Extremely low non-alloyed specific contact resistance ρc (10−8 Ω cm2) to metalorganic molecular beam epitaxy grown super heavily C-doped (1021 cm−3) p++GaAs

Abstract

The specific contact resistance ρc of non-alloyed ohmic metals (Mo/Au and WSix) to p-type GaAs is evaluated by transmission line method (TLM) patterns for various doping concentrations from 8×1018 to 1021 cm−3. The obtained specific contact resistance ρc, less than 10−8 Ω cm2, to metalorganic molecular beam epitaxy grown C-doped ( 1021 cm−3) GaAs is the lowest reported value. From the application point of view for the emitter electrodes of PNp type (two-dimensional electron gas base) heterojunction bipolar transistors, the specific contact resistance of a refractory metal, or the sputter-deposited WSix (x=0.45), is also studied. By reducing the growth temperature of molecular beam epitaxy from 600 to 450 °C and enhancing the As4/Ga flux ratio to 15, a nondiffusive heavily Be doped (1020 cm−3) GaAs is obtained. The specific contact resistance of the WSix to this sample is less than 10−6 Ω cm2. The obtained specific contact resistance can be well explained by a simple modeling based on the tunneling transport of light holes. Secondary ion mass spectroscopy analysis of the depth profile under heat acceleration shows a small diffusion of dopants for Be doped (1020 cm−3) GaAs and C-doped (1021 cm−3) GaAs. In addition, the specific contact resistance ρcISO of the isoheterojunction (p+GaAs/p+AlxGa1−xAs) is also evaluated by TLM patterns.