Silicon sub-bandgap photon linear detection in two-photon experiments: A photo-assisted Shockley-Read-Hall mechanism

We investigate the linear response of silicon p-i-n diodes to sub-bandgap photons (1.4 μm-1.6 μm) that has been reported by many authors and left unexplored till then. The quantum efficiency of this mechanism is extremely low (typically 10^-9) but has a drastic influence on silicon devices harnessing two-photon absorption. We show that this linear photonic current decreases with temperature, displaying an activation energy similar to the dark current one. We show that this behaviour is consistent with a photo-assisted Shockley-Read mechanism in which the occupancy factor of a defect state in the Si band gap is influenced by the sub-band gap photon flux.