Quantum charge sensing using a semiconductor device based on $\delta$-layer tunnel junctions

We report a nanoscale device concept based on a highly doped $\delta$-layer tunnel junction embedded in a semiconductor for charge sensing. Recent advances in Atomic Precision Advanced Manufacturing (APAM) processes have enabled the fabrication of devices based on quasi-2D, highly conductive, highly doped regions, known as $\delta$-layers, in semiconductor materials. In this work, we demonstrate that APAM $\delta$-layer tunnel junctions are ultrasensitive to the presence of charges near the tunnel junction, allowing the use of these devices for detecting charges by observing changes in the electrical current. We demonstrate that these devices can enhance the sensitivity in the limit, i.e., for small concentrations of charges, exhibiting significantly superior sensitivity compared to traditional FET-based sensors. We also propose that the extreme sensitivity arises from the strong quantization of the conduction band in these highly-confined systems.