Quantum interference control of electrical currents in GaAs

In an earlier publication, preliminary observations of the generation of electrical currents were reported in GaAs and low-temperature-grown GaAs (LT-GaAs) at 295 K using quantum interference control of single- and two-photon band-band absorption of 1.55- and 0.775-/spl mu/m ultrashort optical pulses. Time-integrated currents were measured via charge collection in a metal-semiconductor-metal (MSM) electrode structure. Here we present detailed characteristics of this novel effect in terms of a simple circuit model for the MSM device and show how the injected current depends on MSM parameters as well as optical coherence, power, and polarization. For picosecond pulse excitation with peak irradiance of only 30 MW/cm/sup -2/ (1.55 /spl mu/m) and 9 kW/cm/sup -2/ (0.775 /spl mu/m), peak current densities of /spl sim/10 A/cm/sup -2/ at peak carrier densities of 10/sup 15/ cm/sup -3/ are inferred from the steady-state signals. This compares with 50 A/cm/sup -2/ predicted theoretically; the discrepancy mainly reflects inefficient charge collection at the MSM electrodes.