Semiconductor Electronics · Question 57

C and Si both have same lattice structure; having 4 bonding electrons in each. However, C is insulator whereas Si is intrinsic semiconductor. This is because

1. In case of C the valence band is not completely filled at absolute zero temperature.
2. In case of C the conduction band is partly filled even at absolute zero temperature.
3. The four bonding electrons in the case of C lie in the second orbit, whereas in the case of Si they lie in the third.
4. The four bonding electrons in the case of C lie in the third orbit, whereas for Si they lie in the fourth orbit.

The figure shows a logic circuit with two inputs A and B and the output C. The voltage wave forms across A, B and C are as given. The logic circuit gate is [figure]

1. OR gate
2. NOR gate
3. AND gate
4. NAND gate

In a CE transistor amplifier, the audio signal voltage across the collector resistance of 2 k is 2 V. If the base resistance is 1 k and the current amplification of the transistor is 100, the input signal voltage is

1. 0.1 V
2. 1.0 V
3. 1 mV
4. 10 mV

Transfer characteristics [output voltage (V0) vs input voltage (Vi)] for a base biased transistor in CE configuration is as shown in the figure. For using transistor as a switch, it is used [figure]

1. in region III
2. both in region (I) and (III)
3. in region II
4. in region I

A Zener diode, having breakdown voltage equal to 15 V, is used in a voltage regulator circuit shown in figure. The current through the diode is [figure]

1. 5 mA
2. 10 mA
3. 15 mA
4. 20 mA

In the following figure, the diodes which are forward biased, are [figure]

1. (A), (B) and (D)
2. (C) only
3. (C) and (A)
4. (B) and (D)

Pure Si at 500 K has equal number of electron (ne) and hole (nh) concentrations of 1.5 1016 m-3. Doping by indium increases nh to 4.5 1022 m-3. The doped semiconductor is of

1. p-type having electron concentration ne = 5 109 m-3
2. n-type with electron concentration ne = 5 1022 m-3
3. p-type with electron concentration ne = 2.5 1010 m-3
4. n-type with electron concentration ne = 2.5 1023 m-3

In forward biasing of the p-n junction

1. the positive terminal of the battery is connected to p-side and the depletion region becomes thick.
2. the positive terminal of the battery is connected to n-side and the depletion region becomes thin.
3. the positive terminal of the battery is connected to n-side and the depletion region becomes thick.
4. the positive terminal of the battery is connected to p-side and the depletion region becomes thin.

Symbolic representations of four logic gates are shown as [figure] Pick out which ones are for AND, NAND and NOT gates, respectively

1. (ii), (iii) and (iv)
2. (iii), (ii) and (i)
3. (iii), (ii) and (iv)
4. (iii), (iv) and (ii)

If a small amount of antimony is added to germanium crystal

1. it becomes a p-type semiconductor
2. the antimony becomes an acceptor atom
3. there will be more free electrons than holes in the semiconductor
4. its resistance is increased