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Questions and Answers
What defines the energy gap in semiconductors compared to insulators?
What defines the energy gap in semiconductors compared to insulators?
- It is much smaller in semiconductors. (correct)
- It is nonexistent in semiconductors.
- It is equal in both materials.
- It is much larger in semiconductors.
At absolute zero temperature, which statement about the energy levels in a semiconductor is true?
At absolute zero temperature, which statement about the energy levels in a semiconductor is true?
- Both bands are completely empty.
- Conduction electrons occupy the valence band.
- All energy levels in the valence band are filled. (correct)
- All energy levels in the conduction band are filled.
Where does the Fermi level lie in an intrinsic semiconductor?
Where does the Fermi level lie in an intrinsic semiconductor?
- In the mid-part of the forbidden gap. (correct)
- At the bottom of the conduction band.
- At the top of the valence band.
- Outside both bands.
In an n-type semiconductor, what are the donor levels primarily responsible for?
In an n-type semiconductor, what are the donor levels primarily responsible for?
What is the significance of the energy difference $E_g - E_d$ in n-type materials?
What is the significance of the energy difference $E_g - E_d$ in n-type materials?
What is the position of the Fermi level in an n-type material at low temperatures?
What is the position of the Fermi level in an n-type material at low temperatures?
Which statement accurately describes the behavior of holes in p-type materials?
Which statement accurately describes the behavior of holes in p-type materials?
What is the relationship between the total current and current densities in semiconductors?
What is the relationship between the total current and current densities in semiconductors?
What does the symbol $E_a$ represent in the context of p-type semiconductors?
What does the symbol $E_a$ represent in the context of p-type semiconductors?
In semiconductor physics, how does the conductivity ($\sigma$) relate to charge carrier densities and drift velocities?
In semiconductor physics, how does the conductivity ($\sigma$) relate to charge carrier densities and drift velocities?
Flashcards
Energy Gap (Semiconductor)
Energy Gap (Semiconductor)
The energy difference between the bottom of the conduction band and the top of the valence band in a semiconductor material.
Thermal Excitation (Semiconductors)
Thermal Excitation (Semiconductors)
At room temperature, some electrons in the valence band gain enough thermal energy to jump the energy gap and become conduction electrons.
Fermi Level (Intrinsic Semiconductor)
Fermi Level (Intrinsic Semiconductor)
The average energy level of conduction electrons in an intrinsic semiconductor lies approximately halfway between the valence band and the conduction band.
Donor Levels (n-type Semiconductor)
Donor Levels (n-type Semiconductor)
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Conduction in n-type Material (Low Temperature)
Conduction in n-type Material (Low Temperature)
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Fermi Level in n-type Semiconductor at Low Temperatures
Fermi Level in n-type Semiconductor at Low Temperatures
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Fermi Level in p-type Semiconductor at Low Temperatures
Fermi Level in p-type Semiconductor at Low Temperatures
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Current Density in a Semiconductor
Current Density in a Semiconductor
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Conductivity of a Semiconductor
Conductivity of a Semiconductor
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Drift Velocity of Charge Carriers
Drift Velocity of Charge Carriers
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Study Notes
Semiconductors & Dielectric Materials
- Semiconductors have an energy gap, significantly smaller than insulators.
- The gap is between the conduction band bottom and the valence band top.
- Conventionally, valence band top is zero.
Fermi Level in Intrinsic Semiconductors
- At 0 Kelvin, all valence band levels are filled, and conduction band levels are empty.
- At room temperature, some electrons in the valence band can gain thermal energy, jump to the conduction band, and become conduction electrons.
- These electrons return to the valence band, creating a continuous excitation and de-excitation process.
- This electron distribution leads to the Fermi level being roughly in the middle of the gap at room temperature.
Fermi Level in Extrinsic Semiconductors (n-type)
- In n-type materials, donor atoms introduce extra electrons.
- These extra electrons are relatively free in the material and have more energy.
- This elevated energy positions donor levels in the gap, closer to the conduction band.
Fermi Level in Extrinsic Semiconductors (p-type)
- Acceptor atoms in p-type materials introduce holes.
- Holes in the p-type material possess higher energy than those in the conduction band.
- Energy levels for holes are closer to the valence band.
Conductivity of Semiconductors
- Current in semiconductors is generated from both electrons and holes.
- Conductivity is determined by the charge carrier density (number density of charge carriers) and their mobility.
- σ = e * (Ne * µe + Nh * µh), where σ is conductivity, e is the elementary charge, Ne and Nh are electron and hole densities, and µe and µh are their mobilities.
- In intrinsic semiconductors, Ne = Nh, so σ = n¡ * e * (µe + µh), where n¡ is intrinsic carrier density.
- In n-type materials, Ne >> Nh, so σ ≈ Nee µe, and in p-type materials, Nh >> Ne, so σ ≈ Nhe µh.
Hall Effect
- A magnetic field applied perpendicular to current flow generates a Hall voltage.
- The direction of the Hall voltage indicates the type of charge carrier (electrons or holes).
- Hall coefficient (RH) relates Hall voltage to the current density and magnetic field, RH = 1/ ρe, where ρ is the charge density.
Dielectric Materials
- Dielectrics are electrically non-conducting materials, acting as insulators or for charge storage.
- Dielectrics are characterized by their relatively large forbidden gap, hindering electron movement.
- Dielectric polarization describes how charges in the material move when an external field is applied.
Types of Polarization
- Electronic polarization: Displacement of positive and negative charges in atoms due to external field.
- Ionic polarization: Displacement of ions in ionic crystals due to external filed.
- Orientational polarization: Permanent dipoles align with the external electric field.
- Space charge polarization : Occurs in multi-phase dielectrics due to accumulation of charges at interfaces.
Dielectric Constant
- The dielectric constant (εr) quantifies how much a dielectric material increases capacitance compared to a vacuum capacitor.
Light-Emitting Diodes (LEDs)
- LEDs emit light when current flows through the diode.
- Electrons and holes recombine, releasing energy as photons with energy equal to the bandgap difference.
- Different LED materials produce different colors of light.
Photodiodes
- Photodiodes generate current based on light absorption.
- Light striking the diode excites electrons, creating electron-hole pairs, and producing a photocurrent.
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