Enhanced light output of vertical-structured GaN-based light-emitting diode with surface roughening using KrF laser and ZnO nanorods

To further improve the performance of vertical-structured GaN-based light-emitting diodes (V-LEDs), surface roughening using a KrF laser and KOH wet chemical etching, followed by hydrothermal growth of vertically aligned ZnO nanorods on top of the n-GaN surface were investigated and discussed. Compared with that of the V-LEDs (300 × 300 μm² in chip size) with only surface KOH wet etching, the formation of curved protrusions and ZnO nanorods on the n-GaN surface typically enables an increase in light output power (L_op) by 29% at 20mA and 41% at 100mA with a decrease in forward voltage (V_f) from 3.24 to 3.06 V at 20mA and 3.9 to 3.7V at 100 mA, respectively. The cumulative effect of the curved protrusions, hexagonal cones, and vertically aligned ZnO nanorods formed as a result of effectively reducing the effective thickness of the n-GaN layer, improving the ohmic contact to n-GaN, increasing the surface emission area, and enhancing the escape probability of photons was responsible for these improvements.