Study on Polycrystalline Photonics, by Using III-V Nitrides Grown on Amorphous and Polycrystalline Substrates

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Polycrystalline GaN layers were grown on quartz glass substrates by gas source MBE with plasma-excited N2, and it was found that the photoluminescence (PL) emission was as strong as those of single crystalline GaN grown on sapphire substrates by MOVPE. Both n- and p-type doping was achieved and we suggested the possibility of the fabrication of low cost and large area photonic devices. For the polycrystalline GaN pn junctions, the diode characteristics were confirmed. It was found that the origin of the PL emission from the polycrystalline GaN is excitonic transition. We have grown GaN on Mo, W, Ta and Nb metal substrates and observed strong PL emission. It was found that the polycrystalline GaN/metal junctions showed Schottky or ohmic characteristics depending on the difference in the work-function between GaN and metals. By growing GaN layers on glass and metal substrates with ammonia source, much more strong PL emission was obtained. We confirmed the diode characteristics for the GaN/metal pn junctions. These results show the possibility of the fabrication of flexible GaN devices. We also observed strong PL from the polycrystalline GaN grown on magnetic oxide LaSrMnO3 substrates, which shows the possibility of novel functional device fabrications. We also observed good electric-field electron-emission properties for the polycrystalline GaN on metal substrates. Applications to the high performance display devices are expected.