Stationary High-Field Domains as Tools

Abstract

High field domains are analyzed with the field-of-direction method, applied to the set of transport and Poisson equations. Cathode adjacent stationary high-field domains are inferred. These are directly connected to the metal/CdS interface with constant field and electron density. Thereby they shift the space charge layer that is typically directly attached to the cathode, away from it into the inner part of the crystal. This provides a unique opportunity to study the work function as a function of crystal parameters, e.g. the optical excitation. Also since the domain field can be measured directly, it provides an opportunity to measure the electron mobility as a function of the field when the Hall electrodes are placed within the domain. The domain is measured using the Franz-Keldysh effect to determine the domain width as function of the bias. Since the domain is determined by the work function of the cathode, the method of a virtual cathode by means of a shadow band is introduced. When, with increasing bias the domain starts to fill the entire space between the electrodes, a new stationary domain appears in front of the anode with substantially higher fields. These domains stabilize the current in the pre breakdown range since they limit the field. The conditions for the domains to occur are given. Non stationary, moving high field domains provide additional insight of the properties of CdS at higher fields. Specifically, one obtains that within the domain the otherwise n-type CdS is inverted to p-type. A summary concludes the chapter.