaxed nanostructures on polar & non-polar epitaxial GaN films

Abstract

We report formation of aligned nanostructures on epitaxially grown polar and nonpolar GaN films via wet chemical (hot H₃PO₄ and KOH) etching. The morphological evolution exhibited stress relaxed faceted nanopyramids, flat/trigonal nanorods and porous structures with high hydrophilicity and reduced wettability. The nanostructured films divulged significant suppression of defects and displayed an enhanced intensity ratio of the near band edge emission to the defect band. Extensive photoemission analysis revealed variation in oxidation state along with elimination of OH⁻ and adsorbed H₂O molecules from the chemically modified surfaces. Fermi level pinning, and alteration in the surface polarity with substantial changes in the electron affinities were also perceived. The temperature dependent current–voltage analysis of the nanostructured surfaces displayed enhancement in current conduction. The in-depth analysis demonstrates that the chemically etched samples could potentially be utilized as templates in the design/growth of III-nitride based high performance devices.