Self-separated freestanding GaN using a NH4Cl interlayer

Thick GaN films were grown on void buffer layer by hydride vapor phase epitaxy. The void-buffer layers were consisted of NH4Cl, GaN dots, and low-temperature (LT) GaN buffer layer. Instead of GaN, NH4Cl was easily synthesized in NH3 and HCl atmospheres by simply lowering the growth temperature to 500 degrees C, and LT GaN buffer growth was followed during increasing substrate temperature to 600 degrees C. The LT GaN buffer acted as a protecting layer against evaporation of the NH4Cl and a seeding layer for the high temperature (HT) GaN. The NH4Cl layer between a sapphire substrate with GaN dots and the LT GaN buffer were fully evaporated during the HT GaN growth at 1040 degrees C. Many voids were formed at interface caused by evaporation of the NH4Cl layer, which strongly assisted self-separation of thick HT GaN during cooldown after the growth resulting in a 200 mu m thick freestanding (FS) GaN. The FS GaN showed smooth surface morphology and absence of any crack. The a-axis and c-axis lattice constants of FS GaN were 3.189 and 5.185 A, respectively, which well agrees with those of strain-free bulk GaN. The observed donor-bound exciton emission peak at 3.4718 eV agreed with the peak position of bulk GaN. All these features indicate that the obtained FS GaN through the self-separation process is nearly strain-free.