Carrier emission of n-type Gallium Nitride illuminated by femtosecond laser pulses

摘要

The carrier emission efficiency of light emitting diodes is of fundamentalimportance for many technological applications, including the performance ofGaN and other semiconductor photocathodes. We have measured the evolution ofthe emitted carriers and the associated transient electric field afterfemtosecond laser excitation of n-type GaN single crystals. These processeswere studied using subpicosecond, ultrashort, electron pulses and explained bymeans of a three-layer analytical model. We find that for pump laserintensities on the order of 10^11 W/cm^2, the electrons that escaped from thecrystal surface have a charge of about 2.7 pc and a velocity of about 1.8um/ps. The associated transient electrical field evolves at intervals rangingfrom picoseconds to nanoseconds. These results provide a dynamic perspective onthe photoemission properties of semiconductor photocathodes.