GATE EC || ELECTRONIC DEVICES AND CIRCUIT || SEMICONDUCTORS || PYQS (2000-2025)

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Question 1

As shown, a uniformly doped Silicon (Si) bar of length
L = 0.1μm with a donor concentration N_D =10¹⁶ cm^-3 is illuminated at x =0 such that electron and hole pairs are generated at the rate of 

G_L = G_L0 1-xL,0≤x≤L,

where G_L0 = 10¹⁷ cm^–3 s^–1. Hole lifetime is 10^–4s, electronic charge q = 1.6 × 10^–19C, hole diffusion coefficient D_p = 100 cm²/s and low-level injection condition prevails. Assuming a linearly decaying steady state excess hole concentration that goes to 0 at x = L, the magnitude of the diffusion current density at x = L/2, in A/cm², is ____.

( GATE 2017 || EC || NAT ||1 MARK)

• 16

Question 2

In a non-degenerate bulk semiconductor with electron density n=10¹⁶cm−3, the value of EC−EFn=200meV, where EC​ and EFn denote the bottom of the conduction band energy and electron Fermi level energy, respectively. Assume thermal voltage as 26 meV and the intrinsic carrier concentration is 10cm⁻³. For n=0.5×10¹⁶cm−3, the closest approximation of the value of (EC−EFn​), among the given options, is ______.

(GATE 2022 || EC || MCQ ||1 MARK)

• 226 meV

• 174 meV

• 218 meV

• 182 meV

Question 3

Select the CORRECT statement(s) regarding semiconductor devices.

(GATE 2022 || EC || MSQ ||1 MARK)

• Electrons and holes are of equal density in an intrinsic semiconductor at equilibrium

• Collector region is generally more heavily doped than Base region in a BJT.

• Total current is spatially constant in a two terminal electronic device in dark under steady state condition

• Mobility of electrons always increases with temperature in Silicon beyond 300 K.

Question 4

For an intrinsic semiconductor at temperature T=0 KT=0 K, which of the following statement is true?

• All energy states in the valence band are filled with electrons and all energy states in the conduction band are empty of electrons.

• All energy states in the valence band are empty of electrons and all energy states in the conduction band are filled with electrons.

• All energy states in the valence and conduction band are filled with holes.

• All energy states in the valence and conduction band are filled with electrons.

Question 5

For an intrinsic semiconductor at temperature T=0 KT=0 K, which of the following statement is true?

(GATE 2023 || EC || MCQ ||2 MARK)

• All energy states in the valence band are filled with electrons and all energy states in the conduction band are empty of electrons.

• All energy states in the valence band are empty of electrons and all energy states in the conduction band are filled with electrons.

• All energy states in the valence and conduction band are filled with holes.

• All energy states in the valence and conduction band are filled with electrons.

Question 6

The free electron concentration profile n(x)n(x) in a doped semiconductor at equilibrium is shown in the figure, where the points A,BA,B, and CC mark three different positions. Which of the following statements is/are true?

( GATE 2024 || EC || MCQ ||2 MARK)

• For xx between B and C, the electron diffusion current is directed from C to B.

• For xx between B and A, the electron drift current is directed from B to A.

• For xx between B and C, the electric field is directed from B to C.

• For xx between B and A. the electric field is directed from A to B.

Question 7

Consider a MOS capacitor made with p-type silicon. It has an oxide thickness of 100 nm, a fixed positive oxide charge of 10−8C/cm2 at the oxide-silicon interface, and a metal work function of 4.6eV. Assume that the relative permittivity of the oxide is 4 and the absolute permittivity of free space is 8.85×10−14 F/cm. If the flatband voltage is 0 V0 V, the work function of the pp-type silicon (in eV, rounded off to two decimal places) is _

(GATE 2024 || EC || MCQ ||2 MARK)

• 4.32

Question 8

A non-degenerate n-type semiconductor has 5\% neutral dopant atoms. Its Fermi level is located at 0.25eV0.25eV below the conduction band (EC) and the donor energy level (ED) has a degeneracy of 2. Assuming the thermal voltage to be 20mV20mV. The difference between EC​ and ED​ (in eV, rounded off to two decimal places) is

( GATE 2024 || EC || NAT ||2 MARK)

• 0.18

Question 9

The intrinsic carrier concentration of a semiconductor is 2.5×1016/m32.5×1016/m3 at 300 K.

If the electron and hole mobilities are 0.15 m2/Vs and 0.05 m2/Vs, respectively, then the intrinsic resistivity of the semiconductor (in kΩ.m ) at 300 K is __________ .

(Charge of an electron e=1.6×10−19C

(GATE 2025 || EC || MCQ ||1 MARK)

• 1.65

• 1.25

• 0.85

• 1.95

Question 10

The electron mobility μn​ in a non-degenerate germanium semiconductor at 300 K is 0.38 m2/Vs.
The electron diffusivity Dn​ at 300 K (in cm2/s, rounded off to the nearest integer) is __________ .
(Consider the Boltzmann constant kB=1.38×10−23 J/K and the charge of an electron e=1.6×10−19C)

(GATE 2025 || EC || MCQ ||1 MARK)

• 26

• 98

• 38

• 10

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