High-energy hole scattering rates for a full-band Monte Carlo simulation in Si are verified using a quantum-yield experiment. We compare two models that yield the correct drift velocity and ionization coefficient but quite different energy distributions. It is demonstrated that the quantum-yield experiment provides a means for monitoring hole scattering rates in Si; the model based on the ab initio impact ionization rate shows good agreement with the experiments, while the random-k approximation proposed by Kane overestimates the ionization rate of holes near the threshold energy.

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Femtosecond optical response in GaAs thin films has been studied. We prepared GaAs thin films on MgO substrates and on YBa2Cu3O7-δ (YBCO) thin films using pulsed laser deposition (PLD) at temperatures below 250°C. A photocarrier lifetime of less than 1 ps is measured for the prepared GaAs thin films using femtosecond time-domain reflectivity change measurements. Pulsed electromagnetic wave [terahertz (THz) radiaiton] containing a frequency component of up to 1 THz is emitted from fabricated photoconductive switches using the prepared thin films. We also evaluated the THz radiation properties emitted from the photoswitches on the YBCO thin films.

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