Title SEMICONDUCTOR ELECTRONICS.pdf ✅

CHAPTER 14 SEMICONDUCTOR ELECTRONICS Exercise 1: NCERT Based Topic-wise MCQs 14.1 & 14.2 INTRODUCTION & CLASSIFICATION OF METALS, CONDUCTORS AND SEMICONDUCTORS 1. A strip of copper and another of germanium are cooled from room temperature to 80K. The resistance of (a) each of these decreases NCERT Page-468 / N-324 (b) copper strip increases and that of germanium decreases (c) copper strip decreases and that of germanium increases (d) each of these increases 2. The relation between number of free electrons (n) in a semiconductor and temperature (T) is given by (a) n ∝ T NCERT Page-468 / N-324 (b) n ∝ T 2 (c). n ∝ √T (d) n ∝ T 3/2 3. In a semiconductor NCERT Page-468 / N-324 (a) there are no free electrons at 0K (b) there are no free electrons at any temperature (c) the number of free electrons increases with pressure (d) the number of fre electrons is more than that in a conductor 4. The electrical conductivity of pure germanium can be increased by NCERT Page-468 / N-324 (a) increasing the temperature (b) doping acceptor impurities (c) doping donor impurities (d) All of the above 5. If lattice constant of this semiconductor is decreased, then which of the following is correct? NCERT -471/N-326 (a) All Ec , Eg, Ev increase (b) Ec and Ev increase, but Eg decreases (c) Ec and Ev decrease, but Eg increases (d) All Ec , Eg, Ev decrease 6. In the energy band diagram of a material shown below, the open circles and filled circles denote holes and electrons respectively. The material is NCERT Page-471 / N-326 (a) an insulator (b) a metal (c) an n-type semiconductor (d) a p-type semiconductor
7. If a battery of 10V is connected across a plate of the semiconductor of area 4 × 10−4m2 and of thickness 2.2 × 10−3m, then the current flowing through the plate is NCERT Page-471 / N-326 (a) 3.8mA (b) 1.8mA (c) 2.8mA (d) 4.8mA 8. An electric field is applied to a semiconductor. Let the number of charge carriers be n and the average drift speed be v. If the temperature is increased NCERT Page-468 / N-324 (a) both n and v will increase (b) n will increase but v will decrease (c) v will increase but n will decrease (d) both n and v will decrease 9. The intrinsic conductivity of germanium at 27∘C is 2.13mhom−1 and mobilities of electrons and holes are 0.38 and 0.18 m2V −1 s −1 respectively. The density of charge carriers is NCERT Page-468 / N-324 (a) 2.37 × 1019m−3 (b) 3.28 × 1019m−3 (c) 7.83 × 1019m−3 (d) 8.47 × 1019m−3 14.3 INTRINSIC SEMICONDUCTOR 10. Electric conduction in a semiconductor takes place due to (a) electrons only NCERT Page-47.2 / N-327, 328 (b) holes only (c) both electrons and holes (d) neither electrons nor holes 11. The concentration of hole - electron pairs in pure silicon at T = 300K is 7 × 1015. per cubic meter. Antimony is doped into silicon in a proportion of 1 atom in 107Si atoms. Assuming that half of the impurity atoms contribute electron in the conduction band, calculate the factor by which the number of charge carriers increases due to doping. The number of silicon atoms per cubic meter is 5 × 1028 (a) 2.8 × 105 NCERT Page-473 / N-327, 328 (c) 4.2 × 105 (b) 3.1 × 102 (d) 1.8 × 105 14.4 ENTRINSIC SEMICONDUCTOR 12. When an impurity is doped into an intrinsic semiconductor, the conductivity of the semiconductor (a) increases NCERT Page-474 / N-329 (b) decreases (c) remains the same (d) becomes zero 13. If a small amount of antimony is added to germanium crystal NCERT Page-476 / N-331 (a) it becomes a p-type semiconductor (b) the antimony becomes an acceptor atom (c) there will be more free electrons than holes in the semiconductor (d) its resistance is increased 14. A p-type semiconductor is NCERT Page-476/N-331
(a) positively charged (b) negatively charged (c) uncharged (d) uncharged at OK but charged at higher temperatures 15. Let nh and ne be the number of holes and conduction electrons in an extrinsic semiconductor. Then (a) nh > ne NCERT Page- 474/ / N-329 (c) nh < ne (b) nh = ne (d) nh ≠ ne 16. The impurity atoms, with which pure silicon may be doped to make it a p-type semiconductor are those of (a) phosphorus NCERT Page-476 / N-331 (b) boron (c) antimony (d) nitrogen 17. Pure Si at 500K has equal number of electron (ne ) and hole (nh ) concentrations of 1.5 × 1016m−3 . Doping by indium increases nh to 4.5 × 1022m−3 . The doped semiconductor is of NCERT Page-477/ N-332 (a) n-type with electron concentration ne = 5 × 1022m−3 (b) p-type with electron concentration ne = 2.5 × 1010m−3 (c) n-type with electron concentration ne = 2.5 × 1023m−3 (d) p-type having electron concentration ne = 5 × 109m−3 . 18. A pure semiconductor has equal electron and hole concentration of 1016m−3 . Doping by indium increases nh to 5 × 1022m−3 . Then, the value of ne in the doped semiconductor is NCERT Page- 477 / N-332 (a) 106 /m3 (c) 2 × 106 /m3 (b) 1022/m3 (d) 2 × 109 /m3 19. In a p-type semiconductor the acceptor level is situated 60 meV above the valence band. The maximum wavelength of light required to produce a hole will be NCERT Page-477 / N-332 (a) 0.207 × 10−5m (c) 20.7 × 10−5m (b) 2.07 × 10−5m (d) 2075 × 10−5m 14.5 P-N JUNCTION 20. The drift current in a p-n junction is from the (a) n-side to the p-side NCERT Page-478 / N-333 (b) p-side to the n-side (c) n-side to the p-side if the junction is forward-biased and in the opposite direction if it is reverse biased (d) p-side to the n-side if the junction is forward-biased and in the opposite direction if it is reverse-biased 21. If the two ends of a p − n junction are joined by a wire NCERT Page-478 / N-333 (a) there will not be a steady current in the circuit (b) there will be a steady current from the n-side to the p-side (c) there will be a steady current from the p-side to the n-side (d) there may or may not be a current depending upon the resistance of the connecting wire
14.6 SEMICONDUCTOR DIODE 22. In the given circuit the input voltage Vin is shown in figure. The cut-in voltage of p − n junction diode (D1 or D2 ) is 0.6V. Which of the following output voltage (V0 ) waveform across the diode is correct? NCERT Page-481/ N-336 (a) (b) (c) (d) 23. A semiconductor device is connected in a series circuit with a battery and a resistance. A current is found to pass through the circuit. If the polarity of the battery is reversed, the current drops to almost zero. The device may be a/an NCERT Page-479-481 / N-334-336 (a) intrinsic semiconductor (b) p-type semiconductor (c) n-type semiconductor (d) p-n junction diode 24. The I-V characteristics of a p-n junction diode in forward bias is shown in the figure. The ratio of dynamic resistance, corresponding to forward bias voltages of 2V and 4V respectively, is : NCERT Page-481 / N-336 (a) 1: 2 (b) 5: 1 (c) 1: 40 (d) 20: 1