Engineering Physics
UNIT 4Semiconductor Physics Define relaxation time and mean free path. Explain electrical conductivity and derive s = neµ. What is the effect of temperature on Fermi-Dirac distribution function? What are intrinsic semiconductors? Explain with diagram. What are extrinsic semiconductors? Explain with diagram. Explain classification of solids on the basis of energy bands. Explain N type semiconductor in detail. Explain P type semiconductor in detail. Define wave number. What is conductivity and how it is measured? Compare conductor, semi conductor and insulator. Derive equation of energy and wave function when a free particle is trapped in an infinite potential well. Explain the concept of group velocity. Show that group velocity is equal to the velocity of the particle. Calculate energy level difference between first two excited state of a neutron trapped in infinite potential well of width 10–15 m. What is band gap energy? Explain classification of solids into conductors, semiconductors and insulators on the basis of band theory of solids. A strip of copper of thickness 1.5 × 10–4 m is placed in a magnetic field of 1 T perpendicular to the plane of the strip and a current of 10 A is setup in the strip. What Hall voltage would appear across the width of the strip if concentration of charge carries in copper is 8.5 × 1028 electrons/m3. A germanium sample has 4.56×1022 atoms/cc and a donor impurity in the ratio of one part per 1010 is added to create an N type semiconductor. If the mobility of charge carries is 3900 cm2/ V–s, find the conductivity of silicon.
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