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what accounts for the mass of an atom?

neutron and proton


charge on electron

-q = -1.5x10⁻¹⁹

(given in exam)


Boltzmann's constant

governs energy gained by electrons as a result of temp above absolute zero,

value given in exams


Pauli's Exclusion Principle

no two electrons orbiting an atom can have identical quantum numbers, ‘nlms’.

Two orbiting electrons may have the same energy level but have opposite spins in which case s = ±½ and this means their quantum numbers differ in the spin characteristic s.
When several atoms are in close proximity, the energy associated with the individual quanta cannot be identica


continuum or band of energy levels

(Band Theory of Solids)

-spacing between levels decreases as n umber of neighbouring atoms increases

-in crystalline structure of solid element, there are TONS of neighbouring atoms which exert influence on each other

-each individual quantum which existed in an atom considered in isolation becomes a continuum or band of energy levels around the original quantum


energy bands in insulators

-characterised by large energy gap between valence and conduction bands

-at room temp no electrons gain sufficient energy to make transition between bands
-electrons remain firmly bonded to their atoms in valence band


energy bands in conductors

-conduction and valence bands overlap

-plentiful supply of free energy levels close to those occupied by electrons in upper region of valence band of metals

-at room temp e- can easily move into vacant levels in conduction bands
-outer electrons of metals break free of parent atoms + become free charge carriers
-free neg-charged electrons can readily be made to move, forming an electric current


energy bands in semiconductors

-have energy gap between conduction and valence bands that is much lower than that of insulators

-at room temp, no. of electrons can make the transition from valence band to conduction band but much smaller no. than conductors


controlling extent of conduction in semiconductors

-doping the semiconductor materials w/ impurities in the form of another element from neighbouring group in Periodic Table


most common semiconducting material

Silicon Si

also used:
Germanium Ge
Gallium Ga
Arsenic As


Fermi Level

In the context of electronic materials,

defined as the energy associated with the highest energy level occupied by an orbiting electron at absolute zero temperature, 0K


Fermi Level and absolute zero

at absolute zero temp, all available energy orbitals below Fermi Level are occupied + all of those above are unoccupied


Fermi Level for conductors, semiconducts, and insulators

-Conducting materials: Fermi level located somewhere in conduction band

-Semiconducts: it is not an occupied level + lies between valence and conduction band


intrinsic silicon - total current flwoing through material

-consists of sum of both components of positive and negative charges
-why this semiconductor technology is referred to as -bipolar-


free electrons and holes in intrinsic silicon

-always created in pairs


intrinsic silicon

un-doped silicon


Fermi-Dirac Probability Function

-indicates probability at any temp that an energy level is occupied by an electron


Fermi-Dirac Function notes

-function only applies to energy levels that exist + are available in material
-function has rectangular shape at T=0K


probability function - superimposed at room temp, with one curve being probability of occupancy and the other being of vacancy

-sum of all corresponding points on curves is unity for all energy values
-bc free electrons + holes are generated in pairs
-bc of this symmetry, Fermi Level for intrinsic Si is placed midway between conduction and valence bands


concentrations of electrons and holes in intrinsic Silicon

they are equal


density of atoms in intrinsic silicon material

5 x 10²² cm⁻³


femi energy in intrinsic silicon

-halfway between the valence band edge and conduction band edge


degree/intensity of doping

-classified according to number of impurity atoms implanted into Si per unit volume, relative to atomic density of pure Si


intrinsic silicon and temp

-at absolute zero: an insulator

-at room temp: moderate conductor


n-type doped silicon

produced by doping Si with a group V material
eg. Phosphorous (P)

-extra electron, becomes free negative charge carrier


n-type: majority and minority carriers

-conc of electrons greater than holes

-electrons: majority carriers
-holes: minority carreirs


p-type doped silicon

produced by doping Si with a group III material

eg. Aluminium (Al)

-3 electrons in outer shell


p-type: majority and minority carriers

conc of holes greater than of electrons

-holes: majority carriers
-electrons: minority carriers


fermi level in p-type semiconductor

lower, towards valence band


potential difference V between two points

the difference between the two potentials or voltages as measured relative to ground.

unit: Volts