Microstructural analysis of GaN films grown by a two-step technique on patterned GaN and sapphire

Microstructural characterization of a two-step growth process used for the deposition of GaN layers on GaN and sapphire substrates with stripe patterns was performed by transmission electron microscopy. As the initial growth temperature at a low reactor pressure was lowered, TEM images show a triangular-shaped GaN film and the change of propagation direction of dislocations into the horizontal direction due to the enhancement of the vertical growth rate regardless of the underlying layers. This led to the reduction of threading dislocation density in the surface of both window and seed regions. After the initial growth at low temperature designed to bend dislocations, GaN films were grown at a high temperature to enhance the lateral growth for the coalescence of the wing region. For the growth of GaN on the sapphire substrate patterned with SiO₂ thin film, the pattern direction of (112̄0) is more effective for the bending and reduction of dislocations.