Colloidal Quantum Dots (QDs) are heavily investigated for their applications in light emission such as light emitting diodes and, more challenging, lasers due to their appealing processing conditions, compared to e.g. epitaxy, lowering cost and enabling patterning, and tunable optical properties. Using quantum confined Cd-based QDs, several groups have shown light amplification and ensuing lasing action in the red part of the spectrum. Although impressive milestones were achieved, there is to date no single material that can provide the demanding combination of gain metrics to be truly competitive with existing epitaxial growth approaches. In this work, we take a look at CdS/Se nanocrystals in the regime of vanishing quantum confinement, so-called ‘bulk nanocrystals’. We show that these unique materials display disruptive optical gain metrics in the green optical region. Indeed, while showing similar gain thresholds compared to state-of-the-art QD materials, the gain window (440-600 nm, … ), amplitude (up to 50.000/cm) and gain lifetime (up to 3 ns) vastly outpace other QD materials. Using these novel gain materials, we demonstrate lasing in the highly demanded green spectral region (480 – 530 nm) and in the red (650 – 740 nm) both with pulsed and quasi-CW optical excitation. These lasers are made using a Photonic Crystal Surface Emitting Laser (PCSEL) type cavity. As a final step, we attempt to further optimize the lasing properties, be it either narrow linewidth lasers, or high-power output, based on in-depth understanding of the hybrid QD-PCSEL laser system.
Colloidal quantum dots (QDs) are heavily investigated for their applications in light emission such as light emitting diodes and, more challenging, lasers. This is due to their appealing processing conditions, compared to e.g. epitaxy, resulting in lowering cost. They can also be patterned and their optical properties can be tuned. Using quantum confined Cd-based QDs, several groups have shown light amplification and ensuing lasing action in the red part of the spectrum. Although impressive milestones were achieved, there is to date no single material that can provide the demanding combination of gain metrics to be truly competitive with existing epitaxial growth approaches. In this talk, we take a look at material properties of CdS/Se nanocrystals in the regime of vanishing quantum confinement, so-called ‘bulk nanocrystals’. We show that these unique materials display disruptive optical gain metrics in the green optical region. Indeed, while showing similar gain thresholds compared to state-of-the-art QD materials, the gain window (440-600 nm, 640-750 nm), amplitude (up to 50.000/cm) and gain lifetime (up to 3 ns) vastly outpace other solution processible materials. These results, while very impressive, are also puzzling. In the solution processible community a material system without quantum confinement does not exactly inspire confidence to have good emission metrics. We attempt to explain the physics behind these huge gain coefficients, by using a bulk semiconductor model which includes a strong band-gap renormalization effect, and argue why going to a bulk semiconductor can be advantageous compared to confined systems for making integrated lasers.
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