Femtosecond carrier dynamics of InxGa1−xN thin films grown on GaN (0001): Effect of carrier-defect scattering

Abstract

Ultrafast carrier dynamics in ultrathin InxGa1−xN ternary alloys were investigated in detail, using femtosecond transient differential optical absorption measurements. Measurements were performed with probing wavelengths above and below the band edge of the materials. Furthermore, we performed a structural characterization by x-ray diffraction reciprocal space maps and we found that the alloys with the higher InN mole fraction (x=0.89 and x=0.43) present large lattice mismatch-strain relaxation whereas the lower InN content alloy was fully coherent with the underlying GaN (0001) layer. Our analysis showed that the observed nonradiative carrier dynamics was strongly related with the carrier-defect scattering of the materials. Our measurements in conjunction with the numerical analysis showed that when we excite these alloys with ultrashort laser pulses the background carrier concentration for In-rich InGaN samples participates to the photoexcited carrier relaxation process via carrier momentum scattering. For the higher InN content alloys (x=0.89 and 0.43) the relaxation times were short (0.4–1.4ps) whereas for the full strained alloy (x=0.07) a slower nonradiative relaxation time (∼25ps) was observed. Finally, the energy loss rate of this material (2.05±0.10meV∕fs) as well as the optical phonon lifetime (44±2fs) were extracted.