JEE Main Semiconductor PYQ

6. (JEE Main 2021 (Online) 26th August Morning Shift)

Statement I : By doping silicon semiconductor with pentavalent material, the electrons density increases.

Statement II : The n-type semiconductor has net negative charge.

In the light of the above statements, choose the most appropriate answer from the options given below :

A. Statement - I is true but Statement - II is false.

B. Statement - I is false but Statement - II is true.

C. Both Statement I and Statement II are true.

D. Both Statement I and Statement II are false.

The Correct Answer is Option (A)

Pentavalent activities have excess free e^$-$, so e^$-$ density increases but overall semiconductor is neutral.

7. (JEE Main 2021 (Online) 25th February Evening Shift)

For extrinsic semiconductors; when doping level is increased;

A. Fermi-level of both p-type and n-type semiconductors will go upward for T > T_FK and downward for T < T_FK, where T_F is Fermi temperature.

B. Fermi-level of p-type semiconductor will go upward and Fermi-level of n-type semiconductors will go downward

C. Fermi-level of p and n-type semiconductors will not be affected.

D. Fermi-level of p-type semiconductors will go downward and Fermi-level of n-type semiconductor will go upward.

The Correct Answer is Option (D)

In n-type semiconductor pentavalent impurity is added. Each pentavalent impurity donates a free electron. So the Fermi-level of n-type semiconductor will go upward.

And In p-type semiconductor trivalent impurity is added. Each trivalent impurity creates a hole in the valence band. So the Fermi-level of p-type semiconductor will go downward.

8. (JEE Main 2019 (Online) 9th January Morning Slot)

Mobility of electrons in a semiconductor is defined as the ratio of their drift velocity to the applied electric field. If, for an n-type semiconductor, the density of electrons is 10¹⁹ m^{$-$ 3} and their mobility is 1.6 m²/(V.s) then the resistivity of the semiconductor (since it is an n-type semiconductor contribution of holes is ignored) is close to :

A. $2 Ω$ m

B. 4 $Ω$ m

C. 0.4 $Ω$ m

D. 0.2 $Ω$ m

The Correct Answer is Option (C)

For semiconductor,

Conductivity, $σ$ = n_e q $μ$ _e + n_h q $μ$ _h

given that semiconductor is n-type. So contribution of holes is ignored.

$∴$ n_h q $μ$ _h = 0

$∴$ $σ$ = n_e q $μ$ _e

Resistivity, $ρ$ = $\frac{1}{σ}$

= $\frac{1}{n_{e} q μ_{e}}$

= $\frac{1}{10^{19} \times 1.6 \times 10^{- 19} \times 1.6}$

= $\frac{1}{1.6 \times 1.6}$

= 0.4 $Ω$ m

9. (JEE Main 2017 (Online) 8th April Morning Slot)

What is the conductivity of a semiconductor sale having electron concentration of $5 \times 10^{18} m^{- 3},$ hole concentration of $5 \times 10^{19} m^{- 3},$ electron mobility of 2.0 m² V^{$-$ 1} s^-1 and hole mobility of 0.01 m² V^{$-$ 1} s^{$-$ 1} ?

(Take charge of electronas 1.6 $\times$ 10^{$-$ 19} c)

A. 1.68 ( $Ω$ -m)^{$-$ 1}

B. 1.83 ( $Ω$ -m)^{$-$ 1}

C. 0.59 ( $Ω$ -m)^{$-$ 1}

D. 1.20 ( $Ω$ -m)^{$-$ 1}

The Correct Answer is Option (A)

Conductivity of semiconductor,

$σ$ = e $(η_{e} μ_{e} + η^{'} μ_{h})$

= 1.6 $\times$ 10^{$-$ 19} (5 $\times$ 10¹⁸ $\times$ 2 + 5 $\times$ 10¹⁹ $\times$ 0.01)

= 1.6 $\times$ 1.05

= 1.68

10. (JEE Main 2016 (Offline))

The temperature dependence of resistance of $C u$ and undoped $S i$ in the temperature range $300 - 400$ $K,$ is best described by :

A. Linear increases for $C u,$ exponential decrease of $S i .$

B. Linear decrease for $C u,$ linear decrease for $S i$

C. Linear increase for $C u,$ linear increase for $S i .$

D. Linear increase for $C u,$ exponential increase for $S i$

The Correct Answer is Option (A)

JEE Main 2016 (Offline) Physics - Semiconductor Question 186 English Explanation

Semiconductor Electronics