From atomic-scale understanding to wafer-scale growth: Delta-doped AlN/GaN/AlN XHEMTs on single-crystal AlN by molecular beam epitaxy

The development of large-wafer single-crystal AlN substrates has expanded their role beyond UV photonics to enable next-generation integrated electronics. In this study, we investigated δ-doped AlN/GaN/AlN heterostructures, where an n-type δ-doping layer is introduced to suppress the undesired two-dimensional hole gas at the bottom GaN/AlN interface, thereby enhancing the conductivity of the two-dimensional electron gas at the top AlN/GaN interface. We began by systematically identifying epitaxial growth conditions to achieve high crystalline quality, as confirmed by cross-sectional transmission electron microscopy images. To understand the impact of δ-doping density on transport properties, we combined theoretical modeling with experimental measurements, revealing that an optimal δ-doping density of ∼5×1013cm−2 minimizes interface roughness scattering and enhances mobility. Finally, we demonstrated scalability by extending the growth to large-area wafers, supported by structural and transport characterization. A sheet resistance of 246.8 ± 38.1 Ω/□ measured across a 3-in. (75 mm) wafer highlights the uniformity and performance potential of δ-doped AlN/GaN/AlN heterostructures for high-power, high-frequency electronic applications.