Classification of Materials and Semiconductors

Materials are classified based on their electrical conductivity:
- Conductors: Allow free flow of electrons, have a low energy gap between the valence band and conduction band.
- Insulators: Resist electron flow, have a large energy gap between the valence band and conduction band.
- Semiconductors: Have conductivity between conductors and insulators, with a moderate energy gap.

Doping: Introducing impurities to alter the conductivity of semiconductors.
N-type semiconductors: Doped with donor impurities (e.g., phosphorus) to create free electrons.
P-type semiconductor: Doped with acceptor impurities (e.g., Boron) to create holes, which act as charge carriers.

A junction formed by joining P-type and N-type semiconductors.
Depletion region: A region around the junction with no free charge carriers due to diffusion of electrons and holes resulting in a potential barrier.
Forward bias: Applied voltage reduces the potential barrier, allowing current to flow.
Reverse bias: Applied voltage increases the potential barrier, blocking current flow, except for a small leakage current.

Forward bias: Current flow is controlled by the applied voltage, exhibiting exponential relationship.
Reverse bias: Negligible current flow until reaching a critical voltage (breakdown voltage).
Zener Breakdown: Reverse voltage breaks covalent bonds, leading to a sudden increase in current.
Avalanche Breakdown: High electric field leads to collisions, generating more charge carriers, causing large current.

Rectifier: Converting AC to DC using a diode's unidirectional current flow property.
- Half-wave rectifier: Uses one diode, allowing only half of the AC cycle to pass.
- Full-wave rectifier: Uses two diodes, allowing both halves of the AC cycle to pass, producing a smoother DC output.
- Bridge rectifier: Uses four diodes, producing a full-wave rectified output with less ripple.
Filter Circuits: Smoothing the output of a rectifier by removing AC components using capacitors and inductors.
- Capacitor Filter: A capacitor stores charge during the positive half-cycle, discharging during the negative half-cycle, creating a smoother DC output.
- Inductor Filter: An inductor opposes changes in current, smoothing out the rectified output.
Special Purpose Diodes
- Schottky Diode: A metal-semiconductor junction diode with low forward voltage drop, faster switching speed, and less reverse recovery time.
- Varactor Diode: A diode with a capacitance that changes with applied voltage.
- LED (Light Emitting Diode): A diode that emits light when forward biased.
- Photodiode: A diode that generates a current when exposed to light.

A Zener diode can act as a voltage regulator, maintaining a constant output voltage despite changes in the input supply voltage.

Three layers of semiconductor material: emitter, base, and collector.
NPN transistor: Two n-type semiconductors sandwich a p-type semiconductor.
PNP transistor: Two p-type semiconductors sandwich an n-type semiconductor.
Modes of operation:
- Active mode: Used for amplification.
- Saturation mode: Used for switching.
- Cut-off mode: The transistor is off.

Input characteristics: Relationship between base current (IB) and base-emitter voltage (VBE).
Output characteristics: Relationship between collector current (IC) and collector-emitter voltage (VCE) for different values of base current (IB).

Bias: Applying appropriate DC voltages to the transistor to control current flow and ensure proper operation.
Stability factor: Indicates sensitivity of collector current to changes in transistor parameters.

A circuit that amplifies an incoming signal using a transistor's ability to control large collector current with small base current.
Gain: The ratio of output to input signal.
- Voltage gain: Amplification factor.
- Current gain: Ratio of change in collector current to change in base current.
- Power gain: Product of voltage and current gain.
Input impedance: Resistance seen by the input signal source.
Output impedance: Resistance seen by the load connected to the output.

A transistor that controls current flow by varying the electric field created by a voltage applied to a gate electrode.
JFET (Junction Field-Effect Transistor): Operates by modulating the width of a depletion region.
MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor): Operates by creating a channel of charge carriers in a semiconductor using an electric field controlled by the gate voltage.
- Depletion type MOSFET: Has an initial channel, and gate voltage depletes it.
- Enhancement type MOSFET: The channel is created by gate voltage.