Optical spectroscopic investigation of m-plane GaN thin films

[[abstract]]M-plane GaN thin films grown on γ-LiAlO2 substrate were investigated at different temperatures by photoluminescence (PL) and time-resolved photoluminescence (TRPL) spectroscopy. The origin of two distinct emissions, P1 and P2 observed in the PL spectra were established by analyzing their PL and TRPL properties at different temperatures. The P1 emission is attributed to the excitons bound to the stacking faults (SFs). The P2 shows an anomalous “S-shaped” emission shift with increasing temperature (T), and the associated mechanism is discussed. The radiative life time ‘τr’ for P2 emission exhibits the T 3/2 dependence at higher temperatures and deviates at lower temperatures whereas the radiative life time ‘τr’ for P1 emission does not show the T 3/2 dependence with temperature. The polarization-dependent PL study reveals that P2 emission involves free holes in the transition at room temperature.[[notice]]補正完畢[[incitationindex]]SCI[[booktype]]電子

Energy relaxation dynamics in vertically coupled multi-stacked InAs/GaAs quantum dots

[[abstract]]Effect of GaAs spacer layer thickness (dGaAs) on carrier capture, and the relaxation process is studied in multi-stacked InAs/GaAs quantum dots by photoluminescence and time-resolved photoluminescence. Auger scattering is the dominating process for carrier relaxation above dGaAs of 15 nm. At dGaAs of 10 nm, the carrier relaxation process is faster due to the combined effect of both single longitudinal optical phonon and Auger scattering resulting in higher photoluminescence intensity. The photoluminescence rise time corresponding to carrier capture and relaxation in quantum dots is longer at 3.06 eV excitation than that at 1.53 eV due to the effect of intervalley scattering in GaAs.[[notice]]補正完

Observation of weak carrier localization in green emitting InGaN/GaN multi-quantum well structure

[[abstract]]Green emitting InGaN/GaN multi-quantum well samples were investigated using transmission electron microscopy, photoluminescence (PL), and time-resolved photoluminescence (TRPL) spectroscopy. Weak carrier localization with characteristic energy of ∼12 meV due to an inhomogeneous distribution of In in the InGaN quantum (QW) layer is observed. The temperature dependence of the PL peak energy exhibits S-shape phenomenon and is comparatively discussed within the framework of the Varshni's empirical formula. The full width at half maximum of the PL emission band shows an increasing-decreasing-increasing behavior with increasing temperature arising from the localized states caused by potential fluctuations. The radiative life time, τr, extracted from the TRPL profile shows ∼T 3/2 dependence on temperature above 200 K, which confirms the absence of the effect of carrier localization at room temperature.[[notice]]補正完畢[[journaltype]]國外[[incitationindex]]SCI[[ispeerreviewed]]Y[[booktype]]紙本[[countrycodes]]US

Interface Control in Additive Manufacturing of Dissimilar Metals Forming Intermetallic Compounds—Fe-Ti as a Model System

Laser metal deposition (LMD) has demonstrated its ability to produce complex parts and to adjust material composition within a single workpiece. It is also a suitable additive manufacturing (AM) technology for building up dissimilar metals directly. However, brittle intermetallic compounds (IMCs) are formed at the interface of the dissimilar metals fabricated by LMD. Such brittle phases often lead to material failure due to thermal expansion coefficient mismatch, thermal stress, etc. In this work, we studied a Fe-Ti system with two brittle phases, such as FeTi and Fe2Ti, as a model system. Fe was grown on top of Ti at various process parameters. The morphologies and microstructures were characterized by optical microscopy (OM) and scanning electron microscopy (SEM). No cracks along the interface between pure Ti and bottom of the solidified melt pool were observed in the cross-sectional images. Chemical composition in the fabricated parts was measured by Energy-dispersive X-ray spectroscopy (EDS). Electron backscatter diffraction (EBSD) was performed in addition to EDS to identify the crystalline phases. The Vickers hardness test was conducted in areas with different phases. The chemical composition in the melt pool region was found to be a determining factor for the occurrence of major cracks