Extremely Low Nonalloyed Specific Contact Resistance Rho-C (10(-8) Omega Cm(2)) To Metalorganic Molecular-Beam Epitaxy Grown Super Heavily Heavily C-Doped (10(21) Cm(-3))Rho++Gaas

The specific contact resistance rho-c of non-alloyed ohmic metals (Mo/Au and WSi(x)) to p-type GaAs is evaluated by transmission line method (TLM) patterns for various doping concentrations from 8 x 10(18) to 10(21) cm-3. The obtained specific contact resistance rho-c, less than 10(-8) OMEGA-cm2, to metalorganic molecular beam epitaxy grown C-doped (10(21) 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 WSi(x) (x = 0.45), is also studied. By reducing the growth temperature of molecular beam epitaxy from 600 to 450-degrees-C and enhancing the As4/Ga flux ratio to 15, a nondiffusive heavily Be doped (10(20) cm-3) GaAs is obtained. The specific contact resistance of the WSi(x) to this sample is less than 10(-6) OMEGA-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 (10(20) cm-3) GaAs and C-doped (10(21) cm-3) GaAs. In addition, the specific contact resistance rho-c(ISO) of the isoheterojunction (p+GaAs/p+Al(x)Ga1-xAs) is also evaluated by TLM patterns.