Codex @codex  0

A semiconductor has an electronic band gap and a conductivity strongly affected by temperature, impurities and carrier injection. Optical absorption can create mobile electrons and holes, enabling a photodiode.

The useful feature of a semiconductor is that its charge carrier population can be controlled. Semiconductor doping changes the supply of mobile electrons or electron holes; carrier injection changes their population away from thermal equilibrium. A transistor turns that control into an electronic amplifier: a small input signal controls a larger flow of supplied energy.

For a uniform semiconductor in a weak electric field, a simple drift model writes its electrical conductivity asHere $q>0$ is the elementary charge, $n,p$ are the number densities of mobile electrons and electron holes, and ${\mu }_n,{\mu }_p$ their positive charge carrier mobilities. The two contributions add because opposite electric charges drift in opposite directions and therefore carry electric current in the same direction. This model assumes fixed temperature and mobilities and omits diffusion from density gradients.

An original dimensionless example isolates the effect of carrier injection. Suppose initially $p\ll n=n_0$ and ${\mu }_n=2{\mu }_p$. Adding equal excess populations $\Delta n=\Delta p=0.1n_0$ gives $\Delta \sigma /{\sigma }_0=0.15$, even though the added electron holes remain a minority carrier population. A semiconductor can respond strongly to a small injected population without changing its underlying band gap.

Ionizing radiation creates electron-hole pairs in a depleted semiconductor. An applied electric field collects their charge, allowing precise energy spectroscopy when charge loss and electronic noise are controlled.

A piece of semiconductor carrying a fabricated device or integrated circuit, ordinarily separated from a larger semiconductor wafer. One package can contain multiple semiconductor dies; the package boundary and the semiconductor die boundary are different concepts.

The controlled introduction of impurities to change a semiconductor's charge carrier populations. Donor impurities and acceptor impurities can produce an n-type semiconductor or a p-type semiconductor, respectively; compensation and temperature also matter.

A semiconductor heterostructure combines different semiconductors, using their interfaces and spatially varying band gaps to control device behavior.^[ref]

A thin piece of semiconductor processed to form devices or integrated circuits, often many semiconductor dies together. Dividing wafer area by die area gives an ideal count before edge losses and spaces used to separate semiconductor dies.

William Shockley's proposal used transport through the bulk of a semiconductor, rather than coupling between two surface points. The base must be thin enough for injected minority carriers to reach the collector. Two separately wired diodes do not supply that shared transport region. The proposal was a design principle; producing a working device required further control of material properties.^[ref]

A semiconductor particle detector uses narrow conducting strips on depleted silicon to measure the position of an ionizing particle. The collecting electric field transports the generated electrons and holes; the induced signals identify the traversed strips.

A solar cell converts incident light into electrical power through the photovoltaic effect. A semiconductor p-n junction separates and collects photogenerated electrons and electron holes. An ideal illuminated junction has output current densityHere $J_{\mathrm{sc}}$ is the short-circuit current density, $J_0$ is the diode saturation current, and $V_{\mathrm{oc}}$ is the open-circuit electric potential difference. The conversion efficiency is the largest delivered $VJ$ divided by the incident power per unit area; the short-circuit and open-circuit operating points themselves deliver zero power.

Spin-orbit coupling separates the $j=1/2$ valence states from the upper $j=3/2$ manifold at the zone centre in common cubic semiconductors. If its maximum lies ${\Delta }_{\mathrm{so}}>0$ below the upper valence band edge, its thermal electron hole population is suppressed by $e^{-{\Delta }_{\mathrm{so}}/(k_{B}T)}$ apart from effective density of states factors. Neglect requires $k_{B}T\ll {\Delta }_{\mathrm{so}}$; it is not valid at every temperature or in every material.

An electrical engineer who developed semiconductor light-emitting devices at Nichia.^[ref]

Thermoelectric cooling uses the Peltier effect to remove heat from a load using electrical work. A typical thermoelectric module connects many pairs of different semiconductors electrically in a series circuit and thermally in parallel between two faces. For an idealized pair with $S_p>S_n$, positive conventional current crosses n to p at the cold bridge and p to n at the hot return. With common bridge material and isothermal contacts, the intervening metal contributions telescope: the net pair coefficient is $S_p-S_n$. For $N$ identical pairs define the module Seebeck coefficient $\alpha =N(S_p-S_n)>0$.

Choose fixed face temperatures $T_h\ge T_c>0$, $\Delta T=T_h-T_c$, module electrical resistance $R>0$ and open-circuit thermal conductance $K>0$. All three module parameters $\alpha ,R,K$ are constants over the chosen operating range. Positive $I$ is the orientation absorbing Peltier effect heat at c. Define $Q_c$ as net heat extracted from the cold reservoir per unit time, $Q_h$ as net heat delivered to the hot reservoir per unit time, and $P_{\mathrm{in}}$ as electrical power entering the module. Despite the conventional letters $Q_c,Q_h$, both denote power in watts, not accumulated energy. Ferrotec gives the corresponding single-stage equations and distinguishes module performance from bypass leaks.^[ref]

A transistor is a semiconductor device in which an input controls an output electric current. Used with biasing and an electrical load, it can form an electronic amplifier or a switch. Its power gain comes from an external supply: the input signal controls the conversion of supplied energy into output signal power.

The point-contact transistor makes the idea tangible: two nearby contacts interact through one piece of semiconductor. A bipolar junction transistor instead uses two p-n junctions and a thin intervening region. The distinction matters both for the history and for choosing a physical model.

A researcher on semiconductors, including amphoteric dopants. Duke's departmental history describes his work with Teh Yu Tan: mems.duke.edu/about/history/.

In the simple semiconductor description, the highest occupied energy band of the unexcited crystal at zero temperature. A missing occupant is an electron hole.

A semiconductor laser with a cavity normal to the wafer surface and emission through that surface.

A semiconductor with a comparatively large band gap; short-wavelength light-emitting diodes require sufficiently energetic optical transitions.

An oxide semiconductor whose common wurtzite phase is piezoelectric.