High wall-plug efficiency blue III-nitride LEDs designed for low current density operation.

Abstract

Commercial LEDs for solid-state lighting are often designed for operation at current densities in the droop regime (~35 A/cm2) to minimize costly chip area; however, many benefits can be realized by operating at low current density (J ≈1 - 5 A/cm2). Along with mitigation of droop losses and reduction of the operating voltage, low J operation of LEDs opens the design space for high light extraction efficiency (LEE). This work presents detailed ray tracing simulations of an LED design for low J operation with LEE ≈94%. The design is realized experimentally resulting in a peak wall-plug efficiency of 78.1% occurring at 3.45 A/cm2 and producing an output power of 7.2 mW for a 0.1 mm2 emitting area. At this operation point, the photon voltage Vp=hνq exceeds the forward voltage (V), corresponding to a Vp/V = 103%.