| Gallium arsenide | |
|---|---|
| Name | Gallium arsenide |
| Category | III–V compound semiconductor |
| Formula | GaAs |
| Crystal system | Zincblende |
| Band gap | 1.42 eV (300 K) |
| Density | 5.32 g/cm³ |
| Molar mass | 144.64 g·mol⁻¹ |
Gallium arsenide
Gallium arsenide (GaAs) is a III–V compound semiconductor composed of gallium and arsenic. It is a direct-bandgap material with high electron mobility and strong light–matter interaction, making it central to experimental and applied work in quantum physics, solid-state physics, and quantum device engineering. GaAs underpins many quantum electronic and optoelectronic platforms used to study low-dimensional carriers, coherent transport, and quantum confinement.
GaAs occupies a foundational role in the development of quantum electronics and mesoscopic physics. Laboratories such as Bell Labs, IBM Research, and university groups at MIT, Stanford University, and University of Cambridge used GaAs heterostructures to realize the quantum Hall effect and two-dimensional electron gas (2DEG) systems that enabled precise studies of electron correlations and topological states. GaAs is a preferred host for experiments on quantum wells, quantum dots, spin qubits, and single-photon emitters because of its well-characterized material properties and compatibility with molecular beam epitaxy (MBE) and metal–organic chemical vapor deposition (MOCVD). Industrial and research efforts from companies such as Intel and Nokia historically leveraged GaAs for high-frequency electronics and optoelectronics.
GaAs crystallizes in the zincblende lattice (space group F-43m) with strong ionic-covalent bonding between gallium and arsenic atoms. Its direct band gap at the Γ point (~1.42 eV at 300 K) yields efficient radiative recombination, described quantitatively by band-structure methods including k·p perturbation theory, density functional theory, and empirical pseudopotential calculations. Spin–orbit coupling splits the valence bands into heavy-hole, light-hole, and split-off bands, which influence optical selection rules and spin dynamics used in spintronics. The effective masses and dielectric screening in GaAs are key parameters for semiconductor Bloch equations and many-body treatments such as the GW approximation and the Bethe–Salpeter equation for excitonic binding energies.
High electron mobility and low effective mass enable ballistic and mesoscopic transport over micron scales at low temperature. GaAs/AlGaAs modulation-doped heterostructures produce high-mobility 2DEGs exploited to observe the integer and fractional quantum Hall effect, edge-channel transport, and Coulomb blockade in quantum point contacts and quantum dots. Quantum transport in GaAs is modeled using Landauer–Büttiker formalism, non-equilibrium Green's functions, and semiclassical Boltzmann approaches for scattering by phonons, impurities, and interface roughness. Time-resolved transport and terahertz spectroscopy probe carrier scattering, hot-electron relaxation, and nonequilibrium dynamics relevant to quantum-coherent devices and quantum information experiments.
As a direct-gap semiconductor with sizable exciton binding (~4.2 meV in bulk), GaAs exhibits strong optical absorption and emission suited to lasers and single-photon sources. Excitons, trions, and biexcitons in GaAs nanostructures are analyzed with semiconductor quantum optics and many-body theory. Nonlinear optical phenomena such as two-photon absorption, four-wave mixing, and optical Stark effects are routinely studied in GaAs using ultrafast pump–probe and coherent spectroscopy techniques pioneered at institutions like Max Planck Institute for Quantum Optics and FOM Institute AMOLF. Cavity quantum electrodynamics experiments couple GaAs quantum dots to microcavities and photonic crystal resonators to study strong coupling and Purcell enhancement.
GaAs is the material of choice for a range of quantum and high-speed devices: quantum wells (QWs) for band-structure engineering, self-assembled and lithographically defined quantum dots (QDs) as spin and photonic qubits, high-electron-mobility transistors (HEMTs) for microwave and millimeter-wave electronics, and diode lasers and vertical-cavity surface-emitting lasers (VCSELs) for coherent light sources. QW and QD platforms enable demonstration of Rabi oscillations, coherent population trapping, and electrically gated spin control. Integration with superconducting circuits and hybrid systems connects GaAs-based devices to efforts in quantum computing and quantum communication protocols.
High-purity GaAs is synthesized by methods such as liquid-encapsulated Czochralski and vertical gradient freeze growth for bulk substrates. Atomically precise layers and heterostructures are produced by MBE and MOCVD, allowing controlled alloying with aluminum to form AlGaAs barriers and modulation doping layers. Nanofabrication techniques—electron-beam lithography, reactive-ion etching, and focused-ion-beam processing—create gates, quantum point contacts, and photonic nanostructures. Cleanroom facilities at national labs and universities support process flows for heterointegration and coupling to superconducting resonators for hybrid quantum systems.
Point defects (vacancies, antisites), dislocations, and interface roughness act as charge traps and scattering centers that limit mobility and coherence. Unintentional background doping and residual impurities influence carrier density and spin relaxation via mechanisms such as the D'yakonov–Perel' and Elliot–Yafet processes. Nuclear spins of Ga and As isotopes cause hyperfine interactions that decohere electron spin qubits; strategies to mitigate these effects include isotopic purification, dynamical decoupling, and electrical control of spin–orbit coupling. Material characterization by deep-level transient spectroscopy, transmission electron microscopy, and secondary-ion mass spectrometry guides improvements in coherence for quantum applications.
Category:Semiconductor materials Category:III–V semiconductors Category:Quantum electronics