Microwave Resonant Spectroscopy of Semiconductors with Micrometer Resolution

Abstract

We have proposed and experimentally verified a local method of microwave resonant spectroscopy of semiconductors. The microwave circuit of the spectrometer based on the Cascade Microtech probe station is equipped with a coaxial resonator of special geometry. As result, the measurement accuracy of the previously developed volt-impedance spectroscopy method was greatly increased. A technique for spectrometer calibration and resonant measurements of the complex impedance of the probe-sample system has been developed. We have measured the impedance of test structures with Schottky contacts of 30-60 μm in diameter on a single-crystal GaAs wafer at several discrete frequencies in the range of 50-250 MHz. The nontrivial resistive properties of the structures are studied, which consist of the excess resistance that is 1-2 orders higher than the spreading resistance for the alternating current in the unperturbed region of the semiconductor. The discovered effect is presumably associated with the a.c. charge modulation on deep levels of the semiconductor. A model calculation of the impedance spectrum has been performed, which demonstrates a good agreement with the experimental spectra. Keywords: Microwave microscope, near field, probe, resonator, impedance, semiconductor.