Thermal Investigation of AlGaN-GaN Multilayer Structures

This paper presents the experimentally as well as theoretically investigated thermal conductivities and thermal boundary resistances of the constituting materials of a GaN high-electron-mobility transistor. Measurements were carried out in the temperature range of 300 K to 773 K using a thermoreflectance measurement setup. The measurement showed that the thermal conductivities of the AlN and GaN were a magnitude higher than the thermal conductivity of the alloys Al
_0.32
Ga
_0.68
N and Al
_0.17
Ga
_0.83
N. It was shown that the thermal boundary resistance across the Pt/AlN and Pt/GaN interfaces decreased with temperature until reaching the Debye temperature of both adjacent materials. No temperature dependence was found for the thermal boundary resistance across the Pt/Al
_0.32
Ga
_0.68
N, Al
_0.32
Ga
_0.68
N/AlN. and GaN/Al
_0.32
Ga
_0.68
N. The application of the Callaway model provided values for the phonon scattering of AlN, GaN, Al
_0.32
Ga
_0.68
N and Al
_0.17
Ga
_0.83
N, which elucidated the scattering mechanisms of the phonons. Feeding that into the Hua-Minnich model for through plane thermal conductivity showed that size effects from ballistic phonon transport were noticeable for the 1065 nm thick GaN layer and dominant for the 167 nm thick AlN layer, the 423 nm thick Al
_0.17
Ga
_0.83
N, and the 65 nm thick Al
_0.17
Ga
_0.83
N at 300K.