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XII_Phy_New_Chap_15_Semiconductor_Electronics_Materials,_Devices
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Spread the Happiness. Assertion and Reason Statements Feedback: 9008271516XII_Phy_New_Chap-15_SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS
S# Correct Assertion Correct Reason
14.1 INTRODUCTION; 14.2 CLASSIFICATION OF METALS, CONDUCTORS AND SEMICONDUCTORS
The arrangement of atoms in a crystal lattice In a crystal lattice, the close proximity of atoms causes
directly influences the formation of energy their outer electron orbitals to overlap. This merging forms
1
bands. continuous bands of allowed energy levels, impacting a
material's electrical conductivity.
Conductivity is a fundamental property of a A material's conductivity determines how readily it allows
material that reflects its ease of conducting electric current to flow through it. Materials are classified
2
electric current. based on their conductivity values (or resistivity).
The small energy gap (Eg) in semiconductors is Thermal energy at room temperature is sufficient to excite
crucial for their conductivity at room some valence band electrons in semiconductors. These
3
temperature. excited electrons can overcome the Eg and enter the
conduction band, enabling electrical conduction.
The magnitude of the energy band gap (Eg) A larger Eg necessitates a greater energy input for
significantly impacts a material's ability to electrons to jump to the conduction band, hindering
4 conduct electricity. conductivity (insulators). Conversely, a smaller Eg
facilitates easier electron movement, leading to higher
conductivity (conductors).
Semiconductors are a class of materials with The conductivity of semiconductors falls between that of
electrical conductivity intermediate between conductors (metals) and insulators due to their unique
5
conductors and insulators. band structure and the specific size of their energy gap.
The filled valence band and empty conduction At absolute zero, insulators lack mobile charge carriers
band in insulators at 0 K prevent electrical because the valence band is completely filled with
6 conduction. electrons. Additionally, the large Eg gap prevents thermal
excitation from promoting electrons to the conduction
band, hindering current flow.
14.3 INTRINSIC SEMICONDUCTOR
Intrinsic semiconductors at 0 K have a filled At absolute zero, intrinsic semiconductors lack mobile
valence band and empty conduction band. charge carriers because the valence band is full, and the
7
large Eg gap prevents thermal excitation to the conduction
band.
Thermal energy excites electrons from the As temperature increases, thermal energy promotes some
valence band to the conduction band. electrons across the band gap, filling the conduction band
8
and enabling conduction (increased mobile charge
carriers).
The band gap (Eg) of a material significantly A larger Eg necessitates more energy for electrons to
impacts its conductivity. jump, hindering conductivity (insulators). Conversely, a
9
smaller Eg facilitates easier electron movement, leading to
higher conductivity (semiconductors).
Crystal structure and thermal energy together The arrangement of atoms (lattice structure) determines
influence conductivity in intrinsic band gap (Eg). Thermal energy can excite electrons across
10
semiconductors. Eg, impacting the number of mobile charge carriers and
conductivity.
Covalent bonding in intrinsic semiconductors Sharing electrons in covalent bonds prevents free
11 hinders conductivity at 0 K. electrons, crucial for current flow, from existing at very
low temperatures.
Increased temperature generates electron-hole As temperature rises, thermal energy can break covalent
12 pairs in intrinsic semiconductors. bonds, liberating electrons (conduction) and creating
holes, enabling conduction current.
Recombination limits the concentration of free The continuous process of recombination, where electrons
carriers in intrinsic semiconductors. fill holes, reduces the concentration of free charge carriers
13
available for conduction, establishing an equilibrium state.
Intrinsic carrier concentration (ni) influences A higher ni (more electron-hole pairs) signifies a greater
14 conductivity in intrinsic semiconductors. number of mobile charge carriers, leading to increased
conductivity.
The concept of holes simplifies the explanation Holes themselves don't move; instead, neighboring
of current flow in intrinsic semiconductors. electrons jump to fill vacancies, creating a net flow of
15
positive charge (hole current). This simplifies the
explanation of current due to missing electrons.
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XII_Phy_New_Chap-15_SEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS
S# Correct Assertion Correct Reason
Intrinsic semiconductors lack external dopants. Intrinsic semiconductors are undoped, meaning their
lattice structure only contains the element's atoms (like Si
16
or Ge) without any deliberate addition of impurity atoms.
Ionization energy (Eg) explains conductivity The energy required to remove an electron (Eg) is lowest
variations in C, Si, and Ge. for Ge, followed by Si, and highest for C. This directly
17 influences the number of free electrons for conduction,
making Ge and Si semiconductors and C an insulator.
A filled valence band at 0 K prevents conduction In the absence of thermal energy or dopants, a filled
18 in intrinsic semiconductors. valence band at 0 K prevents electrons from jumping to
the conduction band, hindering current flow.
14.4 EXTRINSIC SEMICONDUCTOR
Doping a semiconductor increases its Creates additional charge carriers (electrons in n-type,
19 conductivity. holes in p-type) that enhance conductivity compared to
intrinsic semiconductors.
A donor impurity in a semiconductor has five One more valence electron than the semiconductor atom it
20 valence electrons. replaces, making it easily excited into the conduction
band.
An acceptor impurity in a semiconductor has One less valence electron than the semiconductor atom it
21 three valence electrons. replaces, creating a vacancy (hole) for an electron from
nearby atoms.
Doping with a donor impurity creates n-type Introduces extra electrons that become the majority
22
semiconductors. carriers, defining the semiconductor as n-type.
Doping with an acceptor impurity creates p-type Creates holes that act as the majority carriers in the
23
semiconductors. valence band, resulting in a p-type semiconductor.
Extrinsic semiconductors are semiconductors Doping adds impurity atoms, altering its electrical
24 with controlled impurities introduced through properties and conductivity.
doping.
Doping level influences the concentration of The concentration of dopant atoms directly determines the
majority carriers. number of additional majority carriers (electrons or holes),
25
impacting conductivity. Higher doping levels lead to more.
Dopant type dictates the majority carrier type. The type of dopant atom introduced (donor or acceptor)
26 creates the kind of majority carrier (electrons for donors,
holes for acceptors).
Doping affects both majority and minority Increased doping creates more majority carriers, leading
27 carrier concentrations. to a higher recombination rate and reducing minority
carriers (opposite type).
Doping introduces energy states due to donor Creates new energy levels within the band gap, influencing
28 and acceptor impurities in the band gap. electron and hole mobility and affecting conductivity.
14.5 p-n JUNCTION
Formation of a p-n junction disrupts equilibrium Diffusion of majority carriers creates immobile space-
29 concentrations of mobile charges. charge regions with opposite charges, altering the initial
charge distribution.
Depletion region arises from diffusion of Movement of electrons and holes leaves behind fixed
30 majority carriers across the p-n junction. charges (ionized donors and acceptors), depleting the
region of mobile carriers.
Space-charge regions establish an electric field Separation of positive and negative charges within the
31 within a p-n junction. space-charge regions creates an electric field directed
from positive to negative.
Barrier potential results from the electric field in The electric field opposes further diffusion of majority
32 a p-n junction. carriers, establishing a potential barrier that limits current
flow across the junction.
The electric field in a p-n junction influences The electric field exerts a force on mobile charge carriers,
33 drift current. causing them to drift in the opposite direction of diffusion
current.
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