Semiconductor Flashcards
What is a conductor?
a material which has an energy band partially filled with electrons (look at notes)
What is an insulator?
a material which has an energy band completely filled with electrons (look at notes)
Insulators also have a band gap between the conduction and valence band, whilst conductors do not
What is a real-life example for the flow of electrons in conductors and insulators?
a partially filled water bottle will allow the water to flow (therefore flow of electrons and a good conductor), but a completely filled water bottle does not allow any flow of water (therefore no flow of electrons, thus an insulator)
What is the definition of a semiconductor?
a solid that is an insulator at T=0K, but whose energy bandgap is of such a size that thermal excitation leads to observable conductivity at temperatures below its melting point
How are semiconductors defined in terms of band gap?
insulators with a band gap < 2~3 eV
How does a completely full valence band transform the material into a semiconductor?
Once heat is applied, a semiconductor would have some of the electrons from the completely filled valence band transfer to the conduction band
Therefore, the semiconductor has two partially filled energy bands which contribute to conductivity
(look at notes)
What is electron charge density?
the product of an electron’s charge and velocity, summed over all the electrons in a band
How are the calculations of charge densities in the conduction band treated?
The charge density of the conduction band has the charge be negative
Why are particles in the valence band treated as holes?
Since the valence band is almost completely full, it is computationally expensive to calculate all the full electrons
Therefore, the empty space in a valence band is calculated with fictitious particles called holes
What is the definition of effective mass?
the mass of an electron under the full effects of a lattice, resulting as a consequence of the energy band
How is effective mass calculated by an E vs k energy band diagram?
It can be calculated by taking the inverse of an energy band parabola
The energy used to approximate effective mass in E vs k is thought of as purely kinetic energy
How are the effective masses of electrons and holes measured in an energy band diagram?
The effective mass of an electron can be measured as the inverse of the curvature at the bottom of the conduction band
The effective mass of a hole can be measured as the inverse of the curvature at the top of the valence band
