High field time-domain terahertz spectroscopy (TDS) is used to determine the time dependent transmission and the time-delay and optical-power dependent conductivity of a wafer of gallium arsenide (GaAs). Gallium arsenide is a direct band-gap semiconductor and has potential as a computer processor component. Analysis of the transmission of terahertz (THz) frequencies (10¹² Hz) through GaAs yields the conductivity of the metal at high strength fields and high frequencies. THz radiation is pulsed into the wafer and is absorbed by free carriers. The transmission of the THz radiation is related to the conductivity of the metal via the thin film Fresnel formula.
It is observed that high power optical excitation lowers transmission of the THz radiation, thus increasing optical power increases the material’s conductivity. Positive time delay (optical pulse hitting the wafer after the THz pulse) has shown not to significantly affect the transmission of the THz pulse, or the conductivity of GaAs. A delay of 0.0 ps (optical pulse hitting the wafer at the same time as the THz pulse) slightly increases THz transmission and decreases conductivity from the negative delay. 1.0 ps delay follows the same trend as the 0.0 ps delay. The delay of 3.0 ps slightly decreases transmission of THz radiation from the 2.0 ps delay, and increases conductivity of the wafer.