Pt/Ti ohmic contacts to ultrahigh carbon-doped p-GaAs formed by rapid thermal processing

Abstract

Increasing the concentration of the carbon dopants in p‐GaAs layers grown on semi‐insulating substrates to levels of 1×10²⁰ to 5×10²⁰ cm⁻³ enables the formation of an ohmic contact with low resistance using the refractory Pt/Ti metallization. These contacts showed ohmic behavior prior to any heat treatment with specific contact resistance as low as 7×10⁻⁶ Ω cm² (0.08 Ω mm) for the lower doping level and 8×10⁻⁷ Ω cm² (0.04 Ω mm) for the higher level. Small improvements in the specific resistance of the former contact were achieved by rapid thermal processing at a temperature of 450 °C for 30 s, which yielded a value of 4.9×10⁻⁶ Ω cm². The electrical nature of the contact to the heavily doped GaAs was not affected by heat treatments at temperatures up to 450 °C. Rapid thermal processing of these contacts at higher temperatures, however, caused an increase in the contact resistance which was correlated to the expanded Ti/GaAs and Pt/GaAs interfacial reactions. Current‐voltage characteristics were found to be temperature independent. This suggested that the field emission quantum‐mechanical tunneling was the dominant carrier transport mechanism in these contacts.