4.1 Semiconductors Flashcards
What is a chemical compound?
A chemical combination of 2 or more elements
How many known elements are there?
Over 100
What is the smallest part of a compound which retains all of the compounds characteristics called?
A molecule
What part of an atom has a negative charge?
An electron
What part of an atom has a positive charge?
A proton
What is the mass of a proton?
1827 x bigger than an electron
What part of an atom has no electric charge?
A neutron
What is the principle to predict the number of electrons in a shell?
Pauli’s Principle = 2n ^2
What are the major shells of an atom?
K, L, M… etc
What can the major electron shells of an atom be divided into?
Sub shells
s, p, d and f
What is a valence shell?
The outer shell of an atom
What is a valence electron?
An electron in the outer shell of an atom (the valence shell)
What is a Quanta?
The definite units required to move electrons from one shell to the next highest shell.
What is ionisation?
When an atom gains/loses electrons
What is a negative ion?
An atom that has gained electrons
What is a positive ion?
An atom that has lost electrons
What is the forbidden band?
An energy gap between the conduction band and the valence band where there are no electrons.
What is the conduction band?
Electrons in this band are easily removed by the application of external electric fields. Materials with many electrons here act as good conductors.
What is an electron-hole pair?
When an electron moves to the conduction band and leaves behind a deficiency/hole in the valence band.
What is a covalent bond?
The sharing of valence electrons between two or more atoms. It holds the atoms together in an orderly structure called a crystal.
Pure silicon and germanium are what?
Poor conductors of electricity, but classed as semiconductors.
What is the electron current flow?
The movement of electrons in a crystal towards an applied voltage.
What charge does the hole in the valence shell have when an electron moves to the conduction band?
A positive charge.
What is the hole flow?
The hole in the valence shell moving towards a negative potential (opposite direction of electron flow).
What are intrinsic semiconductors?
Semiconductors with no impurities.
What is special about the number of holes in an electron-hole pair of an intrinsic semiconductor?
They are always equal to the number of conduction electrons.
What periodic table group are most semiconductor materials?
4a
What are the groups in the periodic table of which doping materials come from for semiconductors?
3a and 5a
What is the ‘favourite’ semiconductor used today?
Silicon (Si)
- abundantly available
- 8th most common element by mass in the universe
What is a tetravalent semiconductor?
A pure or intrinsic semiconductor.
What are the two types of doped semiconductor materials?
- N-type
- P-type
Why is silicon the semiconductor of choice?
Ease of processing and more stable temperature characteristics
What advantage does germanium diodes have over silicon diodes?
Intrinsically low voltage drop, 0.3V meaning low power loss and more efficient diode.
Better in signal detection/FM frequencies and low-level digital circuits.
What is the average voltage drop on a silicon diode?
0.7V typically,
