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<jats:p>The performance of type-II superlattice (T2SL) long-wavelength infrared devices is limited by crystalline quality of T2SLs. We optimize the process of growing molecular beam epitaxy deposition T2SL epi-layers on GaSb (100) to improve the material properties. Samples with identical structure but diverse In/Ga beam-equivalent pressure (BEP) ratio are studied by various methods, including high-resolution x-ray diffraction, atomic force microscopy and high-resolution transmission electron microscopy. We find that appropriately increasing the In/Ga BEP ratio contributes to improving the quality of T2SLs, but too large In BEP will much more easily cause a local strain, which can lead to more InSb islands in the InSb interfaces. The InSb islands melt in the InSb interfaces caused by the change of chemical potential of In atoms may result in the “nail” defects covering the whole T2SLs, especially the interfaces of GaSb-on-InAs. When the In/Ga BEP ratio is about 1, the T2SL material possesses a lower full width at half maximum of +1 first-order satellite peak, much smoother surface and excellently larger area uniformity.</jats:p>

<jats:p>Strained HgTe thin films are typical three-dimensional topological insulator materials. Most works have focused on HgTe (100) films due to the topological properties resulting from uniaxial strain. In this study, strained HgTe (111) thin films are grown on GaAs (100) substrates with CdTe (111) buffer layers using molecular beam epitaxy (MBE). The optimal growth conditions for HgTe films are determined to be a growth temperature of 160°C and an Hg/Te flux ratio of 200. The strains of HgTe films with different thicknesses are investigated by high-resolution x-ray diffraction, including reciprocal space mapping measurements. The critical thickness of HgTe (111) film on CdTe/GaAs is estimated to be approximately 284 nm by Matthews’ equations, consistent with the experimental results. Reflection high-energy electron diffraction and high-resolution transmission electron microscopy investigations indicate that high-quality HgTe films are obtained. This exploration of the MBE growth of HgTe (111) films provides valuable information for further studies of HgTe-based topological insulators.</jats:p>

<jats:p> <jats:italic>We demonstrate that a low-temperature GaN insertion layer could significantly improve the surface morphology of non-polar a-plane GaN.The two key factors in improving the surface morphology of non-polar a-plane GaN are growth temperature and growth time of the GaN insertion layer. The root-mean-square roughness of a-plane GaN is reduced by 75% compared to the sample without the GaN insertion layer. Meanwhile, the GaN insertion layer is also beneficial for improving crystal quality. This work provides a simple and effective method to improve the surface morphology of non-polar a-plane GaN</jats:italic>.</jats:p>

<jats:p> <jats:italic>A dual silicide layer structure is proposed for Schottky barrier metal-oxide-semiconductor field effect transistors (MOSFETs) on bulk substrates. The source/drain regions are designed to be composed with dual stacked silicide layers, forming different barrier heights to silicon channel. Performance comparisons between the dual barrier structure and the single barrier structure are carried out with numerical simulations. It is found that the dual barrier structure has significant advantages over the single barrier structure because the drive current and leakage current of the dual barrier structure can be modulated. Furthermore, the dual barrier structure’s performance is nearly insensitive to the total silicide thickness, which can relax the fabrication requirements and even make an SOI substrate unnecessary for planar device design. The formation of ErSi<jats:sub> <jats:italic>x</jats:italic> </jats:sub>/CoSi<jats:sub>2</jats:sub> stacked multilayers has been proved by experiments</jats:italic>.</jats:p>

<jats:p> <jats:italic>The effect of growth temperature of barriers on photoelectric properties of GaN-based yellow light emitting diodes (LEDs) is investigated. It is found that as the barrier temperature increases, the crystal quality of multi-quantum wells (MQWs) and the quality of well/barrier interface are improved, and the quantum well is thermally annealed, so that the indium atoms in the quantum well migrate to the equilibrium position, reducing the phase separation of the quantum well and improving the crystal quality of quantum wells (QWs). However, the external quantum efficiency (EQE) of the samples begins to decrease when raising the barrier temperature even further. One explanation may be that the higher barrier temperature destroys the local state in the quantum well and reduces the well/barrier interface quality. Therefore, a suitable barrier temperature is proposed, contributing to the improvement of the luminous efficiency of the yellow LEDs</jats:italic>.</jats:p>

<jats:p> <jats:italic>Germanium waveguide photodetectors with 4 μm widths and various lengths are fabricated on silicon-on-insulator substrates by selective epitaxial growth. The dependence of the germanium layer length on the responsivity and bandwidth of the photodetectors is studied. The optimal length of the germanium layer to achieve high bandwidth is found to be approximately 8 μm. For the 4 × 8 μm<jats:sup>2</jats:sup> photodetector, the dark current density is as low as 5 mA/cm<jats:sup>2</jats:sup> at −1 V. At a bias of −1 V, the 1550 nm optical responsivity is as high as 0.82 A/W. Bandwidth as high as 29 GHz is obtained at −4 V. Clear opened eye diagrams at 50 Gbits/s are demonstrated at 1550 nm</jats:italic>.</jats:p>

<jats:p> <jats:italic>A spintronic theory is developed to study the effect of lattice distortion on the magnetic tunnel junctions (MTJs) consisting of single-crystal barrier and half-metallic electrodes. In the theory, the lattice distortion is described by strain, defect concentration and recovery temperature. All three parameters will modify the periodic scattering potential, and further alter the tunneling magnetoresistance (TMR). The theoretical results show that: (1) the TMR oscillates with all the three parameters; (2) the strain can change the TMR about 30%; (3) the defect concentration will strongly modify the periodic scattering potential, and further change the TMR about 50%; and (4) the recovery temperature has little effect on the periodic scattering potential, and only can change the TMR about 10%. The present work may provide a theoretical foundation to the application of lattice distortion for MTJs consisting of single-crystal barrier and half-metallic electrodes</jats:italic>.</jats:p>

<jats:p> <jats:italic>We demonstrate high-fidelity manipulation of the quantized motion of a single <jats:sup>87</jats:sup>Rb atom in an optical tweezer via microwave couplings induced by Stern–Gerlach splitting. The Stern–Gerlach splitting is mediated by polarization gradient of a strongly focused tweezer beam that functions as fictitious magnetic field gradient. The spatial splitting removes the orthogonality of the atomic spatial wavefunctions, thus enables the microwave couplings between the motional states. We obtain coherent Rabi oscillations for up to third-order sideband transitions, in which a high fidelity of larger than 0.99 is obtained for the spin-flip transition on the first order sideband after subtraction of the state preparation and detection error. The Stern–Gerlach splitting is measured at a precision of better than 0.05 nm. This work paves the way for quantum engineering of motional states of single atoms, and may have wide applications in few body physics and ultracold chemistry.</jats:italic> </jats:p>

<jats:p> <jats:italic>Lax pairs regarded as foundations of the inverse scattering methods play an important role in integrable systems. In the framework of bidifferential graded algebras, we propose a straightforward approach to constructing the Lax pairs of integrable systems in functional environment. Some continuous equations and discrete equations are presented.</jats:italic> </jats:p>

<jats:p> <jats:italic>We study the quantum phase transition from a superfluid to a Mott insulator of ultracold atoms in a three-dimensional optical lattice with adjustable filling factors. Based on the density-adjustable Bose–Einstein condensate we prepared, the excitation spectrum in the superfluid and the Mott insulator regime is measured with different ensemble-averaged filling factors. We show that for the superfluid phase, the center of the excitation spectrum is positively correlated with the ensemble-averaged filling factor, indicating a higher sound speed of the system. For the Mott insulator phase, the discrete feature of the excitation spectrum becomes less pronounced as the ensemble-averaged filling factor increases, implying that it is harder for the system to enter the Mott insulator regime with higher filling factors. The ability to manipulate the filling factor affords further potential in performing quantum simulation with cold atoms trapped in optical lattices.</jats:italic> </jats:p>