We have studied the electrical characteristics and optical properties of GaN/InGaN multiple quantum well (MQW) light-emitting diodes (LEDs) grown by metalorganic chemical vapor deposition. It appears that there is an essential link between material quality and the mechanism of current transport through the wide-bandgap p-n junction. Tunneling behavior dominates throughout all injection regimes in a device with a high density of defects in the space-charge region, which act as deep-level carrier traps. However, in a high-quality LED diode, temperature-dependent diffusion-recombination current has been identified with an ideality factor of 1.6 at moderate biases. Light output has been found to follow a power law, i.e., in both devices. In the high-quality LED, nonradiative recombination centers are saturated at current densities as low as 1.4 10 2 A/cm 2 . This low saturation level indicates that the defects in GaN, especially the high density of edge dislocations, are generally optically inactive.Index Terms-Carrier injection, GaN, light-emitting diode (LED), multiple quantum well.

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