Negative-Band-Gap Quantum Dots

The spectrum of quantum dots (QDs) made from semiconductors like HgTe and HgS changes from negative gap to positive gap with decreasing size. Furthermore, intrinsic surface states, which are not related to dangling bonds, appear in the negative gap regime. We investigate theoretically the evolution of the spectrum of HgS QDs with decreasing size and show how states evolve from a negative gap to a positive gap as confinement is increased. The lowest confined electron level evolves into an intrinsic surface state with increasing size. This surface state is not derived from a bulk HgS bands. We demonstrate that surface states found do not have characteristic topological properties.