Abstract
The height of the barrier around the AlGaN quantum well has a strong impact on the external quantum efficiency of UVC light emitting diodes (LEDs) as it affects the carrier confinement, the polarization fields, and the injection efficiency as well as the optical polarization and emission profile of the emitted light. The electro-optical properties such as emission wavelength, optical polarization, and light output power of AlGaN multiple quantum well (MQW) LEDs emitting around 270 nm with Al mole fraction in the AlxGa1−xN barriers between x = 55% and x = 76% are investigated by electroluminescence measurements. In order to analyze the experimental results, 6-band k·p method-based simulations as well as single band Schrödinger-Poisson drift-diffusion simulations have been conducted. It was found that for the same current density of 100 A cm−2 the on-wafer emission power reaches a maximum for an Al mole fraction of x = 67% in the AlxGa1−xN barrier of the Al0.53Ga0.47N MQW (0.84 mW at 40 mA). Furthermore, the emission wavelength decreases and the fraction of transverse-electric polarized light emission increases with increasing Al mole fraction in the barrier. This is consistent with drift-diffusion and k·p simulations, attributing the changes of the emission power primarily to changes in charge carrier injection and electrical confinement in the quantum wells rather than to changes in the optical polarization and light extraction.
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