Sucrose is important to be measured in food industry and Raman spectroscopy is preferred method for being fast, accurate, and non-destructive. Different concentration of sucrose was measured using Horiba’s modular probe-based Raman system. The signature peak of 824cm-1 caused by CH out-of-plane deformation was studied as a conventional fingerprint. There is a correlation between the intensity of each Raman peak and the final sample concentration. As one drops the other will follow linearly. Minimum concentration of 0.5% was recorded for short integration time of 0.5s. This finding can be revolutionary for food industry due to the high sensitivity and speed.
A compact economical system for broadband multichannel spectroscopy with exceptionally high SNR, high sensitivity and high throughput is introduced. This system using the state-of-the-art optics and CCD is capable of combining more than 10 channels in one enclosure, any channel fully configurable to each experiment needs. The SNR value, Limit of detection (LOD) and limit of quantitation (LOQ) are identified as well-known criteria for sensitivity measure. These values were found to be superior comparing to the reported values for the leading benchtop fluorimeters. This system was tested measuring very low concentration of different samples simultaneously and demonstrated excellent performance.
Micro-reflectance (μ-R) spectroscopy is a powerful technique for investigating the micro-scaled surfaces and interfaces, such as semiconductors, metals, etc. We discuss and compare the μ-R spectroscopy on specular (Si wafer) and scattering (MoS<sub>2</sub> flake) surfaces using various objectives with different NA. μ-R is calculated by the ratio of sample to reference spectra, it follows the sequence of NA on scattering surface, which is proven by larger NA showing better performance for scattered irradiance due to its wider collection angle. Micro-reflectance difference (μ-RD) of each wavelength is further calculated, and it’s 30 times larger on scattering MoS2 flake surface than specular Si wafer surface.
Commercial LEDs with different colors (ex. InGaN and AlInGaP) were studied using spatially and time resolved Electroluminescence (EL) and Photoluminescence (PL) measurements. A novel experimental setup was used enabling performance of all these techniques at the same point with high temporal resolution, speed and accuracy. LEDs under the study demonstrated inhomogeneous broadening of the luminescence peak. PL and EL spectra observed for these LEDs were different as a result of different radiative transitions attributed to each phenomenon. Time-resolved data for fixed wavelengths demonstrated multiple time spectra at different photon emission energies due to inhomogeneous distribution of Gallium and Indium for InGaN or Gallium and aluminum for AlGaInN.
GaSb thermophotovoltaic (TPV) devices were fabricated using a Molecular Beam Epitaxy (MBE) technique. Different emitter thicknesses (de) were studied to maximize the TPV cell’s short circuit current density. In this regard, the fabricated TPV device’s emitter was incrementally wet-etched and characterized to find the optimal thickness value. Simulations were performed using the Crosslight APSYS® platform over the full-spectrum range in order to predict device performance for different designs, while maximizing the photocurrent generation and enhancing the emitter sheet resistance. TPV devices were characterized electrically and optically. These experimental data showed that the etched emitter has minimal impact on the measured short circuit current density (J<sub>sc</sub>) while simulated results demonstrated an optimal d<sub>e</sub> of 200 nm.
GaSb thermophotovoltaic cells fabricated using Molecular Beam Epitaxy (MBE) and ion implantation techniques are studied. Challenges including different defect formation mechanisms using MBE and ion-induced defects using ion implantation were investigated by cross-sectional Transmission Electron Microscopy (XTEM), X-Ray Diffraction spectroscopy (XRD) and Scanning Electron Microscopy (SEM). For MBE grown TPVs, several approaches were used to suppress defects, including substrate preparation and using different MBE reactors. For ion-implanted TPVs, different implant doses and energies were tested to minimize the crystal damage and various Rapid Thermal Anneal (RTA) process recipes were studied to maximize the crystal recovery. Large area TPV cells with 1 × 1 cm dimensions were fabricated using these techniques, then electrically and optically characterized. Ideality factors and dark saturation currents were measured and compared for various TPVs.
Damage induced by the implantation of beryllium in n-type GaSb and its removal by Rapid Thermal Annealing (RTA) are studied in detail by Atomic Force Microscopy (AFM), Cross Sectional Transmission Electron Microscopy (XTEM) and Energy Dispersive X-ray Spectroscopy (EDS). RTA has been implemented with different times and temperatures in order to optimize ion activation and to avoid Sb outdiffusion during the process. Results indicate a lattice quality that is close to pristine GaSb for samples annealed at 600 °C for 10s using a thick Si3N4 capping layer. Electrical response of the implanted diodes is measured and characterized as function of different annealing conditions.
Low resistance ohmic contacts have been successfully fabricated on n-GaSb layers grown by MBE on semi-insulating (SI) GaAs substrates using the Interfacial Misfit Dislocation (IMF) technique. Although intended for photovoltaic applications, the results are applicable to many antimonide-based devices. The IMF technique enables the growth of epitaxial GaSb layers on semi-insulating GaAs substrates resulting in vertical current confinement not possible on unintentionally doped ~ 1e17 cm<sup>-3</sup> p-doped bulk GaSb. Results for low resistance ohmic contacts using NiGeAu, PdGeAu, GeAuNi and GeAuPd metallizations for various temperatures are reported. Specific transfer resistances down to 0.12 Ω-mm and specific contact resistances of < 2e-6 Ω-cm<sup>2</sup> have been observed.