Enhancing the light extraction efficiency of AlGaN LED with nanowire photonic crystal and graphene transparent electrode

The performance of AlGaN deep ultraviolet(UV) light emitting diodes(LEDs) has been limited by the extremely low light extraction efficiency(LEE), which is due to the severe light absorption by metal electrode and unique transverse magnetic polarization. Here, we propose an ordered nanowire array structure UV-LEDs with transparent graphene electrode. By using the finite-difference time domain simulation, the relationship between LEE and different nanowire structures (including ordered and disordered nanowires array) was studied. We demonstrate that ordered nanowire arrays are better than disordered nanowires in improving the LEE. A high LEE about 80% can, in principle, be expected from top surface with optimized nanowire radius and spacing. In addition, by studying the distribution of electric field intensity on the side and top of UV-LEDs with graphene electrode and Ni/Au electrode, we show that the graphene electrode can reduce the absorption of ultraviolet light and improve LEE more effectively than the conventional Ni/Au electrode. This proposed structure could be a promising candidate for high light extraction efficiency UV-LEDs.