Indium arsenide quantum well hall devices for room-temperature detection of magnetic biomolecular labels

This dissertation presents work on fabrication and room-temperature characterization of mesoscopic Hall sensors from InAs/AlSb quantum well semiconductor heterostructures. It also demonstrates suitability of these devices for detection of micro- and submicrometer-sized superparamagnetic beads that can be used as biomolecular labels in the newly proposed concept of magnetic biomolecular sensing. Detailed analytical analysis of physical factors which determine the magnetic field and the magnetic moment resolution of cross-shaped Hall sensors is presented. The analysis shows that materials with low Hooge's 1/f noise parameter, low density of active charge traps, high carrier mobility and, contrary to the common opinion, high electron density provide the best physical medium for fabricating ultra-sensitive miniaturized Hall sensors. Systematic room-temperature Hall coefficient and electronic noise measurements have been carried out on the sensors with the Hall cross widths of 1 mum and 250 nm. In the low frequency range, from 20 Hz to 1.6 kHz, the sensors show magnetic moment sensitivities on the order of 106 mu B/ Hz and 105 muB/ Hz respectively, where muB is the Bohr magneton. For 250 nm devices, the moment sensitivity reaches the values in 104 muB/ Hz range above ∼ 1 kHz. By using phase-sensitive detection technique based on non-linear magnetization response of superparamagnetic beads to external magnetic field, the presence of a single bead, 1.2 mum in diameter and suitable for biological applications, on the micron-sized Hall cross has been detected with signal to noise ratio of ∼ 33.3 dB. Micro-Hall susceptibility measurements and the subsequent data analysis have shown that the bead consists of ensemble of non-interacting magnetic nanoparticles with broad distribution of magnetic moments. The mean magnetic moment and the mean diameter of nanoparticles in the bead were found to be ∼ 1.55 x 104 mu B and 8.3 nm respectively. Additionally, detection of 250 nm beads has been achieved with signal to noise ratio of 2.3 dB per single bead.