Heteroepitaxy of III-nitride thin films with ultra low defect density

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In-situRHEED and AFM at the initial growth stages indicate nucleation of 6H-GaN at the nanofacets followed by step-flow towards the vicinal direction [1-100] of the substrate. No nuclei on the terraces, generally resulting in 2H-polytype, are observed. Continuous growth under the same condition gives a ~50nm-thick GaN film to be analyzed by Raman and PL. Clear two zone-folded phonon modes are observed between E1(TO) and E2(high), which is indicative of the formation of 6H-polytype. The PL spectrum indicates different energy transitions from 2H-GaN: a peak at 3.33eV is shifted by -0.13eV, which also supports the formation of the 6H-polytype. This is due to the reduced bandgap in 6H-polytype, in agreement with theoretical predictions.