Influence of active nitrogen species on high temperature limitations for (000(1)under-bar) GaN growth by rf plasma-assisted molecular beam epitaxy

A reduced growth rate for plasma-assisted molecular beam epitaxy GaN growth often limits growth to temperatures less than 750 degrees C. The growth rate reduction is significantly larger than expected based on thermal decomposition. Characterization of various rf plasma source configurations indicated that a flux consisting predominantly of either atomic nitrogen or nitrogen metastables can be produced. The use of atomic nitrogen, possibly coupled with the presence of low energy ions, is associated with the premature decrease in growth rate. When the active nitrogen flux consists primarily of nitrogen metastables, the temperature dependence of the decrease is more consistent with decomposition rates. A significant improvement in electrical properties is observed for growth with molecular nitrogen metastables. In addition, atomic hydrogen stabilizes the growing surface of (000 (1) under bar) GaN. (C) 1999 American Vacuum Society. [S0734-211X(99)03304-1].