Room-temperature polariton lasing in GaN microrods with large Rabi splitting.

Room-temperature polariton lasing is achieved in GaN microrods grown by metal-organic vapor phase epitaxy. We demonstrate a large Rabi splitting (Ω = 2g0) up to 162 meV, exceeding the results from both the state-of-the-art nitride-based planar microcavities and previously reported GaN microrods. An ultra-low threshold of 1.8 kW/cm2 is observed by power-dependent photoluminescence spectra, with the linewidth down to 1.31 meV and the blue shift up to 17.8 meV. This large Rabi splitting distinguishes our coherent light emission from a conventional photon lasing, which strongly supports the preparation of coherent light sources in integrated optical circuits and the study of exciting phenomena in macroscopic quantum states.

Analytical models of electron leakage currents in gallium nitride-based laser diodes and light-emitting diodes.

The electrical-to-optical power conversion efficiencies of the light-emitting devices based on gallium nitride (GaN) are seriously limited by electron leakage currents due to the relatively low mobility and activation ratio of holes. However, there have been few theoretical models on the behavior of the leakage current with an increasing total current. We develop an Ohmic-law-like method to describe the transport behaviors of the systems with electron and hole currents simultaneously. Based on reasonable assumptions, the ratio of the leakage current to the total current is related to the differential resistances of the devices. Through the method, we develop analytical models of the leakage currents in GaN-based laser diodes (LDs) and light-emitting diodes (LEDs). The ratios of the leakage currents with total currents in LDs and LEDs are shown to increase, which explains the sublinear behaviors of the luminescence-current (LI) curves of the devices. The theory agrees well with the numerical simulation and experimental results in larger current ranges in comparison to the traditional ABC model. The above analytical model can be used to fast evaluate the leakage currents in GaN-based LDs and LEDs.

Inch-sized aligned polymer nanofiber films with embedded CH3NH3PbBr3 nanocrystals: electrospinning fabrication using a folded aluminum foil as the collector.

Perovskite nanocrystal embedded polymer nanofibers with polarized emissions are interesting materials for down-shifting applications. By using a folded aluminum foil as a collector, we fabricated inch-size aligned polymer nanofiber films with embedded CH3NH3PbBr3 nanocrystals by adapting an electrospinning technique. It was found that the addition of an appropriate amount of cyanoethyl cellulose (CEC) makes the dispersion of MAPbBr3 in the nanofibers more uniform. Using a precursor solution with MAPbBr3 of 10% and CEC of 1 wt%, the resulting nanofiber films show strong polarized emission with quantum yields up to 51%. The emission dichroic ratio and emission polarization ratio can reach 5.21 and 0.43, respectively. These polarized emissive films can be potentially applied as down converters for liquid crystal display backlights and other polarization selective photonic devices.

Performance analysis of PQDCF-coated silicon image sensor using Monte-Carlo ray-trace simulation.

Perovskite quantum dots embedded composite film (PQDCF) exhibits strong photoluminescence emissions and is expected to be excellent down-shifting material for enhancing ultraviolet (UV) response of silicon devices. In this work, light conversion process is analyzed by combining the experiments with Monte-Carlo ray-trace simulation. Results show that external quantum efficiency (EQE) in the UV region was mainly determined by absorption loss and match of peak wavelength. Moreover, resolution was correlated with thickness and reabsorption. This conclusion provides a guideline for designing novel materials with enhanced UV sensitivity and an EQE of 28% is predicted. Our experimental results showed that the use of red emissive PQDCF achieved an EQE of 20%.

Ultralow-Threshold and Color-Tunable Continuous-Wave Lasing at Room-Temperature from In Situ Fabricated Perovskite Quantum Dots.

Room-temperature-operated continuous-wave lasers have been intensively pursed in the field of on-chip photonics. The realization of a continuous-wave laser strongly relies on the development of gain materials. To date, there is still a huge gap between the current gain materials and commercial requirements. In this work, we demonstrate continuous-wave lasers at room temperature using rationally designed in situ fabricated perovskite quantum dots in polyacrylonitrile films on a distributed feedback cavity. The achieved threshold values are 15, 24, and 58 W/cm2 for green, red, and blue lasers, respectively, which are one order lower than the reported values for the conventional CdSe quantum dot-based continuous-wave laser. Except for the high photoluminescence quantum yields, smooth surface, and high thermal conductivity of the resulting films, the key success of an ultralow laser threshold can be explained by the interaction of polyacrylonitrile and perovskite induced "charge spatial separation" effects. This progress opens up a door to achieve on-chip continuous-wave lasers for photonic applications.