Abstract
AlN/GaN superlattices and heterostructures serve as critical building blocks for next-generation high-electron-mobility transistors (HEMTs) operating at high power, high frequency, and elevated temperatures. In this work, we present a comprehensive first-principles study based on density functional theory using the screened hybrid functional of Heyd, Scuseria, and Ernzerhof (HSE06) to investigate the interface thermodynamic stability, internal polarization fields, and electronic structure of (0001)-oriented wurtzite AlN/GaN superlattices. Interfacial formation energies computed under varying chemical potential conditions demonstrate that atomically sharp, pseudomorphically strained interfaces are thermodynamically stable over a wide growth window, with N-rich environments providing enhanced interface stability. The pronounced discontinuity in spontaneous and piezoelectric polarization across the polar interface yields internal macroscopic electric fields exceeding 4.5 MV/cm, leading to substantial band bending and the spontaneous formation of a two-dimensional electron gas (2DEG). The computed valence and conduction band offsets are found to be 0.82 eV and 1.94 eV, respectively, representing a type-I straddling alignment with strong electronic confinement. Detailed projected density of states and spatial charge density analyses clarify the role of interface-localized states and orbital hybridization in preventing parasitic carrier leakage. These atomic-scale insights provide theoretical design guidelines for engineering short-period superlattice barriers and buffer layers in ultra-wide-bandgap RF and power switching devices.
