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 $\mathrm{p–i–n}$ 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 ${\text{1.9×10}}^7 \mathrm{cm/s},$ 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.