MOSFET's on Au-diffused high-resistivity Si substrates

Si MOSFET's on Au-diffused high-resistivity substrates were fabricated and their electrical properties were investigated. At 80 K, the current leakage between the source and drain of both n- and p-channel devices decreased below 10
^-10
A, and the devices exhibited normally-off behaviors. Au concentrations (
N
) in Si substrates as a function of diffusion temperature T
diff
was determined from the change in the threshold voltage.
N
versus T
diff
thus obtained is in fairly good agreement with that obtained by other methods. Dependence of effective mobility on T
diff
was investigated in the form of a MOS device. The effective mobility decreased with increasing T
diff
, and it became clear that the diffusion temperature must be lower than about 700°C to obtain semi-insulating substrates with reasonably high carrier mobility. A C-MOS inverter was fabricated using an Au-diffused Si substrate, where no isolation wells were needed, in operation at low temperatures.