Negative energy gap in HgTe-CdTe heterostructures with thick wells

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Abstract
Magnetotransport measurements have been performed on one multiple quantum well and two superlattices with relatively thick wells (>100 Å). Whereas both superlattices are semimetallic and display considerable electron-mass broadening, the multiple quantum well shows no broadening and is found to have an energy gap of 16 meV at low temperatures. This represents the first experimental confirmation of the recent theoretical prediction that HgTe-CdTe should have two semiconducting regimes, one in the thin-well limit and a second for much thicker wells. It is also unusual that, due to the negative temperature coefficient of the effective mass, the electron mobility for thick-well samples continues to increase with T well into the region where phonons dominate the scattering.