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The 4×1 (respectively 1×1) (001) GaN surfaces obtained when molecular-beam-epitaxy (MBE) growth is carried out on (001) cubic SiC were exposed to an As background pressure in the MBE chamber: The reconstructions rapidly and irreversibly changed to 2×2 [respectively c(2×2)] as usually observed for GaN growth on (001) GaAs. The usual reversible 2×2/c(2×2) transitions were consequently observed when bringing the Ga flux up or down. The respective positions for the 4×1/1×1 and 2×2/c(2×2) transitions were worked out as a function of the growth parameters. These observations indicate that the 2×2 and c(2×2) GaN surface reconstructions are mediated by As atoms which we tentatively assign to a surfactant effect. A simple structural model involving As dimers is proposed that accounts for Ga coverages of 0.5 and 1 monolayer for the 2×2 and c(2×2) growth regimes, respectively.

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Small amounts of As residual pressure were found to affect the structure of cubic GaN growing surfaces in molecular beam epitaxy growth, i.e., modification of surface reconstruction structures, stabilization of reconstructed flat surfaces at high substrate temperatures, and preferential growth of the cubic phase. These As surfactant effects are discussed in relation to the atomic arrangement of the As-passivated surface of GaN. It was shown that the quality of cubic GaN epilayers can be improved by utilizing a small amount of As residual pressure.

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