Opposite atom dependence of isotope engineering of thermal conductivity in bulk and 2D GaN.

Isotope engineering has been shown to be an effective means of regulating
thermal conductivity. In this work, we studied the isotope engineering of thermal
conductivity in bulk and 2D GaN, and diametrically opposed atom isotope dependence
are found. That is, Ga isotope has a large effect (77%) on bulk GaN, while the effect
of N isotope on the thermal conductivity is negligible. In 2D GaN, however, N isotope
effect (20%) is more significant than that of Ga. Understanding of the different isotope
dependence is achieved by deeper insight. Due to the relative magnitude of scattering
rate, isotopic scattering influence the thermal conductivity of bulk and 2D GaN in
different frequency regions, leading to the opposed atom dependence.