AlGaN samples grown by plasma-assisted molecular-beam epitaxy on sapphire (0001) substrates, with 20%–50% Al content and without the use of indium, show intense room-temperature photoluminescence that is significantly redshifted, 200–400meV, from band edge. This intense emission is characterized by a long room-temperature lifetime (∼375ps) comparable to that seen in low defect density (∼108cm−2) GaN. Room-temperature monochromatic cathodoluminescence images at the redshifted peak reveal spatially nonuniform emission similar to that observed in In(Al)GaN alloys and attributed to compositional inhomogeneity. These observations suggest that spatial localization enhances the luminescence efficiency despite the high defect density (>1010cm−2) of the films by inhibiting movement of carriers to nonradiative sites.

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Lifetime measurements on single-chip, packaged 285 nm light-emitting diodes (LEDs) performed under constant current injection at 20 and 75 mA, were compared to the performance of unbiased LEDs baked at the equivalent operating junction temperatures. The thermally stressed devices showed a lesser degradation than those electrically stressed, indicating that elevated temperature alone does not cause degradation. Despite a decay to less than half of the initial power under current injection, time-resolved photoluminescence of the active region exhibits little change, while capacitance-voltage measurements imply that the reduced efficiency and power decay originate from the generation of point defects near the p-side of the p-n junction.

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In this letter, the lateral and vertical transport in lightly doped n−-GaN films, grown by plasma assisted molecular beam epitaxy, were investigated in order to explore the role of electron scattering by charged dislocations. Lateral transport constants were determined by Hall effect measurements on n−-GaN films. The doping concentration and mobility of the investigated films was 1–2×1017 cm−3 and 150–200 cm2/V s, respectively. Vertical transport was studied by etching mesa structures and forming Schottky barrier diodes. The diodes exhibit near ideal forward current–voltage characteristics with reverse saturation current densities in the 1–10×10−9  A cm−2 range. The doping concentrations as well as the barrier height of the diodes were determined from capacitance–voltage measurements to be 8–9×1016 cm−3 and 0.95–1.0 V, respectively. The analysis of the reverse saturation current, using the diffusion theory, leads to vertical mobility values of 950 cm2/V s. The significant increase in mobility for vertical transport is attributed to reduction in scattering by charged dislocations.