Impact of N- and Ga-face polarity on the incorporation of deep levels in n-type GaN grown by molecular beam epitaxy

Abstract

Deep levels in N-face and Ga-face n-type GaN grown by plasma-assisted molecular beam epitaxy were detected, analyzed and compared using deep level optical spectroscopy (DLOS) and conventional thermal deep level transient spectroscopy (DLTS), which together enable deep level detection throughout the GaN band gap. A redistribution of band gap states was observed between the two GaN crystal growth polarities but with a similar total trap density. Most significant was a tenfold concentration increase in a trap at EC-0.25 eV that is likely related to nitrogen vacancies for the N-face polarity material, with no significant change for the Ga-vacancy-related level at EC-2.60 eV. The DLOS results suggest that carbon impurities, which generate several GaN band gap states, appear to incorporate differently for both crystal polarities with the potential carbon interstitial at EC-1.28 eV being undetected for N-face material. Finally, low concentrations of several new levels in the N-face n-GaN not previously observed in Ga-face n-GaN were observed.