Investigations On The Growth And Optical Properties Of Cu Doped ZnO Films

Zinc oxide (ZnO) is an importantâ…¡-â…¥direct band gap semiconductor material, which has band gap of 3.37eV at room temperature (RT), and the exciton binding energy as high as 60meV. Usually ZnO has hexahedron wurtzite structure at the air condition. It has been investigated extensively due to its distinguished performance in electrical, optical and piezoelectric properties making suitable for many applications such as light emitting diodes, photodetectors, electroluminescence, transparent conductive film, surface acoustic waves device and so on.Cu-doped ZnO (ZnO:Cu) films are prepared on glass and Si(100) substrates at different oxygen partial pressures by radio frequency reactive magnetron sputtering technique. The effect of various substrate and oxygen partial pressures on the crystalline and optical properties of ZnO:Cu thin films were investigated by the X-ray diffraction(XRD), atomic force microscopy(AFM) and fluorescence spectro- photometer. In this way some experimental data and the theoretical basis are provided for the application of ZnO films. The results are summarized as follows:1,The influence of oxygen partial pressure on the micro-structural property of ZnO:Cu films have been studied on Si substrates. The results indicated that the intensity of (002) diffraction peak first increased and then decreased With the oxygen partial pressure increased, which indicated that oxygen partial pressure can influence crystallization orientation of ZnO:Cu films. And with increasing oxygen partial pressure, the compressive stress of the films increased first and then decreased.2,The photoluminescence (PL) of the samples were measured at room temperature. A violet peak, two blue peaks and a green peak were observed from the PL spectra of the four samples. The analysis of PL spectra showed that the green emission peak (530nm) originated from electron transition from deep donor level by the oxygen vacancies to valence band; two blue emission peaks (449nm and 484nm) were assigned to the electron transition from both the interstitial Zn levels to valence band and the energy levels of interstitial Zn to Zn vacancies; and the violet emission peak (401nm) relate interface traps existing at the grains boundaries.3,The effect of oxygen partial pressures on the crystalline and optical properties of ZnO:Cu thin films which prepared on glass and Si(100) substrates were Comparatively investigated. The results indicated that films deposited on Si substrates have a better c-axis preferred orientation than glass substrate. The films deposited on the various substrates have the same crystal law with increasing of oxygen partial pressure,and as the ratio of oxygen and argon is increased to 10:10, the c-axis growth orientation of films achieve the best at the same time. Study on photoluminescence have shown that films prepared on the glass substrate have better light-emitting in poor oxygen environment, whereas films prepared on the Si substrate have better PL properties than on the glass substrate in rich oxygen environment.