Silicon radiation detector. A silicon diode is used to detect radiation with an

Question

Silicon radiation detector. A silicon diode is used to detect radiation with an energy of 2.8 MeV. To do so the diode is reverse biased with an 18 V source and a window is provided so that radiation can only enter the device at its center (see Figure 9.30). Assume that the energy is absorbed entirely at the point of entry. The diode is 2 mm thick. 9.12 a. With mobilities of 350 cm?/V-s for holes and 1350 cm?/V-s for electrons, calculate the current through the diode. Neglect the effects of electrodes and of the n and p layers. b. What is the sensitivity of the diode? c. Sketch the current pulse expected if the radiation can be considered as a single event occurring at a time to- FIGURE 9.30 . Silicon radiation sensor Radiation Shield

Explanation / Answer

SOLUTION :

we have

energy = 2.8 MeV

and charge on 1 electron = 1.6 * 10-19 C = 1 eV

therefore number of electron generated at the entry point = 2.8*106/1 = 2.8*106 electrons

= number of holes generated

A)

current density J = q*(un*n+ up*p)*E

where E = electric field = V/L = 18/0.2 = 90 V/cm

un = 1350 cm2/V.s , up = 350 cm2/V.s

J = 1.6*10-19(1350+350)*2.8*106*90 = 1.6*10-19*1700*2.8*106*90 = 685.44 * 10-10 A/cm2

J = 68.544*10-9 A/cm2 = 68.544 nA /cm2

B)

Let energy supplied be E1 eV

then number of electrons generated,n = E1

J = q(un+up)* n*E

where E = electric field = 90 V/cm

therefore J = 1.9*10-19(1350+350)E1*90 = 290.7*10-16 E1

therefore sensitivity = (dJ)/(dE1) =290.7 *10-16 A/cm2.eV  

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