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

The channel resistance of an N-channel JFET shown in the figure below is 600$\Omega$ when the full channel thickness (tch) of 10$\mu$m is available for conduction. The built-in voltage of the gate P+ N junction (Vbi) is - 1 V. When the gate to source voltage (VGS) is 0 V, the channel is depleted by 1$\mu$m on each side due to the built in voltage and hence the thickness available for conduction is only 8$\mu$m

The channel resistance when VGS = - 3 V is
  1. 360$\Omega$
  2. 917$\Omega$
  3. 1000$\Omega$
  4. 3000$\Omega$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Multiple choice

A region of negative differential resistance is observed in the current voltage characteristics of a silicon PN junction if

  1. both the P-region and N-region are heavily doped

  2. the N-region is heavily doped compared to the P-region

  3. the P-region is heavily doped compared to the N-region

  4. an intrinsic silicon region is inserted between the P-region and the N-region
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In case of tunnel diode formed by PN junction, tunnel diode gives negative resistance and works in forward bias. In a tunnel diode, both N and P regions are heavily doped.

Multiple choice

A silicon bar is doped with donor impurities ND 2.25 x 1015 atoms/cm3. Given the intrinsic carrier concentration of silicon at T = 300 K is ni = 1.5 x 1010 cm3. Assuming complete impurity ionization, the equilibrium election and hole concentrations are

  1. n0 = 1.5 x 106 cm–3, p0 = 1.5 x 105 cm-3

  2. n0 = 1.5 x 1010 cm–3, p0 = 1.5 x 1015 cm-3

  3. n0 = 2.25 x 1015 cm–3, p0 = 1.5 x 1010 cm-3

  4. n0 = 2.25 x 1015 cm–3, p0 = 1 x 105 cm-3
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Multiple choice

When a silicon diode having a doping concentration of NA = 9 x 10 cm16 on p-side and ND = 1 x 1016 cm-3 on n-side is reverse biased, the total depletion width is found to be 3 $\mu$m. Given that the permittivity of silicon is 1.04 x 10-12 F/cm, the depletion width on the p-side and the maximum electric field in the depletion region, respectively, are
  1. 2.7 $\mu$m and 2.3 x 105 V/cm
  2. 0.3 $\mu$m and 4.15 x 105 V/cm
  3. 0.3 $\mu$m and 0.42 x 105 V/cm
  4. 2.1 $\mu$m and 0.42 x 105 V/cm
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Multiple choice

A good current buffer has

  1. low input impedance and low output impedance

  2. low input impedance and high output impedance

  3. high input impedance and low output impedance

  4. high input impedance and high output impedance
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

An ideal current buffer must have the zero input impedance and infinite output impedance, i.e. Zin = 0 Zo = $\infty$ Hence, a good current buffer has low input impedance and high output impedance.

Multiple choice

The doping concentrations on the p-side and n-side of a silicon diode are 1 x 1016 cm-3 and 1 x 1017 cm-3, respectively. A forward bias of 0.3 V is applied to the diode. At T = 300 K, the intrinsic carrier concentration of silicon ni = 1.5 x 1010 cm-3 and $\frac{kT}{q}$ = 26 m V. The electron concentration at the edge of the depletion region on the p-side is

  1. 2.3 x 109 cm-3

  2. 1 x 1016 cm-3

  3. 1 x 1017 cm-3

  4. 2.25 x 106 cm-3
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Multiple choice

If the base width in a bipolar junction transistor is doubled, which of the following statements will be TRUE?

  1. Current gain will increase.

  2. Unity gain frequency will increase.

  3. Emitter-base junction capacitance will increase.

  4. Early voltage will increase.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

On increasing the base width, slope of the IC vs. VCE curve decreases due to less (IC). Hence, decrease in slope means increase in early effect. So, early voltage will increase.