Quantum coherence of electrons in random networks of c-axis oriented wedge-shaped GaN nanowalls grown by molecular beam epitaxy

Abstract

The depth distribution of the transport properties as well as the temperature dependence of the low field magneto-conductance for c-axis oriented GaN nanowall network samples grown with different average wall-widths (t(av)) are investigated. Magneto-conductance recorded at low temperatures shows clear signature of weak localization effect in all samples studied here. The scattering mean free path l(e) and the phase coherence time tau(phi), are extracted from the magneto-conductance profile. Electron mobility estimated from l(e) is found to be comparable with those estimated previously from room temperature conductivity data for these samples, confirming independently the substantial mobility enhancement in these nanowalls as compared to bulk. Our study furthermore reveals that the high electron mobility region extends down to several hundreds of nanometer below the tip of the walls. Like mobility, phase coherence length (l(phi)) is found to increase with the reduction of the average wall width. Interestingly, for samples with lower values of the average wall width, l(phi) is estimated to be as high as 60 mu m, which is much larger than those reported for GaN/AlGaN heterostructure based two-dimensional electron gas (2DEG) systems.