SEMICONDUCTOR THEORY
Semiconductor Materials (used most frequently)
1. Si (Silicon)
2. Ge (Germanium)
3. GaAs (Gallium Arsenide)
“Semiconductor Materials have a negative
temperature coefficient.”
Facts:
• In 1947 germanium was used almost
exclusively because it was relatively easy
to find and was available in large
quantities.
• Germanium was relatively easy to refine
to obtain very high purity levels.
“But it was discovered in the early years that
diodes and transistors constructed using
germanium as the base material suffered from
low levels of reliability due primarily to its sensitivity
to changes in temperature.”
• In 1954 the first silicon transistor was
introduced, and silicon quickly became
the semiconductor material of choice.
• Silicon is less temperature-sensitive.
“Silicon is one of the most abundant materials on
earth.”
• In the 1970s GaAs transistors were
developed.
• GaAs transistors are often used as the
base material for new high-speed.
Definition of Terms:
Electronics – studies the behavior of electrons.
– Branch of physics and engineering that
deals with the study of electron behavior,
flow, and control.
Atom – smallest particle of an element
Atomic Mass or Weight – the sum of protons and
neutrons in the nucleus of an atom.
Atomic Number – number of electrons in an
electrically balanced or neutral atom.
Ionization – the process of losing a valence
electron
Positive Ion – positively charged atom; protons are
greater than electrons
Negative Ion – negatively charged atom; protons
are less than electrons
Semiconductor – materials that are between
conductors and insulators in their ability to
conduct electrical current
– intrinsic (pure)
– neither a good conductor nor a good
insulator
Single-Element Semiconductor – tetravalent
Silicon – 2 – 8 – (4); crystalline material
Germanium – 2 – 8 – 18 – (4)
Conductor (metal) – allows electricity to pass
through.
– Less than 4 valence electrons
Insulator (non-metal) – does not allow electricity
to pass through.
– More than 4 valence electrons
Perfect Conductor – consists of 1 valence
electrons.
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Energy Level
Insulator Energy Level – Eg > 5 eV
Conductor Energy Level – The bands overlap
Semiconductor Energy Level
Material
Diode
Energy Gap
Si
0.7 V
1.1 eV
Ge
0.3 V
6.7 eV
GaAs
1.2 V
1.41 eV
“The farther an electron is from the nucleus, the
higher is the energy state, and any electron that
has left its parent atom has a higher energy state
than any electron in the atomic structure.”
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Semiconductor Crystal Structure & Covalent
Bonding
Crystalline Structure – atoms that are bound
together.
Crystal – atoms combined to form a solid material;
arranged in at fixed pattern.
