Atomic Origins of Leakage Paths in Epitaxial Al_1-xSc_xN Thin Films

Al_1-xSc_xN, a CMOS-compatible ferroelectric material with high residual polarization and Curie temperature, possesses excellent promise for high-temperature nanoelectronics. However, its high coercive field and leakage current lead to poor endurance, hindering device applications. Sc concentration is crucial to tune ferroelectric coercive field, but the link between Sc doping and leakage current is rarely explored. Here, we report Sc-rich metallic rocksalt nanoscale precipitates in epitaxial wurtzite Al_0.9Sc_0.1N via atomic resolution microstructural analysis and nanoscale bandgap mapping. These nanoscale precipitates reduce the local bandgap by 1.0 eV, creating percolation paths that elevate leakage current by 3 orders of magnitude─validated by I-V characterization and first-principles calculations. This result is surprising, as the overall Sc concentration (0.1) is far below the thermodynamic wurtzite-rocksalt phase boundary, highlighting that the Sc spatial distribution control is critical to suppress leakage current. Our approach is generic to study the microscopic origins of the leakage current in wurtzite-ferroelectric materials.