Variable temperature-scanning hall probe microscopy with GaN/AlGaN two-dimensional electron gas (2DEG) micro hall sensors in 4.2-425K range using novel quartz tuning fork AFM feedback

Abstract

In this report, we present the fabrication and variable temperature (VT) operation of Hall sensors, based on GaN/AlGaN heterostructure with a two-dimensional electron gas (2DEG) as an active layer, integrated with Quartz Tuning Fork (QTF) in atomic force-guided (AFM) scanning Hall probe microscopy (SHPM). Physical strength and wide band gap of GaN/AlGaN heterostructure makes it a better choice to be used for SHPM at elevated temperatures, compared to other compound semiconductors (AlGaAs/GaAs and InSb), which are unstable due to their narrower band gap and physical degradation at high temperatures. GaN/AlGaN micro Hall probes were produced using optical lithography and reactive ion etching. The active area, Hall coefficient, carrier concentration and series resistance of the Hall sensors were ~14m x 14m, 10m7/G at 4.2K, 6.3 x 10^12cm-2 and 12k7 at room temperature and 7m7/G, 8.9 x 10^12cm-2 and 24k7 at 400K, respectively. A novel method of AFM feedback using QTF has been adopted. This method provides an advantage over STM feedback, which limits the operation of SHPM the conductive samples and failure of feedback due to high leakage currents at high temperatures. Simultaneous scans of magnetic and topographic data at various pressures (from atmospheric pressure to high vacuum) from 4.2K to 425K will be presented for different samples to illustrate the capability of GaN/AlGaN Hall sensors in VT-SHP