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 = B A C) 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%.