Q.1 What is the primary material used in most silicon-based semiconductor devices?
Germanium
Silicon
Gallium arsenide
Copper
Explanation - Silicon is the most widely used semiconductor material in electronics due to its favorable bandgap and mature processing technology.
Correct answer is: Silicon
Q.2 Which process adds donor atoms to a semiconductor to create n-type material?
Ion implantation
P-type doping
Annealing
Doping with acceptors
Explanation - Ion implantation introduces donor atoms (like phosphorus) into silicon, creating n-type material. P-type doping introduces acceptors.
Correct answer is: Ion implantation
Q.3 What is the energy gap of silicon at room temperature?
1.12 eV
1.43 eV
0.66 eV
3.4 eV
Explanation - Silicon has a bandgap of approximately 1.12 eV at 300 K, which determines its intrinsic carrier concentration.
Correct answer is: 1.12 eV
Q.4 Which of the following is NOT a typical application of a semiconductor diode?
Rectification
Amplification
Voltage regulation
Signal demodulation
Explanation - Diodes are mainly used for rectification, voltage regulation, and signal demodulation; amplification requires transistors.
Correct answer is: Amplification
Q.5 In a p-n junction, the depletion region is formed due to:
Electrolyte absorption
Diffusion of minority carriers
Magnetic field
Photons absorption
Explanation - When p and n regions are joined, minority carriers diffuse across the junction, creating a space‑charge region (depletion).
Correct answer is: Diffusion of minority carriers
Q.6 Which semiconductor has the widest bandgap among the options?
Gallium nitride
Silicon
Gallium arsenide
Germanium
Explanation - GaN has a bandgap of about 3.4 eV, much larger than Si (1.12 eV), GaAs (1.43 eV), and Ge (0.66 eV).
Correct answer is: Gallium nitride
Q.7 What does the term 'mobility' refer to in semiconductor physics?
Speed of electrons in vacuum
Rate of carrier movement under an electric field
Electrical resistance of the material
Quantum tunneling probability
Explanation - Carrier mobility indicates how quickly electrons or holes can move when an electric field is applied.
Correct answer is: Rate of carrier movement under an electric field
Q.8 Which process is primarily used to grow silicon crystals for wafers?
Czochralski
Epitaxy
Chemical vapor deposition
Sputtering
Explanation - The Czochralski process pulls a single crystal from molten silicon to form a large wafer.
Correct answer is: Czochralski
Q.9 In a BJT, which transistor configuration provides current amplification?
Common emitter
Common base
Common collector
All of the above
Explanation - Common emitter amplifies current and voltage, whereas common base and collector are mainly for impedance matching.
Correct answer is: Common emitter
Q.10 Which of the following is a key advantage of MOSFETs over BJTs?
Higher current density
Lower input impedance
Higher switching speed
Higher power consumption
Explanation - MOSFETs have very fast switching times and high input impedance, making them ideal for digital circuits.
Correct answer is: Higher switching speed
Q.11 The term 'band-to-band tunneling' refers to:
Electron movement across a depletion region
Carrier movement within the same band
Tunneling of carriers directly from valence to conduction band
Thermal generation of carriers
Explanation - Band-to-band tunneling is a quantum effect where carriers cross the energy bandgap without thermal activation.
Correct answer is: Tunneling of carriers directly from valence to conduction band
Q.12 Which dopant is commonly used to create p-type silicon?
Phosphorus
Arsenic
Boron
Antimony
Explanation - Boron introduces acceptor states, creating holes and forming p‑type silicon.
Correct answer is: Boron
Q.13 What is the primary function of a Schottky diode?
High‑frequency rectification
High voltage rectification
Temperature sensing
Light emission
Explanation - Schottky diodes have very low forward voltage drop and fast switching, suitable for high‑frequency applications.
Correct answer is: High‑frequency rectification
Q.14 Which property of a semiconductor determines its conductivity in the dark?
Bandgap energy
Doping concentration
Crystal lattice structure
Temperature
Explanation - Doping introduces majority carriers, making the semiconductor conductive even in the absence of light.
Correct answer is: Doping concentration
Q.15 What is the effect of increasing temperature on the carrier concentration of an intrinsic semiconductor?
It decreases exponentially
It remains constant
It increases exponentially
It linearly decreases
Explanation - Higher temperatures excite more electrons across the bandgap, increasing intrinsic carrier concentration exponentially.
Correct answer is: It increases exponentially
Q.16 Which of these is NOT a form of silicon used in electronic devices?
Float Zone
Czochralski
Melted
Epitaxial
Explanation - Silicon is grown via Czochralski or Float Zone; 'melted' is not a specific wafer type.
Correct answer is: Melted
Q.17 The term 'transparency' in the context of semiconductors refers to:
Optical transparency to visible light
Electrical transparency at high frequency
Thermal transparency
Magnetic transparency
Explanation - Semiconductors with bandgaps larger than the energy of visible photons can be transparent in the visible spectrum.
Correct answer is: Optical transparency to visible light
Q.18 Which of the following best describes an 'intrinsic' semiconductor?
Doped with acceptors
Doped with donors
Pure, undoped material
Compound of two elements
Explanation - Intrinsic semiconductors are undoped and have equal electron and hole concentrations.
Correct answer is: Pure, undoped material
Q.19 Which device uses a heterojunction to improve performance?
Zener diode
HBT
Silicon MOSFET
Photodiode
Explanation - Heterojunction bipolar transistors use different semiconductor materials for emitter and base to increase efficiency.
Correct answer is: HBT
Q.20 What is the primary source of noise in a MOSFET?
Shot noise
Flicker noise
Thermal noise
Burst noise
Explanation - MOSFETs exhibit 1/f flicker noise due to traps at the oxide‑semiconductor interface.
Correct answer is: Flicker noise
Q.21 Which type of semiconductor exhibits a direct bandgap?
Silicon
Germanium
Gallium arsenide
Silicon carbide
Explanation - GaAs has a direct bandgap (~1.43 eV), making it efficient for optoelectronic devices.
Correct answer is: Gallium arsenide
Q.22 The 'depletion layer' in a p-n junction acts as:
A conductor
An insulator
An amplifier
A light source
Explanation - The depletion region lacks free carriers, so it behaves like an insulating barrier.
Correct answer is: An insulator
Q.23 Which of the following is a characteristic of a MOS capacitor?
Capacitance varies with gate voltage
It has zero threshold voltage
It is a metallic device only
It is always conductive
Explanation - A MOS capacitor shows voltage‑dependent capacitance due to accumulation, depletion, and inversion layers.
Correct answer is: Capacitance varies with gate voltage
Q.24 Which process is used to deposit thin films of silicon nitride?
CVD
PVD
Spin coating
Electroplating
Explanation - Chemical vapor deposition (CVD) can grow silicon nitride films from silane and ammonia precursors.
Correct answer is: CVD
Q.25 The 'breakdown voltage' of a diode is primarily influenced by:
Doping concentration
Device size
Temperature
All of the above
Explanation - Breakdown voltage depends on doping, geometry, and temperature of the junction.
Correct answer is: All of the above
Q.26 Which of the following materials is commonly used for high‑temperature semiconductors?
Silicon carbide
Silicon
Gallium arsenide
Germanium
Explanation - SiC has a wide bandgap (~3.3 eV) and high thermal conductivity, making it suitable for high‑temperature applications.
Correct answer is: Silicon carbide
Q.27 Which phenomenon explains the generation of electron–hole pairs in a semiconductor when exposed to light?
Thermal generation
Impact ionization
Photoelectric effect
Diffusion
Explanation - The photoelectric effect in semiconductors generates carriers when photons have enough energy to cross the bandgap.
Correct answer is: Photoelectric effect
Q.28 What is the typical purpose of a buffer layer in epitaxial growth?
To reduce strain
To increase doping
To provide electrical contact
To act as a gate insulator
Explanation - A buffer layer mitigates lattice mismatch between substrate and epitaxial film, reducing defects.
Correct answer is: To reduce strain
Q.29 Which of the following is NOT a common type of semiconductor device?
Transistor
Capacitor
Diode
Resistor
Explanation - While semiconductors can form capacitors (e.g., MOS capacitor), the traditional semiconductor device categories are transistor, diode, etc.
Correct answer is: Capacitor
Q.30 A 'p‑type' semiconductor is created by adding which kind of impurity?
Donor
Acceptor
Both donor and acceptor
No impurity
Explanation - Acceptor impurities introduce holes, making the material p‑type.
Correct answer is: Acceptor
Q.31 Which measurement technique is used to determine carrier lifetime?
Hall effect
Time‑resolved photoluminescence
Four‑probe resistance
Raman spectroscopy
Explanation - Time‑resolved photoluminescence measures how quickly carriers recombine, providing carrier lifetime.
Correct answer is: Time‑resolved photoluminescence
Q.32 In which region of a MOSFET does the channel form?
Gate
Source
Drain
Body
Explanation - The channel is induced in the semiconductor body under the gate oxide, controlled by the gate voltage.
Correct answer is: Gate
Q.33 Which of the following is a characteristic of a 'forward‑biased' p-n junction?
Large depletion width
Low current flow
High current flow
Zero potential barrier
Explanation - Forward bias reduces the barrier, allowing significant current to flow across the junction.
Correct answer is: High current flow
Q.34 The 'threshold voltage' of a MOSFET is the gate voltage at which:
The channel is fully depleted
A strong inversion layer forms
The device breaks down
The drain current stops increasing
Explanation - At threshold voltage, the surface potential reaches twice the Fermi potential, forming an inversion layer.
Correct answer is: A strong inversion layer forms
Q.35 What is the purpose of using a 'back‑gate' in some CMOS structures?
To reduce leakage
To increase channel width
To control threshold voltage
All of the above
Explanation - A back‑gate can modulate the threshold voltage, reduce leakage, and adjust device characteristics.
Correct answer is: All of the above
Q.36 Which doping method involves introducing dopants during crystal growth?
Diffusion
Ion implantation
Incorporation
Surface treatment
Explanation - Doping during crystal growth (inclusion) introduces dopants directly into the melt.
Correct answer is: Incorporation
Q.37 What is the main advantage of using silicon carbide for power electronics?
Low bandgap
High temperature operation
Easy to process
Low cost
Explanation - SiC's wide bandgap allows operation at higher temperatures and voltages with lower losses.
Correct answer is: High temperature operation
Q.38 Which of the following describes the 'junction capacitance' of a diode?
It is constant across all bias voltages
It increases with reverse bias
It decreases with reverse bias
It is independent of doping
Explanation - Junction capacitance decreases as reverse bias widens the depletion region.
Correct answer is: It decreases with reverse bias
Q.39 What is the primary function of a 'gate oxide' in a MOSFET?
To conduct current
To provide isolation
To enhance doping
To create a magnetic field
Explanation - The gate oxide electrically isolates the gate electrode from the channel, forming a capacitor.
Correct answer is: To provide isolation
Q.40 Which semiconductor material is commonly used in solar cells?
Silicon
Germanium
Gallium arsenide
Silicon carbide
Explanation - Silicon is the most widely used material in photovoltaic cells due to its abundance and suitable bandgap.
Correct answer is: Silicon
Q.41 Which of the following statements is true about 'bandgap engineering'?
It changes the doping concentration
It modifies the lattice constant
It alters the energy difference between conduction and valence bands
It reduces the material's temperature
Explanation - Bandgap engineering tailors material bandgaps via alloying or strain to achieve desired electronic properties.
Correct answer is: It alters the energy difference between conduction and valence bands
Q.42 What does the symbol 'n' represent in semiconductor notation?
Number of electrons
Electron concentration
Type of doping (n‑type)
None of the above
Explanation - 'n' denotes that the semiconductor is n‑type, having extra electrons as majority carriers.
Correct answer is: Type of doping (n‑type)
Q.43 Which technique is used to measure minority carrier diffusion length?
Photocurrent method
Four‑probe method
Hall effect
X‑ray diffraction
Explanation - The photocurrent method measures how far carriers diffuse before recombining.
Correct answer is: Photocurrent method
Q.44 In which region of a bipolar transistor does the emitter inject carriers?
Into the base
Into the collector
Into the emitter itself
None of the above
Explanation - The emitter injects majority carriers into the adjacent base region to achieve current amplification.
Correct answer is: Into the base
Q.45 What is the main advantage of using epitaxial layers in MOSFETs?
Lower leakage current
Higher doping levels
Simpler fabrication
Higher temperature resistance
Explanation - Epitaxial layers provide a high‑quality, defect‑free channel, reducing leakage and improving performance.
Correct answer is: Lower leakage current
Q.46 Which of the following is a common method for creating a shallow junction?
High‑energy ion implantation
Low‑temperature diffusion
Rapid thermal annealing
All of the above
Explanation - Shallow junctions can be achieved through precise implantation, diffusion, or thermal processes.
Correct answer is: All of the above
Q.47 What is the 'bandgap' of a semiconductor?
Energy required to free an electron from the valence band to the conduction band
The distance between the two layers of the device
The difference between the electron and hole concentration
The voltage drop across a diode
Explanation - Bandgap is the minimum energy needed for an electron to transition from the valence to conduction band.
Correct answer is: Energy required to free an electron from the valence band to the conduction band
Q.48 Which device is commonly used as a current mirror?
BJT
MOSFET
Diode
All of the above
Explanation - MOSFETs are frequently employed in analog circuits as current mirrors due to their predictable characteristics.
Correct answer is: MOSFET
Q.49 The term 'Fermi level' refers to:
The highest occupied energy level at 0 K
The energy at which the probability of occupancy is 0.5
The maximum voltage the device can handle
The threshold voltage of a MOSFET
Explanation - The Fermi level is the chemical potential where electrons and holes have equal probability of occupancy.
Correct answer is: The energy at which the probability of occupancy is 0.5
Q.50 Which semiconductor device is used as a voltage reference?
Zener diode
Photodiode
Schottky diode
Resistor
Explanation - Zener diodes are designed to maintain a stable voltage across them when reverse‑biased beyond their Zener voltage.
Correct answer is: Zener diode
Q.51 What is the typical doping concentration range for a moderately doped silicon substrate?
10^10 to 10^12 cm^-3
10^15 to 10^17 cm^-3
10^20 to 10^22 cm^-3
10^25 to 10^27 cm^-3
Explanation - Moderate doping levels for silicon range from 10^15 to 10^17 cm^-3, balancing conductivity and junction properties.
Correct answer is: 10^15 to 10^17 cm^-3
Q.52 Which of the following is a key benefit of using gallium nitride in LEDs?
High efficiency in the blue spectrum
Low electron mobility
High cost of fabrication
Large bandgap at room temperature
Explanation - GaN emits blue light efficiently due to its wide bandgap (~3.4 eV), enabling white LEDs when combined with phosphors.
Correct answer is: High efficiency in the blue spectrum
Q.53 What does the term 'contact resistance' refer to in semiconductor devices?
Resistance between two electrodes
Resistance at the metal–semiconductor interface
Intrinsic resistance of the semiconductor
Resistance of the device packaging
Explanation - Contact resistance arises from the interface between metal contacts and semiconductor material, affecting overall performance.
Correct answer is: Resistance at the metal–semiconductor interface
Q.54 Which phenomenon limits the speed of a MOSFET at high frequencies?
Gate oxide thickness
Drain‑source voltage
Substrate doping
Capacitance between gate and channel
Explanation - The gate‑channel capacitance (C_gs) determines the RC time constant, limiting switching speed.
Correct answer is: Capacitance between gate and channel
Q.55 Which doping element is commonly used for n‑type silicon?
Boron
Phosphorus
Aluminum
Gallium
Explanation - Phosphorus acts as a donor, adding extra electrons to silicon to make it n‑type.
Correct answer is: Phosphorus
Q.56 Which type of junction is used in a PIN diode?
p–n junction
p–i–n junction
i–p–n junction
n–p junction
Explanation - A PIN diode has a heavily doped p‑type, intrinsic, and heavily doped n‑type region for high‑frequency operation.
Correct answer is: p–i–n junction
Q.57 The 'transconductance' of a MOSFET refers to:
Change in drain current per change in gate voltage
Change in drain current per change in drain voltage
Change in channel length per unit temperature
Change in gate leakage current per unit voltage
Explanation - Transconductance (g_m) is defined as dI_D/dV_GS, indicating the amplification capability.
Correct answer is: Change in drain current per change in gate voltage
Q.58 What is the primary difference between a 'vertical' and a 'planar' MOSFET?
Channel orientation
Substrate type
Gate material
None of the above
Explanation - In vertical MOSFETs the current flows vertically through the channel, whereas planar MOSFETs have horizontal channels.
Correct answer is: Channel orientation
Q.59 Which material is a common host for single‑photon emitters in quantum technologies?
Silicon
Diamond
Germanium
Gallium arsenide
Explanation - Diamond hosts nitrogen‑vacancy centers, which are bright, stable single‑photon emitters.
Correct answer is: Diamond
Q.60 A semiconductor's 'effective mass' is important because it:
Determines its melting point
Influences carrier mobility
Controls its optical absorption edge
Sets its bandgap energy
Explanation - Effective mass affects how easily carriers accelerate under an electric field, impacting mobility.
Correct answer is: Influences carrier mobility
Q.61 Which process is used to create thin‑film transistors (TFTs) for display backplanes?
MOCVD
Epitaxy
Chemical vapor deposition
Ion implantation
Explanation - CVD is commonly used to deposit amorphous or polycrystalline silicon films for TFTs.
Correct answer is: Chemical vapor deposition
Q.62 In a photodiode, the 'internal quantum efficiency' measures:
The ratio of collected carriers to incident photons
The efficiency of light generation
The ratio of output current to input voltage
The photon absorption depth
Explanation - IQE reflects how many photoexcited carriers are actually collected as current.
Correct answer is: The ratio of collected carriers to incident photons
Q.63 Which of the following is a direct consequence of increasing doping concentration in a semiconductor?
Increase in bandgap energy
Decrease in resistivity
Increase in depletion width
Decrease in carrier lifetime
Explanation - Higher doping introduces more carriers, reducing resistivity but also often decreasing carrier lifetime.
Correct answer is: Decrease in resistivity
Q.64 What is the main advantage of using 'metal‑oxide‑semiconductor' technology in digital ICs?
High leakage current
Low power consumption
Large gate area
Low fabrication cost
Explanation - MOSFETs have high input impedance and low static power consumption, ideal for digital logic.
Correct answer is: Low power consumption
Q.65 Which of the following is NOT typically found in a semiconductor device package?
Solder paste
Leadframe
Heat sink
Crystal lattice
Explanation - The crystal lattice is part of the semiconductor material, not the external package.
Correct answer is: Crystal lattice
Q.66 The 'diffusion coefficient' of carriers in a semiconductor:
Is independent of temperature
Determines how carriers spread over time
Is the same for electrons and holes
Is inversely proportional to mobility
Explanation - Diffusion coefficient (D) quantifies carrier spread; it relates to mobility via Einstein relation.
Correct answer is: Determines how carriers spread over time
Q.67 Which material is widely used for high‑speed optoelectronic devices?
Silicon carbide
Gallium arsenide
Silicon
Germanium
Explanation - GaAs has high electron mobility and a direct bandgap, making it suitable for high‑speed optoelectronics.
Correct answer is: Gallium arsenide
Q.68 Which of the following is a common method to reduce leakage current in MOSFETs?
Increasing gate oxide thickness
Adding a guard ring
Using high‑k dielectrics
All of the above
Explanation - Thick oxide, guard rings, and high‑k dielectrics all help suppress leakage.
Correct answer is: All of the above
Q.69 What is the primary purpose of a 'p‑type' region in a bipolar junction transistor (BJT)?
To act as emitter
To act as base
To act as collector
None of the above
Explanation - In an NPN transistor, the middle p‑type region serves as the base, controlling carrier injection.
Correct answer is: To act as base
Q.70 Which of the following is a key parameter in the Shockley diode equation?
Temperature
Ideality factor
Bandgap energy
All of the above
Explanation - Shockley’s equation includes saturation current (temperature dependent), ideality factor, and bandgap via saturation current.
Correct answer is: All of the above
Q.71 What is the function of the 'body diode' in a MOSFET?
To provide current conduction when the device is off
To prevent reverse currents
To increase gate voltage
To reduce leakage current
Explanation - The intrinsic diode between source and body conducts in reverse bias when the MOSFET is off.
Correct answer is: To provide current conduction when the device is off
Q.72 Which type of transistor is primarily used in analog amplification due to its high gain?
MOSFET
JFET
BJT
IGBT
Explanation - BJTs exhibit higher current and voltage gain compared to MOSFETs, making them suitable for analog stages.
Correct answer is: BJT
Q.73 Which material has the lowest bandgap among the options?
Silicon
Germanium
Gallium arsenide
Silicon carbide
Explanation - Germanium's bandgap (~0.66 eV) is lower than Si (1.12 eV), GaAs (1.43 eV), and SiC (3.3 eV).
Correct answer is: Germanium
Q.74 The term 'depletion width' refers to:
The width of the p‑type region
The width of the n‑type region
The width of the region devoid of free carriers at a junction
The width of the depletion layer in a MOS capacitor
Explanation - At a p‑n junction, the depletion width is the space where carriers are depleted, forming an electric field.
Correct answer is: The width of the region devoid of free carriers at a junction
Q.75 In which application is a 'MOSFET' commonly used?
Digital logic circuits
Analog amplification
High‑frequency oscillators
All of the above
Explanation - MOSFETs are versatile, used in logic, analog, and RF circuits.
Correct answer is: All of the above
Q.76 Which of the following best describes the 'reverse‑bias breakdown' in a diode?
When the diode starts conducting in forward direction
When the diode allows large reverse current due to avalanche
When the diode stops conducting in forward direction
When the diode is damaged
Explanation - Reverse‑bias breakdown (avalanche) occurs when the reverse voltage exceeds the breakdown voltage, causing current flow.
Correct answer is: When the diode allows large reverse current due to avalanche
Q.77 What is the main benefit of using 'high‑k' dielectrics in MOS devices?
Reduced gate leakage
Increased gate capacitance
Higher breakdown voltage
All of the above
Explanation - High‑k materials allow a thicker physical layer while maintaining capacitance, reducing leakage.
Correct answer is: Reduced gate leakage
Q.78 Which of the following is a property of a 'pinhole' defect in a semiconductor?
It increases carrier recombination
It acts as a deep donor level
It has no effect on device performance
It increases doping concentration
Explanation - Pinhole defects provide recombination centers, degrading device performance.
Correct answer is: It increases carrier recombination
Q.79 Which process is used to grow epitaxial silicon on a silicon wafer?
Molecular beam epitaxy (MBE)
Chemical vapor deposition (CVD)
Physical vapor deposition (PVD)
All of the above
Explanation - MBE, CVD, and PVD can be employed to grow high‑quality epitaxial layers.
Correct answer is: All of the above
Q.80 Which of the following is a typical application of a 'heterojunction bipolar transistor (HBT)'?
Low‑noise RF amplification
High‑power switching
Analog signal amplification
Digital logic gates
Explanation - HBTs, with different emitter and base materials, provide high speed and low noise for RF applications.
Correct answer is: Low‑noise RF amplification
Q.81 The 'bandgap temperature coefficient' describes:
The change of bandgap with temperature
The change of doping concentration with temperature
The change of resistivity with temperature
The change of carrier mobility with temperature
Explanation - It quantifies how the semiconductor bandgap shrinks as temperature rises.
Correct answer is: The change of bandgap with temperature
Q.82 What is the purpose of a 'source follower' configuration in MOSFET circuits?
To increase voltage gain
To provide voltage buffering
To increase current drive
To reduce power consumption
Explanation - The source follower offers unity voltage gain and high input, low output impedance for buffering.
Correct answer is: To provide voltage buffering
Q.83 Which device is best suited for high‑temperature, high‑power applications?
Si MOSFET
GaN HEMT
SiC MOSFET
GaAs MOSFET
Explanation - Silicon carbide devices handle high temperature and voltage, ideal for power electronics.
Correct answer is: SiC MOSFET
Q.84 Which property is NOT a function of doping concentration?
Electrical resistivity
Carrier concentration
Bandgap energy
Depletion width
Explanation - Bandgap energy is an inherent material property, not altered by doping.
Correct answer is: Bandgap energy
Q.85 Which of the following is a consequence of 'quantum confinement' in a semiconductor nanostructure?
Bandgap reduction
Bandgap widening
Increased carrier mobility
Decreased effective mass
Explanation - When dimensions shrink below the de Broglie wavelength, the bandgap widens due to confinement.
Correct answer is: Bandgap widening
Q.86 Which type of contact is commonly used to create low resistance contacts to n‑type silicon?
Aluminum
Gold
Nickel
Copper
Explanation - Aluminum forms an ohmic contact with n‑type silicon due to favorable work function alignment.
Correct answer is: Aluminum
Q.87 What does 'NPN' refer to in a bipolar transistor?
The sequence of doping layers: n‑type, p‑type, n‑type
The number of electrons in the transistor
The negative‑positive‑negative arrangement of charges
The name of the manufacturer
Explanation - NPN indicates the doping sequence of the emitter, base, and collector.
Correct answer is: The sequence of doping layers: n‑type, p‑type, n‑type
Q.88 Which of the following is a typical feature of 'Schottky diodes' compared to standard p‑n diodes?
Higher reverse breakdown voltage
Lower forward voltage drop
Higher capacitance
Longer recovery time
Explanation - Schottky diodes have metal‑semiconductor junctions, offering lower forward voltage and faster switching.
Correct answer is: Lower forward voltage drop
Q.89 What is the main function of a 'MOSFET gate oxide' thickness?
To control channel length
To influence gate leakage current
To set threshold voltage
Both B and C
Explanation - Thickness determines leakage and threshold voltage; thinner oxides reduce leakage but can increase gate current.
Correct answer is: Both B and C
Q.90 Which process is used to produce 'float zone' silicon wafers?
Czochralski method
Zone refinement
Chemical vapor deposition
Molecular beam epitaxy
Explanation - Float zone uses a molten zone to purify silicon without contacting a crucible.
Correct answer is: Zone refinement
Q.91 Which of the following is an advantage of using 'III–V' semiconductors in LEDs?
Low efficiency
High electron mobility
High defect density
Large bandgap
Explanation - III‑V materials offer high electron mobility, enabling efficient light emission.
Correct answer is: High electron mobility
Q.92 What is the significance of the 'carrier lifetime' in a semiconductor?
It determines the speed of switching in devices
It sets the maximum operating temperature
It is unrelated to device performance
It defines the bandgap energy
Explanation - Longer lifetime allows carriers to exist longer, influencing recombination rates and device speed.
Correct answer is: It determines the speed of switching in devices
Q.93 Which device uses 'heterojunctions' to achieve higher electron mobility?
BJT
HBT
MOSFET
Diode
Explanation - Heterojunction bipolar transistors use material interfaces to reduce base transit time.
Correct answer is: HBT
Q.94 Which of the following statements about 'p‑type' silicon is TRUE?
It has excess electrons
It has excess holes
It is not conductive
It has no majority carriers
Explanation - P‑type silicon has acceptor impurities, creating holes as majority carriers.
Correct answer is: It has excess holes
Q.95 Which device is primarily used as a voltage regulator in power supplies?
Zener diode
Transistor
Resistor
Capacitor
Explanation - A Zener diode maintains a constant voltage across its terminals in reverse bias.
Correct answer is: Zener diode
Q.96 Which type of doping produces 'acceptor levels' in silicon?
Phosphorus
Boron
Arsenic
Aluminum
Explanation - Boron introduces acceptor energy levels, creating holes in silicon.
Correct answer is: Boron
Q.97 In a MOSFET, the 'drain current' is controlled primarily by:
Gate voltage
Drain voltage
Source voltage
Temperature
Explanation - The gate voltage controls channel conductivity, which determines drain current.
Correct answer is: Gate voltage
Q.98 Which of the following is NOT a typical semiconductor fabrication step?
Photolithography
Chemical doping
Mechanical polishing
Electroplating
Explanation - Electroplating is not used in semiconductor device fabrication, which relies on deposition and diffusion.
Correct answer is: Electroplating
Q.99 Which of the following is a characteristic of a 'p‑n‑p' transistor structure?
Emitter is n‑type
Emitter is p‑type
Base is n‑type
Collector is p‑type
Explanation - In a p‑n‑p transistor, the emitter and collector are p‑type, with an n‑type base.
Correct answer is: Emitter is p‑type
Q.100 What does 'Ohmic contact' mean in semiconductor devices?
A contact that blocks current flow
A contact that has zero resistance
A contact that shows linear I‑V characteristic
A contact that is magnetic
Explanation - Ohmic contacts allow current to flow freely with a linear I‑V relationship, avoiding rectification.
Correct answer is: A contact that shows linear I‑V characteristic
Q.101 Which material is a common substrate for GaAs devices?
Silicon
SiC
GaAs
Diamond
Explanation - GaAs substrates are used for GaAs devices due to lattice match and high mobility.
Correct answer is: GaAs
Q.102 The 'threshold voltage' of a MOSFET is influenced by:
Doping concentration
Oxide thickness
Temperature
All of the above
Explanation - All listed factors affect the voltage needed to invert the channel.
Correct answer is: All of the above
Q.103 Which of the following statements is true about a 'pn junction diode' under reverse bias?
It conducts current easily
It has a wide depletion region
It behaves like a resistor
It shows zero voltage drop
Explanation - Reverse bias widens the depletion region, reducing current flow.
Correct answer is: It has a wide depletion region
Q.104 Which semiconductor property determines the speed of a transistor?
Carrier mobility
Bandgap
Doping level
All of the above
Explanation - Higher mobility allows carriers to respond faster to electric fields, improving speed.
Correct answer is: Carrier mobility
Q.105 Which of the following is a typical application for a 'MOSFET' in power electronics?
Digital logic
High‑frequency amplification
DC‑to‑DC conversion
All of the above
Explanation - MOSFETs are widely used in power converters due to low conduction loss and high switching frequency.
Correct answer is: DC‑to‑DC conversion
Q.106 Which of the following is NOT a form of 'carrier recombination'?
Shockley‑Read‑Hall
Auger
Diffusion
Radiative
Explanation - Diffusion is a transport process, not a recombination mechanism.
Correct answer is: Diffusion
Q.107 What is the primary difference between a 'BJT' and a 'MOSFET'?
BJT uses current to control current; MOSFET uses voltage to control current
MOSFET uses current to control current; BJT uses voltage to control current
Both use current to control current
Both use voltage to control current
Explanation - BJTs are current‑controlled devices, while MOSFETs are voltage‑controlled.
Correct answer is: BJT uses current to control current; MOSFET uses voltage to control current
Q.108 Which of the following is a characteristic of 'high‑k' dielectric materials?
Low dielectric constant
High physical thickness
Large bandgap
Large dielectric constant
Explanation - High‑k materials have a large dielectric constant, enabling higher capacitance with lower leakage.
Correct answer is: Large dielectric constant
Q.109 Which process is used to create 'thin‑film transistors' on glass?
Photolithography
Spin coating
Electron beam evaporation
All of the above
Explanation - Thin‑film transistors are fabricated using various deposition and patterning techniques.
Correct answer is: All of the above
Q.110 The 'carrier diffusion length' is defined as:
Distance an electron travels before scattering
Distance a carrier can travel before recombining
Distance over which doping changes
Distance over which electric field exists
Explanation - It is the mean distance a carrier travels before recombination.
Correct answer is: Distance a carrier can travel before recombining
Q.111 What does the term 'p‑type doping' refer to?
Adding donor atoms
Adding acceptor atoms
Reducing the bandgap
Increasing the crystal lattice constant
Explanation - Acceptor doping introduces holes, creating p‑type material.
Correct answer is: Adding acceptor atoms
Q.112 Which of the following is a key factor affecting the 'breakdown voltage' of a diode?
Doping concentration
Junction area
Temperature
All of the above
Explanation - All listed parameters influence the breakdown voltage.
Correct answer is: All of the above
Q.113 Which device is commonly used as a switch in digital logic circuits?
Diode
Resistor
MOSFET
Capacitor
Explanation - MOSFETs act as high‑speed, low‑power switches in logic circuits.
Correct answer is: MOSFET
Q.114 The 'forward‑bias' condition in a diode is characterized by:
Large current flow
Large voltage drop
High resistance
Zero current flow
Explanation - Forward bias lowers the barrier, allowing current to flow.
Correct answer is: Large current flow
Q.115 Which of the following is NOT a property of silicon carbide (SiC)?
Wide bandgap
High thermal conductivity
High electrical resistivity
Low melting point
Explanation - SiC has a high melting point (~2730 °C) and is used for high‑temperature applications.
Correct answer is: Low melting point
Q.116 The 'depletion width' of a p-n junction is determined by:
Doping concentration
Applied bias
Both A and B
None of the above
Explanation - Higher doping reduces depletion width; reverse bias increases it.
Correct answer is: Both A and B
Q.117 In which device does the 'body diode' appear naturally?
BJT
MOSFET
Diode
Transistor
Explanation - MOSFETs contain an intrinsic body diode between source and body.
Correct answer is: MOSFET
Q.118 Which of the following materials is NOT commonly used as a substrate for high‑temperature electronics?
Silicon carbide
Gallium nitride
Gallium arsenide
Quartz
Explanation - GaAs is less suited for high‑temperature due to lower melting point compared to SiC and GaN.
Correct answer is: Gallium arsenide
Q.119 Which of these is a 'non‑linear' device characteristic?
Resistor
Capacitor
Diode
Inductor
Explanation - A diode’s I‑V relationship is highly non‑linear, unlike linear components.
Correct answer is: Diode
Q.120 Which of the following is an advantage of 'heterojunctions' in transistors?
Improved thermal stability
Higher electron mobility
Reduced doping concentration
All of the above
Explanation - Heterojunctions can enhance carrier mobility by tailoring band alignments.
Correct answer is: Higher electron mobility
Q.121 What is the primary role of the 'gate oxide' in a MOSFET?
To conduct electrons
To insulate the gate
To provide current path
To generate light
Explanation - Gate oxide electrically isolates the gate electrode from the channel, forming a capacitor.
Correct answer is: To insulate the gate
Q.122 Which semiconductor device is often used for high‑frequency amplification?
BJT
MOSFET
GaAs MESFET
Diode
Explanation - GaAs MESFETs provide high electron mobility for RF applications.
Correct answer is: GaAs MESFET
Q.123 The 'carrier mobility' of holes in silicon is generally:
Higher than electrons
Lower than electrons
Equal to electrons
Independent of temperature
Explanation - Hole mobility in Si is typically ~450 cm²/V·s, lower than electron mobility (~1350 cm²/V·s).
Correct answer is: Lower than electrons
Q.124 Which of the following is a typical doping concentration for an N‑type silicon substrate used in integrated circuits?
10^10 cm⁻³
10^12 cm⁻³
10^15–10^17 cm⁻³
10^20 cm⁻³
Explanation - Typical IC substrates are doped in the 10^15–10^17 cm⁻³ range.
Correct answer is: 10^15–10^17 cm⁻³
Q.125 Which of the following best describes 'band-to-band recombination'?
Recombination via defect states
Recombination through impurity levels
Direct recombination from conduction to valence band
Auger recombination
Explanation - Band‑to‑band recombination occurs directly between the conduction and valence bands.
Correct answer is: Direct recombination from conduction to valence band
Q.126 What is the key difference between 'Schottky' and 'p‑n' diodes?
Schottky has lower forward voltage drop
p‑n has higher reverse breakdown voltage
Both have identical characteristics
Schottky requires doping
Explanation - Schottky diodes have a metal‑semiconductor junction, leading to lower forward drop and faster switching.
Correct answer is: Schottky has lower forward voltage drop
Q.127 Which process is used to grow a thin epitaxial layer of silicon on a silicon wafer?
Molecular beam epitaxy
Chemical vapor deposition
Physical vapor deposition
All of the above
Explanation - All three deposition techniques can produce epitaxial silicon layers.
Correct answer is: All of the above
Q.128 In a MOSFET, the term 'over‑drive voltage' (V_ov) is defined as:
V_GS - V_TH
V_DS - V_GS
V_GS + V_TH
V_DS + V_TH
Explanation - Over‑drive voltage is the gate‑to‑source voltage minus the threshold voltage, controlling channel conduction.
Correct answer is: V_GS - V_TH
Q.129 Which of the following is a typical application of a 'heterojunction bipolar transistor (HBT)'?
Analog amplification
Digital logic
RF amplification
Power switching
Explanation - HBTs are commonly used in RF amplifiers due to high gain and low noise.
Correct answer is: RF amplification
Q.130 What is the primary advantage of using 'silicon carbide (SiC)' in power devices?
Lower cost
Higher breakdown voltage
Lower thermal conductivity
Lower bandgap
Explanation - SiC's wide bandgap allows devices to operate at high voltages and temperatures.
Correct answer is: Higher breakdown voltage
Q.131 Which of the following is true about 'carrier lifetime' in semiconductors?
It is independent of temperature
It is longer in high‑purity crystals
It is irrelevant for device performance
It is shorter in intrinsic material
Explanation - Purity reduces defect levels, increasing carrier lifetime.
Correct answer is: It is longer in high‑purity crystals
Q.132 Which of the following is a key parameter that determines the speed of a MOSFET?
Gate‑drain capacitance
Carrier mobility
Threshold voltage
All of the above
Explanation - Gate‑drain capacitance, mobility, and threshold voltage all influence switching speed.
Correct answer is: All of the above
Q.133 The 'electron affinity' of a semiconductor is defined as:
Energy required to excite an electron across bandgap
Energy difference between vacuum level and conduction band edge
Energy difference between vacuum level and valence band edge
Bandgap energy
Explanation - Electron affinity measures how easily electrons can be added to the conduction band from vacuum.
Correct answer is: Energy difference between vacuum level and conduction band edge
Q.134 Which of the following is a key advantage of using 'GaN' in high‑frequency power devices?
High electron mobility
Low thermal conductivity
Low bandgap
High cost
Explanation - GaN has high electron mobility, enabling fast switching and high power density.
Correct answer is: High electron mobility