Measuring Spatially‐Resolved Potential Drops at Semiconductor Hetero‐Interfaces Using 4D‐STEM

Abstract

Characterizing long‐range electric fields and built‐in potentials in functional materials at nano to micrometer scales is of supreme importance for optimizing devices, e.g., the functionality of semiconductor hetero‐structures or battery materials is determined by the electric fields established at interfaces which can also vary spatially. In this study, momentum‐resolved four‐dimensional scanning transmission electron microscopy (4D‐STEM) is proposed for the quantification of these potentials and the optimization steps required to reach quantitative agreement with simulations for the GaAs/AlAs hetero‐junction model system are shown. Using STEM the differences in the mean inner potentials (∆MIP) of two materials forming an interface and resulting dynamic diffraction effects have to be considered. This study shows that the measurement quality is significantly improved by precession, energy filtering and a off‐zone‐axis alignment of the specimen. Complementary simulations yielding a ∆MIP of 1.3 V confirm that the potential drop due to charge transfer at the intrinsic interface is ≈0.1 V, in agreement with experimental and theoretical values found in literture. These results show the feasibility of accurately measuring built‐in potentials across hetero‐interfaces of real device structures and its promising application for more complex interfaces of other polycrystalline materials on the nanometer scale.