**Part A:** *Consider a silicon p-i-n photodiode exposed to sunlight. Calculate the intrinsic region width so that at least 90% of all photons with wavelength
are absorbed in the intrinsic region. Neglect any absorption in the p+ and n+ regions.*

**Part B:** *Describe advantages of the p-i-n structure over the p-n structure.*

**Part A**The absorption coefficient for Si at 1 m according to |CLEANROOM.BYU| is:

(10)

The number of photons absorbed per s depending on the distance is:

(11)

Where is the photon flux on the surface of the semiconductior. Since we have a non-uniform absorption 90% in the intrinsic region:

(12) (13)

Therefore for x,

(14)

**Part B**For achieving higher senitivity (for lower time) the PIN diode is a sandwitch structure incorporating an intrinsic semiconductor for the purpose of increasing the depletion region width, which thus will affect the device's sensitivity or more exactly the time response of the device leading to sensitivity.