Resonant tunneling through monolayer Si colloidal quantum dots and Ge nanocrystals

Resonant tunneling through a 4 nm nanocrystal Ge (nc-Ge) layer and a 2.4 nm monolayer of Si colloidal quantum dots (QD) is achieved with 0.7 nm amorphous Al₂O₃ (a-Al₂O₃) barriers. The nc-Ge resonant tunneling diode (RTD) demonstrates a peak-to-valley current ratio (PVCR) of 8 and a full width at half maximum (FWHM) of 30 mV at 300 K, the best performance among RTDs based on annealed nanocrystals. The Si QD RTD is first achieved with PVCRs up to 47 and FWHMs as small as 10 mV at room temperature, confirming theoretically expected excellences of 3D carrier confinements. The high performances are partially due to the smooth profile of nc-Ge layer and the uniform distribution of Si QDs, which reduce the adverse influences of many-body effects. More importantly, carrier decoherence is avoided in the 0.7 nm a-Al₂O₃ barriers thinner than the phase coherence length (≈1.5 nm). Ultrathin a-Al₂O₃ also passivates well materials and suppresses leakage currents. Additionally, the interfacial bandgap of ultrathin a-Al₂O₃ is found to be similar to the bulk, forming deep potential wells to sharpen transmission curves. This work can be easily extended to other materials, which may enable resonant tunneling in various nanosystems for diverse purposes.