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

Arehart, A. R.; Corrion, A.; Poblenz, C.; Speck, J. S.; Mishra, U. K.; Ringel, S. A.
September 2008
Applied Physics Letters;9/15/2008, Vol. 93 Issue 11, p112101
Academic Journal
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 EC-3.28, EC-1.28, EC-0.62, and EC-0.25 eV with higher NH3/Ga flux ratio was observed, with the strongest reduction at the EC-0.25 eV level, consistent with expectations for a VN-related defect. The known CN impurity state at EC-3.28 eV and suspected CI-related state at EC-1.28 eV also showed a moderate decrease in concentration at the higher NH3/Ga flux ratio. In contrast, the VGa-related defect at EC-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.


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