Researchers at the University of Maryland and ETH Zurich have demonstrated a simple approach for coupling solution-synthesized cesium lead tribromide (CsPbBr3) perovskite nanocrystals to silicon nitride (SiN) photonic cavities. The reported result is that room temperature light emission is enhanced by an order of magnitude above what perovskites can emit alone.
"Our work shows that it is possible to enhance the spontaneous emission of colloidal perovskite nanocrystals using a photonic cavity," the team said. "Our results provide a path toward compact on-chip light sources with reduced energy consumption and size".
To couple the nanocrystals to the photonic cavity, the group drop-cast perovskite nanocrystals in toluene solution onto the SiN cavity. They then excited the device with a pulsed laser, leading to photon emission from the nanocrystals.
The use of solutions to make colloidal quantum emitters contrasts with the fabrication of epitaxial materials, a widely used process that involves growing crystalline overlayers on an existing substrate. Instead, the researchers said, one can directly deposit colloidal nanocrystals using solvents more easily on different kinds of wafers.
Attempts to emit light with epitaxial materials generally result in materials with lacking efficiency in covering the visible light spectrum, with the wavelength range in the blue-green being particularly problematic. The device that the team demonstrated exhibited emission centered at 510 nanometers in the green.
"The large challenge with this method, however, is that you have to find a very optimized concentration [density] of the crystals on the surface of the cavity," the team said. "It can't be too condensed or else it will be detrimental to the cavity and might lead to nonconformity."
The coupled nanocrystals and nanocavity boasted a tenfold improvement in emission brightness compared to the emitters alone. It resulted in a spontaneous emission rate enhancement of 2.9, reflecting a nearly threefold increase in the photon emitting efficiency within the cavity compared to perovskites on unpatterned surfaces.
These results seem very positive for future optoelectronics, a field that leverages the quantum effects of photons on electronic materials to help build optical circuits that won't suffer from some of the inefficiencies of purely electronic devices, such as heating. Optoelectronic devices also enjoy faster processing speeds and broader signal bandwidths, and may one day be used in quantum computing and quantum communication networks.