Coherent control of photocurrent in bulk semiconductors

grantor: University of TorontoCoherent control of photocurrent via interband transitions in bulk semiconductors is proposed and demonstrated in GaAs. A Fermi's Golden Rule approach is used to calculate the overall transition rate for simultaneous single- and two-photon excitation in direct band gap semiconductors using phase-related beams at frequencies $\omega$ and 2$\omega$, with $\hbar\omega<E\sb{g}<s\hbar\omega$, where $E\sb{g}$ is the band gap energy. The calculation is carried out to obtain the current generation rate as a function of the beams' intensity, polarization and frequency; numerical results are given for GaAs. Coherent control of photocurrent is demonstrated using picosecond and femtosecond laser pulses on GaAs at room temperature. By integrating the current in a metal-semiconductor-metal (MSM) device, peak current densities as high as 20 mA$\mu$m$\sp{-2}$ are measured using phase-related 100 fs pulses at 1550 and 775 nm from an optical parametric generator. Carrier densities of ${\sim}10\sp{18}$ cm$\sp{-3}$ are achieved during the process, but carrier-carrier scattering does not seem to significantly affect the current decay time. Non-degenerate coherent control is also demonstrated with three beams of different frequency such that $\omega\sb1 + \omega\sb2 = \omega\sb3$ and $\hbar\omega\sb1\not=\hbar\omega\sb2<E\sb{g} <\hbar\omega\sb3$. Low-temperature grown GaAs is found to be more suitable for current integration than normally-grown GaAs because the former has a shorter carrier lifetime which prevents the MSM device from discharging during the time between pulses.Ph.D