Room-temperature observation of current bistability and fine structures in germanium quantum dots/SiO2 resonant tunneling diodes

The steady-state and time-dependent current–voltage (I–V) characteristics are experimentally investigated in Ge quantum dot (QD)/SiO2 resonant tunneling diodes (RTDs). Ge QDs embedded in a SiO2 matrix are naturally formed by thermal oxidation of Si0.9Ge0.1 nanowires (30 nm×50 nm) on silicon-on-insulator substrates. The average dot size and spacing between dots are 9±1 and 25 nm, respectively, from TEM observations, which indicate that one or two QDs are embedded between SiO2 tunneling barriers within the nanowires. Room-temperature resonant oscillation, negative differential conductance, bistability, and fine structures are observed in the steady-state tunneling current of Ge-QD/SiO2 RTDs under light illumination. Time-dependent tunneling current characteristics display periodic seesaw features as the Ge-QDs RTD is biased within the voltage regime of the first resonance peak while they exhibit harmonic swing behaviors as the RTD is biased at the current valleys or higher-order current peaks. This possibly originates from the interplay of the random telegraph signals from traps at the QD/SiO2 interface as well as the electron wave interference within a small QD due to substantial quantum mechanics effects.