The recent development of magnetron sputter epitaxy to the growth of high quality GaN films^[1] and the incorporation of high concentrations of transition metals to GaN without segregation^[2] has brought bold interest to deposition routes using reactive magnetron sputtering. In special this investigation reports on the combined effects of substrate orientation, temperature, and energetic particle collisions on the structure of GaN films deposited using radio frequency (RF) reactive magnetron sputtering. In the process a liquid Ga target was exposed to a plasma, generated from a gas mixture of N₂ and Ar. C-plane and a-plane sapphire and silica glass were used as substrates, with temperatures varying in the 100-1000°C range. X-ray diffraction, optical absorption, atomic force and scanning electron microscopies have been employed to characterize the films. The energy distribution of the species generated in the plasma and colliding with the growth surface were estimated using Monte Carlo based computer simulations. 

All films are polycrystalline, presenting wurtzite structure (P6₃mc spatial group), and different degrees of orientation texture with a tendency of the c-axis of the film being perpendicular to the substrate surface. The rocking curves are much sharper (of the order of 1°) on films deposited in the 600-800°C for depositions onto c- and a- plane sapphire substrates, while on amorphous silica the rocking curves remain broad, so the tendency to epitaxy is clearly noticed.  An increase on interplanar spacings of different planes (compatible with the increase of both a and c lattice parameters) for depositions at higher substrate temperatures (T_s = 700°C) is observed.  It is suggested that the effect is associated with the presence of a high density of self interstitial atoms produced by the incidence of energetic N⁺ ions from the plasma and correlates well with the observed redshift of the optical bandgap. The effects of the swelling produced by self interstitials are observed to dominate the structural characteristics of the analyzed films grown at in the 700-1000°C range. The optimization of growth parameters and alternatives to minimize the defects produced by ion collisions in reactive magnetron sputtering are discussed. 

[1] M. Junaid, et al. Applied Physics Letters, Vol. 98, 141915 (2011).

[2] D.M.G. Leite, et al. Journal of Crystal Growth. , Vol. 327, p.209 – 214 (2011).

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1. Effects of substrate orientation, temperature and energetic atomic collisions on the structure of GaN and TiO₂ films grown by reactive sputtering