Fig. 3: Laser system configuration and micromachining pattern of fs-LLO for GaN nanoLEDs. | Microsystems & Nanoengineering

Fig. 3: Laser system configuration and micromachining pattern of fs-LLO for GaN nanoLEDs.

From: Wafer-scale transfer route for top–down III-nitride nanowire LED arrays based on the femtosecond laser lift-off technique

Fig. 3

a Laser beam path in the setup during the fs-LLO process based on raster scanning utilizing a Galvano x-y scanner. b Schematic of fs-LLO for GaN nanoLEDs embedded in an SU-8 layer. The laser light is transmitted through the wafer backside (sapphire). c Energy band diagram of fs-LLO illustrating two-photon absorption in GaN material using femtosecond pulses at 520 nm. The excitation of two photons (2 hv) from the laser possesses higher energy than GaN (E2) but lower energy than the sapphire (E1) bandgap. d Scheme of the fs-LLO pattern showing pulse overlap and number. OL and OT are the percentage amounts of overlap between the diameters of two consecutive pulses in the lateral and transverse directions, respectively. D and a are assigned to diameter of craters in the n-GaN layer caused by the beam spot on the GaN surface and the track displacement (transverse pitch between passes), respectively

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