A surface state is an electronic state localized near a material boundary. Its occupation can store electric charge and change the near-surface electric potential, producing band bending.

Walter Houser Brattain's surface studies combined changes of contact potential under light, electrical conductivity, and transient response to distinguish surface effects from bulk properties. His Nobel lecture distinguishes fast and slow charge responses and warns that slow behavior can involve the surrounding gas rather than a simple electronic state.^[ref]

The less abundant mobile charge carrier species: electron holes in an n-type semiconductor, or electrons in a p-type semiconductor. A small equilibrium population does not imply an unimportant role in an operating transistor.

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 p-n junction joins regions of a semiconductor with opposite majority charge carriers: electrons on one side and electron holes on the other. It provides the junction modeled by the Shockley diode equation.

Near an unbiased p-n junction, diffusion leaves exposed ionized donor impurities and acceptor impurities. Their electric field opposes further majority-carrier transfer. At thermal equilibrium, drift and diffusion balance; there is no net electric current. Forward bias reduces the barrier to carrier injection; reverse bias enlarges it. A heavily doped tunnel diode adds a different transport route, quantum tunnelling, that the ordinary Shockley diode equation omits.

Electron-hole recombination that does not emit a photon; it competes with the radiative channel in a light-emitting diode.

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

A homojunction joins regions of the same semiconductor material with different semiconductor doping. Its bulk band gap is the same on both sides. This distinguishes the electrostatic band bending of a simple equilibrium p-n junction from the material-dependent band offsets possible in a heterojunction.

An intrinsic semiconductor has equilibrium mobile electron and electron hole densities set predominantly by thermal excitation across its band gap, rather than by semiconductor doping. In the nondegenerate regime, charge neutrality gives $n=p=n_i$.

The effective density of states of a parabolic semiconductor band is its density of states integrated against a thermal Boltzmann factor measured from its edge. For one spin-degenerate valley,These quantities have units of number per volume, unlike the energy-resolved density of states. In a nondegenerate semiconductor, $n=N_c{e}^{-(E_c-\mu )/(k_{B}T)}$ and $p=N_v{e}^{-(\mu -E_v)/(k_{B}T)}$; multiple equivalent valleys add their contributions.

A quantum dot confines electrons and electron holes in all three spatial directions, producing discrete energy levels. A semiconductor island surrounded by a larger-band gap material is one realization. Its optical excitation and electron-hole recombination depend on confinement, Coulomb interactions and electric-dipole selection rules.

Indium arsenide, InAs, is a III-V semiconductor. An InAs island in a larger-gap host can provide quantum confinement for electrons and electron holes. The optical transition energy of a strained, confined island is not simply the bulk material's band gap.

Indium antimonide is a narrow-gap semiconductor made of indium and antimony, with chemical formula $\mathrm{InSb}$. Its small band gap permits absorption of comparatively low-energy infrared photons, making it useful in infrared detection.

For an ideal interband threshold, $hc/\lambda$ must reach the gap; actual detector response also depends on optical coupling, carrier collection and temperature. Thermal excitation across a small band gap can supply unwanted carriers, so an operating detector's dark current is an essential measurement alongside quantum efficiency. ^[ref]

A liquid that produces particle scintillation when deposited energy excites its components. Photomultipliers can convert the emitted light into detector pulses.

A quantum computer is a physical device that performs controlled quantum computation and extracts an output through quantum measurement. A programmable quantum computer combines physical qubits, control hardware and classical processing that specifies operations and interprets repeated measurements.

David P. DiVincenzo organized the central physical requirements into five capabilities: scalable and characterized qubits; initialization in a known quantum state; sufficiently long relevant decoherence times compared with operation times; a universal set of quantum gates; and quantum measurement of selected qubits. These requirements connect an abstract quantum circuit with an experiment: knowing the intended gate sequence is useful only if the apparatus can initialize, control and read the encoded system accurately.^[ref]

The encoding can use different physical systems. Two selected internal levels of a trapped ion, for example, can represent the basis states of a qubit. The remaining levels and environmental couplings then become part of the physical control problem.

Ubiquitin is a small protein attached to other proteins in cellular sorting and regulation, including targeting many substrates to a proteasome.

A proteasome is a protein complex that carries out proteolysis; unlike a lysosome, it has no surrounding lipid bilayer.

Hemoglobin is an oxygen-binding protein; its oxygenation can supply a spectroscopic molecular oxygen readout, as in the early Hill reaction work.

A ribonucleoprotein is an association of RNA with proteins.

Nucleoplasmin is a nuclear protein used in the nuclear pore localization experiment.

Its targeting information helped establish that a protein sequence can direct selective nuclear accumulation. Nuclear localization can therefore be tested by comparing intact and altered targeting sequences rather than inferring transport from protein size alone. ^[ref]

An importin is a protein involved in selective import through a nuclear pore complex.

It recognizes suitable cargo directly or through adaptors and participates in passage through the selective pore environment. Directionality depends on the Ran nucleotide cycle and compartment-specific interactions rather than on a permanently one-way opening. ^[ref]