Nitrogen precursors in metalorganic vapor phase epitaxy of (Al,Ga)N

Abstract

Among the difficulties in achieving high quality epitaxial nitrides, the choice of the most suitable nitrogen source remains an open question. NH 3 has been widely used but requires a very high V III ratio and provides a very low concentration of N species other than itself during decomposition. Though the understanding of the MOVPE processes required more refined methods than an equilibrium thermodynamic analysis, the minimization of the Gibbs free energy of the gaseous system at the growth temperature provides pertinent information about the nature of active species. Such a thermodynamic analysis brings some insight into the efficiency of nitrogen precursors. Species produced by thermal decomposition of a standard N precursor as NH 3 are compared to those obtained with N 2H 4 and N(C 2H 5) 3. Preliminary experiments using N(C 2H 5) 3 as nitrogen precursor are reported. The epitaxial growth of AlN on sapphire has been achieved whereas the tentative growth of GaN results in the deposition of Ga droplets. N precursors like N(C 2H 5) 3, although suitable for the deposition of nitrides does not provide significant improvements, in comparison with NH 3. Thermal activation (using a hot filament) or microwave production of active N species seems to provide a significant proportion of highly reactive chemical species.