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Test 3 - Electronic Devices | Electronics and Communication (ECE)

Topic wise test for Electronic Devices of Electronics and Communication (ECE)

20 Questions Published
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Questions

Question 1 Multiple Choice (Single Answer)

Which of the following options is true?

  1. A silicon wafer heavily doped with boron is a p+ substrate.
  2. A silicon wafer lightly doped with boron is a p+ substrate.
  3. A silicon wafer heavily doped with arsenic is a p+ substrate.
  4. A silicon wafer lightly doped with arsenic is a p+ substrate.
Question 2 Multiple Choice (Single Answer)

Group I lists four types of p-n junction diodes. Match each device in Group I with one of the option in Group II to indicate the bias condition of that device in its normal mode of operation.|||
|---|---|
| Group I| Group II|
| (P) Zener Diode| (1) Forward bias|
| (Q) Solar cell| (2) Reverse bias|
| (R) LASER diode| |
| (S) Avalanche Photodiode| |

  1. P-1, Q-2, R-1, S-2
  2. P-2, Q-1, R-1, S-2
  3. P-2, Q-2, R-1, S-1
  4. P-2, Q-1, R-2, S-2
Question 3 Multiple Choice (Single Answer)

A silicon sample A is doped with 1018 atoms/cm3 of Boron. Another sample B of identical dimensions is doped with 1018 atoms/cm3 of Phosphorus. The ratio of electron to hole mobility is 3. The ratio of conductivity of the sample A to B is

  1. 3
  2. $\dfrac{1}{3}$
  3. $\dfrac{2}{3}$
  4. $\dfrac{3}{2}$
Question 4 Multiple Choice (Single Answer)

The DC current gain ($\beta$)of a BJT is 50. Assuming that the emitter injection efficiency is 0.995, the base transport factor is

  1. 0.980
  2. 0.985
  3. 0.990
  4. 0.995
Question 5 Multiple Choice (Single Answer)

The phenomenon known as “Early Effect” in a bipolar transistor refers to a reduction of the effective base-width caused by

  1. electron-hole recombination at the base
  2. the reverse biasing of the base-collector junction
  3. the forward biasing of emitter-base junction
  4. the early removal of stored base charge during saturation-to-cutoff switching
Question 6 Multiple Choice (Single Answer)

The cross section of a JFET is shown in the following figure. Let Vc be − 2V and let VP be the initial pinch -off voltage. If the width W is doubled (with other geometrical parameters and doping levels remaining the same), then the ratio between the mutual trans conductances of the initial and the modified JFET is

  1. 4
  2. $\dfrac{1}{2} \left( \dfrac{1-\sqrt 2 \ V_p}{1-\sqrt {1/2} V_p} \right) $
  3. $ \left( \dfrac{1-\sqrt 2 \ V_p}{1-\sqrt {1/2} V_p} \right) $
  4. $ \left[ \dfrac{1- (2 - \sqrt V_p)} {1- (\sqrt {1/2} V_p) } \right] $
Question 7 Multiple Choice (Single Answer)

The electron and hole concentrations in an intrinsic semiconductor are ni per cm3 at 300 K. Now, if acceptor impurities are introduced with a concentration of NA per cm3 where (where NA >> ni), the electron concentration per cm3 at 300 K will be

  1. ni
  2. ni + NA
  3. NA - ni
  4. $\dfrac{n^2i}{N_A}$
Question 8 Multiple Choice (Single Answer)

The figure shows the high-frequency capacitance-voltage (C-V) characteristics of a Metal/SiO2 /silicon (MOS) capacitor having an area of 1 $\times$10-4 cm2. Assume that the permittivities ($\epsilon_0 \epsilon_r$) of silicon and SiO2 are 1 $\times$ 10-12 F / cm and 3.5 $\times$10-13 F / cm respectively.

The gate oxide thickness in the MOS capacitor is

  1. 50 nm
  2. 143 nm
  3. 350 nm
  4. 1 $\mu$m
Question 9 Multiple Choice (Single Answer)

In the circuit shown below, the switch was connected to position 1 at t < 0 and at t = 0, it is changed to position 2. Assume that the diode has zero voltage drop and a storage time ts For 0 < t$\le$ ts , vR is given by (all in Volts)

  1. vR = − 5
  2. vR = + 5
  3. 0 $\le$ vR < 5
  4. - 5 $\le$ vR < 5
Question 10 Multiple Choice (Single Answer)

A MOS capacitor is made using p-type substrate in the accumulation mode. The dominant charge in the channel is due to the presence of

  1. holes
  2. electrons
  3. positively charged ions
  4. negatively charged ions
Question 11 Multiple Choice (Single Answer)

At room temperature, a possible value for the mobility of electrons in the inversion layer of a silicon n-channel MOSFET is

  1. 450 cm2/ VS
  2. 1350 cm2/ VS
  3. 1800 cm2/ VS
  4. 3600 cm2/ VS
Question 12 Multiple Choice (Single Answer)

The electron concentration in a sample of uniformly doped n-type silicon at 300 K varies linearly from 1017/cm3 at x = 0 to 6 $\times$1016/cm3 at x = 2
$\mu$m. Assume a situation that electrons are supplied to keep this concentration gradient constant with time. If electronic charge is 1.6$\times$10-19 coulomb and the diffusion constant Dn = 35 cm2/s, the current density in the silicon, if no electric field is present, is

  1. zero
  2. -112 A/cm2
  3. +1120 A/cm2
  4. -1120 A/cm2
Question 13 Multiple Choice (Single Answer)

The figure shows the high-frequency capacitance-voltage (C-V) characteristics of a Metal/SiO2 /silicon (MOS) capacitor having an area of 1 $\times$10-4 cm2. Assume that the permittivities ($\epsilon_0 \epsilon_r$) of silicon and SiO2 are 1 $\times$ 10-12 F / cm and 3.5 $\times$10-13 F / cm respectively.

Consider the following statements about the C-V characteristics plot:
S1: The MOS capacitor has an n-type substrate.
S2: If positive charges are introduced in the oxide, the C-V plot will shift to the left.
Which of the following is true?

  1. Both S1 and S2 are true.
  2. S1 is true and S2 is false.
  3. S1 is false and S2 is true.
  4. Both S1 and S2 are false.
Question 14 Multiple Choice (Single Answer)

The figure shows the high-frequency capacitance-voltage (C-V) characteristics of a Metal/SiO2 /silicon (MOS) capacitor having an area of 1 $\times$10-4 cm2. Assume that the permittivities ($\epsilon_0 \epsilon_r$) of silicon and SiO2 are 1 $\times$ 10-12 F / cm and 3.5 $\times$10-13 F / cm respectively.

The maximum depletion layer width in silicon is

  1. 0.143 $\mu$m
  2. 0.857 $\mu$m
  3. 1 $\mu$m
  4. 1.143 $\mu$m
Question 15 Multiple Choice (Single Answer)

If for a silicon npn transistor, the base-to-emitter voltage (VBE) is 0.7 V and the collector-to-base voltage (VCB) is 0.2 V, then the transistor is operating in the

  1. normal active mode
  2. saturation mode
  3. inverse active mode
  4. cut-off mode
Question 16 Multiple Choice (Single Answer)

Consider an abrupt p - n junction. Let Vbi be the built-in potential of this junction and VR be the applied reverse bias. If the junction capacitance (Cj) is 1 pF for Vbi + VR = 1 V, then for Vbi + VR = 4 V, Cj will be

  1. 4 pF
  2. 2 pF
  3. 0.25 pF
  4. 0.5 pF
Question 17 Multiple Choice (Single Answer)

The drain of an n-channel MOSFET is shorted to the gate so that VGS = VDS. The threshold voltage (VT) of the MOSFET is 1 V. If the drain current (ID) is 1 mA for VGS = 2 V, then for VGS = 3 V, ID is

  1. 2 mA
  2. 3 mA
  3. 9 mA
  4. 4 mA
Question 18 Multiple Choice (Single Answer)

The longest wavelength that can be absorbed by silicon, which has the bandgap of 1.12 eV, is 1.1 $\mu$m. If the longest wavelength that can be absorbed by another material is 0.87 $\mu$m, then bandgap of this material is

  1. 1.416 eV
  2. 0.886 eV
  3. 0.854 eV
  4. 0.706 eV
Question 19 Multiple Choice (Single Answer)

The resistivity of a uniformly doped n −type silicon sample is 0.5 ظ - mc. If the electron mobility ($\mu_0$) is 1250 cm2 / V-sec and the charge of an electron is 1.6 x 10-19 Coulomb, the donor impurity concentration (ND) in the sample is

  1. 2 x 1016 / cm3
  2. 1 x 1016 / cm3
  3. 2.5 x 1015 / cm3
  4. 5 x 1015 / cm3
Question 20 Multiple Choice (Single Answer)

The ratio of the mobility to the diffusion coefficient in a semiconductor has the units

  1. V-1
  2. V1 .cm
  3. V. cm-1
  4. V. s
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