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In this work, we demonstrate the epitaxial growth of a gallium-nitride (GaN) buffer structure qualified for 1200 V applications on 200 mm engineered poly-AlN substrates with hard breakdown >1200 V. The manufacturability of a 1200 V qualified buffer structure opens doors to high voltage GaN-based power applications such as in electric cars. Key to achieving the high breakdown voltage is careful engineering of the complex epitaxial material stack in combination with the use of 200 mm engineered poly-AlN substrates. The CMOS-fab friendly engineered poly-AlN substrates have a coefficient of thermal expansion (CTE) that closely matches the CTE of the GaN/AlGaN epitaxial layers, paving the way for a thicker buffer structure on large diameter substrates, while maintaining the mechanical strength of the substrates and reaching higher voltage operation.

High-temperature processing steps are frequently used in manufacture of AlGaN/(AlN/)GaN high electron mobility transistors (HEMTs). The thermal budgets drive Al diffusion into the GaN channel, increase alloy disorder scattering (ADS) of the two-dimensional-electron-gas (2DEG), and degrade the 2DEG mobility. By correlating the ADS to device thermal budget, we propose an analytical model to calculate the ADS limited mobility as a function of Al diffusion lengths (LD,Al) in AlGaN/(AlN/)GaN HEMTs. The simulation indicates that the ADS is a significant mobility degradation mechanism whose scattering rate increases with the 2DEG density and the LD,Al. The findings explain the generally observed trends in the literature that the 2DEG mobility and sheet resistances of GaN heterostructures degrade with increased thermal budgets, especially after >900 °C processing.

The characteristic oxygen diffusion in HfO2∕SiO2∕Si structure during the annealing in oxygen has been investigated by high-resolution Rutherford backscattering spectroscopy in combination with oxygen isotope substitution at 900°C in 0.1Torr O218. The observed O18 profile suggests that oxygen molecules are decomposed into atomic oxygen in the HfO2 layer and diffuse through the oxide layer via exchange mechanism. This is also supported by the observed activation energy of ∼0.6eV for the growth of the interfacial SiO2 layer.

In this paper, two kinds of bi-layered chiral metamaterials were proposed to enhance the asymmetric transmission effects for circular polarized electromagnetic waves which are only found in planar chiral metamaterials according to previous studies. It was found that the magnitude of the asymmetric transmission parameters mainly depends on the distances between the two metal layers. With appropriate distance, the asymmetric transmission parameter for circular polarized electromagnetic waves can increase to 0.6. Moreover, both proposed configurations show no asymmetric transmission for linear polarized electromagnetic waves which is widely studied in other bi-layered metamaterials.

Influence of oxygen vacancies (VO’s) on electronic structures and field emission properties of TiO2 nanotubes (NTs) is investigated by first-principle calculations. It is demonstrated that the formation of 3-fold coordinated VO gives rise to two shallow donor states below the conduction band minimum. Whereas one shallow coupled with another deep donor states appears in the case of a 2-fold bridging vacancy located on the outer side-wall of TiO2 NT. VO’s are found to greatly reduce the barrier for electron extracting. These results can explain why, experimentally, TiO2 NTs with intrinsic VO can overcome the high barrier of electron affinity and exhibit an excellent field-emission performance.

Water is a persistent background in virtually all biosensors, yet is difficult to quantify. We apply an interferometric optical balance to measure water film accumulation from air onto several types of prepared silica surfaces. The optical balance uses in-line common-path interferometry with balanced quadratures to measure the real-time accumulation of molecular films. The accumulated water thickness is sensitive to ambient conditions, with thicknesses that vary from picometers up to nanometers, even on hydrophobic silanized surfaces. These results demonstrate that water adsorption contributes an excess signal in dry label-free protein microarray optical biosensors and presents a fundamental limit to assay sensitivity.

A molecularly thin dielectric film on a multilayer substrate can be treated as an additive perturbation of the substrate reflection coefficient r, for which the perturbation depends only on r and the optical properties of the film. This general result is applied to the problem of graphene on arbitrary substrates that seek to maximize the film contrast. We define clarity to describe the graphene image quality in the presence of charge-coupled device noise. A substrate with r=1 produces the highest graphene clarity in most practical situations.

Shear bands in metallic glasses subject to uniaxial loading such as tension and compression exhibit the inclination angle different from 45° on the maximum resolved shear stress plane with respect to the loading axis. The cause is often attributed to the effective normal stress acting on the shear plane, which also suggests Coulomb–Mohr yield criterion for metallic glasses. We show here that this argument is conceptually ill justified. Instead, shear band inclination angle can be described by a simple model taking into consideration the volume dilatation and the pressure effects.

We present a nonfluorescent protein microarray, the land-contrast BioCD, on which interferometric contrast is induced by a patterned substrate rather than by patterned protein. The substrate is an oxidized silicon wafer with etched spot patterns. Within the spots the SiO2 thickness is 140 nm and on the land it is 77 nm. The spot and the land have equal reflectance but opposite interferometric quadrature responses for protein layer. Protein is evenly immobilized on the entire chip and detected by reflectometry. The contrast between spot and land is directly converted to protein thickness.

MgO nanocrystalline powders prepared by sol-gel method present room-temperature ferromagnetism, whereas MgO bulk exhibits diamagnetism. The vacuum annealing of MgO nanocrystalline powders reduces ferromagnetism. The observed room-temperature ferromagnetism in MgO nanocrystalline powders possibly originates from Mg vacancies at/near the surfaces of nanograins. Mg vacancies can induce local magnetic moments. Large concentrations of Mg vacancies at the surfaces of nanograins possibly establish magnetic percolation.

Strain relaxation of SiGe/Si(110) has been studied by x-ray reciprocal space mapping. To get information about the in-plane lattice mismatch in different directions, two-dimensional maps around, e. ...

We investigate second-harmonic generation (SHG) when light obliquely launches upon optical superlattices, which is optimally devised with the use of a simulated annealing method and can achieve simultaneously a multiple wavelength SHG with a high conversion efficiency. We find that the conversion efficiency at the oblique incidence of light can be increased significantly, compared to that at the normal incidence of light.

We present a general solution of second harmonic generation (SHG) in one-dimensional (1D) inhomogeneous systems. The structure consists of 1D multiple photonic quantum wells (PQWs) made of optical nonlinear material. The optimal arrangement of the polarization directions of the ferroelectric domains in multiple PQWs is determined by a simulated annealing method. We find that the conversion efficiency of SHG can be significantly enhanced when the fundamental wave frequency is aimed at one of the defect states. By tuning the polarization directions of the domains, the conversion efficiencies of “forward” and “backward” SHGs can be flexibly changed.