Abstract
Current crowding effect for AlGaN based ultraviolet-B light-emitting diodes (UVB LEDs) is normally observed at high injection current levels, which can cause non-uniform optical emission and generate very high local heat. In this work, UVB LED with a PNP-AlGaN current spreading layer is fabricated and studied. The PNP-AlGaN current spreading layer is obtained by sandwiching the n-AlGaN layer into the p-AlGaN layer. Owing to the modulated energy band profiles by the different doing types, the formed energy barriers for holes in PNP-AlGaN layer can make the current more uniformly distributed laterally and therefore the hole injection efficiency at the mesa edges can be enhanced. As a result, the measured external quantum efficiency (EQE) and optical output power for the proposed UVB LED is increased. Moreover, thanks to the enhanced current spreading effect, the thermal droop for the optical output power is suppressed and the forward voltage decreases for the proposed architecture.
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