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QUESTION: 1

In germanium semiconductor material at T = 400 K the intrinsic concentration is

Solution:

QUESTION: 2

The intrinsic carrier concentration in silicon is to be no greater than n_{i} = 1x10^{12} cm^{-3} . The maximum temperature allowed for the silicon is (E_{g} = 1.12 eV)

Solution:

(10^{12})^{2} =

= 9.28 x 10^{-8}, By trial T = 385 K

QUESTION: 3

Two semiconductor material have exactly the same properties except that material A has a bandgap of 1.0eV and material B has a bandgap energy of 1.2 eV. The ratio of intrinsic concentration of material A to that of material B is

Solution:

QUESTION: 4

In silicon at T = 300 K the thermal-equilibrium concentration of electron is n_{0} = 5 x 10^{4} cm^{-3 }The hole concentration is

Solution:

QUESTION: 5

In silicon at T = 300 K if the Fermi energy is 0.22 eV above the valence band energy, the value of p_{0} is

Solution:

QUESTION: 6

The thermal-equilibrium concentration of hole p_{0} in silicon at T = 300 K is 10^{15} cm^{-3}. The value of n_{0} is

Solution:

At 300 K, N_{v} = 1.0 x 10^{19} cm^{-3}

At 300 K, N_{c} = 2.8 x 10^{19} cm^{-3 }

E_{c} - E_{F} = 1.12 - 0.239 = 0.881 eV

n = 4.4 x 10^{4} cm^{-3}

QUESTION: 7

In germanium semiconductor at T = 300 K, the acceptor concentrations is N_{a} = 10^{13} cm^{-3} and donor concentration is N_{d} = 0. The thermal equilibrium concentration p_{0} is

Solution:

QUESTION: 8

A thin film resistor is to be made from a GaAs film doped n - type. The resistor is to have a value of 2 kΩ. The resistor length is to be 200 μm and area is to be 10^{-6} cm^{2}. The doping efficiency is known to be 90%. The mobility of electrons is 8000 cm^{2} / V - s . The doping needed is

Solution:

QUESTION: 9

A silicon sample doped n - type at 10^{18 }cm^{-3 } have a resistance of 10 Ω . The sample has an area of 10^{-6} cm^{2} and a length of 10 μm. The doping efficiency of the sample is (μ_{n = } 800 cm^{2}/V - s)

Solution:

QUESTION: 10

Six volts is applied across a 2 cm long semiconductor bar. The average drift velocity is 10^{4 }cm/s. The electron mobility is

Solution:

QUESTION: 11

For a particular semiconductor material following parameters are observed:

These parameters are independent of temperature. The measured conductivity of the intrinsic material is σ = 10^{-6} (Ω - cm)^{-1} at T = 300 K. The conductivity at T = 500 K is

Solution:

= 1.122 eV

QUESTION: 12

An n - type silicon sample has a resistivity of 5 Ω - cm at T = 300 K. The mobility is μ_{n} = 1350 cm^{2} / V - s. The donor impurity concentration is

Solution:

QUESTION: 13

In a silicon sample the electron concentration drops linearly from 10^{18 }cm^{-3 } to 10^{16} cm^{-3} over a length of 2.0 μm. The current density due to the electron diffusion current is D_{n }= 35cm^{2}/s

Solution:

QUESTION: 14

In a GaAs sample the electrons are moving under an electric field of 5 kV cm and the carrier concentration is uniform at 10^{16} cm^{-3}. The electron velocity is the saturated velocity of 10^{7 }cm/s. The drift current density is

Solution:

J = evn = (1.6 x 10^{-19})(10^{7})(10^{16}) = 1.6 x 10^{4} A/cm^{2}

QUESTION: 15

For a sample of GaAs scattering time is τ_{sc} = 10^{-13}s and electron’s effective mass is m_{e}^{*} = 0.067 m_{o}. If an electric field of 1 kV cm is applied, the drift velocity produced is

Solution:

QUESTION: 16

A gallium arsenide semiconductor at T = 300 K is doped with impurity concentration N_{d} = 10^{16 }cm^{-3} The mobility μ_{n} is 7500 cm^{2}/ V - s . For an applied field of 10 V/cm the drift current density is

Solution:

J = eμ_{n} n_{0}E = (1.6 x 10^{-19})(7500)(10^{16})(10) = 120 A/cm^{2}

QUESTION: 17

In a particular semiconductor the donor impurity concentration is N_{d} = 10^{14 }cm^{-3}. Assume the following parameters,

An electric field of E = 10 V cm is applied. The electric current density at 300 K is

Solution:

=(1.6 x 10^{-19})(1000)(10^{14})(100) = 1.6 A/cm^{2}

QUESTION: 18

A semiconductor has following parameter

Q. When conductivity is minimum, the hole concentration is

Solution:

QUESTION: 19

A semiconductor has following parameter

Q. The minimum conductivity is

Solution:

QUESTION: 20

A particular intrinsic semiconductor has a resistivity of 50 (Ω - cm) at T = 300 K and 5(Ω - cm) at T = 330 K. If change in mobility with temperature is neglected, the bandgap energy of the semiconductor is

Solution:

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