MBE growth and characterization of Hg based compounds and heterostructures

Abstract

The MBE growth of Hg 1− x Cd x Te alloys and type III HgTe/Hg 1− x Cd x Te heterostructures has been discussed, including similarities and differences between the (0 0 1) and (1 1 2)B orientations. Furthermore the MBE growth of HgTe based quantum wells (QWs) with the incorporation of Mn are additional topics. An investigation of the optical properties of type III superlattices with a normal band structure has lead to information about band structure of these heterostructures as well as information about the interface and the semimetallic QW. For example, by means of the full 8×8 Kane Hamiltonian in the envelope function approximation, it has been demonstrated that the energy separation between the H1–E1 and L1–E1 intersubband transition energies is primarily determined by the valence band offset, Λ, between HgTe and CdTe. This has led to unambiguous values for the offset and its temperature dependence, i.e. Λ( T)=570±60 meV and dΛ/d T=−0.40±0.04T meV/K. Furthermore the energy gap of HgTe at room temperature has also been determined. Magneto-transport measurements of n-type QWs show very pronounced Shubnikov-de Haas (SdH) oscillations and well developed quantum Hall plateaus for temperatures up to approximately 60 K. A large Rashba spin–orbit splitting of the first conduction subband, H1, has been observed in HgTe/Hg 1− x Cd x Te QWs with an inverted band structure. Self-consistent Hartree calculations of the band structure based on the above model allows us to quantitatively describe the experimental results and demonstrates that the heavy hole nature of the H1 subband greatly influences the spatial distribution of electrons in the QW and thus enhances the Rashba spin splitting, i.e. Δ E H1= βk ∥ 3. Furthermore, the presence of two periodic SdH oscillations in p-type QWs with an inverted band structure has been observed and is the first direct evidence that these heterostructures are indirect semiconductors. The influence of Mn in the upper barrier on the 2D electrons in the well has been investigated as a function of their separation. With spacer thicknesses of 10 and 15 nm, no appreciable change is observed, however, a reduction of the spacer thickness to 5 nm results in an increase in the maximum population difference between the two Rashba spin split H1 subbands by a factor of approximately two.