Design principles for HgTe based topological insulator devices

The topological insulator properties of CdTe/HgTe/CdTe quantum wells are theoretically studied. The CdTe/HgTe/CdTe quantum well behaves as a topological insulator beyond a critical well width dimension. It is shown that if the barrier(CdTe) and well-region(HgTe) are altered by replacing them with the alloy Cd${}_x$Hg${}_{1-x}$Te of various stoichiometries, the critical width can be changed.The critical quantum well width is shown to depend on temperature, applied stress, growth directions and external electric fields. Based on these results, a novel device concept is proposed that allows to switch between a normal semiconducting and topological insulator state through application of moderate external electric fields.