# [SCI] Semiconductor Physics

**Semiconductor Physics** is the quantum mechanical understanding of materials with electrical conductivities intermediate between metals and insulators, which can be precisely controlled by doping, electric fields, and temperature.

## Overview

Semiconductors have a band gap — a range of energies forbidden to electrons. At room temperature, thermal excitation promotes electrons across the gap, making conduction possible. Doping (adding impurity atoms with extra or missing electrons) creates n-type or p-type semiconductors. The p-n junction (Shockley, 1949) rectifies current; the bipolar transistor (Bardeen, Brattain, Shockley, 1947) amplifies it.

Silicon's native oxide (SiO₂) allows the MOSFET (1959), the basis of all modern microchips. Moore's Law — transistor density doubling every ~18 months — held from 1965 to ~2016, driving the digital revolution.

## Key Figures & Recognition

- **William Shockley** (1910–1989), **John Bardeen** (1908–1991), **Walter Brattain** (1902–1987): Transistor. **Nobel Prize 1956**.
- **Nick Holonyak Jr.** (1928–2022): LED (visible light), 1962.
- **Zhores Alferov** (1930–2019) & **Herbert Kroemer** (1928–): Semiconductor heterostructures. **Nobel Prize 2000**.

## Seminal Papers

- Bardeen, J. & Brattain, W. "The Transistor, A Semi-Conductor Triode." *Phys. Rev.* 74 (1948).
- [Shockley, W. "A Unipolar 'Field-Effect' Transistor." *Proc. IRE* 40 (1952)](https://doi.org/10.1109/JRPROC.1952.273964)

## What This Enables

- **[TECH] Transistor** — The p-n junction and field-effect are direct applications of semiconductor band theory to active device physics.
- **[TECH] Solar Cells (Photovoltaics)** — The photovoltaic effect — photons generating electron-hole pairs across a semiconductor junction — requires semiconductor physics.
- **[TECH] Semiconductor Lasers & LEDs** — Stimulated emission in quantum-well heterostructures requires understanding of semiconductor band alignment and confinement.
- **[TECH] Electric Vehicles (EVs)** — Power electronics (SiC/GaN inverters, DC-DC converters, battery management ICs) are semiconductor devices.
- **[TECH] Electric Motors & Power Electronics** — IGBT and SiC MOSFET power switches in variable-frequency drives are semiconductor devices enabling precise motor control.
- **[TECH] Battery Technology** — Solid-state electrolytes, silicon anodes, and battery management system ICs are semiconductor-based battery advances.

## Discovery Character
⏎
**Surprise level**: High — That a piece of germanium at room temperature could amplify electrical signals — replacing a hot, fragile, power-hungry vacuum tube — was stunning in retrospect, though it followed logically from band theory. The transistor effect itself was discovered by an unexpected mechanism.
⏎
**Mode**: Serendipitous discovery within systematic research. Bardeen and Brattain were investigating semiconductor surface states with a field-effect device; what they observed on 16 December 1947 was minority carrier injection — a different and more powerful phenomenon. Shockley, who was away, reanalysed the result and devised the bipolar junction transistor. The planned experiment led to an unplanned discovery that was better than what they planned.
⏎
# Parents

* [SCI] Theory of Metals
* [TECH] Chemical Industry
* [SCI] Quantum Mechanics
* [SCI] Theory of Metals