Semiconductors and Insulators (qualitative ideas only)

Semiconductors and Insulators (qualitative ideas only)

Band Structure in Solids:

Conductors (like metals):

• No Band gap Solids
  • Overlapping Valence and Conduction bands, \(E_g = 0\)
  • Electrons are free to move from valence band to conduction band i.e. high conductivity
  • A small electric field can move electrons
• Partially filled Valence Band
  • Electrons move freely within the band as empty orbitals are available
  • A small electric field can move electrons to nearby empty spaces

• Two conditions for conductors – No Band Gap and Partially filled Valence band
• e.g. Sodium, Magnesium, Copper, Gold, Silver etc.

Semiconductors and Insulators

Insulators

• Completely filled valence band
• Very high Energy gap, \(E_g > 3 eV\)
• Electrons cannot jump to conduction band due to high energy barrier
• Poor conductivity of the materials

Semiconductors

• Definition: Materials whose electrical conductivity lies between those of conductors (like metals) and insulators (like wood or glass).
• Energy Gap: Very small energy gap (energy barrier) between valence band and conduction band. \(E_g < 3 eV\)
• Two types: Intrinsic Semiconductors and Extrinsic Semiconductors

For notes on Energy bands in conductors

Based on NCERT Textbooks