Role of interfacial electric field in thermal conductivity of indium-rich GaN/InxGa1-xN/GaN superlattices (x ≥ 0.7)

Improved thermoelectric (TE) property involves low thermal conductivity (k) but high electrical conductivity (r) and Seebeck coefficient (S). Experiment has confirmed that interfacial polarization electric (IPE) field (similar to 1 MV/cm) of GaN/InxGa1-xN/GaN superlattices (SLs) enhances both S and sigma. In this work, role of IPE field on thermal boundary resistance (TBR) and in-plane (k(ip)) as well as cross-plane thermal conductivities (kcp) of indium-rich GaN/InxGa1-xN /GaN SLs (x C 0.7) are explored theoretically. IPE field influences lattice vibrations on account of the inverse piezoelectric effect, resulting in modification of elastic and phonon properties of the SLs. Our results show that TBR is enhanced (2.10-5.30 9 10-9 m2 KW-1) due to unequal changes in phonon velocity and specific heat on both sides of the interface leading to enhanced interface scattering, decreased phonon transmission, and more mismatches of acoustic properties. This caused reduction in kip and kcp of the SL under the action of IPE field. Room temperature (RT) k(ip) in the presence (absence) of IPE field of GaN (10 nm)/InxGa1-xN (5 nm) SL are 8.204( 9.402) and 9.312(10.564) Wm(-1) K-1 respectively, for x = 0.7 and 0.9, whereas RT kcp for the same x are 4.871(6.012) and 6.083(7.327) Wm(-1) K-1 exhibiting more than 20% reduction and are in good agreement with available experimental results of similar type of SLs. This work demonstrates that desired value of k can be achieved by tailoring polarization mechanism of nitride SLs for optimum TE power production at RT and above.