Colloidal Quantum Dot Laser Diodes

Electrically pumped lasers or laser diodes based on solution-processable materials have been long-desired devices for their compatibility with virtually any substrate, scalability, and ease of integration with on-chip photonics and electronics. Such devices have been pursued across a wide range of materials including polymers, small molecules, perovskites, and colloidal quantum dots (QDs). The latter materials are especially attractive for implementing laser diodes as in addition to being compatible with inexpensive and easily scalable chemical techniques, they offer multiple advantages derived from a zero-dimensional character of their electronic states. These include a size-tunable emission wavelength, a low optical-gain threshold, and high temperature stability of lasing characteristics stemming from a wide energy separation between their atomic-like discrete energy levels.<br/><br/>Several challenges complicate the realization of colloidal QD laser diodes (QLDs). These include extremely fast nonradiative Auger recombination of optical-gain-active multicarrier states, poor stability of QD solids under high current densities required to achieve lasing, and unfavorable balance between optical gain and optical losses in electroluminescent (EL) devices wherein a gain-active QD medium is a small fraction of the overall device stack comprising multiple optically-lossy charge-transport layers.<br/><br/>Here we resolve these challenges and achieve electrically driven laser action due to amplified spontaneous emission (ASE) in a colloidal-QD optical-gain medium. To demonstrate this effect, we employ compact, continuously graded QDs with strongly suppressed Auger recombination incorporated into a low-loss photonic waveguide integrated into a pulsed, high-current density light-emitting diode. These prototype QLDs exhibit strong, broad-band optical gain and demonstrate low-threshold, room-temperature laser action which leads to intense edge-emitted EL with intensity of more than 100 microwatts.