Transmission Electron Microscopy Study of Interface Region of Aln / 6H-Sic
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TRANSMISSION ELECTRON MICROSCOPY STUDY OF INTERFACE REGION OF ALN / 6H-SIC Jharna Chaudhuri1, Luke Owuor Nyakiti2, Peng Lu3, James H Edgar3, and Peng Li4 1 Mechanical Engineering, Texas Tech University, 7th Street & Boston Avenue, Lubbock, TX, 79409-1021 2 Department of Mechanical Engineering, Texas Tech University, 7th Street & Boston, Lubbock, TX, 79409-1021 3 Department of Chemical Engineering, Kansas State University, Manhattan, KS, 66506 4 Department of Earth and Planetary Science, University of New Mexico, Albuquerque, NM, 87131 ABSTRACT Transmission electron microscopy (TEM) study was performed to investigate the interface region of AlN/6H-SiC. Thick AlN layers were grown on a 3.5° off-axis 6H-SiC substrate at a temperature of 1790 °C for 100 hours by sublimation-recondensation method. The energy dispersive x-ray spectroscopy (EDXS) analysis of the interface region indicated incorporation of Si and C in AlN. Lattice images of cross-sectional TEM samples show a faceted interface with step growth. Stacking faults and dislocations were present both in AlN and 6H-SiC at the interface. INTRODUCTION The unique properties of the group III-nitrides, such as wide direct band gap, high thermal conductivity, and high thermal stability have made GaN and AlN the most serious candidates for the high-power and high-frequency electronic and deep ultraviolet (UV) optoelectronic devices [1,2] . AlN is one of the most promising substrates for group III-nitride based devices due to lower lattice constant and thermal expansion coefficient mismatch and hence reduced defect densities and residual thermal stresses as compared to conventional substrates (i. e. SiC and Al2O3) [3]. Bulk AlN crystals are particularly attractive for supporting Al-rich AlxGa1-xN epitaxial layers for ultraviolet emitters and detectors [1]. Sublimation is the most successful growth method for bulk AlN single crystals, as demonstrated by Slack and McNelly [4,5], Bickermann [6], and others [7-10]. Bulk AlN crystals can be produced by self seeding in a tungsten crucible [4,5]. 6H-SiC substrate offer an alternative method of seeding larger size AlN crystals by sublimation due to the easy nucleation and crystal orientation control, and as a small a-lattice constant mismatch (i. e. 0.96%) with AlN. There have been several transmission electron microscopy (TEM) studies of AlN on 6H-SiC but mostly of thin films (< 10 µm) prepared by epitaxy [11-14]. So far few studies have been made of AlN produced by sublimation growth on 6H-SiC. Crystal layers formed by sublimation growth are distinctly different from standard epitaxy, due to much greater temperature employed and larger film thicknesses.
At elevated growth temperatures, SiC thermal stability is substantially compromised, leading to a slow decomposition of Si and C into the AlN layer and interdiffusion of both AlN and SiC across the interface [15]. Since lattice strain and defects formed at AlN/6H-SiC interface by and large determines the quality of AlN, it is therefore prudent to study the interfac
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