Ion milling was used to establish the minimum donor doping level N md required for obtaining n-regions with reproducible electron concentration in HgCdTe-based LWIR and MWIR device structures fabricated with ion treatment. The experiments were performed on n-type films grown by molecular beam epitaxy, un-doped and in situ doped with indium with the concentration N In = 5 × 10 14 -10 17 cm −3 . A study of the electrical properties of the milled films showed that N md comprised ∼2 × 10 15 cm −3 for the LWIR and ∼5 × 10 15 cm −3 for the MWIR films. In the films with N In exceeding these critical values, the electron concentration after the milling strictly followed the doping. A need for consideration of the disintegration of the milling-induced defects is also shown.
We report on the observation of symmetry breaking and the circular photogalvanic effect in Cdx Hg1-x Te alloys. We demonstrate that irradiation of bulk epitaxial films with circularly polarized terahertz radiation leads to the circular photogalvanic effect (CPGE) yielding a photocurrent whose direction reverses upon switching the photon helicity. This effect is forbidden in bulk zinc-blende crystals by symmetry arguments, therefore, its observation indicates either the symmetry reduction of bulk material or that the photocurrent is excited in the topological surface states formed in a material with low Cadmium concentration. We show that the bulk states play a crucial role because the CPGE was also clearly detected in samples with non-inverted band structure. We suggest that strain is a reason of the symmetry reduction. We develop a theory of the CPGE showing that the photocurrent results from the quantum interference of different pathways contributing to the free-carrier absorption (Drude-like) of monochromatic radiation. arXiv:1911.01936v1 [cond-mat.mes-hall]
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