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High‐temperature GaN films were grown at 1120 °C and 1080 °C by atmospheric pressure metalorganic vapor phase epitaxy on silicon nitride (SiN)‐treated sapphire using a GaN buffer layer grown at 600 °C. The effect of a SiN interlayer has been investigated. We have varied the silane (SiH4) flow from 4 to 20 sccm and the duration of SiN treatment from 60 s to 180 s. These layers have been characterized in‐situ by laser reflectometry and ex‐situ by atomic force microscopy (AFM) and low‐temperature photoluminescence. AFM revealed that GaN grown with optimized SiN treatment shows a terrace‐like structure with a reduced density of dislocations of about 5 × 108 cm−2 compared to GaN without SiN treatment. The I2 line is very intense with a 4 meV full width at half maximum. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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The SiN treatment of the sapphire substrate for GaN growth induces a spectacular effect on the in situ reflectometry monitoring signal. Different growth modes are observed. The evolution of the reflectometry signal is simulated by the scattering theory approximation. The point-by-point analysis reveals that the roughness (rms) increases in the first region where the growth mode is dominated by the formation of isolated and three-dimensional hillocks. The rms attains a maximum value exceeding that authorized by the Rayleigh criteria. Another approach based on the effective medium approximation is used to simulate the entire reflectometry signal evolution. An effective refractive index and a growth rate profile are determined. The results obtained are in accordance with the observations done by the in situ ellipsometry monitoring. We have also studied the evolution of the defined recovery time as a function of the SiH 4 flow rate and the SiN duration. Based on the concept of a nano-epitaxial mask, induced by the SiN treatment of the sapphire surface, we have proposed a schematic model of the GaN growth that explains the recoverytime behavior.