We report on a high reflectance low resistance multilayer contact to p-GaN composed of a thin oxidized Ni/Au bilayer overcoated with a thick Al or Ag layer and then capped by Ni/Au. Measurements on 500 μm diameter light emitting diode-like test structures show an operating voltage below 4 V at 20 mA that is comparable to identical devices fabricated with a conventional Ni/Au contact. Back surface light emission is about 70% greater than that from devices with the Ni/Au contact due to lower light absorption by the Al or Ag. Performance for both Al and Ag based contacts is stable at temperatures of up to around 100 °C.

The photoluminescence (PT) properties of Al-doped ZnO thin films grown by the sol-gel dip-coating method have been investigated. At 12 K, nine distinct PL peaks were observed at 2. 037, 2.592, 2.832, 3.027, 3.177, 3.216, 3.260, 3.303, and 3.354 eV. The deep-level emissions (2.037, 2.592, 2.832, and 3.027 eV) were attributed to native defects. The near-band-edge (NBE) emission peaks at 3. 354, 3.303, 3.260, 3.216, and 3.177 eV were attributed to the emission of the neutral-donor-bound excitons (D 0 X), two-electron satellite (TES), free-to-neutral-acceptors (e,A 0 ), donor-acceptor pairs (DAP), and second-order longitudinal optical (2LO) phonon replicas of the TES (TES-2LO), respectively. According to Haynes' empirical rule, we calculated the energy of a free exciton (FX) to be 3.374 eV. The thermal activation energy for D 0 X in the nanocrystalline ZnO thin film was found to be ~25 meV, corresponding to the thermal dissociation energy required for D 0 X transitions.

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