Single-step fabrication of Fresnel microlens array on sapphire substrate of flip-chip gallium nitride light emitting diode by focused ion beam

A simple one-step focused ion beam milling technique was used to fabricate a Fresnel microlens array on the backside of sapphire substrate of a gallium nitride blue light emitting diode. The optical output power from the flip-chip gallium nitride blue light emitting diode is enhanced to about 1.68 times at the injection current of 20mA. The spatial light distribution from the backside of flip-chip gallium nitride blue light emitting diode with a Fresnel microlens array shows a uniform and stronger light emission.