Sensitive detection of holes generated by impact ionization in silicon

Impact ionization, or electron-hole pair creation by charged particles, has been one of the central issues of semiconductor physics and devices. However, due to its complexity of the process, most experimental studies and their analyses have been macroscopic and phenomenological. This situation prevents us from exploring the fundamental physics of impact ionization and of high-energy charged particles in semiconductors. In this report, we propose a novel scheme (and device structure) for the observation of electron-initiated impact ionization process in silicon, which is potentially capable of investigating individual (or single) impact-ionization events. With the scheme, we successfully detected at 6 K single holes generated by the impact ionization, and also suggest the presence of long-lived high-energy electrons, opening up the possibility of monitoring, or even manipulating single high-energy electrons.