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We show that small structures can be defined in high mobility two‐dimensional electron gases formed at a depth of 2770 A below the surface in GaAs/Al0.33Ga0.67As heterostructures. The differential conductance of one‐dimensional constrictions defined by split gates in such deep electron gases showed more than 20 quantised plateaus. The absence of resonant structures on the plateaus demonstrates the absence of potential fluctuations in the constrictions. By applying a dc source‐drain bias we have measured the energy spacings of the first 18 subbands, and the effect of a small perpendicular magnetic field on the energy spacings has been investigated.

We have developed a new technique to contact a submicrometer metal dot gate independently of surrounding gates. With this we have made two ballistic channels in parallel on a GaAs‐AlGaAs heterostructure. Independent control over all the gates allows unprecedented flexibility to adjust both the size of the dot and the widths of the channels. In a perpendicular magnetic field we can obtain extremely large Aharonov–Bohm oscillations and a double‐frequency oscillation indicative of edge state charging in an open system. At low magnetic fields we see no evidence for any interaction between the one‐dimensional subbands in the two channels.

Electron transport is studied in GaAs/AlGaAs asymmetric triple‐barrier resonant tunneling structures in a high magnetic field perpendicular to the interfaces. Besides the resonance peaks arising from tunneling between two quantum wells, a series of fine structure is observed in the valley region of the current‐voltage characteristics, which is attributed to electron transitions between well defined totally quantized levels (Landau levels) in the two wells, together with the emission of a longitudinal optical phonon. In the voltage region of the main current peak, any structures which shift with magnetic field are not observed, suggesting that the tunneling in this bias region is mainly determined by Δn=0 elastic transitions.