In-rich InAlN films were grown directly on Si (111) substrate by RF-MOMBE without any buffer layer. InAlN films were grown at various substrate temperatures in the range of 460–540°C with TMIn/TMAl ~3.3. Structural properties of InAlN ternary alloys were investigated with X-ray diffraction, scanning electron microscopy, and transmission electron microscopy (TEM). It is shown that the deposited In0.8AlM0.2N (0001) films can be in epitaxy with Si (111) substrate with orientation relationship of // . Also, the growth rate around ~0.25？μm/h almost remains constant for growth in the temperature range from 460 to 520°C. Cross-sectional TEM from InAlN grown on Si (111) at 460°C shows that the epitaxial film is in direct contact with Si without any interlayer. 1. Introduction The technological importance of group III nitrides GaN, InN, and AlN, particularly for the light-emitting and laser diodes operating in green and blue spectral regions, has stimulated the study of , , and alloys. The hexagonal InAlN alloy offers various unique properties which may improve the performance of electronic and optoelectronic devices. InAlN has a direct gap that can be tuned in the range from 6.2？eV for AlN to 0.7？eV for InN [1]. In particular, In-rich InAlN is a promising material for multijunction tandem solar cells [2]. For growth of InAlN in large area at low cost, deposition on Si (111) is of great interest. However, it is difficult to grow In-rich InAlN of single phase, and its epitaxy on Si substrate is also a challenge due to large lattice mismatch. Although reports of InAlN-based devices have been published [3–5], the growth mechanism of InAlN on Si substrate is still unclear. Previous studies of InAlN growth indicated that the constituent binary components AlN and InN have very different lattice parameters (13.5% mismatch for the a-parameter) and very different optimum growth temperatures (600°C for InN and 1100°C for AlN for metalorganic chemical vapor deposition (MOCVD)). Also, Koide et al. and Zhao et al. indicated the parasitic reaction may prohibit incorporation of Al content and deteriorate the material quality [6, 7]. Particularly, Guo and coworkers [8] fabricated the high quality films with being from 0 to 0.14 in the low-Al composition regime using metalorganic vapor phase epitaxy. Due to the difficulties of growth, In-rich layers often exhibit poor crystalline quality. The presence of composition fluctuations and surface hillocks has been reported [9, 10]. Also, silicon is a very promising substrate material for the growth of III-nitride materials. Compared
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