Zinc oxide (ZnO) films were grown on sapphire (112̄0) substrates by molecular beam epitaxy under oxygen radical irradiation. The effect of the growth conditions, including the Zn/O ratio supplied to the film surface, on the electrical properties of ZnO films was studied in relation to the film morphology. We found that the growth rate strongly depended on the Zn flux from the Knudsen cell and the optimum condition for high growth rate was very narrow. The grain size in the lateral direction increased with increasing growth rate in the thickness direction. The increase in growth rate, especially in the lateral direction, resulted in the carrier mobility increasing up to 42 cm2 V−1 s−1. The carrier concentration N was sensitive to the substrate temperature, while the value of N was not sensitive to the source supplying ratio Zn/O. We discuss the decrease of the carrier concentration with increasing substrate temperature in regard to the formation of nonequilibrium defects.
Since the seminal observation of room-temperature laser emission from ZnO thin films and nanowires, numerous attempts have been carried out for detailed understanding of the lasing mechanism in ZnO. In spite of the extensive efforts performed over the last decades, the origin of optical gain at room temperature is still a matter of considerable discussion , .We show that ZnO microcrystals with a size of a few micrometers exhibit purely excitonic lasing at room temperature without showing any symptoms of electron-hole plasma emission. We then present the distinct experimental evidence that the room-temperature
Schottky junctions made from platinum and niobium-doped strontium titanate (SrTiO3:Nb) were investigated by hard X-ray photoemission (HXPES) and through a band bending behavior simulation using a phenomenological model, which assumes a decrease in dielectric constant due to an electric field. Thus, we confirmed that the observed HXPES spectra at relatively high temperatures, e.g., >250 K, were well simulated using this phenomenological model. In contrast, it was inferred that the model was not appropriate for junction behavior at lower temperatures, e.g., <150 K. Therefore, a reconstruction of the phenomenological model is necessary to adequately explain the dielectric properties of SrTiO3.
Scandium nitride (ScN) films were grown on (100) MgO single crystals by a molecular beam epitaxy method. The effects of growth conditions, including [Sc]/[N] ratio, growth temperature, and nitrogen radical state, on the electrical properties of the ScN films were studied. The ScN films comprised many small columnar grains. Hall coefficient measurements confirmed that the ScN films were highly degenerate n-type semiconductors and that the carrier concentration of the ScN films was sensitive to the growth temperature and the nitrogen radical states during the film growth. The carrier concentrations of the ScN films ranged from 1019–1021 cm−3 while the Hall mobilities ranged from 50–130 cm2·V−1·s−1 for undoped films. The temperature-dependent Hall coefficient measurements showed that the carrier concentration is nearly independent of temperature, indicating that the change in resistivity with temperature is explained by a change in the Hall mobility. The temperature-dependence of the Hall mobility was strongly affected by the growth conditions.
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