Verify that the photon energy is 225ev how many

Question

How many electron-hole pairs are generated per second in Si by interband impact generation at x₁ If E(x₁)...3x10⁵V/cm. If N(x₁)=n₁=1.0x10¹⁰cm^-3, what is the number of electron-hole pairs generated per unit volume per second? How does this compare with the optical generation rate obtained In problem 1? (Use Figure 1).

Problem 1:-

Si, GaAs and CdS crystals are exposed to a yellow light of wavelength 5500A and intensity 10¹² photons/cm²-sec. Verify that the photon energy Is 2.25eV. How many electron-hole pairs are generated per unit volume per second in each crystal?

Assume that crystal is very thin and the light is absorbed uniformly in the very thin slice. Why do we need to assume the crystal to be very thin? (Use λ-1.24/E and Fig 2.) (Partial answer: Si, 7x10¹⁵cm^-3s^-1.)