SEMICONDUCTOR

• Solid-state device


  Electronic device which operates by virtue of the movement of electrons within a solid piece of semiconductor material
• Advantages of solid-state devices

  • Compactness
  • Efficiency
  • Ruggedness
  • Versatility
• Examples of solid-state devices

  • Junction diode
  • Transistor
  • Zener diode
  • Light-emitting diode
  • Field effect transistor
  • Integrated circuit
• Semiconductor applications


  • Commercial products
  • Science and industry
  • Research laboratories
  • Space systems
  • Computers
  • Data processing equipment
  • Data display systems
  • Aircraft guidance-control assemblies
• Conductor


  Material with low resistance that allows electrical current to flow easily
• Insulator


  Material with high resistance that suppresses electrical current flow
• Semiconductor


  Material that can allow or suppress electrical current flow
• Electronic materials

  • Conductors
  • Insulators
  • Semiconductors
• Conductors

  • Have low resistance so electrons flow through them with ease
  • Best element conductors include copper, silver, gold, aluminum, and nickel
  • Alloys like brass and steel are also good conductors
  • Good conductors can also be liquid like salt water

  
• Solid-state device


  An electronic device, which operates by virtue of the movement of electrons within a solid piece of semiconductor material
• Conductor atomic structure

  • Usually includes only one electron in their outer shell (valence electron)
  • Valence electron is easily stripped from the atom, producing current flow

  
• Solid-state device


  • Offer compactness, efficiency, ruggedness, and versatility
• Insulators


  • Have high resistance so current does not flow in them
  • Good insulators include glass, ceramic, plastics, and wood
  • Most insulators are compounds of several elements
  • Atoms are tightly bound so electrons are difficult to strip away for current flow
• Valence electron


  Only one electron in their outer shell, easily stripped from the atom, producing current flow
• Conductors

  • Copper
  • Silver
  • Gold
  • Aluminum
  • Nickel
  • Alloys (brass and steel)
  • Salt water
• Insulators


  • Glass
  • Ceramic
  • Plastics
  • Wood
• Semiconductors


  • Can be conditioned to act as good conductors, good insulators, or anything in between
  • Common elements like carbon, silicon, and germanium are semiconductors
  • Silicon is the best and most widely used semiconductor
• Semiconductors

  • Carbon
  • Silicon (widely used)
  • Germanium
• Semiconductors

  • Main characteristic = 4 electrons in its outer/valence orbit
• Semiconductor valence orbit

  • Main characteristic is that it has four electrons in its outer or valence orbit

  
• Types of semiconductors

  • Intrinsic
  • Extrinsic
• Intrinsic semiconductor


  Electrical behavior is based on the electronic structure inherent in the pure material, with two types of charge carrier: free electrons and holes (positively charged particle-charge that is of the same magnitude as that for an electron, but of opposite sign)
• Semiconductor crystal lattice structure

  • Semiconductor atoms can link together to form a physical structure called a crystal lattice
  • Atoms link together with one another sharing their outer electrons
  • These links are called covalent bonds
• Extrinsic semiconductor


  Electrical characteristics are dictated by impurity atoms (when present in even minute concentrations, introduce excess electrons or holes)
• Types of extrinsic semiconductors

  • n-Type
  • p-Type
• Intrinsic semiconductor


  Pure semiconductor material like silicon, where the crystal lattice structure forms an excellent insulator since all the atoms are bound to one another and are not free for current flow
• n-Type semiconductor


  Electrons are majority carriers by virtue of their density or concentration; holes, on the other hand, are the minority charge carriers (n >> p), with Fermi energy level shifted upward in the band gap, to within the vicinity of the donor state
• Donor


  Donated single electron to the conduction band in an excitation event
• Doping


  Process of adding other atoms called impurities to make the semiconductor conduct electricity
• p-Type semiconductor


  Opposite effect from n-type, with holes present in much higher concentrations than electrons (p>>n), and a hole imagined to be created in the valence band
• Types of semiconductors

  • Intrinsic semiconductor
  • Extrinsic semiconductor (P-type, N-type)
• Acceptor


  An impurity wherein a free electron is not created in either the impurity level or the conduction band
• Extrinsic semiconductors (both n- and p-type) are produced from materials that are initially of extremely high purity, commonly having total impurity contents on the order of 10^-7 at%
• Doping


  Alloying process in semiconducting materials
• n-type semiconductor


  Semiconductor doped with pentavalent/donor impurities like arsenic, antimony, bismuth, and phosphorous, which provide extra electrons for current flow

  
• p-type semiconductor


  Semiconductor doped with trivalent/acceptor impurities like aluminum, indium, gallium, and boron, which create holes that can attract electrons for current flow
• Majority/minority carriers

  In N-type semiconductors, electrons are the majority carriers and holes are the minority carriers. In P-type semiconductors, holes are the majority carriers and electrons are the minority carriers.
• Doping amount


  Affects the resistance of the semiconductor material - more doping leads to lower resistance and higher current flow
• PN junction


  Junction formed between N-type and P-type semiconductor materials
• Junction barrier


  Barrier formed at the PN junction that opposes the flow of current