Efficient sub-bandgap excitation in near-infrared luminescence of modulation-doped InAs quantum dot system

Abstract

This study investigates highly efficient sub-bandgap excitation and roles of donor–acceptor (D–A) pairs in Si modulation-doped InAs/GaAs quantum dot (QD) systems with low-temperature variable-excitation wavelength photoluminescence (PL) spectroscopy. Such a D–A pair is tentatively assigned to a pair of Si donor and C acceptor with the PL emission at 831.5 nm. It is shown that the resonant excitation of this D–A pair can significantly enhance the near-infrared emission of the InAs QDs, yielding a PL intensity comparable to that under near-band edge excitation. The modulation doping of Si is found to make the D–A pair be in the D+–A− state, which enables efficient sub-bandgap optical excitation. Owing to the proximity (5 nm) between the doped Si donor layers and the QD layers, the D–A pairs strongly couple with both the QDs and GaAs barriers, leading to direct carrier transfer from the excited D–A pairs to QDs and therefore enhanced QD emission. This work reveals the impact of D–A pairs on carrier interactions in the InAs/GaAs QD systems and demonstrates an efficient strategy to engineer carrier interactions by spatial modulation of donor/acceptor dopants in semiconductor quantum structures.