Carrier dynamics in InGaN/GaN multiple quantum wells based on different polishing processes of sapphire substrate

We report on carrier dynamics in the green InGaN/GaN light emitting diodes grown by metal organic chemical vapor deposition. Two LEDs with the same structures grown on pattern sapphire substrates with different surface roughnesses were prepared for comparisons (samples A and B). Sample A had the smoother sapphire surface than sample B. Time-resolved four-wave mixing has been performed at room temperature using 351 and 420 nm picosecond pulses for excitation. The determined diffusion coefficient in the upper InGaN QWs of sample B was twice smaller than that in sample A. The latter observation of better carrier confinement in sample B correlated with higher light emission efficiency in it.