Quantum Hall effect and setback modulation doping in HgTe–CdTe heterostructures

Abstract

HgTe–CdTe superlattices with electron concentrations up to 3×1017 cm−3 have been grown by photoassisted molecular‐beam epitaxy with controlled indium doping of the CdTe barriers. Magnetotransport measurements indicate that the low‐temperature electron mobility is relatively independent of donor concentration at large ND, in contrast to the Hg1−xCdxTe alloy system in which μn strongly decreases with ND. Also studied are the first Hg‐based heterostructures with setback doping, i.e., with an undoped spacer layer between the donors in the middle of the barriers and the electrons in the quantum wells. A 43 Å setback is found to produce a factor of 2 mobility increase over any measured previously in heavily doped samples, and an 81 Å setback leads to further enhancement of μn. All superlattices with doping levels ≥8×1015 cm−3 display the quantum Hall effect. Quantization of the Hall conductivity in multiples of ≊NWe2/h indicates participation by nearly all of the NW periods in the superlattice, implying that the controlled doping is extremely uniform.