(a) Sketch a cross section of a silicon PN photodiode labelling the main
features. How is a PIN photodiode different and what advantage does this
give? [6]

(b) Calculate the number of photons arriving at a photodiode each second if
the wavelength of the source is 600nm and the measured power just in
front of the detector is 5mW. [4]

If for each photon arriving at the photodiode 0.7 electrons are produced
what is the expected size of the photocurrent generated for the power in
2(b)?

(c) What is the bandwidth of the photodiode if it has a depletion region width
of 500 nm, the saturation velocity is 2x105 m/s, the junction capacitance
is 2 pF and the load is 50 Ohms? Draw the equivalent circuit and state
any assumptions made during the calculation

(d)For the photodiode in Q2(b)-(d), calculate the noise equivalent power
under load at room temperature, if the operational bandwidth is
100 MHz. State any assumptions that you made. [5]

(e) Describe an application where high bandwidth low noise photodiodes are required.