Low-voltage electron beam lithography on GaAs substrates for quantum wire fabrication

Abstract

We have studied the benefits of low-voltage electron beam lithography (EBL) in polymethyl methacrylate (PMMA) positive electron beam resist for the fabrication of quantum wire etch masks on GaAs substrates. In order to determine the reduction of electron scattering effects for low-voltage EBL, we have compared point exposures in 100-nm-thick PMMA for energies between 2.3 and 15 keV. The exposure distribution functions were fitted by combinations of Gaussians and exponentials, showing significant energy-dependent deviations from the widely used double-Gaussian function. The results indicate that on GaAs substrates, backscattering at 2.3 keV is reduced by about two orders of magnitude compared to 15 keV exposures. InGaAs/GaAs quantum wires have been fabricated using low-voltage EBL, followed by an aluminum-liftoff step and wet-chemical etching. In sharp contrast to wires delineated at 25 keV, the resulting structures show no width variations at the field edges caused by proximity effects. The photoluminescence spectra show a wire width dependent blue shift up to 8 meV for 18-nm-wide structures, caused by lateral quantization.