unit 11: semiconductors

itp 150 - prof. djassemi - cal poly

semiconductor applications

• used for: making solid-state electronic devices such as diodes & transistors

• importance: operate most modern tech (computers, phones, auto)

• advantage: compact & take small space

semiconductor elements

• silicon, germanium, gallium

• most common: silicon & germanium

  • 4 valence electrons each

conductors vs. non-conductors vs. semiconductors

• conductors: material w/ one valence electron that is easily given up

• non-conductor (insulator): material w/ 8 valence electrons & no free electrons

• semiconductor: material whose conductivity falls btwn a conductor & an insulator

valence electrons

• electrons in the outermost orbit of an atom

• importance of 4 valence electrons in silicon: allow formation fo crystal lattice & controlled conductivity

definition & properties of semiconductors

• semiconductor: crystalline elements btwn a conductor & an insulator in ability to conduct current

• in pure form they act as: insulators

• ⬆ semiconductor conductivity: doping/applying heat

doping/pentavalence/trivalence

• doping: adding impurities to pure silicon to alter electrical conductivity

• pentavalence: elements w/ 5 valence electrons

• trivalence: elements w/ 3 valence electrons

n-type material

• n-type semiconductor: silicon doped to ⬆ free electrons

• elements that create n-type: phosphorus or arsenic

• electron donors

• charge carrier: electrons

p-type material

• p-type semiconductor: silicon doped to increase holes (sites)

• elements that create p-type: boron or gallium

• electron acceptors

• charge carrier: holes (sites)

electron donors vs. acceptors

• donor: n-type material that supplies free electrons

• acceptor: p-type materials that accept electrons

diode & its mechanism of current flow

• PN junction device that allows current in one direction only

• what forms barrier region: junction of p-type & n-type materials

• voltage that breaks barrier: 0.7V for silicon, 0.3V for germanium

diode symbol & parts

• P-side of diode: anode

• N-side of diode: cathode

• stripe on diode indicates: cathode

forward & reverse directions

• forward bias: diode conducts

• reverse bias: diode blocks current

• battery connection in FB: (+) anode, (-) cathode

• current direction in FB: P-type → N-type

diode uses

• major use: rectifying AC → DC

• voltage regulation

• light production: light-emitting diodes (LEDs)

types of diodes

• 2 common diode package types: glass & plastic

• glass-packaged diode used in higher temp environments

• plastic in lower temp

light-emitting diodes (LEDs)

• diode that emits light when electrons recombine w/ holes

• light photon energy released

• symbol shows anode & cathode terminals

LED advantages

• no hazardous materials

• doesn’t produce much heat

• thousand-hour lifespan

• 10x more efficient than incandescent

voltage-rectifying application

• AC → DC

• half-wave rectifier: allows ½ of AC waveform to pass

• example: light dimmer