Each type of wafer has different electrical, mechanical and optical properties.

The material is selected in order to be suitable for the application. Thus, in order to

choose the appropriate wafer, the application has to be known.

A few types of materials used for substrate fabrication are shown below:

• Silicon
  • Advantages
    • abundant (can easily found in nature)
    • high melting temperature
    • good interface with the natural oxide SiO₂
    • indirect bandgap
  • Type
    • Czochralski wafer (name of the growth method)
    • EPI  wafer (on top of the wafer a thin epitaxial Si film is grwon) - less contamination due to the fact that epitaxial films are almost flawless
    • SOI wafer (silicon-on-insulator) made by introducing a burried layer of silicon oxide beneath the surface; a thin layer of silicon will be left between oxide and surface, which will be used for device fabrication - used for high speed devices due to less parasitic capacitances
  • Applications: the most used substrate material for various devices, ICs, MEMS, etc
• Germanium
  • Used in the beginning for transistor fabrication
  • Properties:
    • higher mobility than silicon
    • not good natural oxide - maybe in the future, if high-k dielectrics are introduced as gate dielectrics
    • compatibility with III-V compounds (Ge has a direct bandgap)
  • Applications: epitaxial growth of III-V compounds.
• SiC in micromachining (MEMS), brittle, cannot suffer plastic deformations due to covalent bonds
  • Properties
    • extreme hardness
    • high temperature resistance
    • radiation resistant
    • less elastic than Si, brittle
  • Applications:
    • micromachining (MEMS)
    • high-power/high-frequency devices
    • electronic devices
• GaAs
  • Second most common semiconductor material
  • Properties
    • direct bandgap semiconductor (electrons and holes can recombine directly without requiring a phonon, the probability is much higher thus for direct transitions across the bandgap than for the indirect ones)
    • higher electron mobility than Si
    • lack of natural oxide
  • Applications
    • monolithic microwave integrated circuits (MMICs)
    • semiconductor laser applications
    • LEDs
    • FETs
    • OMEMS
• Glass
  • Applications:
    • for displays
    • wafer bonding
    • low temperature applications
• Plastic
  • Properties
    • flexibility
    • ultra-lightweight
    • durability
    • cost-effective processing
  • Applications:
    • sensors
    • displays
• Quartz with piezo-electric properties for resonating devices and high temperature processing
• Biodegradable organic for medicine applications