Up-and-Down Adjustment of the GaAs Loss Tangent Using Extreme Power Densities in a Subterahertz Cavity

We study variations in the dielectric properties of a semi-insulating Gallium arsenide (GaAs) wafer under millisecond pulses of extreme subterahertz power density of up to 180 kW/mm2 at 263 GHz. Increasing the duration and power of the pulse, we have obtained sequential down- and upshifts within the range of more than two orders in the effective loss tangent of the wafer in experiments. We have observed the existence of an optimal regime of subterahertz irradiation, in which the accurate, simple and selective annealing of the wafer from the 300 nanometer-thick surface layer of oxides is achieved, even in plain air, without a damage to pure GaAs. An finite-difference time-domain-based numerical simulation explains such selectivity with a difference in tangent losses of about 25 times between pure GaAs and its impurities in the subterahertz band.