Table of contents

In situ phosphorus-doped silicon (ISPD) has been actively investigated as a source/drain material. However, defect formation during the epitaxial growth of ISPD layers in 3D structures deteriorate the device performance. In this study, we investigate the elimination of inherent defects in ISPD layers using nanosecond laser annealing (NLA). High-density twin- and stacking-fault defects in the ISPD layers cause strain relaxation and dopant deactivation. The NLA process dramatically reduces or eliminates the defects, consequently generating the strain and electrically activating the incorporated phosphorous. The ISPD epitaxial growth and subsequent NLA processes will be robust methods for the fabrication of advanced 3D devices.

N-type conduction of sputter-deposited polycrystalline Al_0.78Sc_0.22N films was verified by Si ion implantation followed by activation annealing. The activation of dopants was found above an annealing temperature of 800 °C. Under a dose of 2 × 10¹⁵ cm⁻² with an activation annealing at 900 °C, n-type conduction was obtained with Hall mobility and a carrier concentration of 8.6 cm² V⁻¹ s⁻¹ and 8.9 × 10¹⁸ cm⁻³, respectively. The surface of n-type Al_0.78Sc_0.22N films was sensitive to humidity, and two orders of magnitude increase in the sheet resistance were measured. The phenomena can be understood by the formation of depletion from the backside of the film, caused by the balance between the spontaneous polarization and the surface charges.

We demonstrated the marked photoresponsivity enhancement of BaSi₂ epitaxial films by 5 min post-annealing at 850 °C–1000 °C in contrast to those at 600 °C–800 °C. Post-annealing at 1000 °C increased the photoresponsivity up to 9.0 A W⁻¹ at a wavelength of around 800 nm under a bias voltage of 0.5 V applied between the top and bottom electrodes. The hole concentration decreased monotonously with annealing temperature from 8.3 × 10¹⁶ to 5.4 × 10¹⁵ cm^–3, and the mobility exceeded 1000 cm² V^–1 s^–1. The a-axis orientation of the BaSi₂ films was significantly deteriorated at temperatures higher than 800 °C.

Nitrogen-vacancy (N_CV_Si⁻) center in 4H-SiC is spin defect with near-infrared luminescence at room temperature and a promising candidate for quantum technologies. This paper reports on N_CV_Si⁻ center formation in N-doped 4H-SiCs by hydrogen ion irradiation and subsequent thermal annealing. It is revealed photoluminescence for N_CV_Si⁻ centers suddenly appears above the fluence of 5.0 × 10¹⁵ cm⁻² when annealed at 1000 °C. Appearance of a threshold fluence for their formation and/or activation has not been observed for other energetic particle irradiations. The possible mechanism is discussed based on the kinetics of hydrogen-related complexes and the majority carrier depletion caused by irradiation induced damage.

Through first-principles calculations, the photovoltaic properties of Cs₂PdI₆ were investigated and found that (i) Cs₂PdI₆ has a quasi-direct band gap nature, and strong p–d coupling of lower conduction bands is responsible for light electrons; (ii) dominant Pd_i and I_i defects would be produced at a deep level in the band gap which acts as charge trapping states. Thus, should be passivated by suitable external doping, if Cs₂PdI₆ works as a solar cell absorber; (iii) The Cs₂Pd(I_1-xBr_x)₆ alloy is highly miscible. Tunable band gap depending on composition x has a non-linear bowing behavior occurring a lowest band gap at composition Cs₂Pd(I_0.7Br_0.3)₆.

The optical cavity with high quality factor (Q) has been successfully employed to improve the sensitivity of magnetometer. However, complex system design and tedious data processing hinder the progress of application, since synchronized with other equipments and undergo additional post-processing. To overcome the limitation, we propose a single-loop frequency-locking (SLFL) optomagnetic (OM) signal solution system (SLFL-OMSS). SLFL-OMSS solution obtained a scale factor of 0.17 mV μT⁻¹ and the peak sensitivity is 44.1 fT/Hz^1/2 at 200 kHz. SLFL-OMSS reduces the calculating and complexity of the OM sensor system, which provides an efficient way for achieving a high-sensitivity OM sensing.

In a conventional scattering-type scanning near-field optical microscopy setup, the atomic force microscope probe is unable to effectively couple with s-polarized light, resulting in low signal and limited in-plane sensitivity. This study aims to investigate a high-resolution probe with enhanced responsivity to both s- and p-polarized light. Full-wave electromagnetic method of moments simulations are utilized. Simulated near-field spectra on prototypical materials (SiO₂, Si, SrTiO₃), as well as simulated raster scans of a gap nanoantenna, indicate a two order of magnitude increase of the scattering signal for s-polarized incident and detection scheme compared to the conventional probe.

We propose a method for improving the imaging depth of two-photon excitation microscopy using correlated ultrafast intensity fluctuations within pulses. As a proof of principle, we experimentally demonstrate local control of two-photon excitation by using the ultrafast intensity cross-correlation generated by high-gain parametric down-conversion. We show that only the fluorescence intensity emitted from deep inside the fluorescent dye solution can be modulated by harnessing the correlation at ultrashort time scales. It is expected that the influence of the background photons can be suppressed by applying this technique to the two-photon excitation microscopy.

Top-emitting organic light-emitting diodes can achieve high efficiencies due to the strong cavity effect resulting from the relatively thick semi-transparent metallic top electrode. The strong cavity resonance, however, simultaneously brings along negative side effects such as pronounced angular-dependent emission and spectral narrowing. In this work, through numerical simulations, we demonstrate that top-emitting organic light-emitting diodes using a thin Au(2 nm)/Ag(7 nm) top electrode can achieve light-outcoupling efficiency comparable to a thick silver electrode, while reducing spectral narrowing. This can be realized by tuning the organic capping layer thickness without affecting the electrical properties, which can be applied to diodes based on either intrinsic or efficiently doped charge transport layers.

We propose a dual-band metamaterial absorber (MA) based on a stereo resonant structure. The unit cell of the proposed MA is composed of double metallic rings with a rampart on each ring into a dielectric substrate. In contrast to the conventional plane resonator, our proposed metamaterial exhibits wider incident angle stability. The power loss density distribution shows that the standing ramparts play a key role in enhancing the electromagnetic wave absorption. Experimental results verify the wide-incident-angle stability of the absorber. Our proposed strategy paves a new way on developing MAs with wide incident angle stabilities.

In an electron double-slit experiment, an optically zero propagation distance condition (infocus imaging condition), in which the double-slit position was imaged just on the detector plane (image plane), was realized in a 1.2 MV field-emission transmission electron microscope. Interference fringes composed of dot images were controlled by using two electron biprisms. Using a V-shaped double slit, we observed the interference features under the pre-interference condition, interference condition and post-interference condition of electron waves. We conclude that it is possible to observe the interference fringes only when the path information of the individual electrons is not available.

A hyper-lens with planar object/image surfaces and uniform magnification factor is designed based on directional projecting property of optic-null medium (ONM). The proposed planar hyper-lens only requires one homogeneous anisotropic medium, i.e. ONM. We use metallic plates inside -near-zero medium to realize the proposed hyper-lens. 0.191λ₀ resolution is observed (0.238λ₀ can be clearly resolved) in experimental measurement, which consists very well with 3D numerical simulations and verifies the performance of the proposed planar hyper-lens. The planar hyper-lens with uniform pre-designed magnification factor may have some applications in super-resolution imaging technology.

In this work, we demonstrate the contrast enhancement through polarization-resolved pump-probe microscopy, implemented by measuring the spontaneous fluorescence loss induced by stimulated emission. The pump-probe measurement is compared with the conventional fluorescence polarization microscopy. The anisotropy values thus obtained are 0.11 and 0.01, respectively. The contrast improvement is attributed to the multiphoton mechanism in sharpening the point-spread function and the polarization resolving. In addition, the pump-probe technique promises higher temporal resolution in lifetime measurements than time-correlated single-photon counting, enabling more precise determination of the fluorescent molecules' rotational diffusion time constant, which is often in the sub-nanosecond regime.

We propose an optical tweezer with tunable potential wells, by dynamically manipulating the phase gradient of light. Using our proposed method to design holograms, we can obtain desirable phase profiles and intensity distributions of optical traps. Optical force arising from phase gradient creates tunable potential wells for versatile optical nanomanipulation, such as trapping nanoparticles in peanut-shaped optical spots, positioning and shifting nanoparticles in optical gears, and controllable transport, as demonstrated in our experiments. The tunable optical tweezer has several merits including flexible design, easy control and high tunability, which provides a new tool for exploring novel functions in optical nanomanipulation.

To enhance thermal stability while keeping low driven current is difficult in traditional domain wall (DW) motion devices. The increasing of energy barrier for thermal stability inevitably results in the enhancement of driven current. We numerically investigate depinning field (H_depin) and critical current density (J_c) for DW motion as a function of uniaxial magnetic anisotropy (K_u) in vertical DW motion memory with artificial ferromagnet. It is found that H_depin and J_c show different K_u dependence. The results indicate that it is promising to simultaneously achieve high thermal stability and low driven current in artificial ferromagnet based DW motion devices.

Due to the large ionization energy of Mg acceptors in GaN, dynamic punch-through will occur in vertical GaN MOSFETs. To avoid this, higher doping and/or a thicker p-body region should be utilized. However, this increases the channel resistance. In this letter, we suggest that the Poole–Frenkel (P–F) effect has significant impact on dynamic punch-through because of the high electric field in the depletion region under a large bias voltage. Systematic TCAD simulations of simplified vertical GaN MOSFET structures were carried out. We show that the device design considering the P–F effect results in a reduction in the increase in channel resistance.

To adjust the transmission band while keeping the width of a spoof surface plasmon polariton (SSPP) waveguide unchanged, periodic cells with T-shaped conductor branches on both sides are used. By controlling the top lateral strips of branches, the adjustable range of cutoff frequencies can reach approximately 3.5 GHz. Thus, compromised regulation of the field confinement and transmission loss is easily achieved, improving the transmission performance of SSPP modes. By loading open conductor rings onto T-shaped branches to construct a split ring resonator (SRR), a band-rejection filter is realized. When multiple SRRs with gradient lengths are loaded onto one side of the SSPP waveguide, a broad stop band with a relative bandwidth of 18% is achieved. The proposed structures are also advantageous for the miniaturization of microwave circuits.

We report on the growth and characterization of metalorganic vapor-phase epitaxy-grown β-(Al_xGa_1−x)₂O₃/β-Ga₂O₃ modulation-doped heterostructures. Electron channel is realized in the heterostructure by utilizing a delta-doped β-(Al_xGa_1–x)₂O₃ barrier. The electron channel characteristics are studied using transfer length method, capacitance–voltage and Hall measurements. A Hall sheet charge density of 1.06 × 10¹³ cm⁻² and a mobility of 111 cm² V⁻¹ s⁻¹ is measured at room temperature. The fabricated transistor showed a peak current of 22 mA mm⁻¹ and an on–off ratio of 8 × 10⁶. A sheet resistance of 5.3 kΩ/square is measured at room temperature, which includes contribution from a parallel channel in β-(Al_xGa_1–x)₂O₃.

We demonstrate that the critical thickness for Ge-rich strained SiGe layers can be drastically increased by a factor of more then two by means of growth on mesa-patterned Ge-on-Si. The Si_0.2Ge_0.8 layer grown on sub-millimeter mesa Ge-on-Si is fully strained and free from ridge roughness, while the same Si_0.2Ge_0.8 layers grown on unpatterned Ge-on-Si and a Ge substrate are partially strain-relaxed with the surface covered by high-density ridge roughness. This demonstrates that the proposed patterning method can provide thick and stable strained SiGe films as promising templates for realization of strained SiGe-based optoelectronic and spintronic devices.

We applied hydrogen plasma treatment (HPT) on a titanium oxide/silicon oxide/crystalline silicon heterostructure to improve the passivation performance for high-efficiency silicon heterojunction solar cells. To accelerate the time-intensive process optimization of many parameters, we applied Bayesian optimization (BO). Consequently, the optimization of six process parameters of HPT was achieved by BO of only 15 cycles and 10 initial random experiments. Furthermore, the effective carrier lifetime after HPT on the optimized experimental conditions became three times higher compared with that before HPT, which certifies that BO is useful for accelerating optimization of the practical process conditions in multidimensional parameter space.

We propose a novel fabrication technique based on the formation of a Nb protective layer on a MgB₂ thin film and high-temperature post-annealing to increase the critical current density (J_c) of MgB₂ films under an external magnetic field. Analyses of the crystal structure and the composition of the processed MgB₂ films confirmed the suppression of the evaporation and oxidation of Mg by high-temperature annealing above 550 °C. The MgB₂ film annealed at 650 °C exhibited a J_c of 1.62 MA cm⁻² under 5 T, which is the highest reported value for MgB₂ films, wires, and bulk samples to date.

The effect of flash lamp annealing on the crystal growth of amorphous germanium-tin (GeSn) layer deposited on Ge-on-insulator wafer was investigated. It was found that the presence of Sn in the amorphous Ge significantly promoted solid-phase growth (SPG). The diffusion of Sn during the SPG of GeSn was completely suppressed owing to milli-second thermal processing, providing a high-quality GeSn layer with Sn content of 13%, which far exceeds the equilibrium solid solubility limit (∼1%). The fabricated GeSn/Ge-on-insulator wafer exhibited improved infrared absorption beyond 2000 nm, which would be a suitable platform for near-infrared image sensors based on group-IV materials.

Main-chain-scission-type resists have been widely used for the fabrication of nanodevices. A copolymer consisting of methyl α-chloroacrylate and α-methylstyrene, known as the ZEP series of ZEON, is a popular main-chain-scission-type positive-tone resist. In this study, the dissolution kinetics were investigated using the ZEP series to clarify the effects of the molecular weight distribution and developer on the dissolution kinetics of the main-chain-scission-type resist. The thickness of the transiently swelling layer in hexyl acetate development was less than that in pentyl acetate development. The thickness of the transiently swelling layer depended on the molecular weight distribution of resist polymers.

Dihydroxybenzoic acid (DHB) crystal layers were formed via mist deposition. Crystal layers exhibiting whiskers measuring a few hundred micrometers were formed at a nozzle temperature of 200 °C. DHB crystal layers exhibited strong absorbance in the ultra-violet wavelength regions, and Raman spectroscopy confirmed their vibrational property. The lipid component was analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry imaging using a DHB crystal layer as the mass ionization assist agent. Cholesterols, diacylglycerides, and triglycerides were detected as sodium adducts. By preventing heterogeneous co-crystallization with analytes, mass images were clearer than when using the conventional aerosol spray method.

Electro-optic (EO) sampling is employed to measure the electric field profiles generated by a relativistic electron bunch along the propagation and in the radial directions. The longitudinal (temporal) profile is investigated by changing the time delay between the electron bunch and the pulsed probe laser, while the transverse (radial) profile is acquired by laterally shifting the path of the electron bunch. Experimental results show good agreement with three-dimensional particle-in-cell calculations. We demonstrated a promising method to simultaneously obtain the longitudinal and transverse beam sizes by utilizing the detected spatio-temporal electric field distribution around the electron bunch.

A near-field vector sensing (VS) strategy is developed for three-dimensional (3D) large-scale hybrid sound absorption based on a lightweight structure. By simultaneously detecting sound pressures and normal particle velocities at discrete positions on the absorbing surface, the reflected sound power is minimized to obtain the optimal secondary excitation. For the one-dimensional case, low-frequency quasi-perfect absorption could be realized by one-point VS. For the 3D case (at the incident angle of 20°), the optimized two-point VS is able to realize commendable broadband absorption from 50 to 800 Hz and extraordinary absorption between 50 and 300 Hz.

The recent outbreak of a novel coronavirus (SARS-CoV-2) has caused substantial public health issues worldwide. Cold atmospheric plasma (CAP) has shown its potential application in sterilization. It would be interesting to check the possible effect of CAP on the structure of the C-terminal domain of SARS-CoV-2 (SARS-CoV-2-CTD) spike protein and the interaction SARS-CoV-2-CTD with human angiotensin-converting enzyme 2 (hACE2). Therefore, we performed molecular dynamics simulations to calculate the root-mean-square deviation, root-mean-square fluctuation, principal component analysis and solvent-accessible surface area of SARS-CoV-2-CTD and the SARS-CoV-2-CTD/hACE2 complex with and without possible oxidation.

A combination of classical molecular dynamics (MD) simulation and ab initio fragment molecular orbital (FMO) calculation was applied to a complex formed between the main protease of the new coronavirus and the inhibitor N3 to calculate interactions within the complex while incorporating structural fluctuations mimicking physiological conditions. Namely, a statistical evaluation of interaction energies between N3 and amino acid residues was performed by processing a thousand of structure samples. It was found that relative importance of each residue is altered by the structural fluctuation. The MD-FMO combination should be promising to simulate protein related systems in a more realistic way.