quantum efficiency and 2+2=4 (a) Define responsivity of a photodetector. (b) A p-n photodiode has a quantum efficiency of 70% for photons of energy 1-52 × 10-19 J. Calculate (i) the wavelength at which the diode is operating; (i) the optical power required to achieve a photocurrent of 3μA when the wavelength of incident photons is that previous part. calculated in 2+2=4