Performance of high-power III-nitride light emitting diodes

The performance of III-nitride based high-power light emitting diodes (LEDs) is reviewed. Direct color high-power LEDs with 1 x 1 mm(2) chip size in commercial LUXEON (R) Rebel packages are shown to exhibit external quantum efficiencies at a drive current of 350 mA ranging from similar to 60% at a peak wavelength of similar to 420 nm to similar to 27% at similar to 525 run. The short wavelength blue LED emits similar to 615 mW at 350 mA and > 2 W at 1.5 A. The green LED emits similar to 110 lm at 350 mA and similar to 270 lm at 1.5 A. Phosphor-conversion white LEDs (1 x 1 mm(2) chip size) are demonstrated that emit similar to 126 lm of white light when driven at 350 mA and 381 lm when driven at 1.5 A (Correlated Color Temperature, CCT similar to 4700 K). In a similar LED that employs a double heterostructure (DH) in-stead of a multi-quantum well (MQW) active region, the luminous flux increases to 435 lm (CCT similar to 5000 K) at 1.5 A drive current. Also discussed are experimental techniques that enable the separation of internal quantum efficiency and extraction efficiency. One technique derives the internal quantum efficiency from temperature and excitation-dependent photoluminescence measurements. A second technique relies on variable-temperature electroluminescence measurements and enables the estimation of the extraction efficiency. Both techniques are shown to yield consistent results and indicate that the internal quantum efficiency of short wavelength blue (lambda similar to 420 nm) high-power LEDs is as high as 71% even at a drive current of 350 mA.