Transport diagrams of germanium double quantum dots/Si barriers using photocurrent measurement

We reported transport diagrams of self-assembled germanium (Ge) double quantum-dots (DQDs) using direct current measurement under illumination at wavelength (λ) of 850 nm and at the base temperature of 4.5 K. Ge DQDs with a coupling-barrier of Si, tunneling-barriers of Si₃N₄, and self-aligned p⁺-Si reservoirs were fabricated in a self-organized CMOS approach. Charge transport through the Ge-DQDs is facilitated by photon-assisted tunneling. Characteristic gate-controlled hexagonal-shaped cells over a wide range of hole occupancy are acquired thanks to hard-wall confinement. Large dimensions (ΔV_G > 200 mV) of hexagonal-shaped cells are favored for the operation of charge states, indicating that our Ge DQDs system is less susceptible to shot noises arising from external voltage sources. Estimated intra-QD and inter-QD charging energies are E_C,R/E_C,L = 48.9 meV/42.7 meV and E_Cm = 7.8 meV, respectively.