We have studied the structural and electronic properties of InAs bulk and nanowires by using density functional theory – pseudo potential computations, with local density approximation. The stable structure of bulk InAs is Zinc Blende (ZB) although under special experimental conditions Wurtzite (WZ) InAs has also been observed. Due to the high symmetry and low ratio of dangling bonds, we have considered triangular and hexagonal WZ nanowires in [0001] direction and hexagonal ZB nanowires in [111] direction. In order to select facets of the nanowires, we calculated formation energy of nonpolar surfaces of both structures and found that ZB(110) and WZ(1010) are most stable than others. All nanowires were calculated in the optimized and relaxed supercells. Calculating the cohesive energy of nanowires with small diameter nanowires were fitted by a phenomenological model to obtain dangling bond energies and then extrapolate the cohesive energy of large diameter nanowires. The extrapolate results indicate that for diameters up to 50 Angstrom, the WZ nanowires are more stable than ZB nanowires while for larger diameters, the contribution of dangling bonds reduces and the results converge to that of bulk InAs. In spite of the presence of dangling bonds at surfaces, WZ InAs nanowires are semiconducting. By the quantum confinement, the band gap increases as the diameter of nanowires reduces, but the increase seems to be slower than what we expect from simple quantum mechanical model. In WZ nanowires the top of valence band is mainly contributed by As-4p valence electrons, while the bottom of conduction band is contributed by In-5p valence electrons. Key Words: Semiconductor Nanowires, InAs, Density Functional Theory, Pseudo Potential, Nanpolar Surfaces, Cohesive Energy, Dangling Bonds, Quantum Confinement.
