Ultrashort carrier lifetime of vapor-liquid-solid-grown GaN/InGaN multi-quantum-well coaxial nanorods

Luminescence and carrier dynamics of GaN/InGaN multi-quantum-well coaxial nanorods (MCNRs) were studied by means of photoluminescence (PL), cathodoluminescence (CL) and time-resolved PL (TRPL). The PL of as-grown MCNRs showed an intense blue emission together with broad emission at longer wavelengths. CL measurements of several single MCNRs attributed the broad emission to the wetting layer frequently observed in vapor-liquid-solid-grown nanorods. Non-single exponential intensity decays were observed by TRPL, which were ascribed to the In fluctuation in the InGaN alloy. Radiative and non-radiative lifetimes were then calculated via a stretched exponential model. An ultrafast carrier lifetime in the range of a few tens of picoseconds along with a high internal quantum efficiency (IQE) of about 59% resulted. The ultrafast carrier lifetimes were attributed to the improvement in the carrier collection efficiency due to the radial heterostructuring of GaN with InGaN shells, while the high IQE implied that carriers were mostly recombined radiatively. This study reveals that the coaxial growth of InGaN with GaN nanorods resulted in an ultrafast carrier lifetime and a luminescence efficiency that could be controlled by adjusting the growth temperature gap between the GaN and the InGaN. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.