Published online by Cambridge University Press: 15 March 2011
We present an optically-detected time-of-flight technique with femtosecond resolution that monitors the change in the electroabsorption due to charge transport in a p-i-n diode, and show how it may be used to determine the electron transit time and velocity-field characteristic in GaN at room temperature. The transit time drops with increasing electric field E in the intermediate field regime (50-100kV/cm), and the electron velocity possesses a weak, quasi-linear dependence on E attributed to polar optical phonon scattering. In the high field regime the transit time and the electron velocity gradually become independent of E. The peak electron velocity of 1.9×107 cm/sec, corresponding to a transit time of ∼2.5 ps across the 0.53 μm depletion region, is attained at ∼ 225 kV/cm. The experimental results are in qualitative agreement with theoretical steady-state velocity-field characteristics found in the literature.