Influence of As⁺ Ion Implantation on Properties of MBE HgCdTe Near-Surface Layer Characterized by Metal–Insulator–Semiconductor Techniques

The effect of As⁺ ion implantation on the electrical properties of the near-surface layer of n-HgCdTe films grown by molecular beam epitaxy (MBE) on Si (310) substrates was experimentally studied. A specific feature of MBE n-Hg_0.78Cd_0.22Te films is the presence of near-surface graded-gap layers with a high CdTe content, formed during epitaxial growth. The properties of as-grown films and films after As⁺ ion implantation with ion energy of 200 keV and fluence of 10¹⁴ cm⁻² were studied. Post-implantation activation annealing was not performed. Test metal–insulator–semiconductor (MIS) structures were created based on as-grown and as-implanted samples by plasma-enhanced atomic layer deposition of Al₂O₃ insulator films. The admittance of the fabricated MIS structures was measured over a wide range of frequencies and temperatures. When determining the parameters of MIS structures, we used techniques that take into account the presence of near-surface graded-gap layers and series resistance of the HgCdTe film bulk, as well as the high density of slow surface states. It was found that, in as-implanted samples, the donor center concentration in the near-surface layer exceeds 10¹⁷ cm⁻³ and increases with distance from the HgCdTe-Al₂O₃ interface (at least up to 90 nm). After implantation, the conductivity of MBE HgCdTe film bulk increases markedly. It was shown that, for as-implanted samples, the generation rate of minority charge carriers in the MBE HgCdTe surface layer is significantly reduced, which indicates the appearance of a low defect layer with a thickness of at least 90 nm.