Growth of TiN∕GaN metal/semiconductor multilayers by reactive pulsed laser deposition

Ti N ∕ Ga N metal/semiconductor multilayers were grown by reactive pulsed laser deposition in an ammonia ambient on sapphire and MgO substrates for potential application in solid-state thermionic direct energy conversion devices. Crystallographic analysis of the multilayers by high-resolution x-ray diffraction and cross-sectional transmission electron microscopy revealed that, despite the difference in the crystal structures of rocksalt TiN and wurtzite GaN, it is possible to grow thick (micron scale) uniaxially textured columnar-grained multilayers with nanoscale periods and without agglomeration. X-ray scattering suggests that epitaxial growth of TiN∕GaN multilayers on (100) MgO substrates stabilizes ultrathin (1–2nm) GaN layers in the high-pressure rocksalt polymorph yielding (100) oriented rocksalt TiN∕GaN superlattices. The challenges in growth and the chemical and morphological stability of lattice- and structure-mismatched multilayers are discussed on the basis of kinetic and thermodynamic factors.