Problem
An n-type Si sample is doped at 1015 cm-3. We shine light on it to create EHPs at 1019 cm-3 /s. What is the steady state concentration of minority carriers if the lifetime is 100 ns? How long does it take for the hole concentration to drop 10%, after the light is switched off? How long for the hole concentration to reach a value that is 10% higher than the thermal equilibrium value?