Fabrication of a quantum point contact by the dynamic plowing technique and wet-chemical etching

We have fabricated extremely confined ballistic constrictions using a nanolithography technique based on an atomic force microscope. Vector-scan controlled dynamic plowing with the vibrating tip enables to plastically indent a thin resist layer along a prearranged path. Transfer of the resist pattern into the semiconductor substrate is achieved by a strongly diluted aqueous etchant. In this way approximately 30 nm deep gooves were etched in the channel area of a modulation-doped GaAs/GaAlAs field-effect transistor. The quantum point contacts were defined by a broken line whose 60 nm width represents the length and the sub-100 nm gap determines the width of the constriction. At liquid-helium temperature the conductance as a function of gate voltage shows a stepwise increase in units of 2e2/h. Signatures of the conductance quantization persist up to 50 K, which indicates a large subband spacing.