  We study low-frequency noise in current passing through quantum point
contacts fabricated from several GaAs/AlGaAs heterostructures with different
layer structures and fabrication processes. In contrast to previous reports,
there is no gate-dependent random telegraph noise (RTN) originating from
tunneling through a Schottky barrier in devices fabricated using the standard
low-damage process. Gate-dependent RTN appears only in devices fabricated with
a high-damage process that induces charge trap sites. We show that the
insertion of AlAs/GaAs superlattices in the AlGaAs barrier helps to suppress
trap formation. Our results enable the fabrication of damage-resistant and thus
low-noise devices.
