| The frequency range commonly referred to as the terahertz gap occurs between the infrared and microwave regions of the electromagnetic spectrum. This range of frequencies is highly suited to investigating the free carrier interactions of materials, as the range is particularly sensitive to these interactions. Using terahertz time-domain spectroscopy (THz-TDS), it is possible to measure the effect these interactions have on a terahertz pulse and, using classical optical techniques, determine the terahertz refractive index of a given material, which is directly related to the free carrier spectrum of said material. Knowing the refractive index of a material in the THz range opens the possibility of future terahertz applications for said material, including a non-destructive dopant testing of silicon.;In this work, a series of Silicon on Insulator (SOI) wafer samples are implanted with boron in a range of carrier concentrations. Using a photoconducting antenna (PCA), high-frequency laser pulses were converted to THz pulses and the complex terahertz refractive index of the samples was then measured in the 0.2-2 THz frequency range. This measurement is a direct examination of the free carrier spectrum through experimental methods. The results are compared with the predictions of the Drude model for the free carrier spectrum across this frequency range and are found to closely coincide at higher carrier concentrations, indicating that the behavior of free holes in p-type silicon can likely be described classically at high carrier densities, consistent with previous work on n-type silicon. |
