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-cm 2 have been observed.
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.
Characteristics of ion implantation induced damage in GaSb, and its removal by rapid thermal annealing, are investigated by cross-sectional transmission electron microscopy. Rapid thermal annealing (RTA) has been implemented on implanted GaSb for various temperatures and durations with the semiconductor capped, which avoids Sb out-diffusion and Ga agglomeration during the process. The RTA damage induced in the GaSb wafer was studied by scanning electron microscopy and energy dispersive x-ray spectroscopy. The results of the microscopy study were then used to optimize the RTA recipe and the Si3N4 capping layer thickness to achieve doping activation while minimizing crystalline damage. Results indicate a lattice quality that is close to pristine GaSb for samples annealed at 600 °C for 10 s using 260 nm thick Si3N4 capping layer. Secondary ion mass spectrometry measurement indicates that the implanted Be does not migrate in the GaSb at the used annealing temperature. Finally, electrical characteristics of diodes fabricated from the implanted material are presented that exhibit low series resistance and high shunt resistance suitable for photovoltaic applications.
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.
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