AbstractZnO films are being used in many emerging technologies such as high frequency RF filters, substrate/buffer layer for GaN deposition, and as active layers in blue-UV LEDs and lasers. These applications require epitaxial films with high structural quality. In the present paper, results on the structure of ZnO films deposited by MOCVD on c-plane and r-plane sapphire substrates are presented. These films have been investigated by XRD, SEM and TEM. X-ray phi-scans show that the films have a single epitaxial relationship with each substrate orientation. (11.0) ZnO grows on (01.2) sapphire (r-plane), while (00.1) oriented films grow on (00.1) sapphire (c-plane). Smooth films are obtained on r-sapphire, while films with a columnar morphology are obtained on c-sapphire. Based on the morphology of the columnar grains grown on c-sapphire, it is expected that the films are oxygen terminated. The interface between ZnO and sapphire is atomically sharp as observed by HRTEM. Misfit dislocations at the interface between ZnO and r-sapphire have been observed. Grain boundaries between coalescing islands during film growth are the main type of defects. Under certain conditions, very long whiskers were observed to grow by the VLS mechanism. By modifying our system, we have been able to prevent the growth of these whiskers.
Open and Short Stubs Employing the Periodically Arrayed Grounded-strip Structure on the Silicon Substrate and Their Application to Miniaturized RF Filters on the Silicon RFIC
