Enhancement of optical and structural quality of semipolar (11(2)over-bar2) gan by introducing nanoporous sinx interlayers
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Enhancement of optical and structural quality of semipolar (11 (2) over bar2) GaN grown by metal-organic chemical vapor deposition on planar m-sapphire substrates was achieved by using an in situ epitaxial lateral overgrowth technique with nanoporous SiNx layers employed as masks. The effect of SiNx deposition time on optical and structural quality of the films was studied by steady-state photoluminescence (PL) and X-ray diffraction. The intensity of room temperature PL for the (11 (2) over bar2) samples grown with nanoporous SiNx was found to be up to four times higher compared to those for the reference samples having the same thickness but no SiNx interlayers. This finding is attributed to the blockage of dislocation propagation toward the surface by the SiNx interlayers. Low-temperature PL measurements also revealed the improvement of structural quality gained by the employment of the SiNx interlayers which manifests itself as the increase in intensity of donor bound exciton emission. In agreement with the optical data, full width at half maximum values of (11 (2) over bar2) X-ray rocking curves measured for two different in-plane rotational orientations of [1 (1) over bar 00] and [11 (2) over bar3] reduced from 0.33 degrees and 0.26 degrees for the reference samples to 0.2 degrees and 0.16 degrees for the nano-ELO structures grown under optimized conditions, respectively.