Quaternary AlInGaN based vertically conducting light emitting diodes on SiC

One of the most promising approaches to developing solid-state light sources is the use of multicolor light emitting diodes, where relative intensity of primary colors in such diodes can be adjusted to yield white light. We demonstrate the use of a unique polarization energy band engineering (PEBE) approach for tuning of the emission spectra and relative intensities of AlInGaN-InGaN multiple quantum well (MQW) LED structures. This tuning is achieved by controlling the quantum well and barrier composition and by optimizing the thicknesses and number of the quantum wells. Tuning of polarization and strain induced electric fields using the quaternary (AlInGaN) barriers allows us to obtain a nearly independent control of built-in fields and quantum confinement. This, in turn, changes the positions and intensities of the emission peaks by changing the MQW potential profile. Preliminary results on vertically conducting devices (over n-type 4H-SiC) show a dramatic increase of over an order of magnitude in emission-intensity for the structures with AlGaInN barriers compared to those using conventional GaN barriers. We attribute this improvement to the reduction in piezo/spontaneous polarization fields and to the increase in the overlap integral. We also observed a strong nonmonotonic dependence of the PL intensity and the PL peak position on the level of silicon doping. These results are consistent with the expected effect of the electric field in the MQW on the PL intensity.