Prospects and challenges of Colloidal Quantum Dot Laser Diode

Colloidal semiconductor nanocrystals or ‘quantum dots’ (QDs) comprise an inorganic semiconductor core encased into a shell of organic ligand molecules. As a result, they combine superior light-emission characteristics of quantum-confined semiconductors with chemical flexibility and processability of molecular systems. Highly efficient, size-tunable emission from colloidal QDs has been already exploited in commercial televisions and displays.

These materials can also enable highly flexible, solution processable laser diodes with an ultrawide range of accessible colours. However, the realization of such devices has been hampered by several problems including very fast optical gain decay due to nonradiative Auger recombination, and low conductivity and poor thermal stability of QD solids, that complicate achieving high current densities required for the lasing regime. Recently, these challenges have been successfully tackled via novel approaches to Auger decay engineering and special strategies for boosting current densities to ultrahigh values of ~1,000 A cm-2. These advances have brought the QD lasing community very close to its ultimate objective, which is the realization of a QD laser diode (QLD). Here, we overview the principles of light amplification with colloidal QDs, assess the status of the QD lasing field, examine the remaining challenges on a path to a QLD, and, finally, discuss practical strategies for attaining electrically pumped QD lasing.