Mobility spectrum analysis of anisotropic electron transport in N-polar GaN/AlGaN heterostructures on vicinal sapphire substrates

In this work, we present results of a study of anisotropic two-dimensional electron gas (2DEG) transport in N-polar GaN/AlGaN heterostructures grown on slightly mis-oriented sapphire substrates. High-resolution mobility spectrum analysis of magnetic-field dependent Hall-effect and resistivity indicate an isotropic 2DEG sheet carrier density, yet significant anisotropy was observed in carrier mobility. A single electron species with a narrow mobility distribution was found to be responsible for conduction parallel to the multi-atomic steps resulting from growth on the vicinal substrates; whilst in the perpendicular direction two distinct electrons peaks are evident at T ⩽ 150 K, which merge near room temperature. The linewidth of the mobility distributions for transport in the perpendicular direction was found to be significantly broader than that of the single electron in the parallel direction. The broader mobility distribution and the lower average mobility for the 2DEG in the perpendicular direction are attributable to interface roughness scattering associated with the GaN/AlGaN interfacial steps.

Graphical abstractN-polar GaN/AlGaN films grown on vicinal substrates are shown to exhibit significant anisotropy in carrier mobility but isotropic sheet charge density. Mobility spectrum analysis indicated a single electron species in direction parallel to the steps due to growth on vicinal substrates. In the perpendicular direction, two distinct electrons peaks were evident at T = 150 K, which merged near 300 K. The lower mobility is due to interface roughness scattering.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► This work presents a study of transport in N-polar GaN/AlGaN films on vicinal substrates. ► Mobility spectrum analysis indicates isotropic sheet charge density with significant anisotropy in carrier mobility. ► A single electron species was found in direction parallel to the steps due to growth on vicinal substrates. ► In the perpendicular direction, two distinct electrons peaks were evident at T < 150 K, which merged near 300 K. ► The broad mobility distribution and lower mobility in the perpendicular case are due to interface roughness scattering.