Largely reduced cross-plane thermal conductivity of nanoporous In0.1Ga0.9N thin films directly grown by metal organic chemical vapor deposition
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In recent year, nanoporous Si thin films have been widely studied for their potential applications in thermoelectrics, in which high thermoelectric performance can be obtained by combining both the dramatically reduced lattice thermal conductivity and bulk-like electrical properties. Along this line, a high thermoelectric figure of merit (ZT) is also anticipated for other nanoporous thin films, whose bulk counterparts possess superior electrical properties but also high lattice thermal conductivities. Numerous thermoelectric studies have been carried out on Si-based nanoporous thin films, whereas cost-effective nitrides and oxides are not systematically studied for similar thermoelectric benefits. In this work, the cross-plane thermal conductivities of nanoporous In0.1Ga0.9N thin films with varied porous patterns were measured with the time-domain thermoreflectance technique. These alloys are suggested to have better electrical properties than conventional Si x Ge1–x alloys; however, a high ZT is hindered by their intrinsically high lattice thermal conductivity, which can be addressed by introducing nanopores to scatter phonons. In contrast to previous studies using dry-etched nanopores with amorphous pore edges, the measured nanoporous thin films of this work are directly grown on a patterned sapphire substrate to minimize the structural damage by dry etching. This removes the uncertainty in the phonon transport analysis due to amorphous pore edges. Based on the measurement results, remarkable phonon size effects can be found for a thin film with periodic 300-nm-diameter pores of different patterns. This indicates that a significant amount of heat inside these alloys is still carried by phonons with ~300 nm or longer mean free paths. Our studies provide important guidance for ZT enhancement in alloys of nitrides and similar oxides.
Keywordsnanoporous film thermoelectrics phonon mean free path diffusive scattering
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This material is based on research sponsored by Defense Advanced Research Agency (DARPA) under agreement number FA8650-15-1-7523 and US Air Force Office of Scientific Research under award number FA9550-16-1-0025. The US Government is authorized to reproduce and distribute reprints for Governmental purposes notwithstanding any copyright notation thereon. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of Air Force Research Laboratory (AFRL) and the DARPA or the US Government. X.W.W., J.Z., and X.J.W. would like to thank the supports from the National Science Foundation (NSF) through the University of Minnesota MRSEC under Award Number DMR-1420013 and from the Legislative-Citizen Commission on Minnesota Resources (LCCMR).
- 3.Rosker M, Bozada C, Dietrich H, Hung A, Via D, Binari S, Vivierios E, Cohen E, Hodiak J. The DARPA wide band gap semiconductors for RF applications (WBGS-RF) program: Phase II results. In: CS MANTECH Conference. Tampa, Florida, USA, 2009Google Scholar
- 6.Yan Z, Liu G, Khan J M, Balandin A A. Graphene quilts for thermal management of high-power GaN transistors. Nature Communications, 2012, 3(3): 199–202Google Scholar
- 21.Chen G. Nanoscale Energy Transport and Conversion: A Parallel Treatment of Electrons, Molecules, Phonons, and Photons. Oxford: Oxford University Press, 2005Google Scholar
- 31.Kim B, Nguyen J, Clews P J, Reinke CM, Goettler D, Leseman Z C, El-Kady I, Olsson R. Thermal conductivity manipulation in single crystal silicon via lithographycally defined phononic crystals micro electro mechanical systems (MEMS). In: 2012 IEEE 25th International Conference on Micro Electro Mechanical Systems (MEMS), 2012, 176–179CrossRefGoogle Scholar
- 40.Oh D W, Ravichandran J, Liang C W, Siemons W, Jalan B, Brooks C M, Huijben M, Schlom D G, Stemmer S, Martin L W, Majumdar A, Ramesh R, Cahill D G. Thermal conductivity as a metric for the crystalline quality of SrTiO3 epitaxial layers. Applied Physics Letters, 2011, 98(22): 221904CrossRefGoogle Scholar
- 48.Dames C, Chen G. Thermal conductivity of nanostructured thermoelectric materials. In: Rowe D M ed. Thermoelectrics Handbook: Macro to Nano. Boca Raton, USA: CRC Press 2005, 42:1–16Google Scholar
- 50.Klemens P G. Theory of thermal conductivity in solids. In: Tye R P ed. Thermal Conductivity. London: Academic Press, 1969, 1–68Google Scholar
- 54.Leibfried G, Schloemann E. Thermal conductivity of dielectric solids by a variational technique. Nachr Akad Wiss Goettingen, Math-Phys Kl, 2A. Math-Phys-Chem Abt, 1954, 23: 1366–1370Google Scholar
- 68.Koh Y K, Singer S L, Kim W, Zide J M O, Lu H, Cahill D G, Majumdar A, Gossard A C. Comparison of the 3ω method and timedomain thermoreflectance for measurements of the cross-plane thermal conductivity of epitaxial semiconductors. Journal of Applied Physics, 2009, 105(5): 054303CrossRefGoogle Scholar
- 71.Hao Q, Zhao H, Xiao Y. Multi-length scale thermal simulations of GaN-on-SiC high electron mobility transistors. In: Zhang Y, He Y-L ed. Multiscale Thermal Transport in Energy Systems. Hauppauge. New York: Nova Science Publishers, 2016Google Scholar