Can a benign j – V characteristic with current saturation be the beginning of a new area of semiconductor physics? The vanishing space charge cleans up the defect‐level spectrum

The measurement of the current as a function of the applied voltage is a primary tool to investigate the electrical properties and much attention was given to its deviation from ohmicity. Only recently we have learned that even the most simple characteristics with saturation current can be full of surprises. In this paper, we will emphasize how important it is to employ immediately other tools, such as the Franz–Keldysh effect to make the field distribution visible. We will very briefly review the electrode‐adjacent high‐field domain and their ability to render a CdS crystal thermodynamically stable as being n‐ or p‐type, i.e., being ambipolar depending on whether the domain is attached to the cathode or anode, respectively. We will now also point to the differences for junction‐adjacent high‐field domains. We will focus on the small slab between a blocking contact and a high‐field domain that permits a precise spread of the quasi‐Fermi levels within the domains. Within the domains, the crystal is space‐charge‐free and permits to investigate the electronic transitions to defect levels around the quasi‐Fermi levels. The defect levels are free from distortion caused by electric field variation in their neighborhood caused by space charges. A very steep electron quenching minimum is shown in the p ‐ type CdS with anode‐adjacent domain. The domains are stabilized by the electron density at blocking cathodes and by hole densities at blocking anodes.