Solar - Solid State Physics

Question 1

What is the challenege in material-use of PV?

Answer 1

A material absorbs photons into specific electronic state

Question 2

Electrons and degenerate states…

Answer 2

Fill from lowest energy first, alongside the Pauli Exclusion Principle.

Question 3

Ground State

Answer 3

This refers to lowest energy state possible thus susecptibel to filling by electrons

Question 4

Calculating electornic excitations…

Answer 4

Presume nuclei as fixed corresponding to ground state of the atom, solve schordinge equation for the electromagnetic potential in the electron of this state.

Question 5

Imagining a solid…

Answer 5

A large molecule held in place by bonds similar to those of a molecule.

Question 6

Crystal structure microscopically…

Answer 6

Periodic and predictable like diamond lattice

Question 7

Phonons

Answer 7

The production of atomic vibration within crystal lattices in acoustiv waves.

Question 8

Phonons in a lattice…

Answer 8

Vibration of the relative atoms vibrates the crystal structure wiht electrons adjusting configuration to the ground state.

Question 9

Band Gap

Answer 9

Describes the energy required to promote a valence electron bound to an atom to become a conduction electron.

Question 10

Structurally what is the band gap?

Answer 10

Diffenrece in energy betewen highest state in valence band and lowest state in conduction band

Question 11

Gaps

Answer 11

Here there are not allowed electron states, whilst energy levels and bands of energies(electrons taking any value in a continous range)

Question 12

What do bands do?

Answer 12

Segregatre energy levels into intervals of where the electrons energy can take any value

Question 13

Band gap in silicon…

Answer 13

1.13ev seperating the orbital filled with electrons from that of the conduction band.

Question 14

Conduction Band

Answer 14

The lowest empty band available for electron excitation.

Question 15

What is requried of the wavelength to excite valence elextrons?

Answer 15

An e=hv eV equal or greater than the band gap energy.

Question 16

Energy of a material at zero temperature…

Answer 16

All eelctron energy levels are filled to maximal energy, whilst higher energy levels are empty.

Question 17

Fermi Energy

Answer 17

This is the energy difference between the highest and lowest occupied single particle states of non-interacting fermions at absolute temperature.

Question 18

What is the highest filled state?

Answer 18

Fermi energy

Question 19

Fermi Level

Answer 19

Describes the energy where the probabilty of finding the level occupied by an electron passes 1/2.

Question 20

When does fermi level coincide with fermi energy?

Answer 20

At T=0

Question 21

Determination of physical characteristics of a solid?

Answer 21

Positon of the fermi level relative to the band structure.

Question 22

If fermi energy is within the band…

Answer 22

This means there are empty states with energies just above ground state, so only a small amount of energy is needed to excite an electron into conduction band.

Question 23

When does a conduction band arise?

Answer 23

When fermi energy is in the middle of a band, being good thermal/electrical conductors.

Question 24

When does a valence band arise?

Answer 24

When fermi energy is between two bands( meaning large energy seperation betewen the bands, being good insulator.

Question 25

When does a semiconductor arise?

Answer 25

When fermi energy lies between two bands of small seperation.

Question 26

Semiconductor band state at absolute zero…

Answer 26

All electrons in the valence band where romm temperature may allow excitation into conduction band,.

Question 27

Structural changes of electron excitation into conduction band?

Answer 27

Leaves a hole in the valence band

Question 28

Dislocations

Answer 28

Irregularities within crystial structure containing an abrupt change in the atomic arrangement.

Question 29

Impurities

Answer 29

Where atoms are present that are different from the host crystal atoms.

Question 30

What do impurities give rise to?

Answer 30

Quantum states within the regions between bands