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Boron nitride (BN) layers with sp2 bonding have been grown by metal organic chemical vapor deposition on AlN underlayers, which are deposited on c-plane sapphire substrates. Two different boron precursors were employed—trimethylboron and triethylboron—while ammonia was used as the nitrogen precursor. The BN obtained epitaxial BN films contain ordered rhombohedral (rBN) and partially ordered turbostratic (tBN) stackings as evidenced by x-ray diffraction analysis. We discriminatively identify the PL signatures of the rBN and tBN from those typical of the hexagonal (hBN) and Bernal stackings (bBN). The optical signature of tBN appears at 5.45 eV, and it intercalates between the two recombination bands typical of rBN at 5.35 eV (strong intensity) and 5.55 eV(weaker intensity). The analogs of the high intensity band at 5.35 eV in rBN sit at 5.47 eV for hBN and at 5.54 eV for bBN. [ABSTRACT FROM AUTHOR]

Light-emitting devices based on high-Al content (Al,Ga)N suffer from high densities of dislocations or other point defects, counterbalanced by the carrier localization arising from disorder in the ternary alloy. One way to improve the internal quantum efficiency is the controlled Si-doping of Al xGa1− xN/Al yGa1− yN multi-quantum wells, which was assigned to the reduction of point defects by reduction of internal strains, for some ideal concentration of Si. Time-resolved photoluminescence (TR-PL) can be used [S. F. Chichibu et al., Appl. Phys. Lett. 99, 051902 (2011)] to try and correlate the observed PL time-decays with the density of defects, in relation with the nonradiative recombination probability of photoexcited carriers. We present TR-PL studies of MOVPE-grown Si-doped Al xGa1− xN/Al yGa1− yN multi-quantum wells with typical values of x = 0.6 and y = 0.7 and of Al xGa1− xN epilayers with x up to 0.86. High-Al content MQWs and epilayers exhibit similar bi-exponential PL decay dynamics, with the slower component rapidly quenched when T is increased. The fast decay component remains in the nanosecond range at all temperatures and the PL intensity loss is limited by carrier localization. [ABSTRACT FROM AUTHOR]