Transient photo-induced absorption in InGaN thin films

Structure dependent absorption spectrum changes In_0.10Ga_0.90 thin films of different thickness (5.5, 17, 34, and 66 nm) are investigated by nondegenerate femtosecond pump and probe spectroscopy at room temperature. These spectrum changes are caused by excitonic absorption quenching and screening of internal piezoelectric fields by photo-induced carriers. Both fast (500 ps) and slow (100 μs) temporal behaviors are observed in differential absorption spectra. Localized carriers in indium-rich regions and/or carriers captured in midgap traps are considered to keep screening the internal filed and to maintain absorption spectrum changes much longer than the photoluminescence lifetimes.