Low-threshold lasing from colloidal quantum dots under quasi-continuous-wave excitation

Abstract

Colloidal quantum dots (QDs) are promising materials for the development of solution-processed, colour-selectable lasers. However, most reported QD lasing devices rely on high-power femtosecond lasers as the pump source, which is impractical for technological applications. Here we demonstrate QD lasing using excitation from an electrically modulated (0.1–1% duty cycle), low-power continuous-wave laser diode, achieving lasing at a pump intensity just above 500 W cm−2 at 77 K and 3.6 kW cm−2 at room temperature. This achievement is enabled by type-(I + II) QDs, in which optical gain arises from hybrid direct/indirect biexcitons. These biexcitons exhibit strongly suppressed Auger recombination, resulting in a long optical gain lifetime of several nanoseconds. In addition, owing to fast radiative decay via the direct transition, type-(I + II) QDs exhibit a high material gain of approximately 1,200 cm−1. These properties are crucial for achieving lasing under continuous-wave pumping. Type-(I + II) QDs are also well suited for devices pumped by femtosecond optical pulses, enabling the realization of lasing in fully stacked electroluminescent devices and whispering-gallery-mode lasing in microdisks composed of densely packed QDs.