Postannealing effect of GaN on reactive ion beam pre-treated sapphire.

Abstract

Previous study showed that the reactive ion beam (RIB) pretreatment of sapphire prior to GaN deposition results in the reduction of dislocation density in GaN lm. Also there was an amorphous phase remaining at the interface region after the GaN deposition at high temperature. Postannealing process was employed to see the structural change due to the recrystallization of the remaining amorphous phase, and the postannealing e ect on electrical property of the GaN thin lm on RIB treated sapphire (0001) substrate. FWHM of DCXRD spectra and hall mobility of the specimen showed the variation with the various postannealing time at 1000 C in N2 atmosphere. For the postannealed specimen, FWHM of DCXRD reduced about 50arc-sec and the mobility increased about 80 cm2/V sec. The postannealed specimen with the best mobility was compared with not annealed sample by TEM and observe the decrease of lattice strain and reduction of dislocation density about 56 59 %. The present results clearly show that the combination of RIB pretreatment and proper post annealing conditions results in the improved properties of GaN lms grown by MOCVD.