Growth, surface morphology, and electrical resistivity of fully strained substoichiometric epitaxial TiN[sub x] (0.67<=x<1.0) layers on MgO(001).

We have grown single-crystal NaCl-structure δ-TiN[sub x] layers with x ranging from 0.67 to 1.00 on MgO(001) at 700 °C by ultra-high-vacuum reactive magnetron sputtering of Ti in mixed Ar/N[sub 2] discharges in order to investigate microstructural evolution and the physical properties of TiN[sub x] as a function of the N vacancy concentration. High-resolution x-ray diffraction and transmission electron microscopy results show that all layers grow with a cube-on-cube epitaxial relationship to the substrate, (001)[sub TiN]∥(001)[sub MgO] and [100][sub TiN]∥[100][sub MgO]. The relaxed lattice parameter a[sub o](x) decreases linearly from 4.240 Å with x=1.00 to 4.226 Å with x=0.67. Stoichiometric TiN(001) layers are fully relaxed at the growth temperature while layers with 0.67<=x<=0.92 are fully coherent with their substrates. Surface morphologies vary dramatically with x. TiN[sub x](001) layers with x=0.67–0.82 have very flat surfaces arising from large cation surface diffusion lengths approaching values corresponding to step flow. However, the surfaces of the TiN[sub 0.92](001) and TiN[sub 1.00](001) layers, which were grown at higher N[sub 2] partial pressures, consist of a periodic two-domain ripple structure along the <110> directions due to kinetic roughening associated with lower cation surface mobilities resulting from higher steady state N coverages. TiN[sub 1.0](001) layers grown in pure N[sub 2] exhibit growth mounds that are predominantly square with edges aligned along the <110> directions. The room-temperature resistivity, 13 μΩ cm with x=1.00, increases from 52 μΩ cm for TiN[sub x](001) layers with x=0.92 to 192 μΩ cm with x=0.67, due primarily to increased carrier scattering from N vacancies. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]