Sub-single exciton optical gain threshold in colloidal semiconductor quantum wells with gradient alloy shelling

Area of Science:

• Materials Science
• Nanotechnology
• Optoelectronics

Background:

• Colloidal semiconductor quantum wells are promising for solution-processable lasers.
• Nonradiative Auger decay hinders optical gain in II-VI semiconductor nanocrystals due to multi-exciton interactions.

Purpose of the Study:

• To engineer quantum wells with suppressed Auger recombination for reduced optical gain thresholds.
• To demonstrate low-threshold amplified spontaneous emission and lasing in these novel quantum wells.

Main Methods:

• Fabrication of specially engineered CdSe/CdS@CdZnS core/crown@gradient-alloyed shell quantum wells.
• Characterization of optical gain threshold and amplified spontaneous emission.
• Demonstration of a vertical cavity surface-emitting laser (VCSEL).

Main Results:

• Achieved a sub-single exciton ensemble-averaged gain threshold (N_g)≈0.84 per particle, significantly impeding Auger recombination.
• Observed amplified spontaneous emission starting at an ultralow pump fluence of ~800 nJ cm^-2, three-fold better than previous colloidal nanocrystal values.
• Demonstrated a VCSEL with a low lasing threshold of 7.5 μJ cm^-2.

Conclusions:

• The engineered gradient-shelled quantum wells significantly reduce optical gain thresholds.
• These findings represent a major advancement towards developing efficient, solution-processable, electrically-driven colloidal lasers.