Growth, surface morphology, and electrical resistivity of fully strained substoichiometric epitaxial TiNx (0.67 <= x < 1.0) layers on MgO(001)

We have grown single-crystal NaCl-structure delta-TiNx layers with x ranging from 0.67 to 1.00 on MgO(001) at 700 degreesC by ultra-high-vacuum reactive magnetron sputtering of Ti in mixed Ar/N-2 discharges in order to investigate microstructural evolution and the physical properties of TiNx 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)(TiN)parallel to(001)(MgO) and [100](TiN)parallel to[100](MgO). The relaxed lattice parameter a(o)(x) decreases linearly from 4.240 Angstrom with x=1.00 to 4.226 Angstrom with x=0.67. Stoichiometric TiN(001) layers are fully relaxed at the growth temperature while layers with 0.67less than or equal toxless than or equal to0.92 are fully coherent with their substrates. Surface morphologies vary dramatically with x. TiNx(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 TiN0.92(001) and TiN1.00(001) layers, which were grown at higher N-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. TiN1.0(001) layers grown in pure N-2 exhibit growth mounds that are predominantly square with edges aligned along the <110> directions. The room-temperature resistivity, 13 muOmega cm with x=1.00, increases from 52 muOmega cm for TiNx(001) layers with x=0.92 to 192 muOmega cm with x=0.67, due primarily to increased carrier scattering from N vacancies. (C) 2004 American Institute of Physics.