Growth of epitaxial CrN on MgO(001): Role of deposition angle on surface morphological evolution

Abstract

CrN layers, 6 to 500 nm thick, were grown on MgO(001) at 600 °C by ultra-high-vacuum magnetron sputter deposition in pure N 2 discharges at 2.6 Pa. The deposition angle α with respect to the surface normal was varied from 0° to 80° in order to directly probe the effect of atomic shadowing on the surface morphological evolution. Layers grown with α = 0° are single crystals which develop a regular surface mound structure. At low layer thicknesses, t ≲ 25 nm, the surface mounds grow primarily vertically, due to kinetic roughening, and form square-shapes with edges along low-energy 〈100〉, directions. Continued growth at t ≳ 25 nm is dominated by mound-competition and coalescence which leads to a self-similar growth mode with increases in both mound height and width. Layers deposited from oblique angles α = 80° also nucleate as single crystals with a cube-on-cube epitaxial relationship with the substrate. However, rough surfaces with cauliflower-type morphologies cause the nucleation of misoriented CrN grains that develop into cone-shaped grains that protrude out of the epitaxial matrix to form triangular faceted surface mounds. Atomic shadowing exacerbates the growth rate of these misoriented grains, causing a dramatic increase in the root-mean-square surface roughness, which is ∼ 16× higher for layers grown at α = 80° than at α = 0°. The roughening follows a power-law with a roughening exponent β that increases from 0.37 ± 0.04 to 0.57 ± 0.15 as α is increased from 0° to 80°. This increase is attributed to a transition from kinetic roughening to roughening caused by atomic shadowing effects.