P-N Junction Diode and Semiconductor Electronics

Flashcards covering the properties of semiconductors, doping, the operation of p-n junction diodes, rectification methods, and smoothing techniques.

Semiconductors

Materials whose electrical conductivities are higher than those of insulators but lower than those of conductors.

Negative temperature coefficient of resistance

A property of semiconductors where resistivity decreases as temperature increases.

Forbidden band

In energy band theory, a small gap in semiconductors that requires less energy for an electron to move from the valence band to the conduction band.

Hole

A vacancy that remains when an electron leaves the valence band; it acts as a positive charge carrier.

Tetravalent

Having four valence electrons in the outermost shell, a characteristic of both silicon and germanium.

Intrinsic conduction

Conduction that occurs in a pure semiconductor due solely to thermally generated electron-hole pairs.

Doping

The process of introducing impurities into a semiconductor in a controlled manner to achieve an enormous increase in the number of charge carriers.

Extrinsic semiconductor

A semiconductor formed by the introduction of impurities through doping.

Donor impurities

Atoms, such as arsenic, which have five valence electrons and provide free electrons for conduction.

Acceptor impurities

Atoms, such as gallium, which have three valence electrons and create holes in the covalent bonds.

N-type extrinsic semiconductor

A semiconductor where electrons are the majority carriers and holes are the minority carriers, created by adding donor impurities.

P-type extrinsic semiconductor

A semiconductor where holes are the majority carriers and electrons are the minority carriers, created by adding acceptor impurities.

Depletion region

A region in the neighborhood of a p-n junction that is depleted of mobile carriers, typically with a thickness of $0.5 - 1.0\,\mu m$.

Barrier p.d. (Contact potential)

The potential difference across a junction that stops the diffusion of electrons and holes; typical values at room temperature are $Ge \sim 0.2 - 0.4\,V$ and $Si \sim 0.6 - 0.8\,V$.

Forward biased (F.B.)

Applying an external voltage making the P side positive with respect to the N side, decreasing the barrier p.d. and narrowing the depletion band.

Reverse Biased (R.B.)

Applying an external voltage making the P side negative with respect to the N side, increasing the barrier p.d. and widening the depletion band.

Reverse saturation current

Also known as reverse leakage current, a magnitude of current consisting of thermally generated minority carriers urged across the p-n junction under reverse bias.

Turn-on or cut-in voltage ($V_\gamma$)

The threshold voltage for a forward-biased diode where the current increases appreciably from zero, roughly equal to the barrier p.d.

Diode breakdown

A phenomenon occurring when reverse voltage becomes high enough to generate an electrical arc through the crystal, destroying the diode.

Rectification

The process whereby a sinusoidal alternating current is converted into direct current.

Full-wave rectification

A process using a bridge rectifier with 4 diodes that allows current to flow in the same direction through a resistor during both halves of the ac cycle.

Smoothing

The use of a capacitor to filter output voltage by charging as voltage grows and discharging through a resistor as voltage falls to remove voltage variation.

Ripple

A small voltage variation left in the output after smoothing, which can be reduced by increasing the capacitance of the capacitor.