Field dependent ultrafast carrier dynamics in InGaN/GaN p-i(MQW)-n structure

Field dependent ultrafast carrier dynamics in InGaN/GaN multiple quantum wells (MQW) embedded within a p-i-n structure (InGaN/GaNp-i (MQW)-n) was systematically investigated by photoluminescence (PL), time-resolved PL and transient differential reflectivity measurements. We observed two PL peaks (centered at 450 nm and 500 nm) originated from MQW and localized defect states. Excitation density dependent PL spectra shows that the amplified spontaneous emission participates in the quantum well emission. Surprisingly, time-resolved PL clearly exhibits that quantum well emission has an extremely long decay time, which is much slower than the lower energy peak from defect states. We infer that the built-in PN field affects dominantly the carrier recombination more than the piezoelectric polarization field. The distinct excitation-dependent decay kinetic allows us to identify the dynamic interplay of screening and descreening effect by photo-generated carriers. Additionally transient reflectivity measurements also exhibit that carrier thermalization process becomes faster with increasing excitation density, which could be due to the amplified spontaneous emission.