Growth of GaN on Porous SiC by Molecular Beam Epitaxy

1 Department of Physics, Carnegie Mellon University, Pittsburgh, PA, USA 2Naval Research Laboratory, Electronics Materials Branch, 

One of the major hurdles in the epitaxial growth of high quality GaN thin films is the unavailability of suitable substrates. The lack of suitable substrates leads to poor quality epitaxial films with dislocation densities in the range of 1010-1012 cm-2 for GaN grown on sapphire [1,2] and SiC [3]. Such high defect densities are detrimental to the device performance conventional III-V (like GaAs) devices have defect densities about four orders of magnitude lower than presently achievable in GaN. 

Two important crystal properties that should ideally be closely matched between the GaN and the substrate are the lattice parameter and the coefficient of thermal expansion. Any mismatch between these properties can result in defects in the film (misfit and threading dislocations due to lattice mismatch and cracking or bowing due to the thermal 

Porous Silicon Carbide and Gallium Nitride Epitaxy, Catalysis, and Biotechnology Applications Edited by Randall M. Feenstra and Colin E.C. Wood 2008 John Wiley c Sons, Ltd 

Heteroepitaxial growth of GaN is usually performed on sapphire or SiC (13 % and 3.4% lattice mismatch, respectively, with GaN). Such a lattice mismatch between GaN and these substrates results in a high dislocation density in the epitaxial films. A variety of techniques have been employed in the past to reduce this high dislocation density and one of the common methods has been to engineer the substrate surface to control, and thus inhibit, the formation of threading dislocations. 

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