Research On The Nucleation And Growth Of ZnO By MOCVD

Zinc oxide (ZnO) with direct wide bandgap of3.37eV and exciton bindingenergy of60meV is a versatile semiconductor and has attracted considerableattention due to its potential applications in short wavelength optoelectronic devicesand photodetectors. In order to integrate ZnO devices with Si integrated chiptechnology, the growth of ZnO films on Si substrates is of particular interest. However,the fabrication of high-quality ZnO thin films has been being a tough work due to thedifferent crystal structures and the big lattice mismatch between ZnO and Sisubstrates, which has been restricting the device-application process. As the seeds ofepitaxial layers, the density and size of initial NIs will intensely affect the growthmodel and quality of the epitaxial layers. But for ZnO, little has been reportedconcerning the effect of growth conditions on the nucleation。In this work, systematic study on the deposition of ZnO on Si substrates bymetal-organic chemical vapor deposition (MOCVD) is reported. The effects ofnucleation temperature and time on ZnO nucleation and epilayer properties wereinvestigated.1、The nucleation of ZnO was investigated by varying temperature and timeduring the nucleation process. It is found that nucleation temperature and time play akey role on the nucleation process. With the increase of nucleation temperature, thesize of ZnO nuclei and the spacing between nucleation sites increases. And as thenucleation time increases, the size of ZnO nucleation islands (NIs) increases and thedensity decreases due to the coalescence of ZnO nuclei.2、The influence of nucleation temperature and time on ZnO epitaxial growthwas investigated, the density and size of initial ZnO NIs have intensely affected thegrowth model and quality of ZnO epitaxial layers. In addition, the crystalline qualityof ZnO thin films was improved at the nucleation temperature of560oC and for thenucleation time of60s.3、As is known to all that the morphology and crystalline quality of ZnO are determined by both the nucleation and epitaxy process, and in this work, the effect oftemperature on the growth of ZnO films by MOCVD was investigated from the twoprocesses separately. It is found that temperature has a great influence on thenucleation process and the epitaxial growth. With the temperature increases, the sizeof ZnO nuclei increases and the density decreases, which lead to a larger diameter anda lower density of the ZnO nanorods. When the temperature increases to670oC, theZnO nanorod does not increase its diameter as the ZnO nucleus does, due to thesuppression of high temperature on the lateral growth of ZnO nanorods. As a result,the ZnO nanorods with a largest diameter and a lowest density were obtained for thetemperature of560oC. In addition, the crystalline quality of ZnO thin films wasimproved by modifying nucleation temperature.