Temperature and doping dependence of the optical properties of silicon at terahertz frequencies

Understanding the optical properties of semiconductors at terahertz (THz) frequencies is crucial to THz semiconductor characterization and applications. Prediction of the optical properties requires precise knowledge of the dielectric function of semiconductor in different environments, such as variable temperature and dopant concentration. In this work, the optical properties of silicon without and with different helium ion concentrations have been measured by using a THz time-domain spectroscopy (TDS) for the temperature and frequency ranges of 85-520 K and 0.1-3 THz, respectively. The strong frequency dependence of the complex optical constants due to the free carriers in the THz region has been observed and the measured data have been analyzed by using the Drude-Lorentz model. The experimental results and the analytical ones coincide with each other very well. This work is helpful for understanding the physics and designing devices and applications.