Time-resolved electroabsorption measurement of the electron velocity-field characteristic in GaN

A femtosecond optically detected time-of-flight technique that monitors the change in the electroabsorption associated with the transport of photogenerated carriers in a GaN p–i–n diode has been used to determine the room-temperature electron transit time and steady-state velocity as a function of electric field. The peak electron velocity of 1.9×107 cm/s, corresponding to a transit time of 2.5 ps, is attained at 225 kV/cm. The shape of the velocity-field characteristic is in qualitative agreement with theoretical predictions.