Sketch a graph for a 500 mm thick silicon detector showing the thickness of the depletion layer as a function of the applied reverse bias voltage, from the situation of zero voltage to when the detector becomes fully depleted. You may neglect the
thicknesses of the n+ layer and the naturally occurring depletion layer at the junction with the bulk p-type material.
[3 MARKS]
(iv) Sketch a simple circuit diagram showing how you
would connect a voltage supply to a silicon detector made from an n+ layer on one side of a wafer of p-type material, being careful to indicate the polarity of the voltage (which side is positive and which side is grounded).
[2 MARKS]
(v)Estimate the magnitude in volts of the signal produced by an alpha-particle that deposits 5.5 MeV in the depletion region of a silicon detector (assume that the detector has a capacitance of 10 pF).
[3 MARKS]
(c) Use a sketch to show the band structure in a typical
insulator that has been modified to act as an inorganic scintillation (such as NaI(Tl) for example). Indicate on your diagram the typical magnitude of the band gap and show how the energy level structure is modified in a luminescence centre by the addition of an activator material. Describe how the energy of a charged particle moving through this material is converted into optical photons and comment on why this type of detector will have poorer energy resolution for detecting gamma-rays than a typical germanium detector would have.
[4 MARKS]
(a) The linear energy transfer coefficient, for gamma-ray photons interacting in matter is given by the expression
3.
