FABRICATION OF QUANTUM WIRES ON GAAS SUBSTRATES PATTERNED BY IN-SITU ELECTRON-BEAM LITHOGRAPHY

In situ electron-beam (EB) lithography, a processing technique conduct ed entirely under an ultra-high vacuum environment, was used to patter n GaAs substrates on which quantum-wire structures were overgrown. Fir st, a GaAs oxide-layer was selectively formed by EB-stimulated oxidati on under a controlled oxygen atmosphere; it was then used as a mask ma terial to define mesa stripes by Cl-2 gas-etching. Subsequently, ridge structures were formed on the mesa stripes by the overgrowth of a GaA s layer by molecular-beam epitaxy. Quantum-wire structures were fabric ated on the top of the ridges by the growth of an AlGaAs/GaAs quantum well. On the narrowest ridge structures, similar to 20 nm wide quantum wires were successfully fabricated, as confirmed by cathodoluminescen ce measurements at 77 K.