Influence of AlN interlayer on the anisotropic electron mobility and the device characteristics of N-polar AlGaN/GaN metal-insulator-semiconductor-high electron mobility transistors grown on vicinal substrates

This paper presents an experimental investigation of the influence of an AlN interlayer on the electron mobility and the device characteristics of N-polar AlGaN/GaN metal-insulator-semiconductor-high electron mobility transistors grown by metal-organic chemical vapor deposition on miscut sapphire substrates. Use of miscut substrates leads to the formation of multiatomic steps at the AlGaN/GaN interface and anisotropy in electron transport properties. A combination of van der Pauw Hall, gated transfer length measurements, and capacitance-voltage measurements has been used to study the desired properties in directions parallel and perpendicular to the multiatomic steps and qualitative explanations were provided for the observed trends. Similar to the Ga-polar devices, the introduction of AlN interlayer improved the device performance by increasing both the electron mobility and the two-dimensional electron gas charge density in the devices. Orienting the devices such that the conduction occurred parallel to the multiatomic steps was beneficial for better electron transport and device performance.