Deep level optical and thermal spectroscopy of traps in n-GaN grown by ammonia molecular beam epitaxy

The incorporation of deep level defects in n-type GaN grown by ammonia-based molecular beam epitaxy (MBE) is studied via systematic adjustment of the NH3/Ga flux ratio. Deep level optical and transient spectroscopies, which together enable deep level detection throughout the GaN bandgap, reveal defect states whose individual concentrations vary with the NH3/Ga flux ratio. A general trend of lower concentration for deep levels at E-C-3.28, E-C-1.28, E-C-0.62, and E-C-0.25 eV with higher NH3/Ga flux ratio was observed, with the strongest reduction at the E-C-0.25 eV level, consistent with expectations for a V-N-related defect. The known C-N impurity state at E-C-3.28 eV and suspected C-I-related state at E-C-1.28 eV also showed a moderate decrease in concentration at the higher NH3/Ga flux ratio. In contrast, the V-Ga-related defect at E-C-2.62 eV was insensitive to the NH3/Ga flux ratio over the range studied here. Taken together, ammonia-MBE GaN has deep level defects with different sensitivities in flux ratios suggestive of independent physical sources. However, the total trap concentrations were significantly reduced for higher NH3/Ga flux ratios in n-type GaN grown by ammonia-MBE under the range of growth conditions used in this study, suggesting that higher NH3/Ga flux ratios will generate higher electronic quality GaN material when using ammonia-based MBE for device applications. (C) 2008 American Institute of Physics.