Effect of the Nucleation Layer on Stress during Cantilever Epitaxy of GaN on Si (111)

Abstract

We have investigated the effect of the nucleation layer on subsequent film stress of GaN grown on Si (111) patterned with periodic mesas, using the cantilever epitaxy technique. GaN was nucleated on the unetched substrate mesa and proceeded to grow laterally over the trench region with low dislocation density material resulting in the wing region - the area over the trench. We have shown that by reducing the thickness of the AlN nucleation layer to 500 A, the uncoalesced GaN stripes are essentially crack free. We have also studied the effect of inserting a linear grade from the AlN nucleation layer to GaN. The grade increased the crack density from 4.65 × 10 -4 μm -1 with no grade to values ranging from 2.25 × 10 -2 to 1.29 × 10 -3 μm -1 . As the thickness of the grade increased the crack density approaches that obtained with no grade. X-ray diffraction was also used to characterize the nucleation layers effect on both, the structural quality and crystallographic wing tilt.