Studies on Epitaxial Relationship and Interface Structure of AlN/Si(111) and GaN/Si(111) Heterostructures
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Studies on Epitaxial Relationship and Interface Structure of AlN/Si(111) and GaN/Si(111) Heterostructures T. A. Rawdanowicz, H. Wang, A. Kvit and J. Narayan Department of Materials Science and Engineering North Carolina State University Raleigh, NC 27695, USA ABSTRACT We present the details of epitaxial growth interface structure of single wurtzite AlN thin films on (111) Si substrates by laser-molecular-beam-epitaxy. High quality AlN thin films with atomically sharp interfaces can be obtained by Laser-MBE at a substrate temperature of 650 ±10ºC. X-ray diffraction and high resolution transmission electron microscopy was used to study the details of epitaxial growth of AlN on Si(111) substrate. The orientation-relationship of AlN on Si(111) was studied from Si and zone axis and determined to be AlN [ 2 1 1 0 ]║Si[ 1 10 ] and AlN [ 01 1 0 ]║Si[ 211 ]. The atomic structure of the interface was studied by high-resolution transmission electron microscopy and Fourier filtered image of crosssectional AlN/Si(111) samples from both Si and zone axis. The results revealed the domain matching epitaxy of 4:5 ratio between the interplanar distances of Si(110) and AlN [ 2 1 1 0 ]. We also present similarities and differences between the growth mechanism of AlN/Si(111) and GaN/Si(111) heterostructures. INTRODUCTION
There is considerable interest in the growth and characterization of Aluminum Nitride (AlN) and Gallium Nitride (GaN) thin films for application, in optoelectronic and high-temperature devices due to chemical stability at high temperatures, excellent mechanical properties, good thermal conductivity, and a high breakdown field. Particularly, the wide band-gaps of AlN (6.2 eV) and GaN (3.4 eV) make this material promising for ultra-violet (UV) diode emitters. The lack of suitable single-crystal nitride substrates require these devices to be made through heteroepitaxial growth on substrate materials, such as silicon carbide or sapphire. However, silicon carbide and sapphire substrate materials are expensive and limited in size. To overcome these disadvantages, the heteroepitaxial processing of high quality AlN and GaN thin films on silicon (Si) has been under considerable investigation, due to its many advantages regarding low cost, large size, high crystal and surface quality, and high electrical and thermal conductivities. Work in this area is further motivated by the potential for co-integration of wide band-gap optoelectronics devices with large-scale silicon-based microelectronic devices. The Si(111) substrate presents the required hexagonal symmetry for the hexagonal wurzite epilayers of oriented (0001) AlN and GaN. However, the growth of AlN and GaN directly on Si(111) is presented with several commonly known impediments; large lattice mismatch (~19%), and the difference of thermal expansion coefficient and poor nucleation for GaN on Si(111). Despite these impediments wurzite AlN and GaN can be grown directly on the Si(111) plane with good structural properties. The heteroepitaxial growth of AlN and GaN dir
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