Semiconductor Physics and Electronic Devices

These vocabulary flashcards cover the fundamental concepts of semiconductor physics, doping, different types of semiconductors (intrinsic and extrinsic), diode types (P-N, Zener, Photo, LED, Tunnel), and their physical mechanisms.

Semiconductor

A material where the valence band is totally filled and the conduction band is empty, but the energy gap between them is quite small (less than $3\,eV$).

Insulator

A material with a large energy gap ($E_g > 3\,eV$) where no electron is able to go from the valence band to the conduction band, making electrical conduction impossible.

Intrinsic Semiconductor

A pure semiconductor which is free of every impurity, such as silicon ($Si$) and germanium ($Ge$).

Hole

The empty place or vacancy left in a covalent bond when an electron breaks away; it acts as a particle with a positive charge equal to that of an electron.

Doping

The process of adding desirable impurity atoms, called dopants, to a pure semiconductor to modify its properties in a controlled manner.

Extrinsic Semiconductor

A doped semiconductor or a semiconductor with suitable impurity atoms added to it, classified into n-type and p-type.

n-type Semiconductor

An extrinsic semiconductor formed by doping a pure semiconductor with pentavalent atoms (Phosphorus, Arsenic, Antimony, or Bismuth) which provides extra electrons as majority carriers.

Donor Atoms

Pentavalent impurity atoms in n-type semiconductors that denote one free electron to the crystal.

p-type Semiconductor

An extrinsic semiconductor formed by doping a pure semiconductor with trivalent atoms (Boron, Aluminium, Gallium, or Indium) that create holes as majority carriers.

Acceptor Atoms

Trivalent impurity atoms added to p-type semiconductors that create deficiencies of electrons (holes).

Fermi Level in Intrinsic Semiconductors

The energy level located essentially halfway between the valence and conduction bands, indicating equal probability of occupation for both bands.

Fermi-Dirac Distribution Law

The law giving the probability $f(E)$ that an energy state of energy $E$ is occupied at $T\,K$: $f(E) = \frac{1}{1 + e^{\frac{E-E_F}{kT}}}$.

Boltzmann constant ($k$)

A constant used in the Fermi-Dirac distribution, valued at $8.62 \times 10^{-5}\,eV\,K^{-1}$.

P-N Junction

The arrangement resulting from joining a p-type semiconductor crystal with an n-type semiconductor crystal, also known as a junction diode.

Depletion Layer

A region at the P-N junction containing immobile ions (positive donor atoms on the n-side and negative acceptor atoms on the p-side) and free of charge carriers.

Diffusion Current

The motion of charge carriers across the junction due to differences in concentration in the two regions of the p-n junction.

Drift Current

The motion of charge carriers due to the electric field developed at the junction, which is opposite in direction to the diffusion current.

Potential Barrier ($V_B$)

The maximum potential across the junction at equilibrium that stops the movement of majority charge carriers; valued at approximately $0.3\,V$ for Germanium and $0.7\,V$ for Silicon at room temperature.

Forward Biasing

A method of biasing where the positive terminal of an external battery is connected to the p-side and the negative terminal to the n-side, decreasing the width of the depletion layer.

Reverse Biasing

A method of biasing where the positive terminal of an external battery is connected to the n-side and the negative terminal to the p-side, increasing the width of the depletion region.

Knee Voltage ($V_K$)

Also known as threshold voltage, it is the forward voltage (typically $0.3\,V$ for Ge and $0.7\,V$ for Si) beyond which the current through the junction starts increasing rapidly.

Reverse Current (Leakage Current)

A very small current independent of voltage up to the breakdown point, caused by minority carriers crossing the junction under reverse bias.

Zener Diode

A special type of p-n junction diode designed to operate in the reverse breakdown region without being damaged, often used as a voltage stabiliser.

Avalanche Breakdown

A breakdown occurring in lightly doped diodes at high reverse voltages ($> 6\,V$) due to impact ionization creating a chain reaction of electron-hole pairs.

Zener Breakdown

A breakdown occurring in heavily doped diodes at low reverse voltages ($< 6\,V$) where a strong electric field pulls electrons from the valence band to the conduction band (quantum tunneling).

Photodiode

A p-n junction diode that operates in reverse bias and consumes light energy to generate electric current through the inner photoelectric effect.

Dark Current

The leakage current that flows in a photodiode even in the absence of incident light.

Light Emitting Diode (LED)

An optoelectronic device that works on the principle of electro-luminance, converting electrical energy into light energy when forward biased.

Tunnel Diode (Esaki Diode)

A heavily doped p-n junction diode about $10\,nm$ wide that exhibits negative resistance due to the quantum mechanical effect called tunneling.