Self-Assembled Quantum Dot Single Electron Devices

Single electron tunneling and its application to future VLSI systems has been an important subject extensively studied for the last decade [l]. Many types of materials and ideas have been applied to fabricate and implement single electron devices operating at high temperatures. The self-assembled quantum dot (SAQD) system is one of the attractive candidates for single electron devices since high quality Coulomb islands can be obtained in one-step growth processes. Furthermore, the characteristic energy scale of the devices would enhance because the quantum energy is expected to be added to the classical charging energy. on InGaAs SAQD's. lever-arms with nm spacings. staircases at 77 K and higher temperatures. Figure 1 (a) and (b) show an AFM photos of typical SAQD single electron devices fabricated by the lever-arm technique. The InGaAs SAQD's we have used were grown by an MOCVD technique and the typical diameter of the dots is approximately 20 nm [2]. The aluminum lever-arms with spacings from 200 to 40 nm were fabricated by a standard ebeam exposure and a lift-off process. Figure 2 (a) and (b) show the 77 K current-voltage (I V) and its differential conductance - voltage characteristics.(dUdV - V) of lever - arm device with the gap of 40 nm. Several staircases are clearly identified in both the I-V and the dVdV-V. dI/dV-V of the device with the gap of 150 nm. Clear staircases are also seen. These staircases are originated from the single electron tunneling through SAQD's located in the shortest current path between two lever - arms. In conclusion, self-assembled guantum dot single electron devices are made by the lever-arm technique with the minimum gap spacing of 40 nm and clear staircases are observed in the I-V characteristics. The result of more complicated devices with multiple lever-arms will also be presented at the conference.