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0955-I09-01

High Resolution Transmission Electron Microscopy Study of Thermal Oxidation of Single Crystalline Aluminum Nitride Jharna Chaudhuri1, Rac Gyu Lee1, Luke Owuor Nyakiti1, Zheng Gu2, James H Edgar2, and Peng Li3 1 Mechanical Engineering Department, Texas Tech University, 7th Street & Boston Ave, Lubbock, TX, 79409-1021 2 Chemical Engineering Department, Kansas State University, Manhattan, KS, 66506 3 Earth and Planetary Science Department, Univ. of New Mexico, Albuquerque, NM, 87131 ABSTRACT The impact of process conditions on the structure of thermal oxides formed on AlN was determined by high resolution transmission electron microscopy (HRTEM). Oxidation for 2 hours at 800 °C produced mostly amorphous oxide layers whereas oxidation for 6 hours at 1000 °C produced partly crystalline and epitaxial oxide layers. The crystalline oxide was mostly single phase α-Al2O3 except at the surface where it was a mixture of γ-Al2O3 and α-Al2O3. Prior to oxidation AlN crystal was almost free of defects. The AlN contained a high density of defects, and measurable amounts of oxygen and nitrogen near the interface when oxidized at 800 °C but it was nearly defect-free, and nitrogen- and oxygen-free for oxidation at 1000 °C. This could be due to the rapid out diffusion of nitrogen and oxygen at higher temperature leading to equilibrium throughout the sample. INTRODUCTION AlN is a wide-band-gap (6.2 eV) semiconductor that has attracted interest, along with other III-V nitride materials, for its possible applications in optoelectronics, and high temperature electronics [1]. The oxidation of AlN is of interest since its oxide has good thermal and chemical stability. Al2O3 is suitable as a protective coating. The conversion of AlN to Al2O3 may be suitable for creating dielectric films for electronics [2-3]. Finally, the oxidation of metals on GaN and AlxGa1-xN is important for producing the lowest contact resistance possible [4]. The goal of the present study was to investigate the structures produced due to the oxidation of AlN so the steps occurring at the atomic level could be understood [5]. EXPERIMENTAL High purity AlN single crystals, with low defect density, were oxidized in an open ended horizontal quartz tube furnace over the temperature range of 800 to 1000 °C. The oxidation was performed under a pure flowing oxygen gas under one atmospheric pressure. The cross-sectioned TEM samples were prepared either using a focused ion beam (FIB) or a Gatan precision ion milling system. A high resolution field emission analytical TEM JEOL 2010F with 200 kV and 0.24 nm point resolution was used for the HRTEM study. All the image analysis was performed using GATAN digital micrograph software. RESULTS AND DISCUSSION

Figure 1 (a) shows a bright field HRTEM image from the AlN crystal oxidized at 800 °C. The oxide is amorphous and approximately 40 nm thick. Near the interface, the AlN contains a high density of defects. Electron energy loss spectra (EELS) study indicated the presence of oxygen and nitrogen (in N2 form in addition to N