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We measured the transmission through nanoscopic cross-junctions at variable temperature and bias. The devices were prepared by deep etching through a two-dimensional electron gas in InGaAs/InP samples. Our experiments show that the transmission characteristic is partly ballistic even at room temperature. The measurements are analysed in terms of an equivalent network, and the involved resistances are related to the electrons' mean free path. Different scattering mechanisms are considered to account for the transition from ballistic to diffusive transport.

Clear conductance quantization at T=4.2 K has been demonstrated in a 140 nm wide and 200 nm long trench-isolated In0.53Ga0.47As/InP electron waveguide with in-plane gates, using the surrounding two-dimensional electron gas as the gate. It was fabricated using metalorganic vapor phase epitaxy, electron beam lithography, and CH4/H2 reactive ion etching. In a T=20 K measurement on a 60 nm wide and 100 nm long device, only the first conductance plateau of 2e2/h was reached.

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