Quantum Dots as an Active Reservoir for Longer Effective Lifetimes in GaAs Bulk

Abstract

AlInAs/AlGaAs quantum dots (QDs) have emerged as excellent emitters across the visible spectral range, showcasing highly tunable electronic properties through variations in composition and size. This versatility allows for diverse band alignments within the same system. In this study, we present compelling evidence for the coexistence of type-I indirect and direct emissions from QDs, supported by comprehensive analyses of their photoluminescence responses to excitation power, temperature, and time, along with band structure calculations. The high-density QD system exhibits signs of lateral coupling, facilitated by carrier transfer between dots, modulated by energy barriers and recombination times. Additionally, we can unequivocally prove that the QDs act as carrier reservoirs that progressively feed optically active states in the bulk GaAs at low temperatures─an attractive prospect for hot-carrier photovoltaics. Above certain temperatures, the bulk system reverts to the anticipated predominantly radiative recombination dynamics. Our theoretical framework, accounting for the coexistence of QD specimens with varying recombination times, successfully elucidates the optical response at different temperatures, emphasizing the pivotal role of QD excitation in enhancing the effective lifetime of carriers in the bulk.