The Study Of Ultraviolet Emission Based On The Zinc Oxide Material

Dongxu Zhao (Condensed Matter Physics)Directed by Prof. Dezhen Shen and Prof. Yichun Liu Zinc Oxide (ZnO) is a wide band-gap semiconductor (3.37 eV at room temperature) with the high exciton binding energy of 60 meV. Since the ultraviolet (UV) lasing from ZnO was realized in 1997, the study on ZnO has attracted a great deal of attention because of the intense commercial interest in developing practical short-wavelength semiconductor diode lasers (SDLs) for the huge market needs. In order to explore the ZnO-based material with a wider band gap, MgxZn1-xO alloy thin films were fabricated by the sol-gel deposition method. And the structure and optical properties were also studied. When x ≤ 0.36, the alloy thin films keep the wurtzite structure. And the band gap could be varied from 3.40 eV to 3.93 eV. The Mg0.05Zn0.95O and Mg0.15Zn0.85O alloys with wurtzite structure show high thermal stability up to 1000℃. However, when x is 0.36, phase separation will occur at 800℃. The intense ultraviolet photoluminescence (PL) from MgxZn1-xO alloy thin film was observed at room temperature. With increasing the contant of Mg2+ ion in the film, the peak position is blue-shifted to higher energy side. By examining the PL properties of the alloy under different temperatures, we can calculate the exciton binding energy in MgxZn1-xO to be 57 meV, which is quite equal to the binding energy of ZnO. This emission is indicative of the excitonic nature of the material. The ZnO micro rods were also fabricated by a simple thermal oxidation method. The morphologies of the samples were detected by the scanning electron microscope (SEM), showing that the ZnO micro rods are about thirty microns long with a diameter of 5 (m. In the photoluminescence (PL) spectra, a new emission band due to the exciton-exciton collision process (P band) is observed under low excitation intensity at room temperature. And some fine structures origination from the cavity modes of the Fabry-Pérot etalon could also be seen clearly. By detecting the PL spectra under low temperature, a thermal activation process could be seen. And the possible mechanism of P band formation is discussed.