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

HgTe-CdTe superlattices with electron concentrations up to 3 X 10(17) 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 N(D), in contrast to the Hg1-xCdxTe alloy system in which mu(n) strongly decreases with N(D). 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 angstrom setback is found to produce a factor of 2 mobility increase over any measured previously in heavily doped samples, and an 81 angstrom setback leads to further enhancement of mu(n). All superlattices with doping levels greater-than-or-equal-to 8 X 10(15) cm-3 display the quantum Hall effect. Quantization of the Hall conductivity in multiples of almost-equal-to N(W)e2/h indicates participation by nearly all of the N(W) periods in the superlattice, implying that the controlled doping is extremely uniform.