The growth and optical properties of ZnO films deposited on freestanding thick diamond films

Recently, there has been an increasing interest in ZnO due to its electrical, optical and piezoelectric properties making suitable for many applications such as light emitting diodes, photodetectors, surface acoustic waves device and so on. SAW filters with working frequency higher than 1 GHz will be widely applied in the intending wireless communication, whereas higher resonant frequencies (superior to 2.5 GHz) tend to push the limits of conventional photolithography. ZnO/diamond structure as SAW substrates offers an attractive means for relaxation of the lithographic criteria since ZnO has excellent piezoelectricity while diamond has the highest elastic and stiff coefficient and highest sound velocity. The use of ZnO based on diamond as SAW substrates offers an attractive means for relaxation of the lithographic criteria since diamond has the highest stiff coefficient and sound velocity. SAW devices have been reported based on ZnO/diamond/Si layered structures with a diamond layer of 10-100 μ deposited by chemical vappr deposition (CVD) technique. However the silicon substrate restricts the heat dissipation performance of the diamond films. In regard of actual applications, a ZnO/diamond layered structure without a silicon substrate can make full use of the outstanding thermal, elastic, and sound velocity characteristics of diamond while avoiding restriction of heat dispassion due to additional silicon substrates. High quality ZnO films are currently the foundation of device preparation and the variation of deposition technological parameters is an important factor to obtain ZnO films with high quality. In this paper, ZnO thin film have been prepared on the smooth nucleation surfaces of freestanding CVD thick diamond films by reactive radio-frequency magnetron sputtering. With the variation of O₂/Ar, the growth and optical properties of the ZnO films are characterized experimentally by X-ray diffraction, room temperature photoluminescence spectra, and electron probe microanalysis and Hall measurements. The results indicate that the ZnO film de a O₂ /Ar ratio of 1 is of c-preferred orientation and high resistivity and has the best optical property.