Thermoelectric transport in ZnO and GaN nanowires

Thermoelectric transport properties - electron mobility, mu, diffusion thermopower, S-d, and electronic thermal conductivity, kappa(e) - are investigated in ZnO and GaN nanowires (NWs) for 10 < T < 300 K. Expressions for the acoustic phonon limited electron momentum relaxation rates, considering the inelasticity of the electron-acoustic phonon interaction in wurtzite (WZ) and zincblende (ZB) structures, are given. Numerical calculations of acoustic phonon limited mu, S-d and kappa(e), presented as a function of temperature, thickness and the electron concentration of the NWs, bring out the importance of the piezoelectric coupling in the two systems. The properties studied within the elastic scattering approximation, usually used in analyses to explain acoustic-phonon limited transport, are found to be underestimated for both WZ and ZB structures. Calculations of room temperature mu, S-d and kappa(e) including impurity, polar optical phonon and surface roughness scatterings, indicate polar optical phonons (impurities) to be the dominant sources of limiting the thermoelectric properties in ZnO (GaN) NWs. The mobility value for 10 nm GaN NW is in agreement with experimental data of Huang et al. [2] [Y. Huang, Duan, Y. Cui, C.M. Lieber, Nano Lett. 2 (2002), 101]. Detailed studies for ultrathin NWs are required to better understand electron-phonon interaction in these systems. (C) 2015 Elsevier Ltd. All rights reserved.