New applications of THz time-domain spectroscopy

Scope and method of study. The purpose of this study was to apply the THz Time-Domain Spectroscopy (THz-TDS) in thin film and doped silicon. In order to characterize of the samples, two pulse shapes were measured by the THz-TDS technique: the reference pulse without a sample and the output pulse with the sample. In the silicon measurement, transmission and reflection measurements were used to take the output THz pulse. Using Fourier analyses of the reference and output pulses, the frequency-dependent absorption and dispersion of the samples can be obtained.; Findings and conclusions. Via ultrafast optoelectronic THz techniques, the multiple reflections theory was used in the thin film measurement and the theory and the measurement were well fit. The measured index of refraction was 1.51 and the power absorption was less than 1.5 cm{dollar}sp{lcub}-1{rcub}{dollar} from 0.1 THz to 2.5 THz frequency range. In the silicon measurement, alternative theories of conduction were tested by precisely measuring the complex conductivity of doped silicon from low frequencies to frequencies higher than the plasma frequency and carrier damping rate. These results, obtained for both n and p-type samples, spanning a range of more than 2 orders of magnitude in the carrier density, do not fit any standard theory. A Cole-Davidson type distribution applied here for the first time to a crystalline semiconductor is in good agreement over the full frequency range with the complex conductivity and thereby demonstrates that the fractal conductivity is not just found in disordered material.