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The advent of a wide-bandgap GaN p-n junction has enabled highly efficient blue light-emitting diodes (LEDs) in GaInN/GaN heteroepitaxy. The system also enables a much wider range of emission wavelengths. We summarize progress in epitaxial materials development of green, yellow, and orange direct-emitting LEDs that bypass the steps of external phosphor conversion to achieve higher stability, efficiency, and higher overall color rendering quality for wider adoption of one of the widest power savings resources so far identified.

The light output of 530 nm green GalnN/GaN light-emitting diodes on sapphire has been nearly doubled by the insertion of a 130-nm GalnN underlayer (UL) between the n-GaN electron injection layer and the quantum-well (QW) active region. Under variation of the alloy composition, best results were obtained for an x = 6.3% Ga1-xInxN UL. By low-temperature depth-resolved cathodoluminescence spectroscopy, an interplay of the impurity-related donor-acceptor pair recombination, the UL, and the QW emission has been observed. We propose that the resonance and level alignments between the defect and UL levels reroute excitation toward radiative recombination in the QWs.

InGaN quantum well structures on GaN epilayers were exposed to 500 keV alpha particles to fluences above 1014 cm2 to probe the relative radiation tolerance of the epilayer and wells. Performance was estimated by the intensity of ion-beam induced luminescence. Two separate types of quantum well structures emitted at 470 and 510 nm prior to irradiation, and only small wavelength shifts were observed even with the highest alpha fluences. Complementary cathodoluminescence experiments showed that luminescence in the quantum wells is strongly influenced by charges injected deep into the GaN epilayer. The 500 keV alpha penetration depth was ~ 1 mum, so that defects were created at a faster rate in GaN compared to InGaN as alpha particles slowed and stopped within a minority carrier diffusion length of the quantum wells. However, the rate of luminescent decay was similar for both materials. Taken together with the cathodoluminescence data, this ion-beam induced luminescence comparison indicates that the quantum well luminescence decay rate is dominated by radiation-induced defects in the GaN epilayer. InGaN quantum wells are then demonstrated to be not more than a factor of ten more radiation sensitive than GaN, and may be substantially less sensitive than this upper bound.

A review is presented of future issues on wide-bandgap group-III nitride materials and device technology for optoelectronic and high-temperature devices such as LEDs.