Operando Investigation of Nanocrystal Based Optoelectronic Device Using X-Ray Photoemission Imaging

Rational design of device based on emerging materials strongly relies on the determination of their electronic structure. Such measurements are usually conducted on the pristine material asssuming that their electronic spectrum remains mostly unchnaged once integrated into a device. Such assumption is certainly sufficient for a fisrt generation of device but is a clear bottleneck as technology gets more mature. This is why it becomes critical to develop methods than enable to probe material properties direcetly within a device, meaing in their realistic dielectric environement and in presence of driving electric field. Here, i will focus on X-ray photoemission imaging. By focusing a soft X-ray synchrotron beam onto a Fresnel lens, a small sub µm spot can be obtained, thus enabling direct mapping of their energy landscape. I will start by discussing how the method can be applied to simple planar device such as field effect transistor and used it to determine the nature (ohmic vs rectifying) of the contact or the arm lever from the gate. I will then siwtch to more advanced devices such as planar pn junctions and show that the method gives direct access to the built in electric field that is otherwise only obtained through modelling. Last, i will show that the high resolution of the method can be used to get access to the vectorial distribution of the electric field.


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Mapping the Energy Landscape from a Nanocrystal-Based Field Effect Transistor under Operation using Nanobeam Photoemission, M. Cavallo et al, Nano Lett 23, 1363 (2023).