A reduced growth rate for plasma-assisted molecular beam epitaxy of GaN often limits growth to temperatures less than 750 °C. The growth rate reduction can be significantly larger than expected based on thermal decomposition. Conditions producing a flux consisting predominantly of either atomic nitrogen or nitrogen metastables have been established using various radio-frequency sources. 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.
High temperature limitations for GaN growth by rf-plasma assisted molecular beam epitaxy: Effects of active nitrogen species, surface polarity, hydrogen, and excess Ga-overpressure J.The relation of active nitrogen species to high-temperature limitations for (0001) GaN growth by radio-frequencyplasma-assisted molecular beam epitaxy A reduced growth rate for plasma-assisted molecular beam epitaxy GaN growth often limits growth to temperatures less than 750°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 (0001 គ ) GaN.
The operating regimes of two rf-plasma sources, an Oxford CARS-25 and an EPI Unibulb, have been extensively characterized. By changing the exit aperture configuration and using an electrostatic deflector, the Oxford source could produce either primarily atomic nitrogen, atomic nitrogen mixed with low energy ions, or a large flux of higher energy ions (>65 eV) as the active species in a background of neutral molecular nitrogen. The EPI source produced a significant flux of metastable molecular nitrogen as the active species with a smaller atomic nitrogen component. Nitridation of sapphire using each source under the various operating conditions indicate that the reactivity was different for each type of active nitrogen. Boron contamination originating from the pyrolytic boron nitride plasma cell liner was observed.
The operating regimes of two rf-plasma sources, an Oxford CARS-25 and an EPI Unibulb, have been extensively characterized. By changing the exit aperture configuration and using an electrostatic deflector, the Oxford source could produce either primarily atomic nitrogen, atomic nitrogen mixed with low energy ions, or a large flux of higher energy ions (>65 eV) as the active species in a background of neutral molecular nitrogen. The EPI source produced a significant flux of metastable molecular nitrogen as the active species with a smaller atomic nitrogen component. Nitridation of sapphire using each source under the various operating conditions indicate that the reactivity was different for each type of active nitrogen. Boron contamination originating from the pyrolytic boron nitride plasma cell liner was observed.
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