Test 1

Question 1

Semi-Conductors

Answer 1

Materials with conductivity better than insulators but poorer than conductors

Their properties can be modified by adding “dopants”

Both temperature and doping can cause the alteration of the properties by causing relocation of electrons

Question 2

Dopants

Answer 2

Elements with 5 or 3 electrons

Question 3

of valence electrons

Answer 3

Conductors: 1-3 (1-2 good)
Semiconductors: 4
Insulators: 5-8

Question 4

Doping by adding phosphorous

Answer 4

5 valence electrons
N-type
Electron free to move in conduction band

Question 5

Bandgap energy

Answer 5

1.12 eV for silicon

Large for insulators

Almost doesn’t exist for conductors

Question 6

Intrinsic concentration

Answer 6

Number of free electrons per unit volume (cm^-3)

Question 7

Doping by adding aluminum

Answer 7

3 valence electrons

Creates hole

Question 8

If semiconductor doped with Nd concentration of donor atoms

Answer 8

Majority carrier concentration n = Nd

Minority carrier concentration p

Question 9

If semiconductor doped with Na concentration of acceptor atoms

Answer 9

Majority carrier concentration p = Na

Minority carrier concentration n

Question 10

Transport of carriers mechanisms

Answer 10

Drift

Diffusion

Question 11

Drift

Answer 11

Transport of carriers due to electric field

Electrons pushing +particles away, e- towards it

Question 12

Current density

Answer 12

Measure of current passing through a cross-sectional area

Question 13

Diffusion

Answer 13

Movement of carriers due to the difference in concentration

No external force

Faster electrons diffuse, the higher the current

Current flows from low to high concentration

Question 14

PN junction

Answer 14

By doping adjacent parts of a semi-conductor with N and P type dopants respectively

Question 15

PN Junction under Reverse Bias

Answer 15

+ voltage connected to n side
- voltage connected to p side

N type side is more positive than p type side

External voltage enhances the existing electric field

Depletion layer widens

Increase in bound ions sustains the increased electric field

No increase in drift or diffusion

Reverse biased diode acts like a capacitor (2 charged regions separated by a dielectric)

Q=CV not valid (not a linear capacitor because Chris changes with voltage)

As voltage increases, the depletion region wides so the plate distances increases

Question 16

Variable capacitor

Answer 16

Excellent solution for an oscillator

When capacitance changes, the resonant frequency changes

Question 17

Tank circuit

Answer 17

Traps the signal

Question 18

PN Junction under Forward Bias

Answer 18

P-type more positive than n side

External voltage reduces electric field

Diffusion current increases, which leads to increased current flow

Reduces depletion layer

Question 19

Pn

Answer 19

Concentration of holes in n region

Question 20

Pp

Answer 20

Concentration of holes in p region

Question 21

Zener Breakdown

Answer 21

High E, high doping, depletion layer small, starts breaking bonds and pulling electrons away

Temperature increases, aids process; however Vzb reduces

High E breaks bonds, pulls electrons, which are accelerated towards n-side

Happens at E > 10^6 V/cm

Such high E only possible if depletion layer narrow

Narrow depletion layer implies doping must be high

Occurs when device highly doped

3-8V

Negative temp coefficient (if temperature increases, V decreases)

Question 22

Avalanche Breakdown

Answer 22

If doping < 10^5, zener breakdown can’t occur

However, there is already a small leakage current and small number of electrons and holes

When the rev. Bias voltage is large, it pulls these electrons with high intensity, causing them to accelerate

These electrons collide with other atoms, causing bonds to break and releasing further electrons. This results in an avalanche effect

Positive temp coefficient (if temp increases, breakdown voltage increases)

At voltage higher than zener breakdown

12-15V

Question 23

Voltage of diode greater than or equal to 0

Answer 23

Short

Question 24

Voltage of diode less than 0

Answer 24

Open

Question 25

Linear map, or linear function

Answer 25

F(x+y) = f(x) + f(y)
F(ax) = af(x)

Satisfying the principle of superposition

Question 26

Linear circuits

Answer 26

Can be solved by superposition

If you solve a circuit by superposition, the circuit is a linear circuit. If the circuit is a linear circuit, you can solve it by superposition.

Can only be consisting of linear passive elements, linear dependent sources, and independent sources

Question 27

A passive two-terminal circuit is called linear if…

Answer 27

The voltage across it and the current through it are related by a linear map

Resistor, capacitor, inductor

Question 28

Voltage-current relationship for an independent source

Answer 28

Does not satisfy the properties of linearity

Question 29

Linear dependent source

Answer 29

The “gain” of the source is merely a constant

V1(I2) = 2*(I2)

This source’s own current and own voltage would have a linear relationship but a “linear dependent source” does not necessarily have a linear relationship between its own current and its own voltage in a nonlinear circuit

Question 30

Nonlinear circuit element

Answer 30

Diode, BJTs, MOSFETs