Epitaxial Growth and Electrical Characteristics of CaF2/Si/CaF2 Resonant Tunneling Diode Structures Grown on Si(111) 1°-off Substrate

CaF2/Si/CaF2 double-barrier resonant tunneling diode (RTD) structures have been epitaxially grown on a Si(111) substrate using molecular beam epitaxy (MBE) with the partially ionized beam method. A 3.4-nm-thick Si quantum-well layer was epitaxially formed on a 1-nm-thick CaF2 barrier layer grown on the Si(111) substrate tilted 1° toward the <1 12> azimuth, of which the terrace width was uniformly controlled by thermal pretreatment at 1000°C for 30 min in an ultrahigh-vacuum (UHV) chamber. After the growth, thermal annealing, which results in the reduction of leakage current, was carried out at 600°C for 10 min to improve crystallinity. In the current-voltage characteristics of the RTD structures, a clear negative differential resistance has been observed under a pulsed bias condition with a peak-to-valley current ratio of 6.3 at 77 K. In the dc voltage sweep measurement, a memory effect was observed; this implies charge and discharge through the trap states in the RTD structures.