Band Alignment and Leakage Mechanism Analysis of p-Si/n-AlN Heterojunction Diodes with the Al ₂ O ₃ Interlayer

The development of bipolar devices based on ultrawide bandgap (UWBG) aluminum nitride (AlN) has been severely hindered by the absence of efficient p-type doping. This limitation prevents the realization of AlN-based PN junctions, which are essential for enabling high-voltage and low-leakage operation in next-generation power and radio frequency electronics. To address this challenge, heterointegration of n-AlN with highly conductive p-type materials such as silicon (Si) offers a promising alternative pathway. However, understanding the band alignment and reverse leakage behavior is essential for the future practical implementation of such heterojunctions. In this work, we fabricate a p-Si/n-AlN heterojunction PN diode (PND) by incorporating an atomic layer-deposited Al2O3 interlayer at the interface. This ultrathin oxide layer forms chemical bonds with both the Si and AlN surfaces. Band alignment measurements via X-ray photoelectron spectroscopy reveal a type-I alignment with conduction and valence band offsets of 1.6 and 3.35 eV, respectively. The fabricated p-Si/n-AlN PND demonstrates excellent rectifying behaviors, achieving a rectification ratio of ∼1.09 × 107 at ±10 V, reverse leakage current density of ∼4.68 × 10–8 A/cm2 at −10 V, and on-resistance of ∼1.5 Ω·cm2 at 30 V. Temperature-dependent I–V characterization exhibits a stable rectification characteristic across varying temperatures. Furthermore, the forward current follows thermally activated transport, while the reverse leakage current is revealed to be governed by Poole–Frenkel emission at moderate bias and trap-assisted tunneling under high electric fields. These results help to understand the heterojunction’s carrier transport behavior and provide guidance for future improvement of Si/AlN heterojunction PND.