Injection-level-dependent internal quantum efficiency and lasing in low-defect GaN nanowires

Abstract

Measurements of temperature-dependent and time-resolved photoluminescence (PL) on individual GaN nanowires revealed PL lifetimes and values of internal quantum efficiency (IQE) that increased with excitation fluence. With sufficient injection levels, radiative recombination dominated within the nanowire temperature range of 75 K to 175 K, as indicated by the T3/2 temperature dependence of the free-exciton PL lifetimes for this bulk material. The IQE was close to unity here. Free-carrier recombination became more significant as temperatures increased toward room temperature, but excitonic recombination remained important with ultrashort excitation pulse fluences as high as 190 μJ/cm2. The IQE at room temperature fell to a value between 3% and 30% depending on the nature of the recombination, and, considering both excitonic and free-carrier recombination, the effective IQE was roughly 15%. Temperature-dependent measurements of lasing thresholds in optically pumped nanowires showed lower thresholds at temperatures where excitonic radiative recombination was strong, indicating a possible persistence of excitoniclike behavior with high injected carrier densities at temperatures below T = 170 K.