Photocarrier dynamics in thick Si film studied by optical pump-terahertz probe spectroscopy

Optical pump-terahertz probe spectroscopy (OPTP) was employed to investigate the photocarrier dynamics and the optical characteristics of the semiconductor Si. A bulk Si with a relatively high resistivity of similar to 1 k Omega cm was polished to a thickness of about 10 +/- 3 mu m. This thickness is approximately equivalent to the penetration depth of the pump beam in OPTP. We investigated the photocarrier dynamics with the condition that the influence of the inhomogeneous density distribution of the photocarrier is suppressed by using Si with thickness approximately equals to the penetration depth of the pump beam in OPTP. Our results showed a difference in the transmitted terahertz (THz) field amplitude as well as in the peak delay time of the bulk Si and the polished Si which indicates a difference in the photocarrier dynamics, under various applied fluences, between the two types of Si. The observed propagation characteristics of the THz pulse and the obtained optical constants from Fourier analysis illustrate that the thick Si film behaves as a homogeneous material with carrier density generated by photoexcitation.