Physics

Semiconductors and Diodes

461 Questions

Semiconductors and diodes form the foundation of modern electronics, covering topics like intrinsic carrier concentration and Zener breakdown. Questions often explore the characteristics of bipolar junction transistors (BJT) and the properties of doped silicon materials. This topic is crucial for physics and electronics engineering competitive exams.

Zener diode breakdownBJT circuit analysisIntrinsic carrier concentrationDoping in semiconductorsEmitter follower circuit

Semiconductors and Diodes Questions

Multiple choice

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.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Trivalent impurities are used for making p- type semiconductors. So, Silicon wafer heavily doped with boron is a p+ substrate.

Multiple choice

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
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Multiple choice

Consider the following two statements about the internal conditions in a n − channel MOSFET operating in the active region. S1 : The inversion charge decreases from source to drain. S2 : The channel potential increases from source to drain. Which of the following is correct?

  1. Only S2 is true.

  2. Both S1 and S2 are false.

  3. Both S1 and S2 are true, but S2 is not a reason for S1.

  4. Both S1 and S2 are true, and S2 is a reason for S1.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Both S1 and S2 are true and S2 is a reason for S1.

Multiple choice

Compared to a p-n junction with NA=ND=1014/cm3, which one of the following statements is TRUE for a p-n junction with NA=ND=1020/cm3?

  1. Reverse breakdown voltage is lower and depletion capacitance is lower.

  2. Reverse breakdown voltage is higher and depletion capacitance is lower.

  3. Reverse breakdown voltage is lower and depletion capacitance is higher.

  4. Reverse breakdown voltage is higher and depletion capacitance is higher.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Reverse bias breakdown or Zener effect oauts in highly doped PN junction through tunneling mechanism. In a highly doped PN Junction, the conduction and valence beads on opposite tides of the junction are sufficiently doe. dogleg raven. bias that electron may tunnel directly from the valence hand on the p-side into the conduction bend on n-side.

Breakdown voltage $V_B \propto \dfrac{1}{N_AN_D}$

So, breakdown voltage decreases as concentration increases

Depletion capacitance $C = \left[ \dfrac{\epsilon_0 N_AN_D}{2(V_{be} + V_R) (N_A + N_D) } \right]^{8/x} $

Thus $C \propto N_AN_D$

Depletion capacitance increases as concentration increases

Multiple choice

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
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In BJT as the reverse bias voltage increases, The B-C space charge region which increases which $x_B$ (i.e. neutral base width) > A change in neutral base width will change the collector current. A reduction in base width will causes the gradient in minority carrier concentration to increase., which in turn causes an increase in the diffusion current This effect is known as base modulation as early effect.

Multiple choice

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] $
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Multiple choice

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
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In accumulation mode for NMOS having p - substrate, when positive voltage is applied at the gate, this will induce negative charge near p - type surface beneath the gate. When VGS is made sufficiently large, an inversion of electrons is formed and this in effect forms an n - channel.

Multiple choice

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
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation