Detection of a single-charge defect in a metal-oxide-semiconductor structure using vertically coupled Al and Si single-electron transistors

摘要

An Al-AlO_x-Al single-electron transistor (SET) acting as the gate of anarrow (~ 100 nm) metal-oxide-semiconductor field-effect transistor (MOSFET)can induce a vertically aligned Si SET at the Si/SiO_2 interface near theMOSFET channel conductance threshold. By using such a vertically coupled Al andSi SET system, we have detected a single-charge defect which is tunnel-coupledto the Si SET. By solving a simple electrostatic model, the fractions of eachcoupling capacitance associated with the defect are extracted. The resultsreveal that the defect is not a large puddle or metal island, but its size israther small, corresponding to a sphere with a radius less than 1 nm. The smallsize of the defect suggests it is most likely a single-charge trap at theSi/SiO_2 interface. Based on the ratios of the coupling capacitances, theinterface trap is estimated to be about 20 nm away from the Si SET.