Fabrication and characterization of nano-porous GaN template for strain relaxed GaN growth

Abstract

A simple and cost-effective Si-doped porous GaN is fabricated by UV-enhanced electrochemical etching, produces a high density of uniform pores across the surface. TEM reveals that the etching results in layered nano-pores structures along the (0001) direction. A red shift of 0.7 cm-1 in the E2 (high) phonon peak of GaN from micro-Raman corresponds to a relaxation of compressive stress in the porous GaN surface with respect to the underlying epitaxial GaN. Subsequent growth of GaN layer on the porous template results in air gap formation, which is believed to serve as sinks for dislocations for reducing residual strain in the film. Reduction of FWHM of the XRD rocking curve by as much as 0.033° and doubling of the intensity of the PL spectrum clearly show improvement on the crystalline and optical quality of the overgrown GaN layer as compared to the as-grown. A red shift of ∼0.4 cm-1 towards the stress-free GaN also indicates a relaxation of compressive stress in the overgrown GaN layer. Such a template is useful for high quality GaN growth. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.