Electron mobilities and quantum Hall effect in modulation-doped HgTe-CdTe superlattices

Photoassisted molecular-beam epitaxy and controlled modulation doping have been used to grow HgTe-CdTe superlattices with n-type carrier concentrations of up to 3×${10}^{17}$ ${\mathrm{cm}}^{\mathrm{-}3}$. It is found that in contrast to ${\mathrm{Hg}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Cd}}_{\mathit{x}}$Te alloys where the electron mobility decreases strongly with donor concentration, ${\mathrm{\mu }}_{\mathit{n}}$ in the modulation-doped superlattices is nearly independent of ${\mathit{N}}_{\mathit{D}}$ at large ${\mathit{N}}_{\mathit{D}}$. We also discuss an observation of the quantum Hall effect associated with carriers distributed throughout the interior of a HgTe-CdTe superlattice. Whereas previous reports of quantized steps in the Hall conductivity have involved a small number of conduction channels (hence a small fraction of the superlattice periods), we observe plateaus at multiples of ≊200${\mathit{e}}^2$/h in a number of 200-period superlattices with high doping levels. This indicates participation by nearly all wells in the superlattice, and implies that the controlled doping is extremely uniform.