Lecture 3 Flashcards
Give the integral for the total electron density in the conduction band
n = total electron density of conduction band
f_e(ε) = electron state probability
g_e(ε) = density of electron state
Give the equation for the total number density of electrons in the conduction band of an intrinsic semiconductor
n = number density of electrons
µ = chemical potential
E_g = bandgap energy
Give the equation for the total number density of holes in the valence band of an intrinsic semiconductor
p = number density of holes
µ = chemical potential
Give the equation for the product of the number density of electrons and the number density of holes in an intrinsic semiconductor
n = number density of electrons
p = number density of holes
E_g = bandgap energy
Give the equation for the chemical potential of an intrinsic semiconductor in terms of the number of electrons in the conduction band
µ = chemical potential
E_g = bandgap energy
k_B = Boltzmann’s constant
T = temperature
n = total electron density
Give the equation for the chemical potential of an intrinsic semiconductor in terms of the number of holes in the valence band
µ = chemical potential
k_B = Boltzmann’s constant
T = temperature
p = total hole density
Describe the relationship between the number density of holes and the number density of electrons in an intrinsic semiconductor
n = p
Give the equation for the number density of holes and electrons in an intrinsic semiconductor
n = number density of electrons
p = number density of holes
E_g = bandgap energy
Give the equation for the chemical potential of an intrinsic semiconductor in terms of electrons AND holes
µ = chemical potential
Why aren’t intrinsic semiconductors used in semiconductor devices?
Because the electron and hole densities are too temperature dependent.
How are the number and type of carriers (electrons/holes) controlled in an extrinsic semiconductor?
By introducing impurities (doping)
What is an n-type semiconductor?
An extrinsic semiconductor with an excess number of electrons.
How is an extrinsic semiconductor with excess electrons produced?
By substituting an element with 5 valence electrons into a material with 4 valence electrons, generating one excess electron per atom. This produces an n-type semiconductor.
What is a p-type semiconductor?
An extrinsic semiconductor with an excess number of holes.
How is an extrinsic semiconductor with excess holes produced?
By substituting an element with 3 valence electrons into a material with 4 valence electrons, leaving one missing electron per atom. This produces a p-type semiconductor.
How are compound semiconductors doped?
An atom with 1 more/less electrons is substituted into one of the two elements, causing there to be an excess/loss of electrons.
Give an example of an n-type compound semiconductor
Silicon can be used as a substitute for Gallium to dope Gallium Arsenide (GaAs).
Give an example of a p-type compound semiconductor
Carbon can be used as a substitute for Arsenic to dope Gallium Arsenide (GaAs).
What is the ‘donor energy level’?
The energy that binds the extra electron to the positively charged donor ion. It sits at this energy level at T = 0 but, at room temperature, most electrons are activated from the donor energy level to the conduction band.
What is the ‘acceptor energy level’?
The energy that binds the extra hole to the negatively charged acceptor atom. At room temperature, most acceptor levels are filled by electrons from the valence band.
