(a) Design a photoresistor, based on a P-type semiconductor doped with N _A = 10 ¹⁵ cm ^-3 , so that the resistance at the external generation rate of 10 ²² cm ^-3 s ^-1 is 1kΩ. The following technological parameters are known: the thickness of the semiconductor film is 5μm, the minimum width of the semiconductor strip is 500μm, the electron mobility is μ _n =250 cm ² /V-s, the hole mobility is μ _p = 50 cm ² /V-s, and the minority carrier lifetime is t _n = 20μS. 

(b) What is the resistance in the dark?