Trends in reverse-current change in tunnel MIS diodes with calcium fluoride on Si(111) upon the formation of an extra oxide layer

The currents flowing in metal–CaF$_{2}$/$n$-Si and metal–SiO$_{2}$/CaF$_{2}$/$n$-Si structures with the same (about 1.5 nm) fluoride thickness are compared in the reverse-bias mode. It is revealed that the current in the case of a two-layer dielectric can be notably higher within a certain voltage range. Such unexpected behavior is associated with the coexistence of both electron and hole components of the current as well as with the configuration of the SiO$_{2}$–CaF$_2$ barrier through which tunneling occurs. The results of measurements and explanatory simulation data are presented.