Experimental realization of single electron confinement in an InAs quantum dot

We demonstrate an enhancement-mode lateral single electron transistor (SET). In contrast to the depletion-mode SETs that reach one-electron regime by expelling electrons from multi-electron QDs, our SET structure uses a single top gate to create two symmetric tunnel barriers and make electrons tunnel into this empty quantum dot one at a time. The sample used in this work to demonstrate this novel SETs concept is an InAs/GaSb composite quantum well, whose bandgap is tunable by the thicknesses of the two QWs and is $\sim $100meV in our case. Using a gated Hall bar geometry, we show that the device can undergo a transition from hole accumulation to the inversion of electrons. As the widths of the conducting channel and the top gate are reduced to sub-micron, the conductance displays single electron tunneling. The data indicate a 15meV Coulomb charging energy and a 20meV orbital energy spacing, which imply a quantum dot of 20nm in diameter. Combining with the inherent advantage of a large electron g* factor in InAs, our demonstration is significant for solid state implementation of scalable quantum computing.