Intrinsic nanoscale ordering and strain–defect coupling in ferroelectric Al_1−xSc_xN

Al_1−xSc_xN (AlScN) has emerged as a promising ferroelectric material for next-generation memory and logic devices; yet its performance remains limited by poor understanding of nanoscale structural instabilities. Here, we uncover intrinsic short-range chemical ordering and strain–defect coupling in molecular-beam-epitaxy grown Al_0.66Sc_0.34N using a combination of atom probe tomography and transmission electron microscopy. The heterostructure exhibits wurtzite structure with a sharp and clean AlScN/AlN interface with negligible interdiffusion. Frequency distribution and radial distribution analyses reveal statistically significant Sc–Sc enrichment and Sc–N depletion, indicating nanoscale clustering accompanied by local nitrogen deficiency. Corresponding lattice-spacing variations observed by inverse FFT mapping confirm strain variation correlated with Sc-rich domains. These results provide the first atom-by-atom experimental evidence of scandium clustering and its coupling to nitrogen-vacancy formation in the ferroelectric composition regime. These findings identify short-range ordering and strain–defect coupling as intrinsic structural features of ferroelectric AlScN, with important implications for polarization switching behavior and reliability.