On the laser lift-off of lightly doped micrometer-thick $n$-GaN films from substrates via the absorption of IR radiation in sapphire

The intense absorption of CO$_2$ laser radiation in sapphire is used to separate GaN films from GaN templates on sapphire. Scanning of the sapphire substrate by the laser leads to the thermal dissociation of GaN at the GaN/sapphire interface and to the detachment of GaN films from the sapphire. The threshold density of the laser energy at which $n$-GaN started to dissociate is 1.6 $\pm$ 0.5 J/cm$^2$. The mechanical-stress distribution and the surface morphology of GaN films and sapphire substrates before and after laser lift-off are studied by Raman spectroscopy, atomic-force microscopy, and scanning electron microscopy. A vertical Schottky diode with a forward current density of 100 A/cm$^2$ at a voltage of 2 V and a maximum reverse voltage of 150 V is fabricated on the basis of a 9-$\mu$m-thick detached $n$-GaN film.