A8. In a Si wafer with an area of 1 cm, the recombination time for holes is t=10-6 s and the hole mobility is 480 cmV-s. The Si wafer is uniformly illuminated with UV light of 21016 -2 photons cm s and all the photons are absorbed on its surface to generate electron-hole pairs. Each photon can generate one electron-hole pair. Assuming the Si wafer is very thick, find the total excess holes stored in the Si wafer.