Terahertz nanoscopy of semiconductor surface dynamics

Abstract

Most semiconductors have surface dynamics radically different from its bulk counterpart due to surface defect, doping level, and symmetry breaking. Due to the technical challenge of direct observation of the surface carrier dynamics, however, experimental studies have been allowed in severely shrunk structures including nanowires, thin films, or quantum wells where the surface-to-volume ratio is very high. Here, we develop a new type of terahertz (THz) nanoscopy system to investigate the surface dynamics of bulk semiconductors, using metallic nano gap accompanying strong THz field confinement. We observed that carrier lifetimes of InP and GaAs dramatically decrease close to the limit of THz time resolution (~1 ps) as the gap size decreases down to nano scale, and that they return to their original values once the nano-antennas are removed. Furthermore, through both experimental results and calculations, we extracted the surface recombination velocities and diffusion coefficients of the semiconductor materials and that values are consistent with the previous works. Our THz nanoscopy system will open up pathways towards direct, and nondestructive measurements of surface dynamics of bulk semiconductors.