Visible laser light lift-off for UV-A LEDs on free-standing GaN

Meijo and Nagoya universities in Japan have developed a laser lift-off (LLO) technique for removing gallium nitride (GaN) substrates from ultraviolet (UV) light-emitting diodes (LEDs) to improve light extraction efficiency [Daisuke Iida et al, Appl. Phys. Lett., vol105, p072101, 2014]. GaN substrates absorb UV-A light due to impurities such as oxygen and carbon. Typical LLO techniques use UV laser light to separate GaN buffer layers from sapphire substrates. The UV light is strongly absorbed by the GaN layers but not by the sapphire. The absorbed light decomposes the GaN structure and droplets of Ga form, allowing separation of the GaN from sapphire.