  We present a new double-layer design for 2D surface superlattice systems in
GaAs-AlGaAs heterostructures. Unlike previous studies, our device (1) uses an
in-situ gate, which allows very short period superlattice in high mobility,
shallow heterostructures; (2) enables independent control of the carrier
density and the superlattice modulation potential amplitude over a wide range.
We characterise this device design using low-temperature magneto-transport
measurements and show that the fabrication process caused minimal damage to the
system. We demonstrate the tuning of potential modulation from weak (much
smaller than Fermi energy) to strong (larger than the Fermi energy) regimes.
