Photoluminescence, stimulated emission and carrier dynamics in GaN/Si heterostructures studied by time-resolved four-wave mixing technique

Carrier dynamics in highly excited GaN/Si heterostructures have been investigated by means of time-resolved picosecond four-wave mixing (FWM), carrier lifetimes at high excitation energy densities being about 50-150 ps were estimated. The excitation energy density corresponding to the saturation of the FWM diffraction efficiency is correlated with the values of laser thresholds in the investigated samples, whereas the carrier lifetimes and the value of the FWM diffraction efficiency show an agreement with the photoluminescence (PL) intensity below the threshold. This study allowed to clarify the observed laser threshold behaviour of the investigated samples by a difference in carrier lifetimes resulting in a difference of the excited volume of the epitaxial layers.