Fabrication and characterization of aluminum gallium arsenide/gallium arsenide 2DEG hot-electron microbolometers
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In this thesis, a hot-electron bolometric device (detector and mixer), which uses the nonlinearities of the heated two-dimensional electron gas (2DEG) medium in a AlGaAs/GaAs heterostructure, is analyzed and studied. The physics of this 2DEG hot electron bolometer is reviewed. A highly reproducible process for fabricating this microbolometer with fine ohmic contacts is reported. The ohmic contacts are prepared by rapid thermal annealing method, and the resistance is measured using transmission line model. The best contact resistance obtained in this work is around 0.65 Ωmm at 77K for a contact size of 25 μm long by 150 μm wide. Experimental results obtained by studying the main characteristics of the microbolometer are reported. Which electron cooling mechanism prevails mostly depends on the 2DEG channel length of the microbolometer. In the case of a phonon-related mechanism of cooling at a lattice temperature of 77K, the electron-phonon relaxation time is found to be 70 ps, which corresponds to a bandwidth of ∼ 2.25 GHz; for the devices with narrow 2DEG channel, the diffusion-related escape of nonequilibrium charge carriers to the contacts will occur, and in this case, the diffusion coefficient is found to be 1500 cm/s and the bandwidth of our hot electron bolometer is found to be > 10 GHz. We argue that there are several different configurations of hot electron bolometric devices, which will all show wide bandwidth, and that these devices are likely to become important as low-noise THz receivers or mixers in the future.