Impact ionizations in amorphous semiconductors and insulators; Se, Ge2Sb2Te5 and SiO2

Abstract

It is known that impact ionizations occur in amorphous materials such as Se and SiO2 under exposures to high dc fields, pulsed-laser exposures, and high-energy radiations. These processes have been explored from different perspectives, including avalanche carrier multiplications, laser fabrications, and x-ray detections. The present work tries to clarify the relations between such phenomena. Characteristic differences of the ionizations in crystalline and non-crystalline forms are also considered. Among recent topics, specifically interesting is the laser excitation that can produce intense light pulses with the duration between femto- and nano-second ranges, which cover collision times governing impact ionization and electron-lattice interactions. For SiO2, we can connect the collision times with related mean free paths estimated from dc studies. By contrast, optical studies are still insufficient for chalcogenides, except for amorphous Ge2Sb2Te5 films.