Capacitive detection of subband structure in the electron gas in a wide parabolic GaAs/AlxGa1−xAs quantum well

Profiles of the capacitance C(Vg) between a front gate and the electron gas in a wide parabolic well and its derivative dC/dVg are used to study the subband structure and uniformity of the electron gas layer. Subband depopulation events are detected as peaks in the derivative profile dC/dVg as the width of the electron gas is reduced by application of the gate voltage Vg. To separate depopulation events from nonuniformities in electron density, derivative profiles are repeated for increasing in-plane magnetic fields: depopulation peaks move to smaller gate voltages and disappear at characteristic fields, while nonuniformities remain fixed and are accentuated in strong fields.