Control of the confining potential in ballistic constrictions using a persistent charging effect

GaAs/AlGaAs quantum point contacts are fabricated by atomic force microscope lithography and wet chemical etching. The lateral confinement potential of a given ballistic constriction is varied by persistent fractional charging of the donors in the supply layer. A forward bias voltage applied to the gate electrode during sample cooling shifts the conductance threshold at T=4.2 K towards higher gate voltage due to partial neutralization of the donors. Simultaneously, the width of the quantized conductance plateaus at multiples of 2e2/h decreases. Measurements under finite drain voltage reveal a reduction of the lowest subband separation from ΔE1,2=17.5±1 to 13±1 meV as the cooling bias voltage is raised from 0 to +0.6 V.