Nanoscale Mapping of Surface Modulations and Inhomogeneities in Ferroelectric AlN/2D-TMDC Heterostructures

The optoelectronic interactions at nanoscale material interfaces have heightened sensitivity to surface modulations and inhomogeneities. This invokes this study’s correlative nanometric analysis effort, to understand the tunability of multi-functional heterostructures of light-emitting 2D transition metal dichalcogenides (TMDCs) in distinct interface configurations: hexagonal boron nitride (hBN) encapsulated WSe₂and MoS₂ on ferroelectric Aluminum Nitride (AlN) thin films. Spatially correlated spectroscopic measurements, including cathodoluminescence, photoluminescence, and Raman mapping, revealed collective and gradual red-shifting emission energies of WSe₂ excitonic complexes, correlating with variations in intrinsic and defect hBN emission intensity. Through Gaussian fitting and decomposition of spectral features across high-resolution maps, fitted spectral features reveal how nanoscale variations tune excitonic light emission behavior. Leveraging these insights, we then demonstrate multi-functional co-engineering of 2D-TMDC flakes as visible light absorbers impacting ferroelectric interfaces, and the light-emitting 2D-TMDC flakes across a strongly polarized ferroelectric AlScN thin film surface. By doping of AlN thin films, such as with Sc, the coercive field reduces to 3 MV/cm, allowing for ferroelectric switching to occur non-destructively through monolayer to few layer 2D-TMDC flakes. We employ functional atomic force microscopy to spatially resolve the ferroelectric switching dynamics through heterogeneous 2D-TDMC flakes. The AlScN thin film’s large remanent polarization of 120 μC/cm² bolster the interfacial charge transfer and band structure modifications in the heterostructured 2D-layers, where by Kelvin probe force microscopy we resolve the surface potential between oppositely polarized domains in the heterostructure and observe a strong dependence on encapsulation to modify interfacial charge. This study combines several spatially-resolved correlative analyses to provide insights for designing multi-functional and tunable 2D TMDC-based optoelectronic devices through ferroelectric interfaces.