High-resolution diagnostics of GaAs wafer inhomogeneity using an optical switch within the terahertz band

Abstract

We study a technique for diagnostics of the loss tangent inhomogeneity in semi-insulating gallium arsenide within a frequency band of 0.3 THz and higher. The low-oversize-factor resonator of the recently developed optical switch formed by an intersection of a single-mode waveguide and a cutoff waveguide in the presence of a semiconductor is used to analyze small fragments of a movable test wafer. The obtained spatial resolution (0.1 mm2) is much higher than that of the known methods. The results of using the finite difference time domain theory for synthesis of the optimal resonator are compared with the experimental data and with the data of the reference experiment performed by the known alternative method. The intrinsic precision of the loss tangent measured by our method is about 3%. The most significant difference from the known methods is that the test wafer does not overlap the traveling mode waveguide, nor perturb an existing resonator, but creates a resonator by itself. Opportunities of increasing the precision and frequency are discussed.