Effect of AlN interlayers on growth stress in GaN layers deposited on (111) Si

Thin (∼10 nm) AlN interlayers have previously been used to mitigate stress and cracking in GaN epitaxial layers grown on Si substrates. However, multiple AlN interlayers are typically required for the growth of thick (>1 μm) GaN as the initial compressive mismatch stress introduced by the AlN interlayer transitions to a tensile stress within 0.5 μm. To better understand the reasons for the transition, in situ monitoring and transmission electron microscopy have been used to study stress and structural evolution in undoped GaN layers deposited on high temperature (1050-1100 °C) AlN interlayers by metal-organic chemical-vapor deposition. The results show that transition of the initial compressive stress to a final tensile stress is associated with a reduction in the density of dislocations introduced either by the pseudosubstrate or the interlayer itself.