Ferroelectric high-electron mobility transistors (FerroHEMTs)
By alloying scandium into aluminum nitride (AlN), AlScN achieves enhanced spontaneous polarization and robust ferroelectric and piezoelectric behavior, enabling reconfigurable device functionalities and high-density two-dimensional electron gases (2DEGs). [1, 2] High-vacuum sputter system with high-purity targets facilitates the growth of lattice-matched AlScN films on GaN substrates with minimal defects surface features, critical for device performance. The high dielectric constant of AlScN mitigates gate leakage, reduces electric fields, and strengthens gate-channel coupling, while its ferroelectric behavior introduces nonvolatile memory windows and hysteresis, pivotal for energy-efficient logic and memory applications. [3,4] Building on this foundation, the Casamento group is expanding into new nitride chemistries, including novel group-III elements (e.g., AlYN and AlLaN) as well as quaternary alloys (e.g., AlScGaN), to further enhance ferroelectric stability, polarization density, and thermal robustness for next-generation FerroHEMT applications.
Furthermore, device simulation with TCAD Silvaco further facilitates this research by enabling precise modeling of ferroelectric polarization dynamics, charge transport, and interfacial electric field distributions, guiding the optimization of heterostructure design and Sc composition. Coupling experimental growth with TCAD-driven insights can efficiently tailor AlScN/GaN interfaces, refine gate architectures, and validate ferroelectric switching behavior, significantly reducing trial-and-error iterations.
High-K dielectrics passivation of AlGaN/GaN HEMTs
Conventional passivation materials such as silicon nitride are limited by low breakdown strength and thermal stability, whereas gallium oxide, with its ultra-wide bandgap (~4.8 eV) and high dielectric constant (~11), offers robust protection against surface traps and environmental degradation. The plasma-enhanced ALD enables the growth of conformal, high-purity gallium oxide films at a low temperature, featuring high breakdown strength close to theoretical maximum and sub-nanometer smoothness, critical for reliability in high power and RF applications of HEMTs.
Non-linear optical response
Aluminum nitride (AlN)-based wurtzite semiconductors have emerged as a compelling platform for non-linear optical applications due to their inherent non-centrosymmetric cystal structure. [6] The wurtzite phase of AlN, characterized by its strong second-order optical nonlinearity, enables efficient frequency conversion processes such as second-harmonic generation (SHG), sum/difference frequency generation, and optical parametric oscillation. [7-9] In addition, AlN’s wide bandgap grants transparency across UV, visible, and IR spectral regions, making this material ideal for broadband photonic devices. [10] By leveraging its piezoelectric and electro-optic properties, AlN facilitates hybrid devices that merge acousto-optic and non-linear functionalities, positioning it as a promising material for next-generation optoelectronics and ultrafast optical signal processing.
Reference
[1] J Casamento et al. 2023 IEEE BiCMOS and Compound Semiconductor Integrated Circuits and Technology Symposium (BCICTS), pp. 132-136. IEEE (2023).
[2] N Kazuki et al. Applied Physics Express (2025).
[3] J Casamento et al. Applied Physics Letters 120, no. 15 (2022).
[4] J Casamento et al. Applied Physics Letters 121, no. 19 (2022).
[5] N Li et al. Nanophotonics 10, 2347 (2021).
[6] C Xiong et al. New Journal of Physics 14, no. 9 (2012): 095014.
[7] W Pernice et al. Applied Physics Letters 100, no. 22 (2012).
[8] H Jung et al. Nanophotonics 5, no. 2 (2016): 263-271.
[9] A Bruch Optica 6, no. 10 (2019): 1361-1366.
[10] D Singh et al. ACS Applied Electronic Materials 2, no. 4 (2020): 944-953.