Aluminum nitride films on different orientations of sapphire and silicon

The details of epitaxial growth and microstrictural characteristics of AlN films grown on sapphire (0001), (1012) and Si (100), (111) substrates were investigated using plan-view and cross-sectional high-resolution transmission electron microscopy and x-ray diffraction techniques. The films were grown by metalorganic chemical vapor deposition using TMAl +NH₃+N₂ gas mixtures. Different degrees of epitaxy were observed for the films grown on α-Al²O₃ and Si substrates in different orientations. The epitaxial relationship for (0001) sapphire was found to be (0001)_AlN∥(0001)_sap with in-plane orientation relationship of [0110]_AlN∥[1210]_sap. This is equivalent to a 30° rotation in the basal (0001) plane. For (1012) sapphire substrates, the epitaxial relationship was determined to be (1120)_AlN∥(1012)_sap with the in-plane alignment of [0001]_AlN∥[1011]^sap. The AlN films on (0001) α-Al₂O₃, were found to contain inverted domain boundaries and a/3〈1120〉 threading dislocations with the estimated density of 10¹⁰ cm^-2. The density of planar defects (stacking faults) found in AlN films was considerably higher in the case of (1012) compared to (0001) substrates. Films on Si substrates were found to be highly textured c axis oriented when grown on (111) Si, and c axis textured with random in-plane orientation on (100) Si. The role of thin-film defects and interfaces on device fabrication is discussed.