Nanoscale mapping of inhomogeneities in the luminescence of operational nitride LEDs

Nitride LEDs can emit over a wide spectral range with particularly high efficiency in the blue. The active regions of these devices are InGaN/GaN quantum wells (QWs) which exhibit emission spectra that are much broader than expected. This broadening has been widely debated in the literature and is often attributed to spatial fluctuations in the emission energy due either to the intrinsic compositional disorder of the ternary alloy or to extrinsic growth inhomogeneities and structural defects. These different causes of disorder occur at different scales, ranging from a few nm to several hundred nm. To study the effects of disorder on the electroluminescence processes at the relevant scales, we have developed a novel approach based on Scanning Tunneling (Electro-)Luminescence Microscopy. We have applied this technique for the simultaneous mapping of the surface topography and the electroluminescence of an operational InGaN/GaN LED. Significant changes in the local electroluminescence spectrum are observed at the scale of alloy disorder and spectacular effects on the emission energy and intensity are evidenced in the vicinity of V-pits that result from emerging dislocations.