▎ 摘　　要

The thermal conductance of isotopic-superlattice graphene nanoribbons randomly mixed with isotope defects is investigated by atomistic Green's function method. The isotopic-superlattice structure reduces the thermal conductance, which changes non-monotonically as the superlattice period length decreases, and there exists a minimum thermal conductance at the critical period length. About 20% defects just further increase the reduction and shorten the critical period length. As the defect concentration in superlattice increases, the thermal conductance decreases monotonically in the zigzag nanoribbon, but in armchair nanoribbon the thermal conductance first decreases to its minimum value and then increases. The isotopic doping effect is particularly evident for large isotope mass, in armchair nanoribbons and for out-of-plane phonon modes. Isotope defects lead to additional phonon scattering in the superlattice structure, which is explained by analyzing the phonon transmittance.