Conductors

• Materials that easily permit current flow
• Minimal number (non-zero) of valence electrons

Semiconductors

• Elemental semiconductors consist of one atom
• Compound semiconductors are formed with combinations of group III/V or group II and VI elements
• Bandgap energy ($E_G$) is the energy needed to break the covalent bonds between the semiconductor crystals
  • Higher $E_G$ is more suited for applications at higher temps

Intrinsic Semiconductor

• Insulator at room tempearture
• Equal number of electrons $n$ and holes $p$

Extrinsic Semiconductor

• Formed via doping: process of adding small impurities
  • Increases conductivity
  • Impurities from groups III and V
• $n > p \implies n$-type semiconductor and vice-versa
• The carrier with larger population is the majority carrier and vice-versa

Diode

• A semiconductor device that allows current to flow in one direction

$pn$ Junction

• Interfact between $n$ and $p$ regions where the depletion region forms

Depletion Layer

• Current is not permitted until a certain potential difference is reached across its terminals

Currents

• Diffusion/drift current

Diode Types

• Unbiased
  • Unpowered diode that only permits current if a voltage threshold is met (0.7V for Si)
• Forward Bias
• Reverse Bias
  • Reversing the polarity of the $pn$ junction

Reverse Bias Diode

References

• Course slides, chapter 2: Solid-State Electronics