Systematic investigation of AlGaN channels on AlN/sapphire substrates using metal–organic chemical vapor deposition (MOCVD): Toward higher crystallinity and lower surface roughness

Aluminum nitride (AlN) stands out as a wide bandgap semiconductor due to its exceptional combination of high thermal conductivity and high electrical resistivity, a rare pairing that makes it uniquely suited for advanced electronic applications. In addition, its unique ability to support the growth of high-Al-content AlGaN enables power electronic devices, including high electron mobility transistors (HEMTs) and diodes, to surpass the performance limits of conventional GaN-channel HEMTs. However, the influence of Al composition on the electronic band structure of AlGaN channel HEMTs remains insufficiently explored, particularly for structures grown via metalorganic chemical vapor deposition. In this study, a high-quality AlN-on-sapphire platform is established as the foundation for subsequent growth. A series of AlxGa1−xN/AlN heterostructures were grown on this platform, with the Al composition x systematically varied between 0 and 0.70. For x = 0 (GaN), a 2DEG density of 3.49 × 1013 cm−2 was observed. As x increased, the 2DEG density slightly decreased; however, most compositions maintained 2DEG densities above 1 × 1013 cm−2. Both sheet resistance and Hall mobility exhibited a clear dependence on the Al composition, with Hall mobility increasing as x decreased. These findings provide valuable insights into the interplay between Al composition and transport properties in AlGaN/AlN heterostructures, further informing their potential for high power electronic applications.