AlGaN-based ultraviolet light-emitting diodes: challenges and opportunities

Due to low power consumption, tunable wavelength and long lifetime ultraviolet light-emitting diodes (UV LEDs) have found many applications in different fields such as health care, water disinfection, agriculture. In this review, we report different problems that lead to low external quantum efficiency of UV LEDs. We also report various challenges in the growth process of the UV LEDs such as increase in the dislocation density, which affects the optoelectronic performance of the devices. We also report the analysis of the two modes of light polarization, i.e. transverse electric and transverse magnetic in UV LEDs. Moreover, we also summarize various state-of-the-art reported external quantum efficiencies, light output power and peak emission wavelengths in the three UV wavelength regimes, i.e. UV-A, UV-B and UV-C LEDs.