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We report exciton-polariton condensation in a new family of fully hybrid ZnO-based microcavity demonstrating the best-quality ZnO material available (a bulk substrate), a large quality factor (~4000) and large Rabi splittings (~240 meV). Condensation is achieved between 4 and 300 K and for excitonic fractions ranging between 17% and 96%, which corresponds to a tuning of the exciton-polariton mass, lifetime, and interaction constant by 1 order of magnitude. We demonstrate mode switching between polariton branches allowing, just by controlling the pumping power, to tune the photonic fraction by a factor of 4.

Choosing metasurface building blocks to encircle a singularity following an arbitrarily closed trajectory in parameter space, we engineer topologically-protected full 2𝜋 − phase on a specific reflected polarization channel. The ease of implementation together with its compatibility with other phase-addressing mechanisms bring topological properties into the realm of industrial applications at optical frequencies, and prove that metasurface technology represents a convenient test bench to study and validate topological photonic concepts.

The bandgap and band-edge effective mass of single crystal cadmium oxide, epitaxially grown by metal-organic vapor-phase epitaxy, are determined from infrared reflectivity, ultraviolet/visible absorption, and Hall effect measurements. Analysis and simulation of the optical data, including effects of band nonparabolicity, Moss-Burstein band filling and bandgap renormalization, reveal room temperature bandgap and band-edge effective mass values of 2.16± 0.02 eV and 0.21± 0.01m 0 respectively.

The valence-band density of states of single-crystalline rock-salt CdO͑001͒, wurtzite c-plane ZnO, and rocksalt MgO͑001͒ are investigated by high-resolution x-ray photoemission spectroscopy. A classic two-peak structure is observed in the VB-DOS due to the anion 2p-dominated valence bands. Good agreement is found between the experimental results and quasi-particle-corrected density-functional theory calculations. Occupied shallow semicore d levels are observed in CdO and ZnO. While these exhibit similar spectral features to the calculations, they occur at slightly higher binding energies, determined as 8.8 eV and 7.3 eV below the valence band maximum in CdO and ZnO, respectively. The implications of these on the electronic structure are discussed.

An energy gap between the valence and the conduction band is the defining property of a semiconductor, and the gap size plays a crucial role in the design of semiconductor devices. We show that the presence of a two-dimensional electron gas near to the surface of a semiconductor can significantly alter the size of its band gap through many-body effects caused by its high electron density, resulting in a surface band gap that is much smaller than that in the bulk. Apart from reconciling a number of disparate previous experimental findings, the results suggest an entirely new route to spatially inhomogeneous band-gap engineering.

In contrast to conventional semiconductors, native defects, hydrogen impurities, and surface states are all found to be donors in n-type CdO. Using this as a model system, the electrical behaviors of defects, dopants, and surface states in semiconductors are unified by a single energy level, the charge neutrality level, giving much insight into current materials and allowing a band-structure engineering scheme for obtaining desired custom electronic properties in new compound semiconductors.

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