Radiative recombination of a high internal-quantum-efficiency 268 nm ultraviolet C-band light emitting diode

Abstract

After assigning a thickness d to the carrier recombination region of a light emitting diode (LED), we show that the ABC model involving Shockley–Read–Hall non-radiative, radiative, and Auger recombination coefficients, i.e., A, B, and C, respectively, can bring new insight into the radiative recombination process. In order to fit external quantum efficiency (EQE) data of ultraviolet C-band (UVC) as well as blue LEDs, the ABC model requires the product d·B to be invariant of the injection current. This can be understood that as the thickness of the recombination region increases the radiative recombination coefficient decreases due to reduced electron–hole wavefunction overlaps. For an LED with high internal quantum efficiency (IQE), its quality factor Q (Q=BAC) usually undergoes a noticeable drop as the injection current increases to pass the current of maximal EQE. This is due to an increase in the thickness of the recombination region and, hence, a reduction in the radiative recombination coefficient as the injected carriers start to drift or diffuse to involve more quantum wells for light emission. Applying this ABC model, we analyze a high-efficiency 268 nm UVC LED, which delivers ∼199 mW optical power under a direct current of 350 mA and obtains a maximal IQE of ∼86.4% and an effective light extraction efficiency of ∼15.3%.