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The effects of oxygen plasma treatment on epitaxial ZnO thin films grown by molecular beam epitaxy were studied. The Au–ZnO–In junction exhibiting ohmic behaviour before the treatment gradually changes to a Schottky junction with the increase in oxygen plasma treatment time. The crystallinity and the surface microstructure did not change to any great extent after the treatment. However, the x-ray photoelectron spectroscopy studies show the removal of conductive OH layer from the surface of ZnO films and the current–voltage characteristics of Au–ZnO–In junction exhibit the rectifying behaviour after oxygen plasma treatment. The fabricated Au–ZnO–Au ultraviolet (UV) detector was successfully tested and was observed to be sensitive to the two UV sources used. The photoresponsivities of the UV detector for the irradiation of two different power densities 350 (λ = 356 nm) and 420 µW cm−2 (λ = 254 nm) are 13.5 A W−1, 15.3 A W−1 at 5 V and 128.9 A W−1, 160 A W−1 at 10 V, respectively.

High quality gallium doped ZnO ͑Ga:ZnO͒ thin films were grown on c-Al 2 O 3 ͑1000͒ by plasma-assisted molecular beam epitaxy, and Ga concentration N Ga was controlled in the range of 1 ϫ 10 18-2.5ϫ 10 20 /cm 3 by adjusting/changing the Ga cell temperature. From the low-temperature photoluminescence at 10 K, the donor bound exciton I 8 related to Ga impurity was clearly observed and confirmed by comparing the calculated activation energy of 16.8 meV of the emission peak intensity with the known localization energy, 16.1 meV. Observed asymmetric broadening with a long tail on the lower energy side in the photoluminescence ͑PL͒ emission line shape could be fitted by the Stark effect and the compensation ratio was approximately 14-17% at N Ga ജ 1 ϫ 10 20 /cm 3. The measured broadening of photoluminescence PL emission is in good agreement with the total thermal broadening and potential fluctuations caused by random distribution of impurity at N Ga lower than the Mott critical density.

A transparent active matrix organic light emitting diode (AMOLED) display based on a bottom emission structure, which is best for large-sized OLED displays, has been fabricated. The transparent AMOLED display shows an image only to its bottom side, and background images can be seen through the transmissive windows. Pixel layout of the conventional bottom emission structure has been redesigned to merge transmissive openings to a single window per each pixel for higher transmissivity. A prototype of the transparent AMOLED display demonstrated 27% transmissivity and 100% NTSC color gamut.