EECE 310 Exam, Spring 2008

Test 5 (November 12, 2007) A pn junction has NA = ND = 1016/cm3. (a) Calculate the equilibrium junction potential, assuming the impurities are completely ionized, ni = 1010/cm3, and VT = 26mV. (b) If the device is subjected to radiation that generates 1012 electron-hole pairs/cm3/s, determine the magnitude and polarity of the open-circuit voltage that can be measured across the diode, assuming a minority carrier lifetime of 1 s. Solution: (a) Vnpo = V. (b) The equilibrium minority carrier concentration is /cm3. In the presence of radiation, the additional concentration is . The chemical potential of either electrons or holes becomes V. The measured voltage is 0.72 – 0.6 = 0.12 V. The p-side is more positive with respect to the n-side since the p-side is now less negative with respect to the n-side.