Stimulated emission and ultrafast carrier relaxation in AlGaN/GaN multiple quantum wells

Stimulated emission (SE) and ultrafast carrier relaxation dynamics were measured in two AlxGa1-xN/GaN multiple-quantum-well (MQW) structures, grown in a Ga-rich environment with x=0.2 and 0.3, respectively. The threshold density for SE (I-th similar or equal to100 muJ/cm(2)) was found to be independent of x. Room-temperature, time-resolved, differential transmission measurements mapped the carrier relaxation mechanisms for above barrier energy excitation. Photoexcited carriers are observed to relax into the QWs in <1 ps, while carrier recombination times as fast as 30 ps were measured. For excitation above Ith, SE is shown to deplete carriers in the barriers through a cascaded refilling of the QW state undergoing SE. Similar behavior is seen in an Al0.3Ga0.7N/GaN MQW grown with a N-rich atmosphere, but the relaxation phenomena of all AlGaN MQWs are significantly faster than observed in InGaN MQWs of similar structure. (C) 2003 American Institute of Physics.