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We deposited a 4-inch crack-free aluminum nitride (AlN) layer on a flat sapphire substrate and a patterned sapphire substrate grown using metal-organic vapor phase epitaxy method. To use the 4-inch sapphire substrate, we introduce air voids in the AlN layer in the initial growth region. Moreover, we discovered that optical absorption exists in the AlN layer with air voids. The secondary ion mass spectrometry (SIMS) results show that the impurity concentrations are high at the regions where the air voids exist, though the growth conditions are same throughout the AlN layer. We considered that it is most probable that the optical absorption is mainly attributed to the complexes of Al and O. The origin of the optical absorption was identified as a deep emission band due to impurities such as carbon and oxygen around the air voids. In this study, it was possible to obtain a transparent AlN template without air voids by changing the growth conditions and the layer structure. In addition, we could further suppress the underlying layer with the air voids.

Interfacial chemical states and Schottky barrier heights (SBHs) for indium tin oxide (ITO) electrodes on Mg:GaN films have been investigated by high-resolution hard X-ray photoemission spectroscopy (HX-PES), and have been correlated with electrical properties. HX-PES has revealed that the large downward band bending of 2.6 eV was drastically reduced by ITO deposition and annealing, resulting in low SBH of 0.2 eV which is well correlated with good ohmic contact. Improvements of electrical properties can be attributed to the combination of (1) the interfacial layer with large work function, (2) the ordered interfacial dipole layer and (3) activation by ITO catalytic effect.

We have determined the valence band discontinuities of InN/Mg:GaN and InN/Si:GaN heterostructures by hard x-ray photoemission spectroscopy. InN thin films were grown by pulsed laser deposition method and streaky high-energy electron diffraction pattern was observed, indicating that good crystalline InN films were grown. The value of valence band discontinuity for InN/Mg:GaN is as small as 0.3 eV, while that for InN/Si:GaN is 1.4 eV. The fact that the InN/Mg:GaN interface has the small energy barrier suggests that InN is very promising for the interlayer between transparent conductive layers and Mg:GaN in light emitting diode structures. [DOI: 10.1380/ejssnt.2008.254]

Fluorescence, phosphorescence, and the triplet spin sublevel properties (zero-field splitting, total decay rate constants, and relative radiative decay rate constants for individual sublevels) are investigated for a series of complexes of the type MX 2 (phen), where M is Zn(II) or Cd(II), and X is Cl, Br, or I. The fluorescence and the phosphorescence are almost identical to those of free phen indicating that the emission is from the phen localized ππ * state. The rate constants for spin forbidden transitions increase as the atomic number of halogen increases. All the kinetic data as well as the zero-field splitting parameters are satisfactorily interpreted by a configurational mixing between the phen localized ππ * state and the halogen p to phen π * ligand-ligand charge-transfer state. Zero-field splitting and radiative properties of the triplet spin sublevels of the “ligand localized” state of the complexes of closed shell metal ions such as Zn(II) and Cd(II) are all interpreted satisfactorily in terms of the configurational mixing between phen localized ππ * state and the halogen p to phen π * ligand-ligand charge-transfer state. Metal d orbitals do not participate in determining excited state properties. Apparent difference experimentally observed is traced back to the difference of the electronegativity of Zn(II) and Cd(II).

The phosphorescence of [Ru(bhq)(CO) 2 Cl(L)] (L=PEt 3 , p -toluidine and piperidine) in glassy rigid solution and in crystals are observed. We have further obtained zero-field splittings by the method of optical detection of magnetic resonance. The location of the spectrum, lifetime, and the zero-field splittings all indicate that the emission is from the ligand localized 3 ππ* state.

In order to quantify the effect of metal d-orbitals on the radiative properties of the triplet spin sublevels of the ligand-localized 3 ππ * state, we have studied the phosphorescence from the ligand-localized 3 ππ * state of cis-Rh(CN) 2 (phen) 2 Cl and Rh(phen) 3 Cl 3 in the crystalline state at 1.3 K by optical detection of magnetic resonance (ODMR). The ODMR experiments show that only the T x -spin sublevel is emissive for cis-Rh(CN) 2 (phen) 2 Cl, whereas the T x and T z sublevels are both emissive for Rh(phen) 3 Cl 3 . These experimental results are satisfactorily interpreted in terms of the modulation of the configurational mixing of singlet and triplet dπ * and dd states with the phen-localized ππ * and σπ * states induced by changes in ligand-field strength

The activation of metalorganic chemical vapor deposition (MOCVD)-grown Mg-doped GaN by N 2 annealing with thin Pd films has been investigated, p-type GaN with a hole concentration of 7 x 10 16 cm -3 has been obtained at an annealing temperature as low as 200 °C using this technique. Thermal desorption spectroscopy (TDS) measurements have revealed that hydrogen is effectively removed from the Mg-doped GaN layer by the use of the Pd film.

Phosphorescence of [Mo 6 Cl 14 ] 2- is investigated focusing attention on the temperature-dependent spectral shift. The relative radiative rate constants for the emitting sublevels T 2u , E u , and T 1u are 1:5:8:100. The large radiative rate constant for the T 1u sublevel substantiates the previous assignment of the sublevels

Phosphorescence of [Mo 6 Cl 14 ] 2- is investigated focusing attention on the temperature-dependent spectral shift. The relative radiative rate constants for the emitting sublevels T 2u , E u , and T 1u are 1:5:8:100. The large radiative rate constant for the T 1u sublevel substantiates the previous assignment of the sublevels

We have investigated feasibility of GaAs interlayers for the metal/GaN interface with synchrotron-radiation photoelectron spectroscopy. We have found that the use of piranha/HCl solutions is effective as a surface cleaning technique for GaN. We have confirmed that (111) GaAs grows epitaxially on a (0001) GaN substrate. Pd/GaAs/GaN sandwich structures have been successfully fabricated with molecular beam epitaxy. We have confirmed the GaAs interlayer modifies the band diagram at the metal/GaN interface.

The theoretical and experimental aspects of the spin sublevels of transition metal complexes are briefly reviewed. First, the complexes with organic ligands are discussed. For metal-localized dd states and metal-to-ligand charge transfer dπ* states, the splitting among spin sub-levels is mainly governed by the spin-orbit coupling, and the magnitude of the splitting is of the order of 10–100 cm−1. For ligand-localized triplet ππ* states, the splitting is mainly governed by the spin-spin coupling, and the magnitude of the splitting is mainly governed by the spin-spin coupling and the magnitude of the splitting is of the order of 0.1 cm−1. Theoretical evaluation of the radiative rate constants for the individual spin sublevels is discussed, and is compared with experimental data. Finally, the spin sublevels of metal clusters are discussed.

The effect of surface cleaning techniques on the properties of the metal/p-GaN contacts has been studied using X-ray photoelectron spectroscopy (XPS) and I–V measurements. It has been clarified that the contact resistance strongly depends on the amount of the surface residues such as oxygen and carbon just before the electrode deposition. We have also found that the annealing in ultra high vacuum (UHV) is effective to reduce the residues. It has turned out that the combination of the hydrochloric acid and sulfuric acid hydrogen peroxide mixtures cleaning followed by the UHV annealing is promising for the improvement in the contact characteristics.