For future integration of a large number of qubits and complementary metal-oxide-semiconductor (CMOS) controllers, higher operation temperature of qubits is strongly desired. In this work, we fabricate p-channel silicon quantum dot (Si QD) devices on silicon-on-insulator for strong confinement of holes and investigate the temperature dependence of Coulomb oscillations and Coulomb diamonds. The physically defined Si QDs show clear Coulomb diamonds at temperatures up to 25 K, much higher than for gate defined QDs. To verify the temperature dependence of Coulomb diamonds, we carry out simulations and find good agreement with the experiment. The results suggest a possibility for realizing quantum computing chips with qubits integrated with CMOS electronics operating at higher temperature in the future.

Physically defined silicon triple quantum dots (TQDs) are fabricated on a silicon-on-insulator substrate by dry-etching. The fabrication method enables us to realize a simple structure that does not require gates to create quantum dot confinement potentials and is highly advantageous for integration. We observe the few-electron regime and resonant tunneling points in the TQDs by applying voltages to two plunger gates at a temperature of 4.2 K. Moreover, we reproduce the measured charge stability diagram by simulation with an equivalent-circuit model composed of capacitors and resistors. The equivalent-circuit simulation makes it clear that we realize three QDs in series within the nanowire, as planned. This circuit model also elucidates the mechanism of resonant tunneling and identifies a quadruple point of TQDs.