Reduction of thermal conductivity in GaN/In_xAl_1-xN/GaN Superlattice under the influence of interfacial electric field

A decrease in thermal conductivity (k) via electric field in superlattices (SL) is one of the recent attempts to get better thermoelectric efficiency. In this work, we report that interfacial electric (IFE) field of GaN/In_xAl_1-xN/GaN SL arising from crystal asymmetry and lattice mismatch strain can be used to decrease k of the SL. Theoretical results demonstrate that IFE field modifies acoustic phonon properties through elastic modulus and phonon velocity owing to inverse piezoelectric effect. High phonon velocity and size effect enhance interfacial phonon scattering, resulting into irregular change in specific heat at interfaces. This caused higher acoustic mismatch between layers and boosted thermal boundary resistance (TBR). Accordingly, k of SL is decreased, which can be controlled by IFE field engineering via indium composition and layer size. Room-temperature cross-plan thermal conductivities (k_cp) in the presence (absence) of IFE field for GaN (12 nm)/In_xAl_1-xN(6 nm)/GaN SL (x = 0.1, 0.3 0.5, 0.7 and 0.9) are found to be 2.80 (3.46), 3.00 (3.42), 2.00 (4.10), 3.55 (3.98) and 3.99 (4.52) W/(mK), respectively, which demonstrates more than 20% decrease. (author)