PHASE-SEPARATION AND ORDERING IN INGAN ALLOYS GROWN BY MOLECULAR-BEAMEPITAXY

In this study, we investigated phase separation and long-range atomic ordering phenomena in InGaN alloys produced by molecular beam epitaxy. Films grown at substrate temperatures of 700-750 degrees C with indiu m concentration higher than 35% showed phase separation, in good agree ment with thermodynamic predictions for spinodal decomposition. Films grown at lower substrate temperatures (650-675 degrees C) revealed com positional inhomogeneity when the indium content was larger than 25%. These films, upon annealing to 725 degrees C, underwent phase separati on, similar to those grown at the same temperature. The InGaN films al so exhibited long-range atomic ordering. The ordering parameter was fo und to increase with the growth rate of the films, consistent with the notion that ordering is induced at the growth surface. The ordered ph ase was found to be stable up to annealing temperatures of 725 degrees C. A competition between ordering and phase separation has been obser ved, suggesting that the driving force for both phenomena is lattice s train in the alloy. (C) 1998 American Institute of Physics.