Electrically pumped surface-emitting amplified spontaneous emission from colloidal quantum dots
Fengshou Tian, Tianhong Zhou, Xuanyu Zhang, Rui Chen, Shuming Chen
Abstract
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.