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 (Jsc) while simulated results demonstrated an optimal de 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-3 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-cm2 have been observed.