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We investigate a mechanism causing shorting of large area GaSb diodes grown on GaSb substrates using molecular beam epitaxy (MBE). The source of these shorts is determined to be large crystallographic defects on the surface of the diodes that are formed around droplets of gallium ejected from the gallium Knudsen cells during MBE. The gallium droplets cause defects in the crystal structure, and, as the epitaxy continues, the gallium is incorporated into the surrounding material. The shape of the defects is pyramidal with a central void extending from the epi-surface to the gallium core. Processing a GaSb diode with these surface defects results in the top-side contact metal migrating into the defect and shorting the diode. This prevents realization of large area diodes that are critical to applications such as photovoltaics and detectors. The diodes in this study are electrically characterized and the defect formation mechanism is investigated using cross-section transmission electron microscopy and electron dispersive spectroscopy.

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.

Ultra-low resistance ohmic contacts on n-GaSb with specific transfer resistances down to 0.12 Ω-mm and specific contact resistances of ~1.1e-6 Ω-cm2 have been successfully fabricated on semi-insulating (SI) GaAs substrates using the Interfacial Misfit Dislocation (IMF) technique. The IMF technique enables epitaxial growth of GaSb layers on semi-insulating GaAs substrates resulting in vertical current confinement not possible on unintentionally ~ 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. The low annealing temperature of NiGeAu and PdGeAu metallizations show promising results, but the lifetime of a device with these contacts have not yet been studied.

Low resistance ohmic contacts have been successfully fabr icated 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 temp eratures are reported. Specifi c transfer resistances down to 0.12 Ÿ -mm and specific contact resistances of < 2e-6 Ÿ -cm 2 have been observed. Keywords: Ohmic contacts, GaSb, GaAs, Interfacial Misfit Di slocation, TLM pattern, Sp ecific contact resistance 1. INTRODUCTION Antimonide semiconductors such as GaSb and InSb have a great potential to provide heterojunction structures that absorb or emit light in the longer wavelength IR regime. The GaSb lattice parameter is matched with various ternary and quaternary III-V compounds covering bandgaps from 0.3 eV to 1.58 eV

Low resistance ohmic contacts were fabricated on n-type GaSb grown by molecular beam epitaxy. N-type GaSb epilayers with different doping concentrations and thicknesses were fabricated and studied in order to investigate the current transport mechanism between the metal contacts and the semiconductor. Different metallization schemes were implemented to achieve the lowest possible contact resistance. Rapid thermal annealing was performed at various temperatures to achieve the optimal gold penetration into the GaSb epilayers for low resistance. Ohmic contact fabrication and electrical characterization are discussed in detail. The microstructure analysis of the semiconductor and metal contact interfaces was performed using cross-section transmission electron microscopy and energy dispersive spectroscopy. Specific contact resistances as low as 3 × 10−6 Ω cm2 were obtained.

Ultra low resistance ohmic contacts are fabricated on n-GaSb grown by molecular beam epitaxy. Different doping concentrations and n-GaSb thicknesses are studied to understand the tunneling transport mechanism between the metal contacts and the semiconductor. Different contact metallization and anneal process windows are investigated to achieve optimal penetration depth of Au in GaSb for low resistances. The fabrication, electrical characterization, and microstructure analysis of the metal-semiconductor interfaces created during ohmic contact formation are discussed. The characterization techniques include cross-sectional transmission electron microscopy and energy dispersive spectroscopy. Specific transfer resistances down to 0.1 Ω mm and specific contact resistances of 1 × 10−6 Ω cm2 are observed.