Cross-Plane Thermal Conductivity Measurements of Periodical Nanoporous In$_{\mathrm{0.1}}$Ga$_{\mathrm{0.9}}$N Thin Films

Nanoporous thin films are expected to reduce lattice thermal conductivity while maintain the bulk-like electrical properties, which can yield a high thermoelectric figure of merit (ZT) [1,2]. For Si thin films, a room-temperature ZT\textasciitilde 0.4 has been reported for 55-nm-pitch nanoporous patterns [3]. Along this line, a high ZT is also anticipated for other nanoporous thin films whose bulk counterparts have superior electrical properties but high lattice thermal conductivities. In this work, the cross-plane thermal conductivities of nanoporous In$_{\mathrm{0.1}}$Ga$_{\mathrm{0.9}}$N thermoelectric thin films [4] with varied porous patterns are measured with the time-domain thermoreflectance technique. In our measurements, a remarkable thermal conductivity reduction has been observed for In$_{\mathrm{0.1}}$Ga$_{\mathrm{0.9}}$N thin films with relatively large sub-micron nanoporous features. Our studies provide guidance for ZT enhancement in nanostructured nitrides and oxides. References: [1] Marconnet et al., Journal of Heat Transfer 135, 061601-1/10 (2013). [2] Cahill et al., Appl. Phys. Rev. 1, 011305 (2014). [3] Tang et al., Nano Lett. 10, 4279-4283 (2010). [4] Lu et al., Semicond. Sci. Technol. 28, 074023 (2013).