Thermal Resistance of GaN/AlN Graded Interfaces

Compositionally graded interfaces in power electronic devices eliminate dislocations but they can also decrease thermal conduction, leading to overheating. We quantify the thermal resistances of GaN/AlN graded interfaces of varying thickness using ab initio Green's functions and compare them with the abrupt interface case. A non-trivial power dependence of the thermal resistance versus the interface thickness emerges from the interplay of alloy and mismatch scattering mechanisms. We show that the overall behavior of such graded interfaces is very similar to that of a thin film of an effective alloy on the length scales relevant to real interfaces.