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Aluminium Gallium Nitride (AlGaN) based light emitting diodes (LED) are the enabling technology for compact emitters of deep ultraviolet (DUV) radiation and are in high demand for environmental and medical applications. The efficiency of recent DUV LEDs is in the range of a few percent providing some potential for improvement. Apart from the light extraction efficiency the hole injection into the active region presents a major obstacle towards more efficient DUV LEDs. In this work, we investigate the emission spectra of a mixed multi quantum well (MQW) DUV LED to attain details on the active region carrier transport that allow an improvement of the hole injection. Changing the position of the long wavelength marker quantum well yields characteristic emission spectra which have been modelled with a multi scale carrier transport and luminescence simulator. The numerical modelling enables the extraction of opaque carrier transport characteristics in AlGaN such as the hole mobility in the highly doped barriers of the MQW.

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. [ABSTRACT FROM AUTHOR]