Thermal Characterization and Modelling of AlGaN-GaN Multilayer Structures for HEMT Applications

Abstract

To optimize the thermal design of AlGaN-GaN high-electron-mobility transistors (HEMTs), which incorporate high power densities, an accurate prediction of the underlying thermal transport mechanisms is crucial. Here, a HEMT-structure (Al0.17Ga0.83N, GaN, Al0.32Ga0.68N and AlN on a Si substrate) was investigated using a time-domain thermoreflectance (TDTR) setup. The different scattering contributions were investigated in the framework of phonon transport models (Callaway, Holland and Born-von-Karman). The thermal conductivities of all layers were found to decrease with a temperature between 300 K and 773 K, due to Umklapp scattering. The measurement showed that the AlN and GaN thermal conductivities were a magnitude higher than the thermal conductivity of Al0.32Ga0.68N and Al0.17Ga0.83N due to defect scattering. The layer thicknesses of the HEMT structure are in the length scale of the phonon mean free path, causing a reduction of their intrinsic thermal conductivity. The size-effect of the cross-plane thermal conductivity was investigated, which showed that the phonon transport model is a critical factor. At 300 K, we obtained a thermal conductivity of (130 ± 38) Wm−1K−1 for the (167 ± 7) nm thick AlN, (220 ± 38) Wm−1K−1 for the (1065 ± 7) nm thick GaN, (11.2 ± 0.7) Wm−1K−1 for the (423 ± 5) nm thick Al0.32Ga0.68N, and (9.7 ± 0.6) Wm−1K−1 for the (65 ± 5) nm thick Al0.17Ga0.83N. Respectively, these conductivity values were found to be 24%, 90%, 28% and 16% of the bulk values, using the Born-von-Karman model together with the Hua–Minnich suppression function approach. The thermal interface conductance as extracted from the TDTR measurements was compared to results given by the diffuse mismatch model and the phonon radiation limit, suggesting contributions from inelastic phonon-scattering processes at the interface. The knowledge of the individual thermal transport mechanisms is essential for understanding the thermal characteristics of the HEMT, and it is useful for improving the thermal management of HEMTs and their reliability.

Identifying the Bottleneck for Heat Transport in Metal–Organic Frameworks

“…[ 26 ] Notably, for carbon nanotube networks and stacks of semiconducting or dielectric heterolayers, interfacial resistances have also been identified via jumps in the local temperature between individual tubes, [ 27 ] or the different semiconducting and dielectric materials. [ 28 ] To the best of our knowledge, the present case is, however, the first observation of such an effect within a neat bulk material. Moreover, the interfaces causing the resistance have neither been created by deliberately engineering semiconductor superlattices [ 29 ] nor are they the consequence of a random arrangement of building blocks (like in the above‐mentioned sheets of the carbon nanotubes).…”

Diamond/GaN HEMTs: Where from and Where to?

“…Table 2. Typical thermal conductivity of the materials present in an AlGaN/GaN HEMT [1,7,[9][10][11][46][47][48].…”

Effect of the Heat Dissipation System on Hard-Switching GaN-Based Power Converters for Energy Conversion

“…Internally, these devices are composed of layers of different materials. Consequently, the temperature inside the transistors is not homogeneous [64,65]. However, to simplify the model, the junction temperature was assumed to be constant throughout the interior of the device.…”