Electrically pumped surface-emitting amplified spontaneous emission from colloidal quantum dots.

Abstract

Colloidal quantum dots (QDs) are promising gain materials for realizing solution-processable, wavelength-tunable and low-cost laser diodes. However, achieving electrically pumped amplified spontaneous emission (ASE) in QDs, a prerequisite for lasing, is hampered by the low net optical gain and low current injection of the diodes. Here we demonstrate electrically pumped and surface-emitting ASE from QDs by electro-thermal-optically co-designing a quantum-dot light-emitting diode (QLED) with high net optical gain and high current injection. By developing a top-emitting cavity featuring a Ag/indium-zinc-oxide (IZO) bottom reflective electrode and a IZO/Ag top semi-transparent electrode, the QD emission is effectively resonated; moreover, not only are the surface plasmon polariton losses induced by the metallic electrodes completely eliminated, but also the optical field can be confined primarily within the QDs, resulting in a reduction in loss and a 2-fold enhancement in gain. As a result, the QLED exhibits surface-emitting ASE with a threshold of 10 μJ cm^-2 when pumped by a 100 fs laser at 77 K. By building the QLED directly on a Si heat sink and driving the QLED with an ns-pulsed current source, the Joule heat is effectively dissipated, allowing the QLED to operate stably even at a high current of 2000 A cm^-2. At 153 K and an injection current of 94 A cm^-2, the QLED demonstrates surface-emitting ASE with strong directionality, high intensity and narrow bandwidth. The developed QLED, capable of generating surface-emitting ASE, paves the way for the development of QD based vertical cavity surface-emitting laser diodes.