Nitrides Seminar - Haochen Wang

Nitrides Seminar
Tuesday, May 20, 2025, 12:00PM

Attend in person at ESB 1001!
Zoom option also available

Haochen Wang
Graduate Student Researcher, Van de Walle Group
University of California, Santa Barbara

Piezoelectric, dielectric and electro-optic properties of AlScN

Aluminum scandium nitride (AlScN) is an emerging wurtzite-structured material exhibiting exceptional piezoelectric, dielectric, and electro-optic properties, making it a promising candidate for advanced electronic and photonic applications. Pure AlN adopts the wurtzite phase with large spontaneous polarization but is non-ferroelectric due to a high polarization switching barrier. In contrast, ScN adopts the centrosymmetric rocksalt phase, lacking spontaneous polarization. Alloying AlN with ScN induces soft phonons and phase transitions at specific Sc concentrations, enhancing nonlinear effects and altering physical properties.

Incorporating Sc into AlN significantly increases piezoelectric coefficients, enabling large polarization discontinuities at heterojunction interfaces, such as AlScN/GaN, which results in high interfacial carrier density. Additionally, Sc alloying reduces the switching barrier for spontaneous polarization, rendering AlScN ferroelectric. Its compatibility with CMOS fabrication makes AlScN promising for applications including ferroelectric transistors and compute-in-memory devices. The dielectric permittivity of AlScN is also enhanced, establishing its potential as a high-k material for gate dielectrics. Furthermore, Sc incorporation improves the electro-optic response, surpassing conventional materials like lithium niobate in compatibility with integrated nano-photonic circuits. This makes AlScN suitable for ultra-compact broadband modulators and efficient quantum transduction.

Using first-principles calculations, we elucidate the mechanisms driving the enhanced piezoelectric, dielectric, and electro-optic properties in AlScN solid-solution alloys and superlattice structures. Our results provide design strategies for optimizing device performance through tailored alloy composition, cation ordering, strain engineering, and heterostructure design.

HOST: Dr. Yifan Yao

BIO: Haochen obtained his B.S. and M.S. in Applied Physics from University of Science and Technology of China. During the undergraduate and master program, he worked on the ferroelectricity of low-dimensional materials. Haochen joined Prof. Van de Walle’s group in the Materials Department of UC Santa Barbara in 2023 to pursue his PhD. His work focuses on the first-principles studies of dielectric, piezoelectric, ferroelectric and nonlinear optical properties of III-Nitrides.