Magneto–electric properties of magnetic field sensors
fabricated using AlGaN/GaN heterostructures forharsh environments

June, 2014

DOCTOR OF ENGINEERING

Abdelkader Abderrahmane

TOYOHASHI UNIVERSITY OF TECHNOLIOGYABSTRACTHall effect sensors are ubiquitous, being used in the electronics industry for monitoringrotation in optical memory disks, banknote authentication in vending machines, and forsensing currents in cables. Other notable applications of micro Hall sensors include
scanning Hall probe microscopy (SHPM) and medical diagnostics based on thedetection of magnetic tags attached to target molecules. Now, while Hall sensors arewidely used at cryogenic and ambient temperatures, there are still niche demands forHall sensors that are stable at elevated temperatures of about 400°C for applications
such as the determination of the Curie temperatures of ferromagnetic materials. Morerecent demands include the sensing of currents in electric cars, where the ambient iswell above room temperature. Hall sensors are also promising for space applications
such as in electronics systems for space exploration vehicles, where size and power
consumption are important, and monitoring magnetic fields in charged particle
accelerators. Recently there have been reports on indium antimonide (InSb) based Hallsensor devices as candidates to replace magnetic sensors used in thermonuclear powerstations. In such extreme environments Hall sensors must withstand high temperaturesand particles and/or electromagnetic irradiation.
Conventional Hall sensors fabricated using silicon (Si), indium arsenide (InAs) or
indium antimonide are stable up to temperatures of about 125°C, and above thistemperature, the sensors are inoperable due to the onset of intrinsic conduction andphysical degradation of the semiconducting materials. Silicon carbide (SiC) could
potentially be used for fabricating Hall sensors operating at high temperature because of
its large band gap, high electron saturation velocity, and excellent thermal stability athigh temperatures. However, the need for precise control of dopants and the largeb

thickness of the conducting layers of SiC severely limits its sensitivity and stability athigh temperatures. The gallium nitride (GaN) and its related compound aluminumgallium nitride (AlGaN) have wide band gap, high thermal and chemical stabilities. The
gallium nitride has low intrinsic electron concentration, which is several orders ofmagnitude lower with respect to that of Si or gallium arsenide (GaAs), and comparablewith that of SiC, enabling the increase of the maximum operation temperature.
Moreover, gallium nitride has high threshold displacement energy making this material
tolerant against particles irradiation; therefore, Hall sensors based on the GaN are
suitable for magnetic field sensing for high temperature and high-energy particles
irradiation application fields.
In addition, formation of the two–dimensional electron gas at the interface between theAlGaN and GaN gives rise to high electron density in a thin active region of thicknessof few nanometers and to high electron mobility, making the AlGaN/GaN
heterostructures appropriate for Hall sensor devices. The fabrication and thecharacterization at high temperature and high proton irradiation of Hall sensors based on
the AlGaN/GaN heterostructures were described and compared with the conventional
Hall sensors based on AlGaAs/GaAs and AlInSb/InAsSb/AlInSb heterostructures.
Electrical characterizations of the micro–Hall sensors based on AlGaN/GaN
heterostructures at high temperature and high–energy proton irradiation showed thatmicro–Hall sensors based on AlGaN/GaN heterostructures are stable from cryogenic
temperature to a temperature of 400°C and expected to show stability up to about 700°C,
and are tolerant to high–energy proton irradiation up to proton dose of 1014 protons/cm2.
Proton irradiation on the AlGaN/GaN heterostructures based micro-Hall sensors induce
defects and crystal quality damage, however, the possibility of recovering of the crystalc

quality and defect removing by annealing was confirmed by electrical and opticalcharacterizations.
The micro-Hall sensors reported in this study were not protected by any form ofpackaging. The maximum proton fluence at which the AlGaN/GaN heterostructures
based micro-Hall sensors are stable at is equivalent to thousands of years of the sensor
application lifetime at the low-earth orbit (LEO). However, the protection of themicro–Hall sensors by a ferromagnetic materials can in the same time enhances thesensor sensitivity and detectivity and reduces or stops the effect of proton irradiation,
therefore, increases the micro–Hall sensors lifetime in harsh environments.
The AlGaN/GaN heterostructures and the AlInSb/InAsSb/AlInSb quantum wells based
micro–Hall sensors are good candidates to replace the magnetic sensors used in theouter space application in term of size, power consumption, and proton irradiation
hardness.

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