Bipolar transport in a simple illuminated semiconductor bar

zhanghe said:

TL;DR Summary: light-conducivity and the practical movement of electron and hole.

In terms of bipolar transport theory, the delta n and delta p should go together along the bar in the direction as the so-called minority carrier should go (as the e.g. above, the electron for a p-type c-Si)

zhanghe said:

TL;DR Summary: light-conducivity and the practical movement of electron and hole.

I feel quite confused for a few days, when I apply the bipolar transport equation into a voltage-applied semicondutor material (e.g. p-type c-Si bar, or a resistor) which just have some light-generated electron-hole pairs by a pulse of photon at somewhere on the bar. In terms of bipolar transport theory, the delta n and delta p should go together along the bar in the direction as the so-called minority carrier should go (as the e.g. above, the electron for a p-type c-Si) . However, it seems that there will be no net light current, because delta n and delta p always accompany each other on the 1-D bar. On the other hand, we always use the delta n + delta p the sum to give a light electrical current (i.e. light conductivity).
Please give me some hints, there must be somewhere wrong.