Scandium nitride thin film is grown on MgO(001) using radio frequency molecular beam epitaxy. Both X-ray diffraction and reflection high energy electron diffraction show that the grown films have a rocksalt structure and are 001-oriented. For growth under N-rich conditions, at which the N-effective flux is more than the Sc flux, the film is found to be stoichiometric resulting in surface morphology of flat-topped mounds and four-sided spiral pyramids. However, under Sc-rich growth conditions the resultant films are under stoichiometric with surface morphology of rounded spiral mounds. This difference of the surface morphology is attributed to the change of the surface diffusion barrier of both growth modes. Since the Sc (N) atom has 3 (5) electrons in the outer shell, 3d1 4s2 (2s2 2p3), ScN is expected to exhibit a semiconducting behavior. Moreover, due to stabilizing in a rocksalt structure, ScN is predicted to have an optical gap at the X point and an indirect gap between the Γ point (in the valence band) and the X point (in conduction band). Optical absorption measurements confirm the transition at the X point, showing a direct gap of 2.15 eV. However, the measurement of the indirect gap using the same technique is very difficult due to two reasons. First, the absorption coefficient of the indirect gap is significantly less than that of the direct one. Second, the vapor pressure of Sc is low which requires high temperature to evaporate, of 1400 oC, leading to high level of impurity incorporation in the film. This impurity incorporation causes other transitions due to impurity states. In this work, it is presented that how nano-probing, using scanning tunneling microscopy and spectroscopy, is employed to investigate the surface diffusion barriers and the existence of the indirect gap of ScN(001), showing good agreements with the experimental observations and recent theoretical results.

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