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.
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.