Semiconductor Electronics Mind Map

Energy bands are continuous ranges of allowed electron energies in a solid. The valence band contains electrons involved in bonding, the conduction band contains electrons that can move through the solid, and the band gap is the forbidden energy separation between them.

When classifying materials, mention both the relative band gap and the availability of conduction electrons. A diagram with valence band, conduction band, and band gap usually earns clearer credit than a word-only answer.

An intrinsic semiconductor is a pure semiconductor such as silicon or germanium. An extrinsic semiconductor is formed by adding a small controlled amount of impurity, called a dopant, to increase charge carriers; pentavalent dopants produce n-type material and trivalent dopants produce p-type material.

Always name the dopant group and the majority carrier. For n-type write pentavalent donor impurity and electrons; for p-type write trivalent acceptor impurity and holes.

A p-n junction is formed when p-type and n-type semiconductor regions are joined. Electrons and holes diffuse across the junction, recombine near it, and leave behind fixed ionised impurities, creating a depletion region and a built-in potential barrier.

For long answers, write the sequence in order: diffusion, recombination, uncovered ions, electric field, potential barrier, equilibrium. A labelled junction diagram is usually essential.

The p-n diode characteristic is the graph of current through a diode against the voltage applied across it. In forward bias the diode offers low resistance after the knee voltage, while in reverse bias it offers high resistance with a small reverse saturation current until breakdown.

In graph questions, label both axes with units, mark forward and reverse regions, show knee voltage in forward bias, and show breakdown region on the reverse side if required.

A rectifier is a circuit that converts alternating current or voltage into unidirectional output using the one-way conduction property of a p-n junction diode. A half-wave rectifier uses one diode, while a full-wave rectifier uses two diodes with a centre-tapped transformer or a bridge arrangement.

For circuit diagrams, clearly label AC input, diode direction, load resistance, and output waveform. For full-wave rectification, mention which diode conducts in each half-cycle and why the load current direction remains the same.