.55. Jk, 81.15.Gh Wurtzite GaN is usually used for optoelectronic devices. Because of the growth along the polar c-axis, the strong piezoelectric and spontaneous polarizations fields result in a band bending which is responsible for the poor electron-hole overlap in quantum well structures. The growth along the m-plane direction is one possibility to deposit non-polar material and leads to efficient recombination across the entire well of the QW structure. LiAlO 2 (LAO) offers the advantage to grow GaN along the m-plane direction. This work provides the results from investigations on the deposition of GaN-based structures on LAO substrates by metal-organic chemical vapor deposition.1 Introduction There is huge interest worldwide at present in finding an alternative substrate for the GaN-based epitaxial deposition. Currently, silicon carbide (SiC) and sapphire are the most favorite wafers for the AlGaInN material system. These substrates suffer from the limitations that growth is only possible along the polar c-axis which leads to strong piezoelectric and spontaneous polarization fields. The band bending related to polarization-induced fields is responsible for the poor electron-hole overlap. To achieve highly efficient quantum well (QW) structures, growth along non-polar axes is required. The m-plane growth direction demonstrates one of the non-polar axes for the deposition of the nitrides, prevents the band bending and provides direct recombination across the whole well. LiAlO 2 (LAO) substrates, with their huge advantage of low cost and easy substrate removal, offer the possibility to grow GaN along the m-plane direction. The growth of GaN on this substrate has been investigated by several research groups [1][2][3][4][5][6][7][8][9][10][11]. This work provides the results from investigations on the deposition of GaN-based structures on LAO substrates.

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The lifetime of phosphorescent red organic light emitting diodes (OLEDs) is investigated employing either N,N′-diphenyl-N,N′-bis(1-naphthylphenyl)-1,1′-biphenyl-4,4′-diamine (NPB), TMM117, or 4,4′,4″-tris(N-carbazolyl)-triphenylamine (TCTA) as hole-conducting host material (mixed with an electron conductor). All OLED (organic vapor phase deposition-processed) show similar efficiencies around 30 lm/W but strongly different lifetimes. Quickly degrading OLED based on TCTA can be stabilized by doping exciton transfer molecules [tris-(phenyl-pyridyl)-Ir (Ir(ppy)3)] to the emission layer. At a current density of 50 mA/cm2 (12 800 cd/m2), a lifetime of 387 h can be achieved. Employing exciton transfer molecules is suggested to prevent the degradation of the red emission layer in phosphorescent white OLED.

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