Surface states in a HgTe quantum well and scattering by surface roughness

Scattering of two-dimensional electrons in wide ($d=18$–$22$ nm) HgTe-based quantum wells has been thoroughly studied. The mobility has been found to reach a maximum and then to decrease at two-dimensional electron densities above ($2$–$6$)$\times 10^{11}$ cm$^{-2}$ owing to scattering by roughness of the quantum well. The theory of scattering by roughness has been elaborated taking into account transformation of the wavefunction with an increase in the electron density. Good agreement of this theory with the experiment indicates the existence of surface states at the interfaces of the wide HgTe quantum well.