||RF magnetron sputtering has been employed to deposit n-type epitaxial zinc oxide thin films on p-type silicon substrates to form p-n diode structures. Commonly found on silicon, native SiOx layers, typically of a few nanometer thick, would hinder the epitaxial growth of ZnO. In this thesis work, a crystalline metal oxide layer was introduced as a buffer layer by redox reaction between a metal layer and the native SiO2. Aluminum was first sputtered for 20 seconds (4 nm), 40 seconds (8 nm), 60 seconds (12 nm) to produce three sets of samples. Each set was then annealed in situ at 450℃ for 20 minutes, 40 minutes, 60 minutes, respectively, to generate 9 different fabrication conditions meant to ignite a redox reaction between aluminum and the silicon oxide. All samples were treated for comparison by rapid thermal annealing to 900℃, intended to improve the crystalline quality of the buffer layer and thus the epitaxial zinc oxide. Means to characterize the samples included (1) cross-sectional TEM (Transmission Electron Microscopy) observations of the interfaces and defects in various regions of the formed material or device structures; (2) x-ray crystallography via ω-2θ and rocking scans in regards to the perfection of the crystal structures and the relative film-substrate orientations; (3) photoluminescence spectroscopy, which showed oxygen deficiency in the ZnO epitaxial thin films as judged by the peaks of near-edge luminescence and mid-gap impurity states. The resulted material structure is a pin diode with a transparent n-ZnO layer sandwiching in the middle an aluminum oxide insulating layer with the p-Si substrate. The electrically insulating aluminum oxide layer serves to increase the minority carrier accumulation effect, extending carriers’ effective life times and hence enhancing the light emission efficiency. Measuring the current-voltage characteristics of the pin device structures provides insights into the interface charges, while high-frequency capacitance-voltage curves helps give a glimpse of the interfaces between ZnO and Al2O3 or AlOx, as well as those between Al2O3 or AlOx and silicon, all concerning the electronic accumulations at each interface.|
Keywords: sputtering, ZnO, Al2O3 , pin diode.