Characterization of 2DEG microbolometer for mixing at millimeter and sub-millimeter wavelengths
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Described in this thesis is the characterization of 2DEG microbolometer for mixing at millimeter and sub-millimeter wavelengths. We demonstrate that the mixing mechanism in our sample which is a two dimensional electron gas confined in GaAs/AlGaAs heterostructure is mainly due to the hot electron bolometer effect, and has ultra low electron specific heat capacity. Cryogenic prototype has been made operational at liquid nitrogen temperature. Several samples were fabricated with low ohmic contacts, for proper impedance match to other elements in the circuit. Mixer response time (energy relaxation time) is evaluated for the samples from electron mobility, concentration data and from DC measurements. Heating effect due to DC, AC and RF power is shown to be same on the bolometer. Mixing measurements are done with 80-90GHz sources, producing intermediate frequencies close to 20 GHz. Optimum operating temperature for the mixer along with optimum bias is investigated. Conversion loss and bandwidth measurements are demonstrated for the samples. We report that the cooling mechanism in our bolometer device is "diffusion cooled" based on the obtained diffusion constant at 77K. Hence the intermediate frequency bandwidth range is larger.