Fluoride Resonant Tunneling Diodes on Si Substrates Improved by Additional Thermal Oxidation Process

An oxidation process was applied to the fabrication of fluoride resonant tunneling diodes (RTDs) on Si substrates. The oxidation process was carried out after the growth of an ultrathin CaF 2 layer on Si, and expected to passivate the Si surface in pinholes generated in the CaF 2 layer. Leakage currents of Au/Al/CaF 2 /Si(111) metal insulator semiconductor (MIS) diodes were extremely reduced by introducing this process. Au/Al/CaF 2 /CdF 2 /CaF 2 /Si(111) double-barrier RTDs were also fabricated by introducing this process, the leakage currents of which were extremely reduced and a very large peak to valley current ratio (PVCR) of 1500 was obtained. It was also shown that the chemical reaction between a CdF 2 well layer and the Si substrate was suppressed by the oxidation process. Owing to this effect, high-temperature growth (up to 300°C) of the CdF 2 well layer was realized for the first time in the fluoride RTDs, and resulted in the reduction of undesirable current drift.