Figure 2: Schematic of sample for microwave measurement.

(a) Schematic of the microwave measurement set-up. The source and detector are outside the cryostat at room temperature and the coplanar waveguide transmission line is patterned in metal film on top of the sample surface. The microwave conductivity σ_xx is calculated from loss through the line. (b) The microwave set-up shown in a cutaway side view. Slots of width s separate the centre, driven conductor and the ground planes. (c) The growth-direction electron charge distribution for a well of width w=80 nm at n=1.26 × 10¹¹ cm⁻² obtained from one-dimensional simulations. The growth-direction separation of charge density peaks is ∼54 nm.