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12003 FEE > Electrons and PN junctions > Flashcards

Electrons and PN junctions Flashcards

1
Q

What’s the mass of an electron?

A

9.11x10^-31 kg

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2
Q

What does the effective mass of an electron mean?

A

How easily an electron can be accelerated in a material

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3
Q

What does the effective mass of an electron depend on?

A

The material the electron is being accelerated through.

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4
Q

What’s the charge of an electron?

A

e = 1.6x10^-19 C

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5
Q

What is the “spin” of an electron?

A

An intrinsic (natural) angular momentum of ℏ/2

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6
Q

What directions can an electron spin?

A

Up(+ve) or Down(-ve)
with a magnitude of 1/2

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7
Q

What’s an electric field?

A

Region or space where a charged particle experiences a force

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8
Q

What is the equation for a charged particle in an electric field?

A

F = qE
Force = charge x Field strength

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9
Q

What is the equation for 2 charged particles interacting?

A

F = k(q1)(q2) / r^2
where k = 8.99x10^9
r is the distance between the particles

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10
Q

What is a magnetic field?

A

A vector field (perpendicular to the electric field) or space where a MOVING charged particle experiences a force.

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11
Q

What is the equation for a particle in a magnetic field?

A

F = Bqvsin(x)
B - field strength
v - velocity

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12
Q

What is the equation for a charged particle in an electromagnetic field?

A

F = qE + q( v x B)
where q is a scalar
E is a vector (electric field strength)
v is a vector (velocity)
x is the cross-product
B is a vector ( magnetic field strength)

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13
Q

What does quantum theory say?

A
  1. Everything can be quantised (restricted to set/discrete values)
  2. We only know the probability of where a quantum particle is.

(see wave functions notes for visuals)

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14
Q

What are wave functions?

A

Represents the probability of finding a particle in a specific location

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15
Q

What is the fermi-dirac distribution?

A

Represents the probability of an electron being in a certain energy level at a given temp

(see notes for visuals)

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16
Q

What are fermions?

A

particles that follow the fermi-dirac distribution with a spin of 1/2

(e.g electrons)

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17
Q

What are bosons?

A

particles that follow the s.n bose distribution with no spin. These particles transfer energy

(e.g photons)

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18
Q

What is the Pauli exclusion principle?

A

2 identical fermions can’t exist in the same state at the same time.

(may cause electrons to exist in different energy levels)

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19
Q

What are the quantum numbers?

A

Principal
Angular momentum
Magnetic number
Spin

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20
Q

What is the “Principal”?

A

The main energy level of the fermion

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21
Q

What does the angular momentum of the fermion dictate?

A

The shape of the subshell

(refer to the diagram in wave functions)

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22
Q

What does the magnetic number of the electron dictate?

A

The orientation of the fermion.

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23
Q

What type of bonding do metals use?

A

Metallic bonding (sea of electrons)

(It is called a sea of electrons because the conduction and valence band overlap)

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24
Q

What are insulators used for?

A

Used to direct current

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25
Q

What are semiconductors?

A

Materials that conduct in certain conditions.

(e.g when energy is added to the system)

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26
Q

What is the formula for
conductivity?

A

σ = 1/ ρ
ρ - resistivity

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27
Q

What happens to electron energy levels when atoms form molecules?

A

Electron energy levels change

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28
Q

What is the formula for the KE of an electron relating to momentum?

A

p^2/2m
where p is the momentum

(special note p^2 means a parabola shape for the curve like x^2)

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29
Q

What is the valence band?

A

The band of electrons that represents the outermost shell of the material

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30
Q

What is the conduction band?

A

The region/ band that allows electrons to move freely.

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31
Q

What is the band gap?

A

The difference in energy between the valence and conduction band?

32
Q

What are “holes”?

A

A gap (unfilled part of the valence band) after an electron jumps to the conduction band.

(they are treated as positively charged particles)

33
Q

What is “hole” current?

A

A current in the valence band that is caused by electrons in the valence band filling the “hole”, and therefore creating a new hole next to it.

34
Q

What is doping?

A

Adding impurities into a material to change the conductive properties of it

35
Q

What is N doping?

A

Adding an impurity with an extra electron in the valence band

36
Q

What is P doping?

A

Adding an impurity with 1 less electron in the valence band

(technically an extra “hole”)

37
Q

What is an intrinsic semiconductor?

A

An undoped and natural semiconductor.

38
Q

In an intrinsic semiconductor, what is the relationship between the number of holes and the number of electrons?

A

There are the same number of holes and there are electrons

39
Q

How do intrinsic semiconductors work?

A

Energy is added to the system and then they release an electron from the valence band into the conduction band.

40
Q

What is an extrinsic semiconductor?

A

A doped semiconductor, with either pentavalent (n-type) or trivalent (p-type) atoms

Big yap incoming below
————————-
pentavalent (penta meaning 5) (valent meaning outer shell electron)

tri (meaning 3) (valent meaning outer shell electron)

silicon has 4 valence electrons so 5 would be 1 more and 3 1 less hence n and p-type

41
Q

What are PN junctions?

A

When you combine a p-type and n-type material.

42
Q

How do you combine the P and N parts?

A

Diffusion junctions
Ion implantation
Grown junctions

43
Q

What are diffusion junctions?

A

Diffuse impurities (from high to low conc) using high temps

44
Q

What is ion implantation?

A

Shooting high energy ions to make the pn junction

45
Q

What are grown junctions?

A

Adding impurities while creating the material

46
Q

What are majority/minority charge carriers?

A

The most abundant/ dominant charge carrier in a semi-conductor

47
Q

How do you form a PN junction?
(recommend you refer to the notes for the diagram)

A
  1. join the p and n material together
  2. the majority carriers from each diffuse from a high to low conc
  3. The holes and electrons in each material combine forming a depletion region
  4. the depletion region grows until the ion’s electric field causes the charge carriers to drift
  5. This drifting causes a current
  6. Equilibrium when drift current and diffusion current are the same
48
Q

What is the potential barrier?

A

The difference in potential between the n and p regions prevents the electrons and holes from recombining

49
Q

What is forward bias?

A

A “forward/+ve” voltage is added causing the potential barrier to reduce making it easier for holes and electrons to recombine.

(charge carrier can move so causes current)

50
Q

What is reverse bias?

A

A “reverse/-ve” voltage causing the potential barrier to widen. No recombination and no current

51
Q

What are the PN junctions IV characteristics?

A

Acts as a diode (current flows in 1 direction as V increases)

(look at notes for the Shokely Diode Equation)

52
Q

What is the Shokely Diode Equation?

A

An equation that dictates the current in a diode
(refer to notes for diagram)

53
Q

What is breakdown?

A

When the Shockley Diode Equation “breaks” allowing a large amount of current to flow when reverse biased (in the other direction)

54
Q

What is zener breakdown?

A

A strong electric field from the voltage causes the holes and electrons to get close enough to recombine through quantum tunnelling.

55
Q

What is quantum tunneling?

A

Quantum particles only have a probability of being in a field/ radius of a location. If close enough to a barrier (in that field they can exist past it.

56
Q

In what type of material does zener doping occur?

A

Heavily doped diodes

57
Q

What is avalanche breakdown?

A

The voltage gives minority carriers a lot of KE. They knock into each other causing a jump out of the valence band, causing holes and electrons to recombine.

58
Q

What type of material does avalanche breakdown occur in?

A

Low doped diodes

59
Q

What is photon energy?

A

E = hf

60
Q

What is the photon energy released by an electron?

A

It is the same as the energy of the band gap

61
Q

What is an LED?

(look at notes for diagram)

A

Light emitting diode

62
Q

What does encapsulation do?

A

Protects the LED
Enhances the output
Changes in the emission patterns

63
Q

What is an indirect band gap dictated by? (video dis pls)

A

When the energy of the conduction band is at a minimum the electrons have no momentum.

When the energy of the valence band is at a minimum the holes have no momentum

64
Q

What is a direct band gap dictated by? (video dis thx)

A

When the energy of the conduction band is at a minimum, both holes and electrons have no momentum.

65
Q

What makes an efficient LED?

A
  1. Electrons have a direct band gap | so can preferentially (whenever they want) combine
  2. Electrons and holes are close together.
66
Q

How can you make electrons and holes closer together in an LED?

A

By fine-tuning the combination of alloys

67
Q

Why does a direct band gap make an efficient LED? (research pls thx)

A

The energy and the momentum are conserved. ( God knows why)

68
Q

What is a photodiode?

A

Use of PN junctions to detect electrons

(similar to solar panels)

69
Q

What is diode rectification?
(look at notes for diagrams pls)

A

Restricting an AC to DC

70
Q

What is a transistor?

A

A semiconductor that can amplify and switch electronic signals.

71
Q

TRANSISTORS!!!!! OPEN MEEE

A

This part is understanding not memeorisation based so look at ntoes and yt vids

72
Q

What controls the current through a BJT?

A

The current into the base (3rd terminal)

73
Q

What controls the current through a FET?

A

The voltage applied on the gate (3rd terminal)

74
Q

What does the current in a JFET rely on?

A

The majority carriers only

75
Q

What does the current in a BJT rely on?

A

both holes and electrons

76
Q

What is the main difference between a BJT and a FET

A

BJT is current-controlled and relies on gain
JFET is voltage-controlled and relies on transconductance (btec gain)

12003 FEE (4 decks)

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