Terahertz emission from narrow band gap semiconductors

摘要

We report an experimental study on THz-emission from narrow band gap semiconductors excited by femtosecond nearinfrared laser pulses. In particular, we studied GaSb, Ga_(1-x)In_xSb and InN. The Ga_(1-x)In_xSb material system enables the study of the influence of carrier concentrations on THz emission process in narrow band gap semiconductors. The study demonstrates the existence of a compromise between the positive effect of high electron temperature provided by narrow band gap materials and the negative effect of high intrinsic carrier concentrations. The influence of the majority and minority carrier types and concentrations on THz emission strength was investigated using GaSb:Te. By varying the majority and minority carrier type and carrier concentrations over three orders of magnitude the THz emission mechanism in GaSb can be tuned from being dominated by the photo-Dember effect to being dominated by surface field acceleration. Within each regime photo-Dember based THz emission and surface field acceleration based THz emission are maximized under specific majority and minority carrier concentrations. Strong advantages of InN as THz-emitter over other narrow band gap materials, are strong intrinsic electric fields, low intrinsic carrier concentration and most importantly, very low probability of intervalley scattering.