We prepared ZnO nanostructures using chemical and thermal evaporation methods. The properties of the fabricated nanostructures were studied using scanning electron microscopy, x-ray diffraction, photoluminescence, and electron paramagnetic resonance (EPR) spectroscopy. It was found that the luminescence in the visible region has different peak positions in samples prepared by chemical and evaporation methods. The samples fabricated by evaporation exhibited green luminescence due to surface centers, while the samples fabricated by chemical methods exhibited yellow luminescence which was not affected by the surface modification. No relationship was found between green emission and g ϳ 1.96 EPR signal, while the sample with yellow emission exhibited strong EPR signal.

Epitaxial growth of topological insulator Bi 2 Se 3 thin films on nominally flat and vicinal Si(111) substrates is studied. In order to achieve planner growth front and better quality epifilms, a two-step growth method is adopted for the van der Waal epitaxy of Bi 2 Se 3 to proceed. By employing vicinal Si (111) substrate surfaces, the in-pane growth rate anisotropy of Bi 2 Se 3 is explored to achieve single crystalline Bi 2 Se 3 epifilms, in which threading defects and twins are effectively suppressed. Optimization of the growth parameters has resulted in vicinal Bi 2 Se 3 films showing a carrier mobility of ~ 2000 cm 2 V -1 s -1 and the background doping of ~ 3 × 10 18 cm -3 of the as-grown layers. Such samples not only show relatively high magnetoresistance but also a linear dependence on magnetic field.

The stress states in unintentionally doped GaN epilayers grown on Si͑111͒, 6H-SiC͑0001͒, and c-plane sapphire, and their effects on optical properties of GaN films were investigated by means of room-temperature confocal micro-Raman scattering and photoluminescence techniques. Relatively large tensile stress exists in GaN epilayers grown on Si and 6H-SiC while a small compressive stress appears in the film grown on sapphire. The latter indicates effective strain relaxation in the GaN buffer layer inserted in the GaN/sapphire sample, while the 50-nm-thick AlN buffer adopted in the GaN/Si sample remains highly strained. The analysis shows that the thermal mismatch between the epilayers and the substrates plays a major role in determining the residual strain in the films. Finally, a linear coefficient of 21.1Ϯ3.2 meV/GPa characterizing the relationship between the luminescent bandgap and the biaxial stress of the GaN films is obtained.

A distribution function for localized carriers, f (E, T ) = It reduces to the well-known band-tail and luminescence quenching models under certain approximations.