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12003 FEE > Electrons and PN junctions > Flashcards

Electrons and PN junctions Flashcards

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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
What are semiconductors?
Materials that conduct in certain conditions. (e.g when energy is added to the system)
26
What is the formula for conductivity?
σ = 1/ ρ ρ - resistivity
27
What happens to electron energy levels when atoms form molecules?
Electron energy levels change
28
What is the formula for the KE of an electron relating to momentum?
p^2/2m where p is the momentum (special note p^2 means a parabola shape for the curve like x^2)
29
What is the valence band?
The band of electrons that represents the outermost shell of the material
30
What is the conduction band?
The region/ band that allows electrons to move freely.
31
What is the band gap?
The difference in energy between the valence and conduction band?
32
What are "holes"?
A gap (unfilled part of the valence band) after an electron jumps to the conduction band. (they are treated as positively charged particles)
33
What is "hole" current?
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
What is doping?
Adding impurities into a material to change the conductive properties of it
35
What is N doping?
Adding an impurity with an extra electron in the valence band
36
What is P doping?
Adding an impurity with 1 less electron in the valence band (technically an extra "hole")
37
What is an intrinsic semiconductor?
An undoped and natural semiconductor.
38
In an intrinsic semiconductor, what is the relationship between the number of holes and the number of electrons?
There are the same number of holes and there are electrons
39
How do intrinsic semiconductors work?
Energy is added to the system and then they release an electron from the valence band into the conduction band.
40
What is an extrinsic semiconductor?
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
What are PN junctions?
When you combine a p-type and n-type material.
42
How do you combine the P and N parts?
Diffusion junctions Ion implantation Grown junctions
43
What are diffusion junctions?
Diffuse impurities (from high to low conc) using high temps
44
What is ion implantation?
Shooting high energy ions to make the pn junction
45
What are grown junctions?
Adding impurities while creating the material
46
What are majority/minority charge carriers?
The most abundant/ dominant charge carrier in a semi-conductor
47
How do you form a PN junction? (recommend you refer to the notes for the diagram)
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
What is the potential barrier?
The difference in potential between the n and p regions prevents the electrons and holes from recombining
49
What is forward bias?
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
What is reverse bias?
A "reverse/-ve" voltage causing the potential barrier to widen. No recombination and no current
51
What are the PN junctions IV characteristics?
Acts as a diode (current flows in 1 direction as V increases) (look at notes for the Shokely Diode Equation)
52
What is the Shokely Diode Equation?
An equation that dictates the current in a diode (refer to notes for diagram)
53
What is breakdown?
When the Shockley Diode Equation "breaks" allowing a large amount of current to flow when reverse biased (in the other direction)
54
What is zener breakdown?
A strong electric field from the voltage causes the holes and electrons to get close enough to recombine through quantum tunnelling.
55
What is quantum tunneling?
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
In what type of material does zener doping occur?
Heavily doped diodes
57
What is avalanche breakdown?
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
What type of material does avalanche breakdown occur in?
Low doped diodes
59
What is photon energy?
E = hf
60
What is the photon energy released by an electron?
It is the same as the energy of the band gap
61
What is an LED? (look at notes for diagram)
Light emitting diode
62
What does encapsulation do?
Protects the LED Enhances the output Changes in the emission patterns
63
What is an indirect band gap dictated by? (video dis pls)
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
What is a direct band gap dictated by?
When the energy of the conduction band is at a min valence band is at max, both holes and electrons have no momentum. So no change in ρ for recombination.
65
What makes an efficient LED?
1. Electrons have a direct band gap | so can preferentially (whenever they want) combine 2. Electrons and holes are close together.
66
How can you make electrons and holes closer together in an LED?
By fine-tuning the combination of alloys
67
Why does a direct band gap make an efficient LED? (research pls thx)
The E and the ρ are conserved. Since conduction band minimum and the valence band maximum occur at the same ρ, no need for a change of ρ for recombination
68
What is a photodiode?
Use of PN junctions to detect electrons (similar to solar panels)
69
What is diode rectification? (look at notes for diagrams pls)
Restricting an AC to DC
70
What is a transistor?
A semiconductor that can amplify and switch electronic signals.
71
TRANSISTORS!!!!! OPEN MEEE
This part is understanding not memeorisation based so look at ntoes and yt vids
72
What controls the current through a BJT?
The current into the base (3rd terminal)
73
What controls the current through a FET?
The voltage applied on the gate (3rd terminal)
74
What does the current in a JFET rely on?
The majority carriers only
75
What does the current in a BJT rely on?
both holes and electrons
76
What is the main difference between a BJT and a FET
BJT is current-controlled and relies on gain JFET is voltage-controlled and relies on transconductance (btec gain)

12003 FEE (5 decks)

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