The absorption coefficient of silicon has a strong dependence on photon energy, as shown in Figure 25.16

For simplicity, consider an idealized material, material S, similar to crystalline silicon, with an absorption coefficient of ? = 7?10³ m^?1 for light at any wavelength. What fraction of (normally incident) light will be absorbed by a wafer of material S that is 200 ?m thick? If we could fabricate a layer of material S just 1 ?m thick, what fraction of incident radiation would it absorb? The absorption coefficient of amorphous silicon is significantly higher than that of crystalline silicon. If we had another material, material A, with an absorption coefficient ? = 1.5?10⁶ m^?1 (again independent of wavelength), what fraction would be absorbed by a 1 ?m layer?

Transcribed Image Text:

I(V) = ldiffusion (V) – lield (V) = 1o (eev/ko? – 1)