Type-II strained-layer superlattices (T2SL) based on InAs1−xSbx are a promising photovoltaic detector material technology for thermal imaging; however, Shockley–Read–Hall recombination and generation rates are still too high for thermal imagers based on InAs1−xSbx T2SL to reach their ideal performance. Molecular dynamics simulations using the Stillinger–Weber (SW) empirical potentials are a useful tool to study the growth of tetrahedral coordinated crystals and the nonequilibrium formation of defects within them, including the long-range effects of strain. SW potentials for the possible atomic interactions among {Ga, In, As, Sb} were developed by fitting to ab initio calculations of elastically distorted zinc blende and diamond unit cells. The SW potentials were tested against experimental observations of molecular beam epitaxial (MBE) growth and then used to simulate the MBE growth of InAs/InAs0.5Sb0.5 T2SL on GaSb substrates over a range of processes parameters. The simulations showed and helped to explain Sb cross-incorporation into the InAs T2SL layers, Sb segregation within the InAsSb layers, and identified medium-range defect clusters involving interstitials and their induction of interstitial-vacancy pairs. Defect formation was also found to be affected by growth temperature and flux stoichiometry.
The realization of the MeRAM is based on the voltage control of the interfacial magnetocrystalline anisotropy (MCA) of heavy-metal/ferromagnet/insulator (HM/FM/I) nanojunctions, where the non-magnetic HM contact electrode (Ta, Pd, Pt, Au) has strong spin-orbit coupling (SOC). Employing ab initio electronic structure calculations we have investigated the effect of electric-field (E-field) and epitaxial strain on the MCA of Ta/FeCo/MgO heterostructure. We predict that uniaxial strain leads to a wide range of interesting voltage behavior of the MCA ranging from linear behavior with positive or negative magnetoelectronic coefficient, to non-monotonic ⋁-shape or inverse-⋀-shape E-field dependence with asymmetric magnetoelectronic coefficients. The calculations reveal that under a 4% compressive strain on MgO reaches the giant value of ~ 1126 fJ/(V.m). The underlying mechanism is the synergistic effects of strain and E-field on the orbital characters, the energy level shifts of the SOC d-states, and the dielectric constant of MgO. These results demonstrate for the first time the feasibility of highly sensitive E-field-controlled MCA through strain engineering, which in turn open a viable pathway towards tailoring magnetoelectric properties for spintronic applications.
* nick.kioussis@csun.edu
This research was supported by NSF Grant No. ERC-TANMS-1160504
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