Optimization and performance of AlGaN-based multi-quantum-well deep-UV LEDs

In this paper, we overview the critical materials challenges in the development of AlGaN-based deep ultraviolet light emitting diodes (LEDs) and present our recent advances in the performance of LEDs in the 275-290 nm range. Our primary device design involves a flip-chip, bottom emitting, transparent AlGaN (Al = 47-60%) buffer layer structure with interdigitated contacts. To date, under direct current operation, we have demonstrated greater than 1 mW of output power at 290 nm with 1 mm x 1 mm LEDs, and greater than 0.5 mW output power from LEDs emitting at wavelengths as short at 276 nm. Electroluminescence spectra demonstrate both a main peak from quantum well emission as well as sub-bandgap emission originating from radiative recombination involving deep level states. The heterostructure designs that we have employed have greatly suppressed this deep level emission, resulting in deep level peak intensities that are 40-125X lower than the primary quantum well emission for different LED designs and applied current densities.