electrical thermal Flashcards
n type vs p type
n type more electrons (P, As, Sb, group VA)
p type more holes (B, Al, Ga, IIIA)
MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor)
Controls the flow of current between source and drain terminals based on a voltage applied to its metal gate
electrical conductivity of polymers
§ Conducting polymers, such as polyacetylene and polypyrrole, match metallic conductors in electrical conductivity.
§ Achieved conductivities reach 1.5 × 107 (Ω·m)−1, comparable to copper on different volume and weight bases.
§ Enhanced conductivity results from a unique chain structure with alternating single and double bonds or aromatic units.
how does conductivity change with doping
Data for Doped Silicon:
– σ increases with doping
imperfection sites
lower the activation energy to produce mobile electrons.
p-n Junction Diode
Allows current in one direction only.
Forward bias: current flows.
Reverse bias: current blocked.
Ohm’s law
relates the current I—or time rate of charge passage—to the applied voltage V
V=IR
ELECTRICAL CONDUCTIVITY
Capability of a material to transmit the electricity through it.
Resistivity, ρ
a material property that is independent of sample size and
geometry
order of conductivity
metal > semiconductor>ceramics>polymers
two types of band structures for metals
Partially filled band
Overlapping bands
Energy Band Structures: Insulators
Wide band gap (>2eV)
* Few electrons excited
across band gap
Energy Band Structures: Semiconductors
- Narrow band gap (< 2 eV)
- Electrons with enough energy excited across band gap (high temp)
How does presence of imperfections affect metal resistivity
Increases
– grain boundaries
– dislocations
– impurity atoms
– vacancies
These act to scatter electrons so that they take a less direct path.
metals:
how does resistivity change with temp and cw%
Resistivity increases with:
– temperature – wt% impurity
– %CW
Two types of electronic charge carriers in semiconductors:
Free Electron
– negative charge
– in conduction band
Hole
– positive charge
– vacant electron state in
the valence band
resistivity equation
rho = R*A/l
Extrinsic Semiconductors:
- Include both n-type and p-type semiconductors.
- Produced from initially highly pure materials with impurity contents around
10^-7 at%.
Intrinsic semiconductors
§ Materials that inherently exhibit semiconductor properties without intentional doping or the addition of impurities characterized by having a small but nonzero energy gap
pure materials (Si, Ge)
Compound semiconductors: III-V (e.g., GaAs), II-VI (e.g., CdS)
how does intrinsic conductivity change with temperature for silicon
semiconductor
– σ increases with T
– opposite to metals
Heat capacity
The energy required to produce a unit rise in
temperature for one mole of a material.
Phonon
: A quantized unit of lattice vibration (like a “sound” particle in solids).
Energy stored as vibrational energy contributes to heat capacity and thermal conduction.
metals ceramics polymer heat capacity
Polymers have high Cp → due to flexible chains and rotational motions.
Metals have moderate Cp.
Ceramics have low Cp → due to stiff atomic bonds.
Thermal expansion
Stronger bonds (ceramics) → lower expansion.
Weaker bonds (polymers) → higher expansion.
Coefficient of Thermal Expansion: Comparison
polymers> metals>ceramics
