We report the experimental results of the valence band offset at a ZnO/GaN (0001) heterointerface. The ZnO/GaN (0001) heterointerface is prepared by growing a ZnO layer on (0001) ${\mathrm{GaN/Al}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}},$ in which the ZnO layer is epitaxially deposited by plasma-assisted molecular-beam epitaxy, while the GaN template is prepared by metalorganic chemical-vapor deposition. Ex situ ultraviolet and x-ray photoelectron spectroscopy have been used to measure the valence band offset ${\mathrm{\Delta E}}_V.$ The photoelectron spectroscopy measurements are done before and after ${\mathrm{Ar}}^{\mathrm{+}}$ ion cleaning of the surfaces. Type-II band alignments with band offsets of ${\mathrm{\Delta E}}_V\text{=1.0\hspace{0.05em}}\mathrm{eV}$ (before cleaning) and 0.8 eV (after cleaning) with the valence band maximum of GaN being placed above that of ZnO are obtained.

Transparent conducting polycrystalline Ga-doped ZnO (GZO) films with different thicknesses were deposited on glass substrates at a substrate temperature of $200°\text{C}$ by ion-plating deposition with direct current arc-discharge. The dependences of crystal structure, electrical, and optical properties of the GZO films on thickness have been systematically studied. Optical response due to free electrons of the GZO films was characterized in the photon energy range from 0.73 to 3.8 eV by spectroscopic ellipsometry (SE). The free electron response was expressed by the simple Drude model combined with the Tauc–Lorentz model. From the SE analysis and the results of Hall measurements, electron effective mass, $m^{\ast }$ , and optical mobility, ${\mu }_{\text{opt}}$ , of the GZO films were determined, based on the assumptions that the films are homogeneous and optically isotropic. By comparing the ${\mu }_{\text{opt}}$ and Hall mobility, ${\mu }_{\text{Hall}}$ , an indication on the effect of ingrain and grain boundary scattering limiting the electron mobility has been obtained. Moreover, the variation in scattering mechanism causing thickness dependence of ${\mu }_{\text{Hall}}$ was correlated with the development of polycrystalline grain structure.

Optical conductivity spectra of single crystals of the perovskite-type ${3d}^1$ metallic alloy system ${\mathrm{Ca}}_{1-x}{\mathrm{Sr}}_x{\mathrm{VO}}_3$ have been studied to elucidate how the electronic behavior depends on the strength of the electron correlation without changing the nominal number of electrons. The reflectivity measurements were made at room temperature between 0.05 eV and 40 eV. The effective mass deduced by the analysis of the Drude-like contribution to the optical conductivity and the plasma frequency do not show critical enhancement, even though the system is close to the Mott transition. Besides the Drude-like contribution, two anomalous features were observed in the optical conductivity spectra of the intraband transition within the $3d$ band. These features can be assigned to transitions involving the incoherent and coherent bands near the Fermi level. The large spectral weight redistribution in this system, however, does not involve a large mass enhancement.