TiN/GaN Metal/Semiconductor Multilayers for Thermionic Energy Conversion

TiN-GaN multilayers were grown for potential application as solid-state thermionic direct energy conversion devices using reactive pulsed laser deposition in an ammonia ambient. The crystallographic analysis of the multilayers by high-resolution x-ray diffraction and crosssectional TEM revealed that, despite the difference in crystal structures of TiN and GaN, it was possible to grow thick uniaxially textured columnar-grained multilayers. Inplane electronic transport was assessed using Hall effect and Seebeck coefficient measurements. Thermal conductivity measurements have shown that by increasing the interface density, the cross-plane thermal conductivity of the multilayers can be reduced to 3.6 W/m-K, compared to 135 W/mK for bulk GaN and 38 W/mK for bulk TiN.