Scattering mechanism of 2DEG in ScAlN/GaN heterostructures grown by plasma-assisted molecular beam epitaxy

We investigated the transport properties of 2DEG in ScAlN/GaN heterostructures prepared by plasma-assisted molecular beam epitaxy. Four samples with Sc compositions of 3%–17% and ScAlN barrier thickness of 4–6.6 nm were grown on GaN/SiC template substrates. In situ reflection high energy electron diffraction patterns and atomic force microscopy images confirmed the atomically smooth surface. The atomic-resolution scanning transmission electron microscopy image demonstrated an abrupt ScAlN/GaN interface. At room temperature, the sample exhibited a sheet electron density of 2.0–3.1 × 1013 cm−2 and an electron mobility of 179–468 cm2/Vs. The sheet electron density remained nearly constant across temperatures from 2 to 400 K, indicating that the 2DEG is induced solely by the polarization effect. As the temperature decreased, the mobility increased and eventually saturated. The scattering mechanisms limiting electron mobility were analyzed, accounting for the increased effective mass due to the non-parabolicity of the conduction band at a high sheet electron density. The calculated total mobility shows excellent agreement with the experimental data, suggesting that temperature-independent interface roughness scattering is the dominant mechanism. These findings provide critical insights for understanding and improving the transport properties of 2DEG in ScAlN/GaN for HEMT applications.