Lecture 1 Flashcards
State the 3 most common applications of semiconductors
- Transistors
- Diodes
- Light emitting diodes (LEDs)
In the low temperature limit, all materials are either __________ or _______.
Insulators
Metals
Describe how the resistivity of a pure metal changes with temperature
The resistivity rapidly increases with increasing temperature.
How does the resistivity of a semiconductor relate to that of a metal or an insulator?
It is an intermediate between metals and insulators at room temperature.
Describe how the resistivity of a pure (intrinsic) semiconductor changes with temperature
The resistivity decreases rapidly with increasing temperature.
Describe how the resistivity of a doped (extrinsic) semiconductor changes with temperature
The resistivity is approximately temperature independent.
What is a bandgap?
A range of energy for which there are no allowed electron states. This allows well defined energy levels to be formed.
Are the valence and conduction bands filled for semiconductors at T = 0?
Valence band: filled (the highest energy band that is filled)
Conduction band: unfilled (the lowest energy band that isn’t filled)
Are the valence and conduction bands filled for semiconductors at T > 0?
Valence band: filled
Conduction band: partially filled (due to the thermal excitation of electrons across a relatively small bandgap)
What are doped semiconductors?
Semiconductors with added impurities. These impurities add electrons to the conduction band or remove electrons from the valence band.
Give the equation for the energy of a photon
E = energy
f = frequency
c = speed of light
λ = wavelength
Where are elemental semiconductors found in the periodic table?
In group IV
Give 2 examples of elemental semiconductors
- Silicon (Si)
- Germanium (Ge)
How many valence electrons per atom do elemental semiconductors have?
4
What crystal structure do elemental semiconductors have?
Diamond structure
Where are compound semiconductors found in the periodic table?
They are either a combinations of groups III and V or a combination of groups II and VI
Give 2 examples of compound semiconductors for each bonding combination
III-V: GaAs, InP, GaN
II-VI: ZnO, HgTe
How many valence electrons per atom do compound semiconductors have on average?
4
What crystal structure do compound semiconductors have?
Zincblende structure
Electrons in a nearly filled band can behave as if they have ________ charge.
Positive
What is a hole?
An empty state (vacancy) with positive energy, charge, and effective mass due to the absence of an electron. It is at the top of the valence band so when an electron is removed the total energy of the band increases positively (by +ε as an electron with -ε energy has been removed).
When are the dynamical properties of electron states equivalent to those of hole states?
In the case of a nearly filled band with n empty electron states, this is equivalent to n hole states with a positive charge and a positive effective mass.
The properties of a hole equal the properties of a _____ with one missing ________.
Band
Electron
What is the energy of a hole?
Equal and opposite energy to that of an electron.
+ε
What is the wavevector of a full energy band?
k = wavevector
What is the wave vector of a hole?
Equal and opposite to the wave vector of an electron.
What is the charge of a hole?
It behaves as a positively charged particle in response to an electric field. The charge is of the same magnitude as that of an electron.
+e
Give the equation for the effective mass of an electron state
m_e* = effective mass
ε_e = electron energy state
k_e = electron wavevector
What is the effective mass of an electron?
negative
What is the effective mass of a hole?
positive
The effective mass of a hole is _____ and ________ to that of an electron.
Equal
Opposite
