The electrical, optical, and structural properties of light emitting diodes (LEDs) fabricated from the III–V nitride material system have been studied. LEDs with external quantum efficiencies as high as 4% were characterized by transmission electron microscopy and found to contain dislocation densities in excess of 2×1010 cm−2. A comparison to other III–V arsenide and phosphide LEDs shows that minority carries in GaN-based LEDs are remarkably insensitive to the presence of structural defects. Dislocations do not act as efficient nonradiative recombination sites in nitride materials. It is hypothesized that the benign character of dislocations arises from the ionic nature of bonding in the III–V nitrides.

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We demonstrate the growth and optical characterization of semipolar (1 1 2 2) GaN light-emitting diodes (LEDs) on sapphire utilizing two distinct heteroepitaxial growth methodologies. The properties of semipolar (1 1 2 2) LEDs are analyzed by the simultaneous growth of LED structures on templates prepared by both two-step growth on m-sapphire and selective growth on etched r-plane sapphire. Typically, growth on m-sapphire yields a high density of microstructural defects and surface morphological features which complicate the understanding of emission properties in devices. In this study, we find improved spectral properties of devices grown on etched r-sapphire due to improved surface roughness and microstructural quality (x-ray diffraction rocking curves of 280-550 arcsec for on-axis (1 1 2 2) and off-axis (1 0 1 n), n = 0-5 diffractions), and reveal that the commonly observed broad emission and sub-bandgap peak in semipolar LEDs on sapphire are caused by a tunneling-assisted radiative recombination mechanism.

An examination of low-temperature photoluminescence from chemically thinned InP illustrates the effect of multiple absorption and reemission of photons in bulk liquid-encapsulated Czochralski grown material. Luminescence spectra show that such photon recycling dramatically increases the nonequilibrium carrier density in the material and causes excess carrier distribution to penetrate tens of micrometers beneath the sample surface, an order of magnitude more than a diffusion length. Nonequilibrium carriers also penetrate deeper with increasing excitation levels as a consequence of more efficient radiative recombination. Although these effects have not been widely recognized, they have important consequences in the interpretation of luminescence spectra and the design of electronic and optical devices based on InP that are sensitive to minority-carrier diffusion lengths.