In-situ biasing DPC STEM observation of GaAs p-n junction

In-situ biasing differential phase contrast (DPC) scanning transmission electron microscopy (STEM) offers a powerful tool for visualizing local electric fields in devices under operating conditions. However, robust protocols for quantitative operando analysis remain underdeveloped. In this study, we established a methodology for quantitative electric field mapping of a GaAs p-n junction using in-situ biasing DPC-STEM, thereby extending previous quantitative DPC studies to device characterization under applied bias. We successfully visualized the modulation of the depletion layer under forward and reverse biases. By systematically comparing the experimental projected electric field profiles with two-dimensional Poisson simulations, we further revealed that focused ion beam induced electrically inactive layers were formed asymmetrically across the p-n junction, depending on the dopant concentration difference between the n- and p-type regions. These inactive layers significantly modify not only the field intensity but also its spatial distribution compared with the ideal case. Our results demonstrate that quantitative interpretation of in-situ DPC-STEM measurements requires simulation models incorporating realistic specimen structures, particularly asymmetric inactive layers, and provide practical guidance for quantitative characterization of functional semiconductor devices.