When you state the photons with less energy than the semiconductor band gap interact weakly, what does this infer. Because it states that the photon just passes through it if the material as if they were transparent. What I can tell is that they do not interact at all. Not even weakly.
In principle, the semiconductor is completely transparent to low energy photons but there are second order effects such as free carrier absorption and defect states within the band gap.
It should be Eph=hcf instead of Eph=hf below the animation