ALGAAS INGAAS/GAAS SINGLE-ELECTRON TRANSISTORS FABRICATED BY GA FOCUSED ION-BEAM IMPLANTATION/

Single electron transistors are formed in an AlGaAs/InGaAs/GaAs modula tion-doped heterostructure by Ga focused ion beam implantation. The Al GaAs/InGaAs/GaAs system has a high two-dimensional electron gas densit y and facilitates a lateral constriction whose depletion length is muc h smaller than that in a conventional AlGaAs/GaAs system. A dot struct ure confined by a small depletion spreading of less than 0.15 mum is f ormed by the ion implantation. This ion implantation is also employed to form in-plane gates for controlling the tunneling junctions between the dot and reservoirs, and the number of electrons in the dot. Coulo mb oscillations and a Coulomb staircase have been clearly observed by controlling three in-plane gates.