Recent Advances in Low-Dimensional Metal Oxides via Sol-Gel Method for Gas Detection

Low-dimensional metal oxides have drawn significant attention across various scientific domains due to their multifaceted applications, particularly in the field of environment monitoring. Their popularity is attributed to a constellation of unique properties, including their high surface area, robust chemical stability, and remarkable electrical conductivity, among others, which allow them to be a good candidate for detecting CO, CO2, H2, NH3, NO2, CH4, H2S, and volatile organic compound gases. In recent years, the Sol-Gel method has emerged as a powerful and versatile technique for the controlled synthesis of low-dimensional metal oxide materials with diverse morphologies tailored for gas sensing applications. This review delves into the manifold facets of the Sol-Gel processing of metal oxides and reports their derived morphologies and remarkable gas-sensing properties. We comprehensively examine the synthesis conditions and critical parameters governing the formation of distinct morphologies, including nanoparticles, nanowires, nanorods, and hierarchical nanostructures. Furthermore, we provide insights into the fundamental principles underpinning the gas-sensing mechanisms of these materials. Notably, we assess the influence of morphology on gas-sensing performance, highlighting the pivotal role it plays in achieving exceptional sensitivity, selectivity, and response kinetics. Additionally, we highlight the impact of doping and composite formation on improving the sensitivity of pure metal oxides and reducing their operation temperature. A discussion of recent advances and emerging trends in the field is also presented, shedding light on the potential of Sol-Gel-derived nanostructures to revolutionize the landscape of gas sensing technologies

Theoretical analyses of the carrier localization effect on the photoluminescence of In-rich InGaAs layer grown on InP

The free buffer InGaAs/InP structure has been elaborated by Metal Organic Vapor Phase Epitaxy (MOVPE). High indium content is chosen to reduce the bandgap energy of the ternary material with direct bandgap to be pro-moted for Infrared optoelectronic devices. In this work, the temperature dependent photoluminescence (TDPL) analysis of In-rich InxGa1_xAs (x = 0.65: S-1, x = 0.661: S-2, and x = 0.667 S-3) samples is of the central focus. The S-shaped behavior recorded at low temperature range in the III-V ternary is quantitatively studied herein by Localized State Ensemble (LSE) model. A comparison between the semi-empirical evolution of luminescence versus temperature and our numerical simulation proves the adequacy of computational details, used in LSE model, in well reproducing the S-shape feature. The numerical simulation well matched with PL spectra proving that the localization phenomenon is stronger when increasing the Indium mole fraction. The clustering effect in In-rich structure seems to be beneficial for enhancing the carrier localization within InxGa1_xAs by localizing carriers from away extended defects that behave probably as non-radiative centers. This is indicative of the utmost importance of localization phenomenon in trapping carriers within localized states instead of dislocations and defects, owing to clustering of indium atoms

Optical and structural properties of In-rich InxGa1−xAs epitaxial layers on (1 0 0) InP for SWIR detectors

International audienceIn-rich InxGa1−xAs epitaxial layers were grown on InP (1 0 0) substrates by a metalorganic vapor phase epitaxy (MOVPE) technique. The effect of Indium (In) composition on the crystalline quality and optical properties are investigated. High resolution X-ray diffraction (HR-XRD) measurement and Raman scattering spectrum are used to evaluate the crystalline quality, the residual strain and dislocation density property. The number of dislocations in the epitaxial layers is found to increase by increasing the Indium content in order to release the stresses due to the epitaxial clamping. Photoluminescence (PL) measurement is used to characterize the optical properties. At 10 K, PL measurements show that the InGaAs band gap redshifts with the indium content. Moreover, the asymmetry at the low-energy side of the PL peak has been attributed to the presence of localized excitons. In all samples, a blue shift of PL peaks is evidenced by increasing the excitation power density, which is in line with the presence of carrier’s localization and non-idealities in this system. Moreover, the temperature-dependence of the PL peak energy displays an unusual red-blue-red shift (S-shaped) behavior when raising the temperature. These observations can be related to the inhomogeneous distribution of indium which gives rise to the appearance of dislocations and other defects which serve as traps for charge carriers. Interestingly, those highly In-content InxGa1−xAs epitaxial layers show PL emission located between 1637 and 1811 nm (depending on In content) and thus might be suitable for in the design of novel heterostructure devices such as short wave infrared (SWIR) detectors