![]() 1a, top-right inset and Supplementary Fig. These ‘compact’ cg-QDs (abbreviated as ccg-QDs) 13 comprise a CdSe core of 2.5 nm radius, a 2.4-nm-thick graded Cd 1− xZn xSe layer and a final protective shell made of ZnSe 0.5S 0.5 and ZnS layers with 0.9 nm and 0.2 nm thicknesses, respectively (Fig. In this study, we use an optical gain medium based on a revised version of continuously graded QDs (cg-QDs), which are similar to our previously introduced CdSe/Cd 1− xZn xSe cg-QDs 9 but feature a reduced thickness of the graded layer. As a result, we achieve large net optical gain with electrical pumping and demonstrate room-temperature ASE at the band-edge (1S) and excited-state (1P) transitions. It also facilitates the build-up of ASE owing to improved collection of spontaneous seed photons and the increased propagation path in the QD medium. The transverse optical cavity formed by the DBR and the Ag mirror improves field confinement in the QD gain medium and simultaneously reduces optical losses in charge-conducting layers. Here we resolve these challenges using engineered QDs with suppressed Auger recombination and a special electroluminescent-device architecture, which features a photonic waveguide consisting of a bottom distributed Bragg reflector (DBR) and a top silver (Ag) electrode. These include extremely fast nonradiative Auger recombination of optical-gain-active multicarrier states 1, 8, poor stability of QD solids under high current densities required to achieve lasing 9, 10 and unfavourable balance between optical gain and optical losses in electroluminescent devices wherein a gain-active QD medium is a small fraction of the overall device stack comprising several optically lossy charge-transport layers 11, 12, 13. Several challenges complicate the realization of colloidal QD laser diodes. These include a size-tunable emission wavelength, low optical-gain thresholds and high temperature stability of lasing characteristics stemming from a wide separation between their atomic-like energy levels 21, 22, 23. The last materials are especially attractive for implementing laser diodes because, as well as being compatible with inexpensive and easily scalable chemical techniques, they offer several advantages derived from a zero-dimensional character of their electronic states 21, 22. Such devices have been pursued across a wide range of materials, including polymers 14, 15, 16, small molecules 17, 18, perovskites 19, 20 and colloidal QDs 1, 2, 3, 4, 5, 6, 7. These colloidal QD ASE diodes exhibit strong, broadband optical gain and demonstrate bright edge emission with instantaneous power of up to 170 μW.Įlectrically pumped lasers or laser diodes based on solution-processable materials have long been desired devices for their compatibility with virtually any substrate, scalability and ease of integration with on-chip photonics and electronics. The developed devices use compact, continuously graded QDs with suppressed Auger recombination incorporated into a pulsed, high-current-density charge-injection structure supplemented by a low-loss photonic waveguide. Here we resolve these challenges and achieve amplified spontaneous emission (ASE) from electrically pumped colloidal QDs. ![]() However, the implementation of such devices has been hampered by fast Auger recombination of gain-active multicarrier states 1, 8, poor stability of QD films at high current densities 9, 10 and the difficulty to obtain net optical gain in a complex device stack wherein a thin electroluminescent QD layer is combined with optically lossy charge-conducting layers 11, 12, 13. Colloidal quantum dots (QDs) are attractive materials for realizing solution-processable laser diodes that could benefit from size-controlled emission wavelengths, low optical-gain thresholds and ease of integration with photonic and electronic circuits 1, 2, 3, 4, 5, 6, 7. ![]()
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