The optical spectra of zinc aluminate (ZnAl 2 O 4 ), zinc gallate (ZnGa 2 O 4 ), and zinc aluminogallate (ZnAlGaO 4 ) spinel powders were studied at wavelengths in the range of 250-900 nm using reflectance spectroscopy. The ZnAl 2 O 4 and ZnGa 2 O 4 powders were synthesized by using conventional ceramic processing techniques and had systematic variations in the molar ratio of ZnO to M 2 O 3 (M = Al or Ga). The cubic spinel crystal structure of each composition was confirmed via powder X-ray diffractometry. The ZnAl 2 O 4 powders showed optical properties in the ultraviolet wavelength region and had combined characteristics that were similar to that of ZnO (wurtzite structure) and Al 2 O 3 (corundum structure), which result from the similar local environments of the zinc and aluminum cations within the cubic spinel crystal structure. A mechanically induced optical absorption (optomechanical effect) in the ultraviolet wavelength region was also observed in ZnAl 2 O 4 . The ZnGa 2 O 4 powder followed a similar behavior, with the exception that the optomechanical effect did not occur in the gallate. The ZnAlGaO 4 showed optical spectra that were intermediate to that of the endpoint compositions.

An electron trap of 0.3 eV depth was characterized in hydrothermally grown, single-crystal zinc oxide using deep-level transient spectroscopy. Specimens were fabricated with Ag Schottky contacts on (0001) surfaces. The capture cross section was determined to be 2.6×10−14 cm2. The defect is a native donor and is attributed to a singly ionized oxygen vacancy V•O.

Three types of commercial zinc oxide varistor materials were examined using admittance spectroscopy between 30 and 350 K. Maxima in the ac conductance at frequencies from 1 to l~ ~Hz are obs~rved. ~he maxima are interpreted as arising from electron traps located wlthm the depletion regIOns of double Schottky barriers at ZnO-ZnO grain boundaries. Two traps are observed in each material and are likely to be from common origin. The trap energies are found to be 0.17 and 0.33 e V below the conduction-band edge. The traps are likely to be associated with native defects in ZnO and may influence device characteristics such as voltage overshoot.4186