What traumatic event does Zitkala-Sa describe at the school?

The forcible cutting of her long hair

Why was the cutting of her hair so humiliating to Zitkala-Sa?

Among her people, shingled hair was worn by cowards and mourners

How are conductors, insulators and semiconductors distinguished by bands?

Conductors have overlapping bands, insulators a large gap, and semiconductors a small forbidden gap.

What carries current in an intrinsic semiconductor?

Equal numbers of free electrons and holes generated by thermal excitation.

What is an n-type semiconductor?

A semiconductor doped with pentavalent atoms, giving electrons as majority carriers.

What is a p-type semiconductor?

A semiconductor doped with trivalent atoms, giving holes as majority carriers.

What is the depletion region of a p-n junction?

A carrier-free zone near the junction with an internal barrier potential opposing diffusion.

How does a diode behave under forward and reverse bias?

It conducts readily under forward bias and almost not at all under reverse bias.

What is the function of a rectifier?

To convert alternating current into direct current using the one-way conduction of diodes.

What is special about a Zener diode?

It is designed to operate in reverse breakdown at a fixed voltage, used for voltage regulation.

It emits light when forward biased, as electrons and holes recombine across the junction.

How does a solar cell work?

A p-n junction generates a voltage when light creates electron-hole pairs in the depletion region.

Semiconductor Electronics: Materials, Devices and Simple Circuits

Class 12 Physics · Physics Part II · Chapter 6

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Summary

Solids are classified by their energy bands: conductors have overlapping or partly filled bands, insulators a large forbidden gap, and semiconductors a small gap that allows modest conduction. In a pure (intrinsic) semiconductor, equal numbers of electrons and holes carry current. Doping with pentavalent atoms gives an n-type semiconductor (electrons as majority carriers) and with trivalent atoms a p-type (holes majority). Joining the two forms a p-n junction, where diffusion creates a depletion region and a built-in barrier potential. The junction conducts readily under forward bias but barely under reverse bias, acting as a diode whose characteristic curve shows this rectifying behaviour. Diodes are used in half-wave and full-wave rectifiers to convert AC to DC, while special diodes such as the Zener (voltage regulation), photodiode, LED and solar cell exploit junction properties for sensing and light. These devices, compact and reliable, replaced bulky vacuum tubes and form the foundation of all modern electronics, from power supplies and displays to the integrated circuits at the heart of computing and communication.

Energy bands in solidsIntrinsic and extrinsic semiconductorsp-n junction and biasingDiode as a rectifierSpecial purpose diodesApplications in circuits

Key terms

Energy band gap

Forbidden energy range between valence and conduction bands.

Intrinsic semiconductor

Pure semiconductor with equal electron and hole concentrations.

Doping

Adding impurity atoms to create n-type or p-type semiconductors.

p-n junction

Boundary between p and n regions forming a depletion layer and barrier.

Diode

A p-n junction that conducts mainly in one direction, used for rectification.

Rectifier

Circuit converting alternating current to direct current using diodes.

Extra questions & answers

Try one from this chapter

In terms of energy bands, a semiconductor has:

Flashcards & interactive practice