We report the results of capacitance measurements on quantum wires in which only the lowest one-dimensional subband is occupied. The wires are generated in metal-insulator-semiconductor-field-effect-transistor-type AlAs/GaAs heterojunctions with an interdigitated gate. In such devices strong lateral confinement and a well-defined threshold voltage are achieved. In the quantum limit at very low electron density the capacitance signal recorded as a function of the gate voltage exhibits a substructure that we discuss in view of a drastic change of the effective channel width when the wire starts to be occupied. At very high magnetic fields we observe spin polarization of the lowest subband. The position of the capacitance minimum that corresponds to the minimum of the density of states between the spin-polarized subbands clearly reflects the asymmetry of the one-dimensional density of states that even persists at high magnetic fields.

• Received 8 November 1993

DOI:https://doi.org/10.1103/PhysRevB.49.14074