Electronic Devices
Semiconductor Physics
Practice questions from Semiconductor Physics.
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IncorrectWhich of the following can be used as an n-type dopant for silicon?
Select the correct option(s).
The correct options are:
(A) Arsenic and (D) Phosphorous
These are both -type dopants for silicon because they have five valence electrons (group elements), which provide extra electrons to the silicon lattice, making it an n-type semiconductor.
while, Boron and Gallium are p-type dopants because they have only three valence electrons, creating holes in the silicon lattice.
Alternate Solution:
Arsenic (As) and Phosphorous (P) are Group 15 elements, they have an extra electrons (5 electrons in valence shell) to contribute to lattice when doped in silicon.
n-type means material has more electrons than holes,
n-type dopants are (a) and (d)
The intrinsic carrier concentration of a semiconductor is at 300 K.
If the electron and hole mobilities are and , respectively, then the intrinsic resistivity of the semiconductor (in ) at 300 K is _________.
(Charge of an electron .)
Intrinsic Carrier Concentration,
Hence, option (B) is correct.
Alternate Solution:
charge of electron (magnitude)
intrinsic carrier concentration
mobility of holes
mobility of electrons
Upon substitution,
The electron mobility in a non-degenerate germanium semiconductor at 300 K is .
The electron diffusivity at 300 K (in , rounded off to the nearest integer) is _________.
(Consider the Boltzmann constant and the charge of an electron .)
Given:
Hence, option (B) is correct.
Alternate Solution:
By Einstein's relation, Thermal Voltage
Given and
For non-degenerately doped n-type silicon, which one of the following plots represents the temperature (𝑇) dependence of free electron concentration (𝑛)
The graph of log(n) vs 1/T is mentioned.
A non-degenerate n-type semiconductor has neutral dopant atoms. Its Fermi level is located at below the conduction band and the donor energy level has a degeneracy of 2. Assuming the thermal voltage to be . The difference between and (in , rounded off to two decimal places) is __________.
neutral donor atoms/dopant atoms means donor atoms are ionized. Concentration of electrons occupying the donor level is given as
and where is ionized donor atoms concentration.
according to question
The free electron concentration profile in a doped semiconductor at equilibrium is shown in the figure, where the points , and mark three different positions. Which of the following statements is/are true?
For between B and C, the electron diffusion current is directed from to .
For between B and A, the electron drift current is directed from B to A.
For between B and C, the electric field is directed from B to C.
For between B and A, the electric field is directed from to .
- Density of is maximum at point and minimum at .
- will move from , and from to .
In a semiconductor, if the Fermi energy level lies in the conduction band, then the semiconductor is known as
degenerate -type.
degenerate -type.
non-degenerate -type.
non-degenerate -type.
In degenerate semiconductor, fermi level lies inside conduction band or valence band.
As the Fermi lies inside the conduction band hence it is degenerate -type semiconductor.
For an intrinsic semiconductor at temperature , which of the following statement is true?
Intrinsic semiconductor at behaves as an insulator.
Hence, valence band is completely filled with electrons and conduction band is completely empty.
In an extrinsic semiconductor, the hole concentration is given to be where is the intrinsic carrier concentration of . The ratio of electron to hole mobility for equal hole and electron drift current is given as _________(rounded off to two decimal places).
Given,
Given hold drift currentdrift current (In)
In a semiconductor device, the Fermi-energy level is above the valence band energy. The effective density of states in the valence band at is . The thermal equilibrium hole concentration in silicon at is _________. (rounded off to two decimal places). Given KT at is .
Given,
[Considering it is given at ]
Also, at
Given, effective density of states in the valence band,
Now, hole concentration at is given as
