Semiconductor Diode and Junction Theory Flashcards

Vocabulary flashcards covering PN-junction theory, bias conditions, diode resistances, rectifiers, filters, zener diodes, and light-emitting diodes based on the lecture text.

PN-Junction

A single semiconductor crystal having a P-type region and an N-type region, characterized by its ability to conduct current in one direction while offering very high resistance in the reverse direction.

Depletion Region

The region near the junction containing uncompensated acceptor and donor ions that is depleted of mobile charge carriers (holes and free electrons); also referred to as the space-charge region.

Potential Barrier

An electric field developed between uncompensated acceptor and donor ions in the depletion region that stops further diffusion of majority carriers across the junction.

Barrier Height

The potential difference across the depletion region with no external voltage applied, which is approximately $0.7\,V$ for a silicon PN-junction and $0.3\,V$ for a germanium PN-junction.

Forward Bias

The connection of a PN-junction where the positive terminal of a battery is connected to the P-side and the negative terminal to the N-side, reducing the potential barrier and allowing majority carriers to flow.

Reverse Bias

The connection of a PN-junction where the negative terminal of a battery is connected to the P-side and the positive terminal to the N-side, widening the depletion region and increasing the potential barrier.

Reverse Saturation Current

A small, constant current flowing through a reverse-biased PN-junction produced by the drift of thermally generated minority carriers across the junction.

Transition Capacitance

The effective capacitance formed in a reverse-biased PN-junction, where the P and N regions act as capacitor plates and the depletion space-charge region acts as the dielectric; also called depletion capacitance.

Breakdown Voltage ($V_z$)

The value of reverse-bias voltage at which the crystal structure breaks down, causing the reverse current through the PN-junction to increase abruptly.

Zener Breakdown

A junction breakdown mechanism caused by a high electric field (about $3 \times 10^7\,V/m$) breaking covalent bonds directly to generate charge carriers, predominant for breakdown voltages less than about $4\,V$.

Avalanche Breakdown

A junction breakdown mechanism where an increased electric field accelerates minority carriers to high velocities, causing them to break covalent bonds through collision in a cumulative chain reaction, predominant for breakdown voltages greater than $6\,V$.

Cut-in Voltage ($V_o$)

The forward voltage at which diode current begins to increase rapidly, equal to approximately $0.7\,V$ for silicon diodes and $0.3\,V$ for germanium diodes; also known as knee voltage.

Anode

The terminal of a semiconductor diode connected to the P region.

Cathode

The terminal of a semiconductor diode connected to the N region.

Ideal Diode

A theoretical diode that acts as a perfect conductor with zero resistance when forward-biased, and as a perfect insulator with infinite resistance when reverse-biased.

Static Resistance ($R_F$)

The dc resistance offered by a forward-biased diode at a specific operating point, calculated as the ratio of dc voltage across the diode to dc current flowing through it ($R_F = \frac{V_{dc}}{I_{dc}}$).

Dynamic Resistance ($r_f$)

The ac resistance offered by a diode to a small ac signal, calculated as the ratio of an incremental change in voltage to the resulting incremental change in current ($r_f = \frac{\Delta V}{\Delta I}$).

Rectifier

A diode circuit used within a power supply to convert alternating voltage (ac) into direct voltage (dc).

Half-Wave Rectifier

A rectifier circuit that converts ac into dc by conducting current during only the positive half-cycles of the input ac voltage.

Peak Inverse Voltage (PIV)

The maximum reverse voltage that a diode must withstand without breakdown during the negative half-cycle of the input voltage.

Full-Wave Rectifier

A rectifier circuit that utilizes both half-cycles of the input ac voltage waveform by inverting alternate half-cycles to produce a continuous unidirectional load current.

Centre-Tap Rectifier

A full-wave rectifier circuit using two diodes and a centre-tapped secondary transformer winding, where each diode experiences a peak inverse voltage of $2 V_m$.

Bridge Rectifier

A full-wave rectifier circuit using four diodes in a bridge configuration, avoiding the need for a centre-tapped transformer and subjecting each non-conducting diode to a peak inverse voltage of $V_m$.

Shunt Capacitor Filter

A smoothing circuit consisting of a large-value capacitor connected in parallel with the load resistor, offering a low-reactance path to ac ripple components while passing dc to the load.

Zener Diode

A semiconductor diode specially designed to operate safely in the reverse-breakdown region, commonly used in voltage-stabilizing or regulator circuits.

Light-Emitting Diode (LED)

A forward-biased PN-junction diode made from compound semiconductors (such as GaAsP or GaP) that emits radiated energy in the form of light when electron-hole recombinations occur.

Seven-Segment Display Unit

A display device constructed using multiple LEDs that can display any digit from $0$ to $9$ by activating specific combinations of LED segments.