Fabrication of AlGaN/GaN quantum nanostructures by methane-based dry etching and characterization of their electrical properties

Attempts were made to fabricate AlGaN/GaN quantum nanostructures by dry etching, and to assess etching damage through characterization of their electrical properties. An electron-cyclotron-resonance-assisted reactive ion beam,etching (ECR-RIBE) process using a CH4-based gas mixture was applied to AlGaN/GaN heterostructure wafers, and the process was characterized and optimized using in situ X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM) and photoluminescence (PL) measurements. Addition of nitrogen gas to the standard gas mixture of CH4/H-2/Ar was found to be extremely effective in improving the etching characteristics, etched surface morphology and surface stoichiometry, and in preventing accumulation of Ga and Al metallic clusters. After testing the fabrication feasibility of various nanostructures, AlGaN/GaN quantum wire (QWR) structures of various widths were fabricated, and their electrical characteristics were investigated to detect etching damage. Clear Shubnikov-de Haas (SdH) oscillations were observed at 1.6 K in the QWR structures under strong magnetic fields. A nonlinear Landau plot indicated the presence of a one-dimensional confinement potential with a subband energy spacing of 1.4 meV. The measured wire conductance can be well explained by a simple theory, taking account of the sidewall depletion of 23 nm due to Fermi level pinning. No clear changes in sheet carrier concentration and mobility due to plasma damage were detected.