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Bandgap measurements are an important application of low-loss electron energy loss spectroscopy (EELS), especially for optoelectronic devices. Although optical methods can provide better energy resolution, measuring the local bandgap in these devices requires the high spatial resolution provided by the nanoscale probe in aberration-corrected scanning transmission electron microscopy (STEM). Extraction of the bandgap from EELS is complicated and time-consuming due to the presence of other low loss signals. It is critical to establish a quick way to check the bandgap at nanoscale without interrupting the fast-paced workflow required in industry. The complexity of this task increases when dealing with structures consisting of different materials.

In this work, we demonstrate an automated bandgap measurement process applied to a complex semiconductor heterostructure composed of three types of materials commonly found in optoelectronic devices: a III-nitride multilayer stack, indium tin oxide (ITO) and SiO₂. Multiple functions are combined to fit the different shapes of the bandgap edge onset and switching between is handled smoothly by estimating initial parameters and in correlation with the STEM image. This enables us to quickly measure the bandgap with high spatial resolution from a single spectrum image and better understand the electronic properties of the device.