Thermal transport in GaN/AlN HEMTs on 4H-SiC: Role of layer thickness and hetero-interfaces

Abstract

Thermal transport in high-electron-mobility-transistor (HEMT) structures grown on 4H-SiC substrates by metalorganic-vapour-phase epitaxy (MOCVD) is systematically investigated. The thermal conductivity of the GaN channel and AlN buffer layers is measured by thermoreflectance (TTR). A pronounced thickness dependence of thermal conductivity as a result of phonon-boundary scattering is observed at low temperatures, while this effect becomes significantly weaker at elevated temperatures. The thermal boundary resistance (TBR) at the AlN/4H-SiC and GaN/AlN interfaces is also examined, showing a substantial reduction and eventual saturation with increasing temperature, indicating elastic phonon transport as the dominant mechanism. Reliable simulations of the temperature profile across the structures based on the measured thermal metrics highlight the critical role of TBR in thin-channel device and the advantage of thicker channel and buffer layers for efficient heat dissipation in the HEMTs.

Figures (3)

• Figure 1: (a) Schematic illustration of the HEMT structures grown on a 4H-SiC substrate, along with the thermal propagation path across the layers. (b) and (c) Temperature-dependent thermal conductivity of the AlN buffer and GaN channel layers, respectively. The solid lines represent the calculated thermal conductivity.
• Figure 2: (a) Thermal resistance at the AlN/4H-SiC and GaN/AlN interfaces, (b) phonon density of states of GaN, AlN, and 4H-SiC, and (c) phonon transmission coefficients at the AlN/4H-SiC and GaN/AlN interfaces.
• Figure 3: (a) Steady-state temperature distribution across the HEMT structures and (b) vertical temperature profiles scanned along the line under hot spot.