Design an InGaAs$/$Si APD i$.$e$.1)$ determine the thickness of the absorber to achieve a responsivity of $0\mathrm{.}7$ A$/$W for a gain of $1$ at a wavelength of $1\mathrm{.}31$m if the absorption coefficient is $0\mathrm{.}9$m$-1,2)$ determine the electric field in the multiplication layer necessary to give a gain of $20$ if the multiplier thickness is $1$m$.3)$ determine the charge value $($between the absorber and gain regions so that the carriers move at saturated velocity in the absorber but do not have significant gain in the absorber