Basic Electronics
, Semiconductor —I
• Materials that permit flow of electrons are called
conductors (e.g., gold, silver, copper, etc.).
• Materials that block flow of electrons are called
insulators (e.g., rubber, glass, Teflon, mica, etc.).
• Materials whose conductivity falls between those
of conductors and insulators are called germanium
semiconductors. Semiconductors
silicon
• Semiconductors are “part-time” conductors
whose conductivity can be controlled.
, Semiconductor —II
• Silicon is the most common material used to build semiconductor devices.
• Si is the main ingredient of sand and it is estimated that a cubic mile of seawater
contains 15,000 tons of Si.
• Si is spun and grown into a crystalline structure and cut into wafers to make
electronic devices.
, Semiconductor —III
• Atoms in a pure silicon wafer contains four electrons in outer orbit (called valence
electrons).
– Germanium is another semiconductor material with four valence electrons.
• In the crystalline lattice structure of Si, the valence electrons of every Si atom are
locked up in covalent bonds with the valence electrons of four neighboring Si atoms.
– In pure form, Si wafer does not contain any free charge carriers.
– An applied voltage across pure Si wafer does not yield electron flow through the wafer.
– A pure Si wafer is said to act as an insulator.
• In order to make useful semiconductor devices, materials such as phosphorus (P) and
boron (B) are added to Si to change Si’s conductivity.
4 valence electrons
, Semiconductor —I
• Materials that permit flow of electrons are called
conductors (e.g., gold, silver, copper, etc.).
• Materials that block flow of electrons are called
insulators (e.g., rubber, glass, Teflon, mica, etc.).
• Materials whose conductivity falls between those
of conductors and insulators are called germanium
semiconductors. Semiconductors
silicon
• Semiconductors are “part-time” conductors
whose conductivity can be controlled.
, Semiconductor —II
• Silicon is the most common material used to build semiconductor devices.
• Si is the main ingredient of sand and it is estimated that a cubic mile of seawater
contains 15,000 tons of Si.
• Si is spun and grown into a crystalline structure and cut into wafers to make
electronic devices.
, Semiconductor —III
• Atoms in a pure silicon wafer contains four electrons in outer orbit (called valence
electrons).
– Germanium is another semiconductor material with four valence electrons.
• In the crystalline lattice structure of Si, the valence electrons of every Si atom are
locked up in covalent bonds with the valence electrons of four neighboring Si atoms.
– In pure form, Si wafer does not contain any free charge carriers.
– An applied voltage across pure Si wafer does not yield electron flow through the wafer.
– A pure Si wafer is said to act as an insulator.
• In order to make useful semiconductor devices, materials such as phosphorus (P) and
boron (B) are added to Si to change Si’s conductivity.
4 valence electrons
