What are the two main electrical properties of materials?
Conducting and insulating.
What determines whether a material is a conductor or an insulator?
The number of valence electrons and how closely they are bound to the nucleus.
When is a material considered a conductor?
When its electrons are easily removed and can move to adjacent atoms.
When is a material considered an insulator?
When its electrons are not easily removed.
Why are semiconductors neither conductors nor insulators?
Because they allow only a minuscule amount of current flow – not enough to be a conductor, but not zero to be an insulator.
What external factors affect the resistance of semiconductors?
Temperature, electrical charge, and light.
What metal’s properties led to early semiconductor research in 1873?
Selenium.
What discovery was made about selenium’s resistance?
It decreased with higher temperature and when exposed to light.
Why did semiconductor use initially decline in the early 1900s?
Thermionic valves were more reliable and provided amplification, unlike semiconductor detectors.
Why were semiconductors revisited during WWII?
Valves could not operate at high radar frequencies, prompting research into semiconductors.
What was the first successful semiconductor-based amplifying device?
The transistor, developed in 1948 by Bell Telephone.
What effect does ‘doping’ have on semiconductor materials?
It alters their electrical characteristics by creating excess or lack of electrons.
What are the two most common semiconductor materials?
Germanium (Ge) and Silicon (Si).
What do both silicon and germanium have in common?
They each have four valence electrons and a lattice structure.
What is an Intrinsic Semiconductor?
A pure crystal of semiconductor material with no other atoms added.
What limits the use of intrinsic semiconductors, what is conductivity heavily dependent on?
Conductivity is affected by Temperature, Electrons and holes are created in equal numbers
What is an Extrinsic Semiconductor?
A semiconductor that has been doped with impurity atoms to change its electrical properties.
What is the purpose of doping with pentavalent elements like arsenic?
To donate extra electrons, forming an n-type semiconductor.
What are Donor atoms?
Impurities that donate extra electrons when doping semiconductor material.
What is the result of doping with trivalent elements like boron?
A p-type semiconductor is formed with free positive holes.
What are Acceptor atoms?
Trivalent impurity atoms that create positive holes in the lattice structure.
In an n-type semiconductor, what are the majority and minority carriers?
Majority carriers: electrons; Minority carriers: holes.
In a p-type semiconductor, what are the majority and minority carriers?
Majority carriers: holes; Minority carriers: electrons.
On what does the conductivity of an extrinsic semiconductor depend?
The level of doping (density of impurity atoms).
