Size-Controlled Carrier Multiplication in Graphene Nanoribbons

Carrier multiplication (CM) is a fundamental dynamic process of an excited carrier generating multi-electron-hole pairs from single-photon absorption. As such, CM can improve the efficiency of optoelectronic devices. However, CM is rarely witnessed in conventional semiconductors, calling for the need to discover unconventional materials. Here, using real-time time-dependent density functional theory, we show that CM occurs in armchair graphene nanoribbons (AGNRs). The subband structure of AGNRs plays a key role, as it releases the constraints of energy and momentum conservation in the CM process. The subband structure varies depending on nanoribbon width, and thus it provides the way to control the carrier dynamics and carrier multiplication in AGNRs.