CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 1

    Suppose a ‘n’-type wafer is created by doping Si crystal having
    5 × 1028 atoms/m3 with 1ppm concentration of As. On the
    surface 200 ppm Boron is added to create ‘P’ region in this wafer.
    Considering ni = 1.5 × 1016 m–3, (i) Calculate the densities of the
    charge carriers in the n & p regions. (ii) Comment which charge
    carriers would contribute largely for the reverse saturation
    current when diode is reverse biased.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 2

    Explain why elemental semiconductor cannot be used to make
    visible LEDs.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 3

    How would you set up a circuit to obtain NOT gate using a
    transistor?

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 4

    Two car garages have a common gate which needs to open
    automatically when a car enters either of the garages or cars
    enter both. Devise a circuit that resembles this situation using
    diodes for this situation.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 5

    Three photo diodes D1, D2 and D3 are made of semiconductors
    having band gaps of 2.5eV, 2eV and 3eV, respectively. Which
    ones will be able to detect light of wavelength 6000
    0A
    ?

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 6

    In a CE transistor amplifier there is a current and voltage gain
    associated with the circuit. In other words there is a power gain.
    Considering power a measure of energy, does the circuit voilate
    conservation of energy?

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 7

    The amplifiers X, Y and Z are connected in series. If the voltage
    gains of X, Y and Z are 10, 20 and 30, respectively and the
    input signal is 1 mV peak value, then what is the output signal
    voltage (peak value)
    (i) if dc supply voltage is 10V?
    (ii) if dc supply voltage is 5V?

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 8

    Sn, C, and Si, Ge are all group XIV elements. Yet, Sn is a
    conductor, C is an insulator while Si and Ge are semiconductors.
    Why?

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 9

    Why are elemental dopants for Silicon or Germanium usually
    chosen from group XIII or group XV?

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 10

    What is LED with the help of a diagram, show the biasing of a Light Emitting Diode (LED). Give its two uses.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 11

    What is a solar cell. Draw its circuit diagram. Draw  I- V characteristics of a solar cell.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 12

    What is a solar cell? How does it works? Give its one use.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 13

    In half wave rectification, What is the output frequency if the input frequency is 50 Hz. What is the output frequency of a full wave rectifier for the same input frequency.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 14

    If the output of a two input NOR gate is fed as the input to a NOT gate (i) Name the new logic gate abstained  and (ii) write down its truth table.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 15

    Define the depletion layer and the potential barrier in a p-n junction diode.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 16

    How is an n-type semiconductor formed? Name the major charge carriers in it. Draw the energy              band diagram of an n-type semiconductor.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 17

    Which special type of device can act as a voltage regulator? Give the symbol of this divide and draw the general shape of its V-I characteristics.           

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 18

    Draw a circuit diagram to slow how a photo diode is viewed. Draw its characteristics curres  for two different illumination intensities. 

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 19

    How does  a light emitting diode (LED) works? Give two advantages of LED’s over the conventional incandescent lamps.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 20

    Write two character feature to distinguish between n-type and p-type semiconductor.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 21

    Draw the circuit symbol for LED.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 22

    Draw the Circuits Symbol for npn transition.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 23

    How does the width of depletion layer change in reverse li of p-n. junction diode? 

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 24

    Give the ratio of the number of holes and the number of electrons in an intrinsic semi-conductor.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 25

    Name two factors on which electrical conductivity of a pure semiconductor at a given temperature depends.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 26

    Draw energy band diagram of a p- type semiconductor.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 27

    Name one imparity each, which when added to pure Si, produces (i) n- type  and (ii) p- type  semiconductor.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 28

    Name the type of biasing of p-n junction diode. So that the junction offers very high resistance.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 29

    A change of 0.2 mA in the base current cause a change of 5mA in the collector

    current for a common emitter amplifier.

    (i) Find the a.c. current gain of the transistor

    (ii) If the input resistance is 2kΩ, and its voltage gain is 75, calculate the load

    resistor used in the circuit.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 30

    A semiconductor has equal electron and hole concentration of 2*108/m3. On

    doping with certain impurity, hole concentration increases to 4*1010/m3.

    (i) What type of semiconductor is obtained on doping.

    (ii) Calculate the new electron and hole concentration of the semiconductor.

    (iii) How does the energy gap vary with doping.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 31

    A semiconductor has equal electron and hole concentration of 6X108/m3. On

    doping with certain impurity, electron concentration increases to 9X1012/m3.

    (i) Identify the new semiconductor obtained after doping.

    (ii) Calculate the new hole concentration.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 32

    In a common emitter mode of a transister, the dc current gain is 20, the emitter

    curent is 7mA.

    Calculate (i)base current and (ii)collector curent.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 33

    Two amplifiers are connected one after another in series (cascaded). The first

    amplifier has a voltage gain of 10 and the second has a voltage gain of 20. If the

    input signal is 0.01 volt, calculate the output signal.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 34

    The current gain (α) of a transister in common base configuration is 0.98. What

    does It physically mean?

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 35

    What is the width of dipletion layer in p-n junction diode?

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 36

    The energy gaps in the energy band diagrams of a conductor, semiconductor and

    insulator are E1, E2 and E3. Arrange them in increasing order.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 37

    In a semiconductor the concentration of electorns is 8x1013cm-3 and that of  holes

    is 5x1012cm-3. Is a p-type or n-type semiconductor?

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 38

    What is a solar cell? How does it works? Give its one use.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 39

    Distinguish between intrinsic & extrinsic semiconductor.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 40

    What is half wave rectifier. Giving circuit diagram & input-output

    waveform explain its working.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 41

    What is logic gate. Name the basic gates. Give symbol, Boolean expression &

    truth table for AND gate.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 42

    (a) Draw transfer characteristic curve of Base-biased C-E transistor.

    (b) Mention the region where the transistor used as switch & where as

    Amplifier.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 43

    What is amplifier. Discuss use of n-p-n transistor as an amplifier with circuit diagram. What is phase relation between input & output waveform.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 44

    What is junction transistor. Write its types with symbol. Giving circuit

    diagram of p-n-p transistor in CE draw input & output characteristic curve.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 45

    What is zener diode. Draw V-I characteristic curve of zener diode. Explain its

    use as an voltage regulator with circuit diagram.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 46

    What is semiconductor diode . How a diode can be made forward and reverse

    bias. Draw its V-I characteristic curve .

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 47

    Distinguish between conductor , insulator and semiconductor on the basis of

    energy band diagram ?

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 48

     

    Write the truth table for the circuits given in Fig. 14.48 consisting of NOR gates only. Identify the logic operations (OR, AND, NOT) performed by the two circuits.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 49

     

    Write the truth table for circuit given in Fig. 14.47 below consisting of NOR gates and identify the logic operation (OR, AND, NOT) which this circuit is performing.

    (Hint: A = 0, B = 1 then A and B inputs of second NOR gate will be 0 and hence Y=1. Similarly work out the values of Y for other combinations of A and B. Compare with the truth table of OR, AND, NOT gates and find the correct one.)

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 50

     

    You are given two circuits as shown in Fig. 14.46, which consist of NAND gates. Identify the logic operation carried out by the two circuits.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 51

     

    Write the truth table for a NAND gate connected as given in Fig. 14.45.

    Hence identify the exact logic operation carried out by this circuit.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 52

     

    You are given the two circuits as shown in Fig. 14.44. Show that circuit (a) acts as OR gate while the circuit (b) acts as AND gate.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 53

     

    In a p-n junction diode, the current I can be expressed as

    where I0 is called the reverse saturation current, V is the voltage across the diode and is positive for forward bias and negative for reverse bias, and I is the current through the diode, kBis the Boltzmann constant (8.6×10 - 5 eV/K) and T is the absolute temperature. If for a given diode I0 = 5 × 10 - 12 A and T = 300 K, then

    (a) What will be the forward current at a forward voltage of 0.6 V?

    (b) What will be the increase in the current if the voltage across the diode is increased to 0.7 V?

    (c) What is the dynamic resistance?

    (d) What will be the current if reverse bias voltage changes from 1 V to 2 V?

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 54

     

    In an intrinsic semiconductor the energy gap Egis 1.2 eV. Its hole mobility is much smaller than electron mobility and independent of temperature. What is the ratio between conductivity at 600K and that at 300K? Assume that the temperature dependence of intrinsic carrier concentration niis given by

    where n0 is a constant.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 55

     

    The number of silicon atoms per m3 is 5 x 1028. This is doped simultaneously with 5 x 1022 atoms per m3 of Arsenic and 5 x 1020 per m3 atoms of Indium. Calculate the number of electrons and holes. Given that ni= 1.5 x 1016 m-3. Is the material n-type or p-type?

     

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 56

     

    A p-n photodiode is fabricated from a semiconductor with band gap of 2.8 eV. Can it detect a wavelength of 6000 nm?

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 57

    Two amplifiers are connected one after the other in series (cascaded). The first amplifier has a voltage gain of 10 and the second has a voltage gain of 20. If the input signal is 0.01 volt, calculate the output ac signal.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 58

      

    For a CE-transistor amplifier, the audio signal voltage across the collected resistance of 2 kΩ is 2 V. Suppose the current amplification factor of the transistor is 100, find the input signal voltage and base current, if the base resistance is 1 kΩ.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 59

     

    In half-wave rectification, what is the output frequency if the input frequency is 50 Hz. What is the output frequency of a full-wave rectifier for the same input frequency.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 60

     

    For a transistor amplifier, the voltage gain

    (a) remains constant for all frequencies.

    (b) is high at high and low frequencies and constant in the middle frequency range.

    (c) is low at high and low frequencies and constant at mid frequencies.

    (d) None of the above

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 61

     

    For transistor action, which of the following statements are correct:

    (a) Base, emitter and collector regions should have similar size and doping concentrations.

    (b) The base region must be very thin and lightly doped.

    (c) The emitter junction is forward biased and collector junction is reverse biased.

    (d) Both the emitter junction as well as the collector junction are forward biased

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 62

     

    When a forward bias is applied to a p-n junction, it

    (a) raises the potential barrier.

    (b) reduces the majority carrier current to zero.

    (c) lowers the potential barrier.

    (d) None of the above.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 63

     

    In an unbiased p-n junction, holes diffuse from the p-region to n-region because

    (a) free electrons in the n-region attract them.

    (b) they move across the junction by the potential difference.

    (c) hole concentration in p-region is more as compared to n-region.

    (d) All the above.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 64

     

    Carbon, silicon and germanium have four valence electrons each. These are characterised by valence and conduction bands separated by energy band gap respectively equal to (Eg)C, (Eg)Si and (Eg)Ge. Which of the following statements is true?

    (a) (Eg)Si < (Eg)Ge < (Eg)C

    (b) (Eg)C< (Eg)Ge> (Eg)Si

    (c) (Eg)C> (Eg)Si> (Eg)Ge

    (d) (Eg)C = (Eg)Si = (Eg)Ge

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 65

     

    Which of the statements given in Exercise 14.1 is true for p-type semiconductors.

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  • CHAPTER -14 SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS Assignments 66

     

    In an n-type silicon, which of the following statement is true:

    (a) Electrons are majority carriers and trivalent atoms are the dopants.

    (b) Electrons are minority carriers and pentavalent atoms are the dopants.

    (c) Holes are minority carriers and pentavalent atoms are the dopants.

    (d) Holes are majority carriers and trivalent atoms are the dopants.

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