Effects of TMAl predose time on the quality of submicron-thick GaN on Si

Submicron-thick (∼350 nm) gallium nitride (GaN) thin films with lower dislocation densities are grown on silicon (Si) substrate by metal organic chemical vapour deposition (MOCVD). Prior to the growth, a trimethylalluminum (TMAl) predose is performed. The effects of different TMAl predose time on the surface morphology and crystalline quality of submicron-thick GaN are investigated in this study. With prolonged TMAl predose time, the surface becomes rougher, while the screw dislocation densities both for GaN and aluminum nitride (AlN) are reduced. The edge dislocation densities tend to decrease first then increase again when the TMAl predose time is elongated from 90 s over 135 s to 180 s. From the high resolution transmission electron microscopy (HRTEM), we found the thickness of amorphous layer between Si and AlN decreases with the increase of TMAl predose time. Such an amorphous layer should play an important role in the surface morphology and crystalline quality of submicron-thick GaN. A possible mechanism has also been proposed to elucidate the effects of TMAl predose time.