CaF2/Si/CaF2 double-barrier resonant-tunnelling diodes on Si substrates

Abstract

CaF2/Si/CaF2 double-barrier resonant-tunnelling diodes have been fabricated by various processes with molecular beamepitaxy in SiO2 windows patterned on Si(111) substrates. Two types ofI–V characteristics with negative differential resistance (NDR) were observed in thetemperature range from 75 K up to about 200 K. The one is very stable in forward andbackward voltage sweeps, and, in contrast to earlier reports, it does not showany hysteresis or trapping effects. Typical diode parameters were: peak voltageVp = 0.7 V, peak-to-valleycurrent ratio P/V = 1.7 and peakcurrent density Ip = 2 mA cm−2 at105 K. The second is less stable and the NDR appeared only during forwardbias sweeps, possibly due to local trapping effects. But it has largerP/V ratios, the typicalparameters being: Vp = 1.2 V,P/V = 5 and Ip = 11 mA cm−2 at 77 K. The observed peak current densities of both NDR types are about five orders ofmagnitude higher than those reported previously for diodes with the similar structure. Weassume that an inhomogeneous Si quantum-well thickness with the current flow localized insmall regions of the diode area causes the observed variations in peak voltages,multiple NDR regions, peak spreading and exponentially rising background currents.