Energy Band Diagram for Semiconductors
Characteristics of energy bands in semiconductors, with a small forbidden energy gap allowing limited electron excitation to the conduction band.
What is Energy Band Diagram for Semiconductors?
The highest energy band that is completely or partially filled with electrons at absolute zero temperature. These electrons are typically involved in covalent bonding.
Key formula / rule: Energy of photon for excitation
Key points
- Define valence band, conduction band, and forbidden energy gap.
- Describe the energy band diagram for a semiconductor.
- Explain how electrons and holes are generated in a semiconductor.
- Relate the band gap energy to the electrical properties of semiconductors.
Common exam trap
Confusing energy bands with discrete atomic energy levels.
Definitions
- Term
Valence Band (VB)
- Meaning
The highest energy band that is completely or partially filled with electrons at absolute zero temperature. These electrons are typically involved in covalent bonding.
- Term
Conduction Band (CB)
- Meaning
The lowest energy band that is empty or partially filled with electrons, allowing them to move freely and conduct electricity.
- Term
Forbidden Energy Gap (Eg)
- Meaning
The energy difference between the top of the valence band and the bottom of the conduction band, where no electron can exist.
- Term
Hole
- Meaning
A vacant electron state in the valence band, which behaves as a positive charge carrier and contributes to current flow.
Learning objectives
Define valence band, conduction band, and forbidden energy gap.
Describe the energy band diagram for a semiconductor.
Explain how electrons and holes are generated in a semiconductor.
Relate the band gap energy to the electrical properties of semiconductors.
Compare the energy band diagrams of conductors, semiconductors, and insulators.
Formulae
- Name
Energy of photon for excitation
- Note
Where Eg is the band gap energy, h is Planck's constant, and ν is the frequency of the photon.
- Expression
Eg = hν
- Name
Wavelength of photon for excitation
- Note
Where c is the speed of light and λ is the wavelength of the photon. This gives the maximum wavelength of light that can excite an electron across the band gap.
- Expression
Eg = hc/λ
Prerequisites
Basic understanding of atomic structure and electron configuration.
Knowledge of quantum numbers and energy levels in atoms.
Elementary concepts of electrical conductivity and resistance.
Familiarity with the concept of covalent bonding.
Common mistakes
Confusing energy bands with discrete atomic energy levels.
Assuming semiconductors conduct electricity well at absolute zero temperature.
Not understanding that holes are also charge carriers and contribute to current.
Incorrectly stating the relative sizes of band gaps for conductors, semiconductors, and insulators.
Believing that the forbidden gap is a region where electrons are simply 'missing' rather than a forbidden energy range.
Keywords
Energy Bands
Valence Band
Conduction Band
Forbidden Energy Gap
Band Gap
Semiconductor
Electron-Hole Pair
Charge Carriers
Intrinsic Semiconductor
Practice preview
In a semiconductor, the energy gap between the valence band and the conduction band is:…
easy
Which of the following statements accurately describes the valence band in a semiconductor at absolute zero temperature (0 K)?…
easy
In a semiconductor, the Fermi level at 0 K for an intrinsic semiconductor lies:…
medium