ELECTRONICS

• Semiconductor


  Material having conductivity in between conductors and insulators
• Semiconductor


  • Junction diode and transistor are two widely known examples
  • Solid-state devices made from semiconductor materials offer compactness, efficiency, ruggedness, and versatility
• Semiconductor Theory


  Explores the fundamentals of semiconductors, including energy bands, covalent bonding, and conduction processes
• Energy bands


  In a semiconductor, there are two main energy bands: the valence band (lower energy) and the conduction band (higher energy)
• Energy gap (band gap)


  The energy difference between the top of the valence band and the bottom of the conduction band, which determines the electrical properties of the material
• Covalent bonding


  The sharing of valence electrons between atoms, which holds the atoms together in a crystal structure

  
• Conduction process


  1. Electrons can break covalent bonds and move to the conduction band, supporting electric current flow

  2. Holes can also move through the crystal, resulting in hole flow
• Electron-hole pairs


  The negative electrons and positive holes created by the breaking of covalent bonds

  
• Intrinsic semiconductor


  A pure semiconductor with no impurities, where the number of holes is equal to the number of conduction electrons
• Doping


  The process of adding impurity atoms to a pure semiconductor to increase its conductivity
• 1. type semiconductor


  • Increases the number of free electrons (majority carriers)
  • Impurities have 5 valence electrons (pentavalent)
• 1. type semiconductor


  • Decreases the number of free electrons, with holes as the majority carriers
  • Impurities have 3 valence electrons (trivalent)
• 1. Type Semiconductors


  • Loses its extra valence electron when added to a semiconductor material
  • Has a 5 valence electron called Pentavalent impurity
  • Examples: Arsenic, Antimony, Bismuth, and phosphorus
  • Electrons are considered Majority carriers, while the holes are the minority carriers
• 1. Type Semiconductors


  • Tends to compensate for its deficiency of 1 valence electron by acquiring an electron from its neighbor
  • Has a 3 valence electron called Trivalent impurities
  • Examples: Aluminum, Indium, Gallium and boron
  • Holes are considered Majority carriers, electrons are the minority carriers
• Semiconductors are materials with conductivity between conductors and insulators. Examples include silicon and germanium.
• Solid-state devices are electronic devices that use semiconductors, like transistors and diodes. They are compact, efficient, rugged, and versatile.
• Energy Bands


  • Electrons orbit the nucleus in shells with specific energy levels
  • In solids, these energy levels spread into bands
  • Enough energy can cause electrons to jump to a higher band
• Covalent Bonding

  • Sharing of valence electrons between atoms creates strong bonds
  • Silicon and germanium have 4 valence electrons and form covalent bonds with 4 neighbors
  • Pure silicon and germanium are poor conductors because electrons are tightly bound

  
• Conduction Process


  1. Applying heat or voltage can break covalent bonds and create free electrons (conduction) and holes (absence of an electron)

  2. Electrons flow towards positive voltage (electron current flow)

  3. Holes flow towards negative voltage (hole current flow)
• Doping Process


  • Adding impurities to semiconductors (doping) creates N-type or P-type semiconductors
  • N-type (donor impurity) has extra electrons (majority carriers) and few holes (minority carriers)
  • P-type (acceptor impurity) has holes (majority carriers) and few electrons (minority carriers)
• Diode


  Used to protect circuits by limiting the voltage and to also transform AC into DC
• Diode Characteristics


  • Junction Capacitance
  • Operating point
• Diode Analysis


  • Ideal and Piecewise Diode Model
  • Load Line Analysis
• Diode Applications


  • Rectifier
  • Clipping and Clamping
  • Level Shifting
  • Voltage Regulator
• Silicon (Si) Diode - 0.7 V, Germanium (Ge) Diode - 0.3 V
• Zener Diode


  Heavily doped diode with negative resistance region, used in voltage regulators
• Tunnel Diode


  Heavily doped diode with very thin depletion region for electrons to easily tunnel through
• Schottky Diode


  Rectifying metal semiconductor junction, improves conductivity
• Pin Diode


  Intrinsic material between P and N type, used for high speed switching
• Varactor Diode


  Used to make changes in capacitance of a reversed biased junction
• Light Emitting Diode (LED)


  Semiconductor diode that illuminates when forward biased, releases energy as electrons and holes recombine
• Photodiode


  Semiconductor diode whose resistance decreases as light intensity increases, used in remote control and sensor systems
• Laser Diode


  Semiconductor diode that emits coherent and monochromatic light due to lasing
• Step Recovery Diode


  Fastest diode in terms of switching, has variable doping level
• Point Contact Diode


  Semiconductor diode with a fine wire (cat whisker) in contact with the semiconductor material, used in microwave applications
• Thyrector


  Silicon diode exhibiting very high resistance up to a certain voltage, then switches to low conducting state, used to suppress voltage surges and transients
• Gunn Diode


  Diode that exhibits Gunn effect, a form of quantum mechanical band structure, used as a microwave oscillator
• Bipolar Junction Transistor (BJT)


  Three-terminal semiconductor device consisting of two p-n junctions, can amplify or magnify a signal, current controlled device, manufactured in PNP and NPN types
• BJT Operating Regions


  • Active region (amplifier)
  • Saturation region (switch fully on)
  • Cut-off region (fully off, collector current zero)
• Applications of BJT: used as amplifier, oscillator, demodulator