Electronic and defect processes in oxides. The polaron in action

The basic processes involving space charge are charge localization (including trapping) and charge transport. These processes may be associated with energy localization. At the molecular scale, energy localization is an initiator of electrical breakdown and aging phenomena. At the mesoscopic scale, energy localization generates the damage observed macroscopically and is associated with discharge. Processes on one length scale determine behavior on another scale, Most applications concentrate on macroscopic space charge, yet processes on the atomic scale determine the build-up and consequences of space charge. In non-metals, one key concept is that of self-trapping (formation of small polarons). This survey discusses the phenomenon of self-trapping and its effects on charge transport, charge trapping, and the measurement of localized charges. Most examples will relate to oxides, including bulk transition metal oxides, oxide interfaces, thin layers of oxide on silicon, and laser- and radiation-induced charges in alumina. The paper also links some of the ideas to the outstanding problems in the generation of space charge, including contact charging, tribocharging, and impact charging.