Initial stages of GaN/GaAs(100) growth by metalorganic chemical vapor deposition

A study of GaN buffers grown by metalorganic chemical vapor deposition on (001) GaAs substrates was performed. Nucleation images obtained by atomic force microscopy (AFM) were employed to investigate the growth temperature, growth time, and growth rate dependence of the nucleation mechanisms. The growth mode corresponds to two-dimensional (2D) island nucleation at low temperatures, while three-dimensional (3D) island growth is observed at high temperatures. Large grain sizes and good surface coverage was obtained for 3 min growth. Higher growth rates help nucleation on mismatched substrate and promote the 2D growth mode. GaN films 0.5 μm thick were grown on different buffers using a two-step technique as suggested by the AFM analysis and their morphology was found to improve when grown on optimized buffers.