Inside a pure silicon crystal at thermal equilibrium, what relation holds between electrons and holes?
A Hole concentration exceeds electron concentration
B Both concentrations are equal
C Electron concentration exceeds hole concentration
D Neither carrier is present
Answer: B. Both concentrations are equal An intrinsic semiconductor has equal electron and hole concentrations at equilibrium because carriers are generated in pairs.
Doping silicon with phosphorus generally produces which conductivity type?
A n-type
B intrinsic
C insulating
D p-type
Answer: A. n-type Phosphorus is a donor in silicon and supplies an extra electron, producing n-type material.
Introducing boron into silicon creates which type of semiconductor?
A p-type
B metallic
C n-type
D intrinsic
Answer: A. p-type Boron has three valence electrons and acts as an acceptor in silicon, creating p-type material.
Within p-type silicon, which carrier is the majority carrier?
A Protons
B Ions
C Electrons
D Holes
Answer: D. Holes Acceptor doping makes holes the majority carriers in p-type silicon.
For n-type material, which carrier is present in the greater concentration?
A Neutrons
B Electrons
C Holes
D Photons
Answer: B. Electrons Donor doping supplies electrons, which become the majority carriers in n-type material.
How many valence electrons does a silicon atom have?
A Five
B Two
C Three
D Four
Answer: D. Four Silicon is a Group 14 element with four valence electrons.
Neighboring silicon atoms share electrons through which bond type?
A Metallic bond
B Covalent bond
C Hydrogen bond
D Ionic bond
Answer: B. Covalent bond A silicon crystal is held together by covalent bonds formed by shared valence electrons.
Why is a Group 15 impurity called a donor in silicon?
A It captures a hole
B It creates a metal bond
C It removes a proton
D It supplies an electron
Answer: D. It supplies an electron A pentavalent donor has one extra valence electron that can become available for conduction.
What carrier effect follows when an acceptor atom captures a valence electron?
A Metallic bond
B Mobile hole
C Free proton
D Extra neutron
Answer: B. Mobile hole Capturing a valence electron leaves an unoccupied state, represented as a mobile hole.
Heating a semiconductor can generate which carrier pair?
A Two holes
B Electron and hole
C Two electrons
D Proton and neutron
Answer: B. Electron and hole Thermal energy can lift an electron into the conduction band, leaving a hole in the valence band.
Where is the Fermi level located in an ideal intrinsic semiconductor?
A Near the bandgap middle
B At the valence-band edge
C Inside the conduction band
D Outside the bandgap
Answer: A. Near the bandgap middle For an ideal intrinsic semiconductor, the Fermi level lies approximately near the middle of the bandgap.
The conduction band contains which mobile carriers?
A Forbidden band
B Valence band
C Core band
D Conduction band
Answer: D. Conduction band Electrons promoted to the conduction band can move through the crystal and contribute to current.
In the band model, a hole represents what?
A An empty valence state
B A free neutron
C A conduction band
D A donor atom
Answer: A. An empty valence state A hole is an unoccupied valence-band state that behaves as a positive charge carrier.
Carrier mobility describes a carrier’s response to what?
A Optical color
B Crystal size
C Electric field
D Temperature only
Answer: C. Electric field Mobility measures how readily carriers drift in response to an applied electric field.
Transport caused by an applied electric field is called what?
A Generation
B Diffusion
C Drift
D Recombination
Answer: C. Drift Drift is carrier motion driven by an electric field.
Concentration gradients drive which carrier-transport mechanism?
A Ionization
B Reflection
C Diffusion
D Drift
Answer: C. Diffusion Diffusion moves carriers from regions of higher concentration toward lower concentration.
What region forms near a p–n junction when mobile carriers diffuse and recombine?
A Depletion region
B Optical cavity
C Neutral core
D Metal layer
Answer: A. Depletion region Carrier diffusion and recombination leave a region depleted of mobile electrons and holes.
Joining p-type and n-type regions creates which basic semiconductor junction?
A p–n junction
B Ohmic resistor
C MOS capacitor
D Schottky contact
Answer: A. p–n junction A p–n junction forms where p-type and n-type semiconductor regions meet.
During forward bias, which side of a p–n diode is at the higher potential?
A n-side
B Both sides equal
C Neither side
D p-side
Answer: D. p-side Forward bias connects the p-side positive relative to the n-side, reducing the junction barrier.
How does forward bias affect the p–n junction’s built-in barrier?
A It raises the barrier
B It widens the bandgap
C It lowers the barrier
D It removes the dopants
Answer: C. It lowers the barrier Forward bias opposes the built-in field and lowers the potential barrier to carrier injection.
Why does a reverse-biased p–n junction normally conduct only a small current before breakdown?
A The barrier vanishes
B The bandgap becomes zero
C The depletion region widens
D Majority carriers cross freely
Answer: C. The depletion region widens Reverse bias widens the depletion region and blocks majority-carrier flow; a small minority-carrier current remains.
What is the basic output of a rectifier supplied with AC?
A Pure AC
B Stored charge
C Pulsating DC
D Optical power
Answer: C. Pulsating DC A rectifier converts alternating input into a unidirectional, usually pulsating, output.
Radiative recombination produces light in which device?
A Auger recombination
B Radiative recombination
C Carrier diffusion
D Impact ionization
Answer: B. Radiative recombination In a light-emitting diode, radiative recombination releases energy as photons.
Illumination-induced photocurrent is sensed by which semiconductor device?
A Photodiode
B Tunnel diode
C Varactor
D Zener diode
Answer: A. Photodiode Incident light creates electron–hole pairs in a photodiode, producing a measurable photocurrent.
How does intrinsic carrier concentration usually respond to higher temperature?
A It stays constant
B It becomes negative
C It falls to zero
D It increases strongly
Answer: D. It increases strongly Thermal generation creates more electron–hole pairs as temperature rises, so intrinsic carrier concentration increases strongly.