Test 1 Flashcards
Semi-Conductors
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
Dopants
Elements with 5 or 3 electrons
of valence electrons
Conductors: 1-3 (1-2 good)
Semiconductors: 4
Insulators: 5-8
Doping by adding phosphorous
5 valence electrons
N-type
Electron free to move in conduction band
Bandgap energy
1.12 eV for silicon
Large for insulators
Almost doesn’t exist for conductors
Intrinsic concentration
Number of free electrons per unit volume (cm^-3)
Doping by adding aluminum
3 valence electrons
Creates hole
If semiconductor doped with Nd concentration of donor atoms
Majority carrier concentration n = Nd
Minority carrier concentration p
If semiconductor doped with Na concentration of acceptor atoms
Majority carrier concentration p = Na
Minority carrier concentration n
Transport of carriers mechanisms
Drift
Diffusion
Drift
Transport of carriers due to electric field
Electrons pushing +particles away, e- towards it
Current density
Measure of current passing through a cross-sectional area
Diffusion
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
PN junction
By doping adjacent parts of a semi-conductor with N and P type dopants respectively
PN Junction under Reverse Bias
+ 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
Variable capacitor
Excellent solution for an oscillator
When capacitance changes, the resonant frequency changes
Tank circuit
Traps the signal
PN Junction under Forward Bias
P-type more positive than n side
External voltage reduces electric field
Diffusion current increases, which leads to increased current flow
Reduces depletion layer
Pn
Concentration of holes in n region
Pp
Concentration of holes in p region
Zener Breakdown
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)
Avalanche Breakdown
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
Voltage of diode greater than or equal to 0
Short
Voltage of diode less than 0
Open
Linear map, or linear function
F(x+y) = f(x) + f(y) F(ax) = af(x)
Satisfying the principle of superposition
Linear circuits
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
A passive two-terminal circuit is called linear if…
The voltage across it and the current through it are related by a linear map
Resistor, capacitor, inductor
Voltage-current relationship for an independent source
Does not satisfy the properties of linearity
Linear dependent source
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
Nonlinear circuit element
Diode, BJTs, MOSFETs
