High active nitrogen flux growth of GaN by plasma assisted molecular beam epitaxy

In the present study, the authors report on a modified Riber radio frequency (RF) nitrogen plasma source that provides active nitrogen fluxes more than 30 times higher than those commonly used for plasma assisted molecular beam epitaxy (PAMBE) growth of gallium nitride (GaN) and thus a significantly higher growth rate than has been previously reported. GaN films were grown using N-2 gas flow rates between 5 and 25 sccm while varying the plasma source's RF forward power from 200 to 600 W. The highest growth rate, and therefore the highest active nitrogen flux, achieved was similar to 7.6 mu m/h. For optimized growth conditions, the surfaces displayed a clear step-terrace structure with an average RMS roughness (3 x 3 mu m) on the order of 1 nm. Secondary ion mass spectroscopy impurity analysis demonstrates oxygen and hydrogen incorporation of 1 x 10(16) and similar to 5 x 10(17), respectively. In addition, the authors have achieved PAMBE growth of GaN at a substrate temperature more than 150 degrees C greater than our standard Ga rich GaN growth regime and similar to 100 degrees C greater than any previously reported PAMBE growth of GaN. This growth temperature corresponds to GaN decomposition in vacuum of more than 20 nm/min; a regime previously unattainable with conventional nitrogen plasma sources. Arrhenius analysis of the decomposition rate shows that samples with a flux ratio below stoichiometry have an activation energy greater than decomposition of GaN in vacuum while samples grown at or above stoichiometry have decreased activation energy. The activation energy of decomposition for GaN in vacuum was previously determined to be similar to 3.1 eV. For a Ga/N flux ratio of similar to 1.5, this activation energy was found to be similar to 2.8 eV, while for a Ga/N flux ratio of similar to 0.5, it was found to be similar to 7.9 eV. (C) 2015 American Vacuum Society.