Influence of defects on the electrical and optical characteristics of blue light-emitting diodes based on III–V nitrides

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Abstract
We have measured the electrical and optical properties of blue light-emitting diodes (LEDs) based on III–V nitrides. The current–voltage characteristic is described by means of the relation I=I0 exp(αV). In this equation α is temperature independent, suggesting a process of conduction by tunneling, as was recently reported also for blue-green LEDs based on III–V nitrides [Appl. Phys. Lett. 68, 2867 (1996)]. We explain the differences between blue and blue-green devices taking into account the tunneling process across semiconductor interfaces, in which a great number of defects is present. The light output intensity of the LED as a function of junction–voltage data reveals a dependence on the junction–voltage of the type L=L0 exp(qV/1.4 KT), indicating that the radiative recombination path is via deep levels located at the forbidden gap. Furthermore, we find that the light output–current characteristic follows a power law like L∝Ip. From the analysis of data it appears that, contrary to expectations, the nonradiative centers are saturated at very low current values that are comparable to the values at which this saturation takes place in LEDs based on III–V arsenides with a low content of defects.