Variable Temperature-Scanning Hall Probe Microscopy With GaN/AlGaN Two-Dimensional Electron Gas (2DEG) Micro Hall Sensors in 4.2–425 K Range Using Novel Quartz Tuning Fork AFM Feedback

Abstract

In this paper, 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 a wide bandgap 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 bandgap 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 1 1 m, 10 m/G at 4.2 K, 6.3 10 12 cm 2 and 12 k at room temperature and 7 m/G, 8.9 10 12 cm 2 and 24 k at 400 K, respectively. A novel method of AFM feedback using QTF has been adopted. This method provides an advantage over scanning tunneling-guided 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. to 425K will be presented for different samples to illustrate the capability of GaN/AlGaN Hall sensors in VT-SHPM.Index Terms-Atomic force microscopy (AFM), GaN/AlGaN heterostructure, Hall probe, quartz tuning fork (QTF), scanning Hall probe microscopy (SHPM).

Application of silicon micro hall sensors in variable temperature scanning hall probe microscopy (SHPM) using multiple feedback techniques

“…As fabrication of Hall probe on cantilevers is cumbersome, a novel method of using QTF has been adopted in this study. In this study, 17.864kHz QTFs with dimensions (l × w × t) for prongs 3.81 × 0.34 × 0.62mm resulting in stiffness of 29kN/m have been used (Akram et al, 2008). In order to integrate these force sensors (QTF) in SHPM for AFM feedback, they are extracted from their cans and their leads have been replaced with a nonmagnetic wiring.…”

“…So in order to compensate the drawbacks of STM feedback, QTF-AFM feedback has opted for high temperatures SHPM. Whereas a comprehensive study of theoretical modeling and experimental results on the characteristics of QTF AFM are presented somewhere else (Akram et al, 2008). In order to investigate the high-temperature operation of these Si micro-Hall probes, a low noise heater stage has been embedded in the LT system.…”

“…SHPM technique offers various advantages and complements the other magnetic imaging methods like Scanning Superconducting Quantum Interference Device Microscopy (SSM) (Kirtley and Wikswo, 1999), Magnetic Force Microscopy (MFM) (Martin and Wickramasinghe, 1987), Magnetic Near-Field Scanning Optical Microscopy (Betzig et al, 1992) and Kerr Microscopy (Schmidt and Hubert, 1986). However, there have been few reports on magnetic imaging with Hall sensors at hightemperature regime too (Yamamura et al, 2006;Akram et al, 2008). Scanning Hall Probe Microscopy (SHPM) has been demonstrated as a quantitative and non-invasive technique for imaging localized surface magnetic field fluctuations of ferromagnetic domains with high spatial and magnetic field resolution of ∼50 nm and 7 mG/Hz 1/2 at room temperature (Sandhu et al, 2004).…”

“…In this study an application of Si sub-micron (~0.7μm × 0.7μm) Hall sensors with optimized thickness, 510nm, in variable temperature SHPM system have investigated using two main feedback techniques, STM and AFM (using quartz crystal tuning fork fork (QTF) sensor (Guethner et al, 1989;Akram et al, 2008). The focus has been to explore the bottlenecks associated with each method for their use at variable temperature applications of Si based SHPM.…”

An ultra-low temperature scanning Hall probe microscope for magnetic imaging below 40 mK

“…Single layer graphene has recently been shown to be one of the alternative materials to increase the spatial resolutions of the current Hall sensors. 5 SHPM sensors have a wide range of operation temperatures for scanning between 300 mK and 425 K. 6 Despite availability of many reports on SHPM for 2 K-300 K temperature ranges in the literature, only a single report from Professor Bending's group from Bath University is seen below 1 K. 7 They reported a scanning Hall probe microscope designed for 3 He system and operated at 372 mK. Our group also designed a SHPM for a 3 He system (Oxford Instruments, Heliox VT−50) and was able to measure at 322 mK.…”