【Device Papers】Polarity-Dependent Band Alignment and Two-Dimensional Electron Gas Localization in β-Ga₂O₃/AlN Heterostructures

      Researchers from the Shandong University have published a dissertation titled "Polarity-Dependent Band Alignment and Two-Dimensional Electron Gas Localization in β-Ga₂O₃/AlN Heterostructures" in Journal of Alloys and Compounds.

Abstract

      The formation of β-Ga₂O₃/AlN heterojunction electrical contacts, with AlN serving as a dielectric or barrier layer, demonstrates great potential to address the challenges of low mobility and poor thermal conductivity in β-Ga₂O₃-based field-effect transistors. However, band offsets crucial for oxide capacitance and gate leakage strongly depend on deposition methods, necessitating a unified predictive framework. Additionally, AlN’s strong spontaneous and piezoelectric polarization offers promising opportunities for interface engineering and carrier modulation, yet remains underexplored. Herein, guided by established epitaxial growth strategies on β-Ga₂O₃ substrates, we construct β-Ga₂O₃/AlN heterojunctions featuring Al-polar AlN as the dielectric and N-polar AlN as the barrier layer. First-principles calculations reveal band offsets and polarity-dependent band bending, alongside distinct two-dimensional electron gas (2DEG) formation mechanisms, via atomic-resolution local density of states and polarization analysis. Both β-Ga₂O₃/AlN heterojunctions exhibit type-II band alignment with valence and conduction band offsets of −0.64 ± 0.5 eV and −1.84 ± 0.3 eV, respectively. Band offsets vary with β-Ga₂O₃ interface orientation, governed by electronic distributions at the polar interface driven by long-range Coulomb interactions. The large conduction band offset (|CBO| ≥ 1.50 eV) ensures strong carrier confinement and suppresses gate leakage. Surface states induce polarity-specific band bending, upward at O-terminated and downward at Ga-terminated surfaces, forming quantum wells in N-polar heterojunctions. In N-polar HEMTs, donor-like surface states promote polarization-induced 2DEG formation, whereas Al-polar configurations deplete 2DEG due to electron transfer to acceptor-like states, requiring δ-doping for channel recovery. This work demonstrates the potential of AlN as a dielectric and introduces a coupling model involving polarity, surface states, and band structure to guide the design of high-performance β-Ga₂O₃ FETs.

DOI：

https://doi.org/10.1016/j.jallcom.2025.182985