Home > Uncategorized > Introduction to Solid State Chemistry Lecture 14 Notes: Semiconductors

Introduction to Solid State Chemistry Lecture 14 Notes: Semiconductors

Today is another exploration of semiconductors. Cost is 47 minutes.

Thermal excitation of electrons across the bandgap. Electrons live in a bond, jump up into a CB. CB has bonding orbitals, VB has antibonding orbitals. A broken bond or hole is left behind. This is mobile and highly unstable. Thermal excitation gives rise to pair generation.

Average thermal energy = Kb x Temperature
300K = 1/40 eV

Electron in CB, hole in VB generated for every excitation.

The velocity of different gas species differ. 300K is only the average.

Boltzmann claims that different velocities to different energies.

Number of atoms or atom fraction versus energy on the x axis. Increaing temperature will shift the curve to the right and broaden it.

e^-critical energy/(Kb T)
Modest increases in temperature can lead to huge increases in excited population.

Charge carrier generation by chemical change. Doping or introducing impurities. There are contaminants and dopants. Aliovalent is an atom with another valence.P is group 15, Si is group 14.

Gas phase reactions lead to dopant deposition. Silicon wafers are flat to one atom.

Ionized electrons come out of the donor level.

Dope at a million Si per one P.

BG>3 eV Insulator
BG<1 semiconductor
BG=0 metal
E = hc/lambda = hf
conductivity = population x charge x mobility
Bandgap and the periodic table:
C 5.4
Si 1.1
Ge 0.72
Sn 0.8
Pb 0
11IE, electron acceptor, nonmetal

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