CHARACTERIZATION OF MISFIT DISLOCATIONS IN EPITAXIAL (001)-ORIENTED TIN, NBN, VN, AND (TI,NB)N FILM HETEROSTRUCTURES BY TRANSMISSION ELECTRON-MICROSCOPY

Transmission electron microscopy (TEM) was employed to characterize the misfit dislocation systems in epitaxial bilayer films of TiN, NbN, VN, and TiNbN as a function of overlayer film thickness and degree of lattice mismatch. Thin epitaxial nitride overlayers on 100 nm thick nitride buffer layers were deposited by dual-cathode ultra-high vacuum magnetron sputtering onto MgO(001) substrates. Plan-view weak-beam TEM showed that the primary misfit dislocations were of edge type with line direction [110] and Burgers vectors 1/2[110BAR] within the plane of the interface. The critical thickness for the onset of strain relaxation increased with decreasing mismatch epsilon from < 2 nm for NbN/TiN (epsilon = 3.6%) to 2-3 nm for VN/TiN and TiN/Ti0.3Nb0.7N (epsilon = 2.4%) and to 3 5 nm for NbN/Ti0.3Nb0.7N (epsilon = 1%). Domain formation was observed in all systems above a critical thickness.