Localized States and Quantum Spin Hall Effect in Si-Doped InAs/GaSb Quantum Wells

We study localized in-gap states and quantum spin Hall effect in Si-doped InAs/GaSb quantum wells. We propose a model describing donor and/or acceptor impurities to describe Si dopants. This model shows in-gap bound states and wide conductance plateau with the quantized value $2e^{2}/h$ in light dopant concentration, consistent with recent experiments by Du et al.[arXiv: 1306.1925] We predict a conductance dip structure due to backward scattering in the region where the localization length $\xi $ is comparable with the sample width $L_{y} $ but much smaller than the sample length $L_{x} $.