p- and n-Type doping of AlN: Current challenges, emerging solutions, and device applications

Abstract

Ultrawide bandgap aluminum nitride (AlN) has recently gained significant attention for high-power electronics and deep-ultraviolet (DUV) optoelectronics applications owing to its exceptionally large and direct bandgap, high breakdown field, and thermal and chemical stability. While these intrinsic properties promise substantial performance improvements over silicon (Si), silicon carbide (SiC), gallium nitride (GaN), gallium oxide (Ga2O3), and diamond devices, the core challenge lies in achieving a reliable n- and p-type doping due to deep impurity levels, carrier compensation, and native defect formation. This review is motivated by the urgent need to bridge fundamental doping science with device engineering to unlock the full potential of AlN in high-power devices and solar-blind DUV devices. We discuss a clear roadmap, beginning with a contextual overview of wide- and ultrawide bandgap semiconductors, highlighting why AlN stands out for high-power applications. The body of the review is structured into four core sections, starting with n-type doping techniques, covering silicon, oxygen, and germanium donors, compensation effects, and deep-level centers. Then, the challenges and progress in p-type doping are discussed, evaluating acceptor species (e.g., Mg, Be, C), co-doping schemes, and impurity-band engineering. Section IV focuses on different doping methods, including metal-organic chemical vapor deposition, molecular-beam epitaxy, metal-modulated epitaxy, ion implantation, and polarization doping, and their role in defect control and non-equilibrium activation. Section V presents how these material innovations translate to device prototypes, including Schottky diodes, polarization-doped field effect transistors, and deep-UV emitters, illustrating gradual improvements in the current technology. The review concludes with existing challenges and prospects of AlN, including vacancy-engineered contacts, scalable single-crystal substrates, co-doping strategies, and emerging device architectures that could yield reliable bipolar conductivity and practical AlN-based power electronics. By discussing critical components in theory, fundamental growth science, and device-level demonstrations of AlN, this review aims to serve as a comprehensive guide for researchers and engineers seeking to position AlN as a foundational material for next-generation power and optoelectronic systems.