Growth of dislocation-free GaN islands on Si(1 1 1) using a scandium nitride buffer layer

Gallium nitride was deposited using metal-organic vapour-phase epitaxy (MOVPE) on Si(1 1 1) substrates, using buffer layers of scandium nitride grown by gas-source molecular beam epitaxy (GS-MBE). A series of ScN buffer layers with varying roughness, thickness and crystallinity were used. The buffer layer crystallinity was shown to affect the morphology, residual strain and crystallinity of the subsequently grown GaN as well as the degree of wetting of ScN by GaN. The orientation of the GaN with respect to the ScN and the Si substrate was (0 0 0 1)GaN∥(1 1 1)ScN∥(1 1 1)Si, [0 1 1¯ 0]GaN∥[1 1 2¯]ScN∥[2 1¯ 1¯]Si. GaN grown directly onto ScN buffer layers at 1020 °C displayed island growth with limited wetting of the ScN. The reduced ScN–GaN interfacial area resulted in the growth of dislocation-free GaN islands of several microns in diameter. Predeposition of small amounts of GaN on the ScN at either 750 or 540 °C promoted wetting of the ScN by GaN and hence increased coalescence, allowing a continuous film to form; however, the increased ScN–GaN interfacial area resulted in the presence of threading dislocations. These were predominantly screw and mixed-type dislocations.