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electronic Flashcards

1
Q

what accounts for the mass of an atom?

A

neutron and proton

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2
Q

charge on electron

A

-q = -1.5x10⁻¹⁹

given in exam

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3
Q

Boltzmann’s constant

A

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

value given in exams

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4
Q

Pauli’s Exclusion Principle

A

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

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5
Q

continuum or band of energy levels

Band Theory of Solids

A
  • 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
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6
Q

energy bands in insulators

A

-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
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7
Q

energy bands in conductors

A
  • 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
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8
Q

energy bands in semiconductors

A
  • 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
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9
Q

controlling extent of conduction in semiconductors

A

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

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10
Q

most common semiconducting material

A

Silicon Si

also used:
Germanium Ge
Gallium Ga
Arsenic As

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11
Q

Fermi Level

A

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

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12
Q

Fermi Level and absolute zero

A

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

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13
Q

Fermi Level for conductors, semiconducts, and insulators

A
  • Conducting materials: Fermi level located somewhere in conduction band
  • Semiconducts: it is not an occupied level + lies between valence and conduction band
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14
Q

intrinsic silicon - total current flwoing through material

A
  • consists of sum of both components of positive and negative charges
  • why this semiconductor technology is referred to as -bipolar-
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15
Q

free electrons and holes in intrinsic silicon

A

-always created in pairs

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16
Q

intrinsic silicon

A

un-doped silicon

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17
Q

Fermi-Dirac Probability Function

A

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

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18
Q

Fermi-Dirac Function notes

A
  • function only applies to energy levels that exist + are available in material
  • function has rectangular shape at T=0K
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19
Q

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

A
  • 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
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20
Q

concentrations of electrons and holes in intrinsic Silicon

A

they are equal

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21
Q

density of atoms in intrinsic silicon material

A

5 x 10²² cm⁻³

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22
Q

femi energy in intrinsic silicon

A

-halfway between the valence band edge and conduction band edge

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23
Q

degree/intensity of doping

A

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

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24
Q

intrinsic silicon and temp

A
  • at absolute zero: an insulator

- at room temp: moderate conductor

25
Q

n-type doped silicon

A

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

-extra electron, becomes free negative charge carrier

26
Q

n-type: majority and minority carriers

A

-conc of electrons greater than holes

  • electrons: majority carriers
  • holes: minority carreirs
27
Q

p-type doped silicon

A

produced by doping Si with a group III material

eg. Aluminium (Al)
- 3 electrons in outer shell

28
Q

p-type: majority and minority carriers

A

conc of holes greater than of electrons

  • holes: majority carriers
  • electrons: minority carriers
29
Q

fermi level in p-type semiconductor

A

lower, towards valence band

30
Q

potential difference V between two points

A

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

unit: Volts

31
Q

potential difference and sign

A

-positive when Potential V₁ relative to grund is more positive than potential V₂ relative to ground

32
Q

electromotive force EMF

A

When an electric field acts along a path where charged particles are free to move, it exerts an influence on the mobile charge carriers called an electromotive force

-measured in Volts

33
Q

EMF in an electric circuit

A

voltage between terminals of battery is the EMF which it generates

34
Q

electric current

A

When charged particles free to move in a conducting material are placed under influence of an electric field acting in a defined direction, they will tend to move in a direction determined by that of the field

35
Q

electric current definition

A

the quantity of charge flowing through a piece of conducting material per unit time

measured im Amperes (A)

36
Q

electric field strength definiton

A

force per unit charge acting at a point in the field

37
Q

carrier mobility

A

velocity with which a carrier will drift, on average, in a unit field strength of Vm⁻¹

unit: m²V⁻¹s⁻¹

38
Q

mobility of electrons in conduction band and valence band

A

Generally, mobility of electrons in conduction band is somewhat greater than that of holes in valence band, i.e.
μₙ > μₚ

39
Q

charge flux density

A

-average charge flow considered per unit area normal to direction of flow

40
Q

electrons and holes and current

A

Electrons and holes drift in opposite directions in any given electric field.

However, since charge on the electron is negative, both electrons and holes make positive contributions to conventional current which is specified as being positive in the direction of the electric field

41
Q

diffusion current

A

rate at which diffusion takes place

-determines charge flux density due to diffusion

42
Q

diffusion coefficients

A

measure of relative ease with which the carriers can spread outward on a wave-like surface with decreasing concentration

43
Q

dimensions of coefficients

A

cm₂s₋₁ (area/unit time)

44
Q

thermal voltage

A

the equivalent potential difference within an electric field through which an electron having a charge of magnitude q must accelerate in order to gain the same amount of energy as it has due to temperature, i.e. kT Joules.

45
Q

p-n junction

A

-two pieces of semiconductor are joined together,
-imbalance of free carrier concentrations in both
conduction + valence bands on each side of junction formed between p-type and n-type materials.
-gives rise to carrier concentration gradients across junction.
-electrons diffuse across the junction from n-type to p-type, while holes diffuse from p-type to n-type material, setting up associated diffusion currents.
-Electrons entering p-type material readily recombine with the plentiful holes present here
-holes entering the n-type material readily recombine with the plentiful electrons here

46
Q

junction region

A

referred to as the depletion region, having a much reduced conc of mobile or free charge carriers

47
Q

equilibrium conditions: net transfer of either type of carrier

A

Under equilibrium conditions, there is no net transfer of either type of carrier from one material to the other i.e. the combined diffusion and drift currents are zero for both holes and electrons.

48
Q

capacitance depends on

A
  • dependent on the width of the junction region + on the doping concentrations of both p-type and ntype materials
  • dependent on any electric field which may be applied externally + is hence a bias voltage dependent property in semiconductor devices
49
Q

effect of presence of junction capacitance

A

-has effect of slowing down changes in current which may be induced in response to externally applied conditions

50
Q

ideal diode equation

A

characterizes current-voltage relationship of diode as an electrical circuit element

51
Q

resistivity

A

measure of how strongly a material opposes flow of electric current through it

52
Q

what resistivity depends on

A
  • particular atomic strcuture

- measured in Ohm-metres

53
Q

what resistance depends on

A
  • resistivity of material

- physical dimensions

54
Q

resistance unit

A

Ohm Ω

55
Q

capacitance

A

ability of a body to store electrical energy in form of charge associated with an electric field

56
Q

permeability

A

-property which determines degree to which material becomes magnetised when subjected to influence of a magnetic field

57
Q

Hall Effect - where it applies

A

-applies to materials which conduct electricity and are also magnetisable

58
Q

seebeck coefficient

A

measure of sensitivity of the thermal emf, Vₜₕ to temp gradient

Mat (5 decks)

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