Study on the self-absorption of InGaN quantum wells at high photon density.

In this paper, the self-absorption of InGaN quantum wells at high photon density is studied based on a rectangular ridge structure. The ridge structure was fabricated based on a standard GaN-based blue LED wafer grown on (0001) patterned sapphire substrate. The high-density photons were obtained by a high-power femtosecond laser with high excitation of 42kW/cm2 at room temperature. Based on the analysis of the photoluminescence intensities of the InGaN quantum wells, we found that the absorption coefficient of the InGaN quantum wells varies with the background photon density. The results revealed that the final absorption coefficient of the InGaN quantum well decreases with the increase of photon density, which can be 48.7% lower than its normal value under our experimental conditions.

An ultra-sensitive and selective nitrogen dioxide sensor based on a novel P2C2 monolayer from a theoretical perspective.

The sensing properties of an α phase black phosphorus carbide (P2C2) monolayer for the adsorption of CO2, H2, H2O, N2, H2S, NH3, O2 and NO2 gases are theoretically investigated using first-principles calculations. We calculate the adsorption energy, equilibrium distance, Mulliken charge transfer, electron localization function, and work function to explore whether P2C2 is suitable for detecting NO2 gas. The results demonstrate that the P2C2 monolayer is highly sensitive and selective to NO2 gas molecules with robust adsorption energy and superior charge transfer due to the existence of strong orbital hybridization between the NO2 molecule and monolayer P2C2. In addition, the results of the work function calculations indicate that field effect transistor type NO2 gas sensors based on P2C2 monolayers are also feasible. Furthermore, the current-voltage curves reveal that the adsorption of NO2 can greatly modify the resistance of the P2C2 monolayer. Our results show that gas sensors based on P2C2 monolayers could be better than those based on black phosphorene (BP) for detecting NO2 molecules in an air mixture. In addition, the recovery time of the P2C2 sensor at T = 300 K was estimated to be short (and even shorter at higher temperatures) for NO2 which satisfies the demands for sustainable use.