GaN on Si plays an important role in the integration and promotion of GaN-based wide-gap materials with Si-based integrated circuits (IC) technology. A series of GaN film materials were grown on Si (111) substrate using a unique plasma assistant molecular beam epitaxy (PA-MBE) technology and investigated using multiple characterization techniques of Nomarski microscopy (NM), high-resolution X-ray diffraction (HR-XRD), variable angular spectroscopic ellipsometry (VASE), Raman scattering, photoluminescence (PL), and synchrotron radiation (SR) near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. NM confirmed crack-free wurtzite (w-) GaN thin films in a large range of 180–1500 nm. XRD identified the w- single crystalline structure for these GaN films with the orientation along the c-axis in the normal growth direction. An optimized 700 °C growth temperature, plus other corresponding parameters, was obtained for the PA-MBE growth of GaN on Si, exhibiting strong PL emission, narrow/strong Raman phonon modes, XRD w-GaN peaks, and high crystalline perfection. VASE studies identified this set of MBE-grown GaN/Si as having very low Urbach energy of about 18 meV. UV (325 nm)-excited Raman spectra of GaN/Si samples exhibited the GaN E₂(low) and E₂(high) phonon modes clearly without Raman features from the Si substrate, overcoming the difficulties from visible (532 nm) Raman measurements with strong Si Raman features overwhelming the GaN signals. The combined UV excitation Raman–PL spectra revealed multiple LO phonons spread over the GaN fundamental band edge emission PL band due to the outgoing resonance effect. Calculation of the UV Raman spectra determined the carrier concentrations with excellent values. Angular-dependent NEXAFS on Ga K-edge revealed the significant anisotropy of the conduction band of w-GaN and identified the NEXAFS resonances corresponding to different final states in the hexagonal GaN films on Si. Comparative GaN material properties are investigated in depth.

Coherent diffractive imaging (CDI), with its lensless geometry and theoretically perfect transfer function, is considered as one of the most promising paradigms to achieve the Abbe resolution limit. However, recent advances on pushing the resolution limit in high-numerical-aperture (NA) CDIs has thus far been challenging. Here, we report a nearly 0.9NA CDI with an optimized imaging factor (k = 0.501), pushing the Abbe resolution diffraction limit for the first time in ultra-high-NA scenarios. Leveraging this the ultra-high NA and the Abbe-limit k-factor, we demonstrate a record-high imaging resolution of 0.57 λ for CDIs. Our approach builds upon a novel computational framework termed ‘rigorous Fraunhofer diffraction’ that eliminates the Ewald sphere effect in CDIs, particularly for high NAs. Our framework transforms the general challenge of high-NA, resolution-limited CDIs from relying on approximate and complicated geometric corrections to a solvable problem through rigorous model-based computation.

Strain engineering has been extensively explored to modulate the various intrinsic properties of flexible inorganic semiconductor films. However, experimental characterization of tensile and compressive strain-induced modulation of optoelectronic properties and their differences has not been easily implemented in flexible inorganic semiconductor films. Herein, the strain-dependent structural, optical, and optoelectronic properties of flexible ZnO films under pre-tensile and pre-compressive strains are systemically investigated by a Mueller matrix ellipsometry-based quantitative characterization method combined with x-ray diffraction and first-principle calculation. With extended prestress-driven deposition processing under bi-direction bending modes, pre-tensile and pre-compressive strains with symmetric magnitudes can be achieved in flexible ZnO films, which allows precise observation of the strain-driven asymmetric modulation of optoelectronic properties. When the applied prestrain varies approximately equally from 0% (baseline) to −0.99% (compression) and 1.07% (tensility), respectively, the relative changes for the c-axis lattice constant are 0.0133 and 0.0104 Å, respectively. Meanwhile, the dependence factors of the bandgap energy on the pre-compression and pre-tensile strains were determined as −0.0099 and −0.0156 eV/%, respectively, and the complex refractive index also presents an asymmetric varying trend. With the help of the strain–stress analysis and the first-principle calculation, the intriguing asymmetric strain-optical modulation effect could be attributed to the biaxial strain mechanism and the difference in the deformation potential between the two prestrain modes. These systematic investigation consequences are thus promising as a basis for the booming applications of the flexible inorganic semiconductor ensemble.

In sub-28-nm nodes, existing optical critical dimension (OCD) metrology tools are challenging to simultaneously and thoroughly meet the metrology requirements of the wafer-level nanostructures in terms of measurement precision, efficiency, and robustness. To tackle the challenge, we propose a Mueller matrix ellipsometry (MME)-based integrated OCD metrology (IM OCD) technique to achieve fast, accurate, and robust in-line metrology of wafer-level nanostructures at advanced nodes. The MME probe is integrated into the integrated circuit (IC) process platform via a polar-coordinate stage, allowing high-throughput measurement of the geometrical parameters of nanostructures with 144 wafers per hour. Meanwhile, we propose an ensemble learning-fused regression (ELFR) approach to improve the solution to the typical inverse problem in nanostructure metrology, effectively addressing the fluctuations in measurement sensitivity and precision caused by the measurement azimuth variations in the IM OCD. The essential of the ELFR approach is the weighted averaging of the respective results from ridge regression (RR) based on the Levenberg-Marquardt algorithm and from bagging-mode neural networks (BMNNs). It improves the metrology results of wafer-level nanostructures to an ultrahigh coefficient of determination better than 0.93, an average deviation, and a maximum deviation less than 1.0 and 2.0 nm, respectively. Characterizations of wafer-level shallow trench isolation (STI) and interconnect-layer nanostructures have demonstrated the feasibility and effectiveness of the proposed MME-based IM OCD method, especially the capability of the ELFR approach to suppress azimuthal-dependent errors.

Numerical electromagnetic field solvers are significant for nanophotonic and photoelectronic technology, especially for computational imaging, metasurface, and biomedical microscopy, in which large-scale simulations serve as the core. Conventionally, these simulations use absorbing boundary conditions (ABC) to simulate open-domain systems. However, the existing ABCs require large memory to sufficiently suppress reflection at boundaries, which is prohibitive for large-scale applications. This work proposes a virtual absorbing boundary condition based on the angular spectrum method (ASM) to reduce the memory usage of ABC. The ASM is used to cover the polluted field in the boundary region, which eliminates the need to store the field in the boundary region. Combined with the Fourier transforms-based modified Born series, memory usage can be reduced to a level close to the theoretical limit. This proposed method offers a substantial boost for applications related to large-scale simulations and memory-constrained devices like GPU.