We study properties of the line at 3.33 eV observed in photoluminescence (PL) emission spectra of various ZnO films prepared using pulsed laser deposition method. The influence of deposition parameters, such as oxygen pressure, laser fluence, post-annealing, and electric field exposure on intensity of this luminescence band has been investigated. The recombination characteristics are probed by temperature and excitation dependent PL spectroscopy. The obtained experimental data suggest that the 3.33 eV luminescence line in ZnO depends strongly on surface band bending and originates from recombination of bound excitons (BEs) complex located near the surface and grain boundaries. The anomalously small thermal activation energy of BE in comparison with the localization energy is explained by decreasing of the interface barrier. Possible nature of defects that bind free excitons and cause the 3.33 eV emission line in ZnO is proposed.

Schottky diodes based on metal–semiconductor (MS) and metal–insulator–semiconductor (MIS) configurations are nowadays widely regarded as key components for the realization of a number of improved electronic and optoelectronic functions. In this regard, hafnium dioxide (HfO₂) nanostructures were processed through a facile chemical route for application in MIS Schottky diodes. Their monoclinic phase and micro-structural characteristics were studied in detail using the X-ray diffraction, Raman and electron microscopic measurements. The nanostructures were studied to evolve in form of particulate structures at an average scale of 8–10 nm. The low-temperature photoluminescence measurements revealed the optical activity of HfO₂ to spread across the blue region of electromagnetic spectrum. And their origin has been related to the transitions taking place across the intermediary energy levels established by the oxygen related vacancies. The power of incident laser irradiation was also noted to have a significant influence on the surface-state related defect emissions. The electrical properties of HfO₂ were studied using the Bode, Nyquist and Mott–Schottky type plots extracted from the impedance spectroscopic measurements. MIS Schottky diode architectures were finally fabricated using the HfO₂ thin films that were spin cast on n-Si. A significant improvement in the diode characteristics were noted for the heat treated devices, suggesting the improved tunnelling and limiting of charge leakages across the integrated heterojunctions.

We have presented a study of the bipolar resistance switching characteristics in the Ag/ZnO/Pt cell. This switching is accompanied by a change in intensity of the photoluminescence emission at 3.33 eV which is attributed to zinc vacancy related transitions in ZnO film. Besides voltage-driven resistance switching phenomena, a transition from a high-resistance state to a lower one is observed under laser illumination at low temperature. These results demonstrate that the bipolar resistance switching can originate due to an electron trapping/de-trapping process at zinc-vacancy defects localized in the interface layer. The Mott metal-insulator transition is proposed as a possible mechanism of the memory effect.

The thermal conductivity of a single ZnO nanowire with diameter of ~150 nm was measured using a four-point-probe 3omega method over a temperature range of 140-300 K. The measured ther- mal conductivity of ZnO nanowire is strongly reduced compared to bulk ZnO crystal due to the enhanced phonon-boundary and impurity (isotope) scattering. The maximum of the thermal conductivity is shifted to a higher temperature than that of bulk counterpart. Temperature dependent measurements show that beyond the low-temperature maximum, the thermal conductivity decreases with temperature as T(-1.5) indicating strong impurity (isotope) scattering at intermediate and high temperatures.