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AlGaN/GaN metal-oxide-semiconductor (MOS) capacitor structures using atomic layer deposited high-dielectric-constant (High-k) Al2O3/La2O3 bilayer films as dielectric have been investigated using high-frequency capacitance-voltage measurement. The stable thickness and uniform surface morphology of the bilayer films with different La/Al deposition cycle ratio (La/Al ratio) were observed after rapid thermal annealing by spectroscopic ellipsometry and atomic force microscopy, respectively. We have found that with a decrease of the La/Al ratio, the dipole layer observed by X-ray photoelectron spectroscopy at Al2O3/La2O3 interfaces is close to the surface of semiconductor and the flat band voltage shifts to the negative direction. Furthermore, the dramatic drop in dielectric constant of the films as La/Al ratio decrease was caused by the formation of La(OH)3 in La2O3. Finally, the reason for the flat band voltage shifts, which is based on the dielectric constant of Al2O3 and La2O3 comprising the position of dipole layer in the dielectric films, is proposed.

We present a QCD study on $B, D\to\pi$ semileptonic transitions at zero momentum transfer and an estimate of magnitudes of the associated CKM matrix elements. Light cone sum rules (LCSRs) with chiral correlator are applied to calculate the form factors $f^{B\to \pi}_+(0)$ and $f^{D\to \pi}_+(0)$. We show that there is no twist-3 and-5 component involved in the light-cone expansions such that the resulting sum rules have a good convergence and offer an understanding of these form factors at twist-5 level. A detailed $\mathcal{O}(\alpha_s)$ computation is carried out in leading twist-2 approximation and the $\bar{MS}$ masses are employed for the underlying heavy quarks. With the updated inputs and experimental data, we have $f^{B\to \pi}_+(0)=0.28^{+0.05}_{-0.02}$ and $|V_{ub}|=(3.4^{+0.2}_{-0.6}\pm0.1\pm0.1)\times10^{-3}$; $f^{D\to \pi}_+(0)=0.62\pm0.03$ and $|V_{cd}|=0.244\pm0.005\pm0.003\pm0.008$. As a by-product, a numerical estimate for the decay constant $f_D$ is yielded as $f_{D}=190^{+12}_{-11}\mathrm{MeV}$., Comment: 23 pages, 4 figures, 3 tables, published in JHEP

Within the QCD factorization formalism, we study the possible impacts of the nonuniversal ${Z}^{\ensuremath{'}}$ model, which provides a flavor-changing neutral current at the tree level, on rare decays $B\ensuremath{\rightarrow}{K}_{0}^{*}(1430)\ensuremath{\pi}$. Under two different scenarios, Scenerio-1 (S1) and Scenerio-2 (S2), for identifying the scalar meson ${K}_{0}^{*}(1430)$, the branching ratios, $CP$ asymmetries, and isospin asymmetries are calculated in both the standard model and the family nonuniversal ${Z}^{\ensuremath{'}}$ model. We find that the branching ratios and $CP$ asymmetries are sensitive to weak annihilation. In the standard model, with ${\ensuremath{\rho}}_{A}=1$ and ${\ensuremath{\phi}}_{A}\ensuremath{\in}[\ensuremath{-}30\ifmmode^\circ\else\textdegree\fi{},30\ifmmode^\circ\else\textdegree\fi{}]$, the branching ratios of S1 (S2) are smaller (larger) than the experimental data. Adding the contribution of the ${Z}^{\ensuremath{'}}$ boson in two different cases (Case I and Case II), for S1, the branching ratios are still far away from experiment. For S2, in Case II, the branching ratios become smaller and can accommodate the data; in Case I, although the center values are enhanced, they can also explain the data with large uncertainties. Similar conclusions are also reached for $CP$ asymmetries. Our results indicate that S2 is more favored than S1, even after considering new physics effects. Moreover, if there exists a nonuniversal ${Z}^{\ensuremath{'}}$ boson, Case II is preferred. All results can be tested in the LHC-b experiment and forthcoming super-$B$ factory.