We have applied a newly developed transient terahertz time-domain spectrometer to study the temporal development of the dynamics of photogenerated carriers in semiconductor materials. The study presented here include semiinsulating (SI) and low-temperature-grown (LT) GaAs. By measuring the detailed shape of a subpicosecond electrical field pulse (THz pulse) transmitted through the sample at a time T after excitation with a femtosecond laser pulse, the absorption coefficient and refractive index in the region between 0.1 THz and 3 THz can be measured with high accuracy. By varying the time T, the transient absorption and index spectra can be measured with subpicosecond time resolution. Temporal and spectral behaviour of the carrier dynamics in SI and LT GaAs, in dependence of intensity and wavelength of the excitation pulse, is measured. We directly observe carrier scattering to the sidevalleys and the subsequent return of the carriers to the central valley. The experimental data strongly suggest that the transmission of the THz pulse through the photoconducting surface layer of the semiconductor can be described as instantaneous tunneling of the electric field through a metal-like barrier.
|Conference||Conference on Terahertz Spectroscopy and Applications II|
|Period||16/06/1999 → 18/06/1999|
|Series||Proceedings of SPIE, the International Society for Optical Engineering|