Gallium arsenide integrated circuit technology: Ion implantation techniques and palladium-germanium ohmic contact processing

This work investigates two areas of gallium arsenide integrated circuit technology: ion implantation and ohmic contact formation. In the area of ion implantation, work on the formation of p-type GaAs by ion implantation and annealing is first presented. The use of carbon, a group IV element, was investigated as an alternative to group II acceptors. Coimplantation of the group II species Mg, Zn, and Cd with carbon was studied as well. It was determined that coimplantation of Zn and carbon or Cd and carbon can result in higher peak hole concentrations than single species implantations. Magnesium coimplantation fails to create a significant amount of lattice damage and consequently results in poor activation of the implanted species. Implanted carbon is seen to reduce the redistribution of the group II species during high temperature annealing, which is explained in terms of a substitutional-interstitial diffusion model.; Investigations on the formation of n-type GaAs by ion implantation and annealing are presented next. The electrical properties of silicon implanted GaAs were found to be dictated by not only the point defect mechanisms that are thought to control n-type activation, but the implantation induced damage as well. Implantation conditions such as dose rate and GaAs substrate temperature were seen to influence the radiation damage significantly. Work was also done with the coimplantation of silicon and the group VI elements sulfur and selenium. It was found that sulfur diffusion could be reduced by the presence of a silicon coimplantation. The studies involving the implantation of selenium confirmed the importance of minimizing implantation damage for n-type activation.; The last part of this work was devoted to the development of a manufacturable PdGe ohmic contact to GaAs. The contact was optimized for low contact resistivity and then integrated into a standard GaAs IC process at TriQuint Semiconductor. GaAs MESFETs were fabricated that utilized PdGe source and drain ohmic contacts and were shown to offer performance that is suitable for use in high-speed circuits. MESFET devices employing PdGe ohmics were compared to those using standard AuGeNi contacts. The results demonstrate that PdGe ohmic contacts are an attractive alternative to conventional AuGeNi ohmic contacts.