CaF2/CdF2 Double-Barrier Resonant Tunneling Diode with High Room-Temperature Peak-to-Valley Ratio

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Abstract
We have demonstrated room-temperature negative differential resistance (NDR) with a high peak-to-valley ratio (PVR) on the order of 105 using CaF2/CdF2 double-barrier resonant tunneling diode (DBRTD) structures grown on Si(111) substrates. A CdF2 quantum-well layer was grown by molecular-beam epitaxy (MBE) and CaF2 barrier layers were formed by MBE combined with the partially ionized beam technique on an n+-Si(111) substrate with 0.07° miscut, in order to reduce the pinhole density of CaF2 barrier layers. The dispersion of the peak current density and bias voltage of the NDR implies that the layer thickness fluctuation of each CaF2 barrier and CdF2 quantum-well layer is suppressed below ±1 unit layer of the (111) atomic plane for DBRTDs with an 18 µm diameter electrode. The peak and valley currents agreed reasonably with those obtained by theoretical estimation.