Inter-layer subband mixing in MBE-grown HgTe/CdTe superlattices

We report transport results for molecular beam epitaxially grown HgTe/CdTe superlattices (SLs) with CdTe barrier thickness of L_b systematically varied from 100Å down to 20Å, and demonstrate the increasing intersubband mixing between adjacent layers with decreasing L_b. Magnetotransport data measured at 1.5K and for B up to 10T show monotonously varying features with L_b, implying a dimensional change from 2D to quasi-3D. As L_b decreases, the quantum Hall plateaus become weaker and the number of effective 2D channels are decreased, which indicates increasing growth-direction energy dispersion. This enhanced interlayer subband coupling with decreasing L_b is further confirmed by the angle-dependence of SdH oscillations. For L_b = 20Å, all of 2D-related transport behavior are washed out. A quantitative analysis with calculated subband energy dispersion relations demonstrates the close interplay between superlattice barrier thickness and the strength of the intersubband mixing. These transport results are directly related to successful control of the growth-axis carrier effective mass and will contribute to the development of high-performance HgTe/CdTe SL-based IR photo-voltaic devices and lasers, in which tunneling noise due to diffusion currents can be considerably reduced.