Advantages of AlGaN Tunnel Junction in N-Polar 284 nm Ultraviolet-B Light Emitting Diode

Abstract

Smart, low cost and environmentally safe aluminum gallium nitride (AlGaN)-based ultraviolet-B light-emitting diodes (UV-B LEDs) are promising in real-world applications including medical as well as agricultural sciences. Higher efficiency droops, low hole injection efficiency, and high operating voltage are the key problems that AlGaN-based UV-B LEDs are facing. In this work, a smart and clean AlGaN-based UV-B LED at 284 nm emission wavelength has been studied. Here an approach is presented to electrically operate the quantum tunnelling probability by exploiting the transported carriers at the interface of p-AlGaN/n-AlGaN/n++-AlGaN tunnel junction (TJ) with moderate Si and Mg-doping levels and optimized thickness with the help of simulation study. The simulation results show that the Augur recombination rate is successfully suppressed and quite a high radiative recombination rate is achieved in the 284 nm N-polar AlGaN-based TJ UV-B LEDs, which is attributed to the improved hole injection toward the MQWs when compared to C-LED (conventional-LED). It is found that C-LED has a maximum IQE (internal quantum efficiency) of 40% under 200 A cm−2 injection current with an efficiency drop of 15%, while the TJ-LED has a maximum IQE of 93% with an efficiency droop of 0%. In addition, TJ-based AlGaN LED emitted power has been improved by 6 times compared to the C-LED structure. The emitted powers of TJ-LED increase linearly under varying current densities, whereas in the case of C-LED, the emitted power changes nonlinearly under varying current densities. This is attributed to the lower Augur recombination rate in the MQWs of N-AlGaN-based TJ UV-B LED. The operating voltages were reduced from 5.2 V to 4.1 V under 200 mA operation, which is attributed to the thickness and doping optimization in TJ and better selection of relatively lower Al-content in the contact layer. N-polar AlGaN-based TJ is explored for UV-B LEDs and the demonstrated work opens the door to epitaxial growth of high-performance UV emitters in MOCVD and MBE for a plethora of biomedical applications.