Photoelectrochemical Liftoff of Patterned Sapphire Substrate for Fabricating Vertical Light-Emitting Diode

A low-cost large-area effective sapphire substrate liftoff method based on the photoelectrochemical (PEC) etching technique is demonstrated. By preparing patterned sapphire substrate (PSS) with 1-D periodic grooves and an epitaxial structure with the grooves preserved to form tunnels, PEC electrolyte can flow along the tunnels to etch the bottom of the GaN layer for separating the PSS from the wafer-bonded epitaxial layer. Assisted by the device isolation procedure, the PSS liftoff of a quarter-wafer sample can be completed in 8 min. After a smoothing process of the exposed N-face surface after liftoff, a vertical light-emitting diode (LED) is fabricated for comparing its characteristics with those of a conventional LED.