Electronics Lecture 1: Semiconductors, Diodes, and Applications

Vocabulary terms and definitions covering basic semiconductor physics, diode operations, LED characteristics, Zener diodes, and rectifier circuits.

Conductors

Materials like silver, copper, gold, and aluminium that have many free electrons available in the conduction band to contribute to current.

Insulators

Materials such as glass, paper, and air where electrons are tightly bound to atoms and very few can acquire enough energy to reach the conduction band.

Semiconductors

Materials like Silicon and Germanium that are used to manufacture diodes, transistors, and integrated circuits; Silicon atoms have 4 valence electrons forming covalent bonds.

Intrinsic semiconductor

A pure semiconductor without impurities that has very few thermally generated free electrons in the conduction band at room temperature.

Band gap of Crystalline Silicon

$1.12\,eV$ (where $1\,eV = 1.602 \times 10^{-19}\,J$) at a temperature of $300K$.

Doping

The process of adding impurities to a pure semiconductor to increase its conductivity.

N-type semiconductor

Silicon doped with group 5 elements (Phosphorus, Arsenic, Antimony) resulting in excess electrons as majority carriers and holes as minority carriers.

P-type semiconductor

Silicon doped with group 3 elements (Boron, Aluminum, Gallium) resulting in holes as majority carriers and electrons as minority carriers.

Resistivity formula

The resistance of a material with uniform cross-sectional area $A$ and length $l$ is defined as $R = \frac{\rho l}{A}$, where $\rho$ is the resistivity.

Conductivity ($\sigma$)

The inverse of resistivity, expressed as $\sigma = \frac{1}{\rho}$ with units of $1/\Omega\cdot m$.

Depletion region

An area around a PN junction depleted of free charge carriers formed when majority carriers diffuse across the junction and recombine.

Barrier potential

The potential difference required to move electrons through the depletion region; approximately $0.7V$ for Silicon and $0.3V$ for Germanium at $25^\circ C$.

Forward bias

Applying DC voltage with the positive terminal to the p-type and negative to the n-type, narrowing the depletion region and allowing exponential current flow.

Reverse bias

Applying DC voltage with the negative terminal to the p-type and positive to the n-type, widening the depletion region and preventing charge diffusion except for a small saturation current.

Reverse saturation current ($I_s$)

A very small current produced by minority carriers during reverse bias; for a Silicon diode, an indicative value is $1.0 \times 10^{-12}\,A$ ($1\,pA$).

Thermal voltage ($V_T$)

Represented as $\frac{kT}{q}$, it is approximately $0.0258V$ (or $\approx 26\,mV$) at an absolute temperature of $300K$.

Ideal Diode

A theoretical model that passes current in one direction with zero voltage drop under forward bias and acts as an open circuit when reverse biased.

Electroluminescence

The process in an LED where electron-hole recombination under forward bias releases energy as photons in the infrared or visible range.

Gallium Arsenide (GaAs)

Semiconductor material used for infrared LEDs with a typical forward voltage ($V_F$) of $1.2V$.

Indium Gallium Nitride (InGaN)

Semiconductor material used for white LEDs with a typical forward voltage ($V_F$) of $4.0V$.

LED Wavelength formula

The wavelength of emitted light is calculated as $\lambda(nm) = \frac{1240}{E_g(eV)}$.

Zener Diode

A Silicon PN junction designed for operation in the reverse breakdown region to produce a stable output reference voltage ($V_Z$).

Avalanche breakdown

A type of reverse breakdown occurring at high reverse bias voltages ($> 6V$), similar to a standard rectifier diode.

Zener breakdown

A type of reverse breakdown occurring at low reverse voltages ($< 6V$) in heavily doped diodes with narrow depletion regions.

Half-wave rectifier

A circuit that provides rectification from an AC source where the diode is forward biased only during the positive input cycle; current flows to the load when $V_{in} > 0.6V$.

Full-wave rectifier

A diode bridge circuit where two diodes conduct during the positive half cycle and the other two conduct during the negative half cycle, providing a smoother direct voltage.

Half-wave ripple voltage formula

The output ripple with a smoothing capacitor is defined as $V_{ripple} = \frac{V_p}{f R_L C}$.

Full-wave ripple voltage formula

The output ripple for a full-wave bridge rectifier is defined as $V_{ripple} = \frac{V_p}{2 f R_L C}$, assuming $R_L C \gg T$.