| GaAs | |
|---|---|
| Name | Gallium arsenide |
| Caption | Crystal structure schematic |
| Category | III–V compound semiconductor |
| Band gap | 1.424 eV (300 K) |
| Lattice constant | 5.653 Å |
| Applications | Optoelectronics, high-frequency electronics, quantum devices |
GaAs
Gallium arsenide (GaAs) is a III–V compound semiconductor widely used in optoelectronics and high-speed electronics. In quantum physics, GaAs provides a clean, well-characterized platform for studying quantum confinement, low-dimensional systems, and coherent charge and spin dynamics, underpinning technologies from semiconductor lasers to solid-state qubits.
GaAs occupies a central role in experimental and applied Quantum Physics because of its direct band gap and high electron mobility, which enable clear observation of quantum phenomena such as two-dimensional electron gases (2DEGs), quantum wells, and excitonic effects. Institutions like Bell Labs, IBM Research, University of Cambridge, Massachusetts Institute of Technology, and Stanford University have used GaAs to advance semiconductor quantum theory and device demonstrations. GaAs-based platforms bridge condensed matter theory (e.g., Bloch theorem, Band theory of solids) and engineered quantum systems studied at facilities such as CERN and national laboratories including Sandia National Laboratories.
GaAs crystallizes in the cubic zinc blende structure with a lattice constant near 5.65 Å, producing a direct conduction-band minimum at the Γ point that simplifies optical transitions. Band-structure calculations often employ k·p perturbation theory and density functional theory methods developed by researchers like Walter Kohn and implemented in codes used at Argonne National Laboratory. The direct band gap (~1.42 eV at 300 K) contrasts with indirect-gap semiconductors and enables efficient radiative recombination exploited in laser and light-emitting diode devices. Alloying with AlAs to form AlGaAs permits band-offset engineering and formation of heterostructures essential for quantum wells and superlattices, concepts tied to pioneers such as Leo Esaki and Herbert Kroemer.
Charge carriers in GaAs exhibit low effective mass (electron effective mass me* ≈ 0.067 m0) and high electron mobility, leading to long mean free paths at cryogenic temperatures and enabling ballistic transport experiments at institutes like NIST and Max Planck Society. Effective mass concepts connect to effective mass theory and the envelope function approximation used to model carriers in heterostructures. Quantum confinement in GaAs/AlGaAs quantum wells, wires, and dots produces discrete energy levels exploited in studies of the quantum Hall effect and mesoscopic physics by researchers such as Klaus von Klitzing and R. B. Laughlin.
GaAs supports strong optical transitions and tightly bound excitons at low temperature; the excitonic Rydberg and binding energies are central to optical spectroscopy. Techniques like photoluminescence spectroscopy, absorption spectroscopy, and time-resolved spectroscopy probe exciton dynamics and coherence, pursued in groups at Bell Labs and University of California, Santa Barbara. Phenomena such as exciton-polaritons in microcavities and Bose–Einstein condensation analogues leverage GaAs microcavity structures developed by laboratories including EPFL and University of Cambridge’s Cavendish Laboratory. Optical nonlinearity and carrier recombination dynamics are important for devices and for experiments in cavity quantum electrodynamics (cQED).
GaAs is foundational to semiconductor lasers (e.g., vertical-cavity surface-emitting lasers, edge-emitting lasers) and high-efficiency photodetectors used in telecommunications standards such as DWDM. In quantum information, GaAs heterostructures host electron-spin qubits in gated quantum dots demonstrated by groups at University of New South Wales, Harvard University, and University of Cambridge. Spin coherence in GaAs is influenced by hyperfine interactions with nuclear spins (isotopes of gallium and arsenic), a subject addressed by techniques including dynamic nuclear polarization and isotopic engineering as practiced at Microsoft Quantum and academic labs. Superconducting-semiconductor hybrid devices and photon–electron interfaces leverage GaAs for single-photon detectors and optically active qubits, connecting with work in quantum optics and solid-state physics.
High-purity GaAs heterostructures are produced by techniques such as molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD), with leading equipment and process development by companies like Veeco Instruments and research centers at University of California, Santa Barbara. MBE-grown GaAs/AlGaAs heterojunctions form high-mobility 2DEGs used to observe the fractional quantum Hall effect and to fabricate gated quantum-dot qubits. Precise interface control enables quantum wells, superlattices, and modulation-doped structures, relying on process expertise from national labs and commercial foundries including IQE plc and Sumitomo Electric.
Despite excellent electronic and optical properties, GaAs has limitations: mechanical brittleness, chemical sensitivity, and the presence of nuclear spin-bearing isotopes that limit electron spin coherence relative to isotopically purified silicon. Thermal management and integration with silicon-based CMOS processes pose engineering challenges addressed through heterointegration efforts at companies like Intel and research programs within DARPA. Environmental and supply considerations for gallium and arsenic, and regulations governing arsenic handling, influence manufacturing stability and national technology policy. Nevertheless, GaAs remains critical for national infrastructure in communications, sensing, and quantum technology demonstrations that emphasize reliability and continuity.
Category:Semiconductor materials Category:III–V semiconductors Category:Quantum devices