ISRO EC 2018:Electronics Devices & CIrcuits Booster Quiz 4

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Question 1

A pure semiconductor is doped with donor impurities to the extent of 1:10⁷. How many times the conductivity is increased in semiconductor due to doping. If the total number of atoms is 4.421 x 10²² /cm³, intrinsic concentration is 2.5 x 10¹³ atoms/ cm³, electron mobility is 3800 cm²/V-s and hole mobility is 1800 cm²/V-s

• A130 times
• B20 times
• C120 times
• Dcannot be determined

Question 2

Determine the resistivity of an intrinsic Si specimen at 300⁰K if the electron mobility is 1300 cm²/V. s, hole mobility is 500 cm²/V. s and carrier density 1.48x10¹⁰ electrons (holes)/cm³ at 300⁰K. [Assume n=p].

• A2.35x10⁵Ω.cm
• B3.35x10⁵Ω.cm
• C5.75x10⁵Ω.cm
• D3.75x10⁵Ω.cm

Question 3

Find the per unit change in current of a ‘Si’ diode if V_T=26mV and the forward voltage drop increases by 50mV.

• A2.616
• B1.616
• C3.616
• D1.308

Question 4

For what value of V_D will the reverse current of Ge reach 99% of its saturation value at a temperature of 300⁰K?

• A-0.11913 V
• B0.11913 V
• C-0.7132 V
• D0.7132 V

Question 5

A Ge diode has a saturation current of 10μA at 300^oK. Find the saturation current at 400^oK.

• A6.35 mA
• B10.24 mA
• C13.33 mA
• D20 mA

Question 6

A GaAs pn⁺ junction LED has following parameters:-



assume ni=1.8 *10⁶ cm^-3
The injection efficiency of LED is :-

• A0.83
• B0.99
• C0.64
• D0.46

Question 7

What is the expression for the minimum conductivity σ_min ?

• A2q n_i²
• B2q n_i
• C2q n_i
• D2q n_i

Question 8

Diffusion potential across a p-n junction

• Adecreases with increase in doping concentration
• Bincreases with decrease in band gap
• Cdoes not depend on doping
• Dincrease with increase in doping

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