| gallium arsenide | |
|---|---|
| Name | Gallium arsenide |
| Caption | Crystal of gallium arsenide |
| Category | III-V semiconductor |
| Crystal structure | Zincblende |
| Band gap | 1.424 eV (300 K) |
| Lattice constant | 5.653 Å |
| Applications | Optoelectronics, high-speed electronics, quantum devices |
gallium arsenide
Gallium arsenide is a binary III–V compound semiconductor composed of Gallium and Arsenic with the chemical formula GaAs. It is a direct-bandgap material central to Quantum Physics and quantum engineering because of its well-defined electronic band structure, strong light–matter interactions, and compatibility with epitaxial heterostructures used to realize low-dimensional quantum systems and devices.
Gallium arsenide crystallizes in the cubic zincblende lattice, isostructural with diamond-derived III–V semiconductors such as Indium phosphide and AlGaAs. The lattice constant (≈5.653 Å) enables lattice-matched growth on substrates including native GaAs and engineered templates used by groups at institutions like Bell Labs and IBM Research. The polar nature of the Ga–As bond leads to optical phonon modes observable by Raman spectroscopy and infrared spectroscopy; phonon dispersion plays a role in carrier relaxation and decoherence studied in solid-state physics and condensed matter physics.
GaAs has a direct conduction-band minimum at the Γ point, with a room-temperature band gap (~1.424 eV) that places interband optical transitions in the near-infrared, exploited by lasers and photodetectors. The band structure is described using k·p perturbation theory and ab initio methods such as DFT and GW approximation calculations by groups at universities like Stanford University and MIT. Spin–orbit coupling splits the valence band into heavy-hole, light-hole, and split-off bands; this splitting underpins selection rules for optical transitions and spin dynamics exploited in spintronics experiments at centers including Harvard University and the UCSB Materials Research Laboratory. GaAs heterostructures host two-dimensional electron gases (2DEGs) in AlGaAs/GaAs quantum wells, used to observe quantum Hall effects first measured in experiments at Columbia University and Bell Labs.
Carrier transport in GaAs is characterized by high electron mobility due to low effective mass and weak intervalley scattering compared to silicon. Typical room-temperature electron mobilities surpass those of silicon in comparable doping regimes, enabling high-frequency operation in devices such as heterojunction bipolar transistors developed by companies like Intel and Texas Instruments. Scattering mechanisms include acoustic and optical phonon scattering, ionized impurity scattering, alloy scattering in AlGaAs alloys, and interface roughness scattering in quantum wells; these processes determine relaxation times relevant to quantum coherence and decoherence studied in quantum transport experiments. Low-temperature mobility and mean free path measurements in modulation-doped structures were pioneered by research at Bell Labs and AT&T Laboratories.
GaAs exhibits strong excitonic resonances near the band edge due to Coulomb binding of electron–hole pairs; excitons in GaAs quantum wells and wires have been extensively studied by groups at Max Planck Institute for Solid State Research and CNRS. The direct gap produces efficient radiative recombination, underpinning diode lasers and light-emitting devices. Nonlinear optical properties such as second-harmonic generation and electro-optic effects derive from the noncentrosymmetric zincblende lattice and are exploited in frequency converters and modulators used in fiber-optic systems developed by companies like Nokia and Ericsson. Time-resolved photoluminescence and pump–probe spectroscopy performed at facilities like the SLAC National Accelerator Laboratory probe exciton dynamics, carrier relaxation, and many-body effects relevant to quantum optics.
GaAs is foundational for solid-state quantum devices: semiconductor lasers (including quantum-well lasers) were commercialized by firms such as Agilent Technologies and Sumitomo Electric. High-electron-mobility transistors (HEMTs) based on GaAs/AlGaAs heterostructures provide microwave amplification for radar and satellite communications. In quantum information, GaAs quantum dots fabricated by groups at University of New South Wales and University of Tokyo have been used to implement spin qubits, demonstrating coherent control, exchange gates, and entanglement; notable experimental platforms include lateral gated quantum dots and vertical quantum dot systems. Photodetectors and photomultipliers using GaAs and GaAsP alloys are integral to single-photon detection schemes employed in quantum optics experiments at institutions like NIST.
High-quality GaAs is grown by molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD), techniques developed and refined at laboratories such as Tokyo Institute of Technology and Weizmann Institute of Science. MBE enables atomically abrupt heterostructure interfaces for AlGaAs/GaAs quantum wells, superlattices, and two-dimensional systems. Nanostructures include self-assembled quantum dots (e.g., InGaAs/GaAs) investigated by groups at University of Cambridge and Ecole Polytechnique. Fabrication methods combine electron-beam lithography, etching, and epitaxial regrowth to realize single-electron transistors and hybrid devices integrating superconducting qubits and GaAs-based circuits for hybrid quantum architectures.
Intrinsic limitations include sensitivity to radiation damage, relatively high background defect concentrations when compared to ultra-pure silicon, and chemical instability of arsenic-terminated surfaces. Native defects (vacancies, antisites) and DX centers in doped alloys act as charge traps and recombination centers; these were characterized in studies at Bell Labs and Argonne National Laboratory. Surface states and Fermi-level pinning complicate contact formation and quantum device gating; passivation techniques using caps like Silicon nitride or sulphur treatments are standard in device processing. Mitigating decoherence from nuclear spins (Ga and As isotopes) has led teams at University of Basel and University of Sydney to explore isotopic purification, dynamical decoupling, and hybrid materials to extend coherence times for spin qubits.
Category:Semiconductors Category:III–V compounds