Physics · Textbook solutions

Semiconductors

Every solved example, exercise, and miscellaneous question — in the order the textbook teaches them. · 18 questions

14. Semiconductors — worked examples

3 q

Solved Examples

Worked · 3
  1. Solved Ex.14.1
    A pure Si crystal has 4×10284 \times 10^{28} atoms m−3^{-3}. It is doped by 1ppm concentration of antimony. Calculate the number of electrons and holes. Given ni=1.2×1016n_{i} = 1.2 \times 10^{16}/m3^{3}.
  2. Solved Ex.14.2
    A pure silicon crystal at temperature of 300 K has electron and hole concentration 1.5×10161.5 \times 10^{16} m−3^{-3} each. (ne=nh)(n_{e} = n_{h}). Doping by indium increases nhn_{h} to 4.5×10224.5 \times 10^{22} m−3^{-3}. Calculate nen_{e} for the doped silicon crystal.
  3. The question refers to figure (a) printed with it. Between the points A and B there are two parallel branches. The upper branch, path ACB, carries a 30 Ω30\ \Omega resistor marked C in series with an ideal diode. The lower branch, path ADB, carries a 30 Ω30\ \Omega resistor marked D. The book prints two further figures, (b) and (c), which redraw this same network for the two bias conditions.
    Solved Ex.14.3
    Refer to the figure a shown below and find the resistance between point A and B when an ideal diode is (1) forward biased and (2) reverse biased.

Exercises

15 q

Choose the correct option

Practice · 5
  1. Choose the correct option.
    Ex Q.1 (i)
    Electric conduction through a semiconductor is due to:
    1. A.
      electrons
    2. B.
      holes
    3. C.
      none of these
    4. D.
      both electrons and holes
  2. Ex Q.1 (ii)
    The energy levels of holes are:
    1. A.
      in the valence band
    2. B.
      in the conduction band
    3. C.
      in the band gap but close to valence band
    4. D.
      in the band gap but close to conduction band
  3. Ex Q.1 (iii)
    Current through a reverse biased p-n junction, increases abruptly at:
    1. A.
      breakdown voltage
    2. B.
      0.0 V
    3. C.
      0.3V
    4. D.
      0.7V
  4. Ex Q.1 (iv)
    A reverse biased diode, is equivalent to:
    1. A.
      an off switch
    2. B.
      an on switch
    3. C.
      a low resistance
    4. D.
      none of the above
  5. Ex Q.1 (v)
    The potential barrier in p-n diode is due to:
    1. A.
      depletion of positive charges near the junction
    2. B.
      accumulation of positive charges near the junction
    3. C.
      depletion of negative charges near the junction,
    4. D.
      accumulation of positive and negative charges near the junction

Answer the following questions

Practice · 5
  1. Answer the following questions.
    Ex Q.2 (i)
    What is the importance of energy gap in a semiconductor?
  2. Ex Q.2 (ii)
    Which element would you use as an impurity to make germanium an n-type semiconductor?
  3. Ex Q.2 (iii)
    What causes a larger current through a p-n junction diode when forward biased?
  4. Ex Q.2 (iv)
    On which factors does the electrical conductivity of a pure semiconductor depend at a given temperature?
  5. Ex Q.2 (v)
    Why is the conductivity of a n-type semiconductor greater than that of p-type semiconductor even when both of these have same level of doping?

Answer in detail

Practice · 5
  1. Answer in detail.
    Ex Q.3 (i)
    Explain how solids are classified on the basis of band theory of solids.
  2. Ex Q.3 (ii)
    Distinguish between intrinsic semiconductors and extrinsic semiconductors.
  3. Ex Q.3 (iii)
    Explain the importance of the depletion region in a p-n junction diode.
  4. Ex Q.3 (iv)
    Explain the I-V characteristic of a forward biased junction diode.
  5. Ex Q.3 (v)
    Discuss the effect of external voltage on the width of depletion region of a p-n junction