Drude's Parameters of Heated Crystalline Silicon from Reflection THz-TDS Measurements

The spectroscopic properties of crystalline silicon wafers are investigated experimentally as a function of the temperature. To this goal, samples of phosphorus-doped silicon are characterized using Terahertz Time-Domain Spectroscopy (THz-TDS) in reflection. Four different samples span resistivities from ∼0.04 − 50Ω cm, for temperatures ranging from room temperature to 200 C. The measurements confirm that the widely used Drude's theory is adequate also to model the dispersion of silicon at higher temperatures. When comparing the corresponding scattering times obtained here using THz TDS pulses with the scattering time derived from the well accepted DC based empirical model of the mobility, differences emerge depending on the doping level. The scattering times predicted and measured are on the same order of magnitude and the anticipated reduction of the scattering time with increasing temperature has also been confirmed by the high frequency measurements. The absorptivity of the samples is also estimated accurately as a function of the frequency up to 1 THz.