The importance of gold‐electrode‐adjacent stationary high‐field Böer domains for the photoconductivity of CdS

When the electron density decreases stronger than linearly with the electric field in photoconductive CdS due to field quenching, high‐field domains must occur that remain attached to either the cathode or anode in slit electrode geometry with blocking cathodes. These Böer domains¹ are easily seen by their shift in optical absorption due to the Franz‐Keldysh effect and offer unique opportunities to analyze field dependent parameters within the range of constant electron density and electric field, such as the carrier density or mobility as a function of the field, and give information of the light dependent work function. They also provide insight why a 200 Å thick cover layer of CdS on top of a CdTe solar cell increases its efficiency from 8 to 16% . The behavior of these Böer domains escapes conventional current voltage analyses except for their visual observation, while other high‐field domains with their current fluctuations or oscillations are easily observed and are the subjects of thousands of publications and many books. In this review we will exclude detailed discussion of dynamic domains, but include some new specifics that help to understand the mechanisms of the Böer domains and their applications. Only properties at low optical excitation intensities are discussed that exclude Joules heating. Within the p‐type regime of the anode‐adjacent domain extremely steep electronic quenching signal becomes visible that could signalize an intrinsic donor level slightly above the middle of the band gap that may be responsible for not allowing CdS to ever become p‐type by doping.