We have fabricated AlGaAs/GaAs split‐gate field‐effect quantum wires with different lengths and widths in order to study the effect of the dimensions of the confining gates on one‐dimensional (1D) transport. Two threshold voltages arise as the two‐dimensional (2D) electron gas is turned off first underneath the gates and then as the 1D electron gas is turned off in between the split‐gates through their fringing fields. In particular, our room‐temperature experiments reveal the existence of acriticalwidthof 0.2–0.25 mgr;m between the confining gates below which the 1D regime is not observed in 1.0‐mgr;m‐long split‐gate quantum wires. This can be explained if the potential at the surface near the metal confining gates is influenced by the gate voltage through exchange of electrons between the metal gates and the surface states.
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