Evidence of non-local impact ionization in CNT and HgCdTe

Two aspects of the non-local nature of impact ionization, dead space and resonance, are investigated. The very small excess noise factor measured for mercury cadmium telluride photodiodes can only be explained if the hole to electron ionization coefficient ratio, k, is very small and the impact ionization dead space is also considered. A maximum value of k for HgCdTe is estimated in this paper. In addition, recent measurements of the reverse photocurrent in single wall carbon nanotubes show a well defined flat region at a multiplication of 1.6. This is argued to be evidence for resonant behaviour in impact ionization for carbon nanotubes.