Gallium arsenide is a direct-bandgap III-V semiconductor substrate that has become the default host material for solid-state quantum light sources, ultra-low-noise crystalline mirror coatings and ultra-clean two-dimensional electron gases, and the 2026 literature shows it functioning less as a novel material than as the reference platform on which precision quantum and photonic engineering is done.
Summary
Gallium arsenide (GaAs) is a compound semiconductor from the III-V family, grown as bulk crystals and, more relevantly here, as epitaxial layers by molecular beam epitaxy (MBE). Unlike silicon it has a direct bandgap, so it emits light efficiently; it also forms near-perfect lattice-matched heterostructures with aluminium gallium arsenide (AlGaAs) and can host indium gallium arsenide (InGaAs/InAs) inclusions. Those three properties generate almost all of its current research use: quantum dots that emit single or entangled photons, quantum wells and two-dimensional electron gases with very high carrier mobility, and epitaxial AlGaAs/GaAs multilayer stacks used as crystalline mirror coatings.
The parameters that decide whether GaAs wins in any given application are: growth control (facet dynamics, twin defects, selectivity of regrowth masks), emitter placement accuracy relative to a photonic cavity, extraction and fibre-coupling efficiency of the emitted photons, optical absorption at the wavelengths a system needs to use, and the refractive index mismatch when bonding III-V material onto silicon. Several 2026 papers are effectively attacks on one of these parameters: aspect-ratio-dependent etching to make free-standing circular Bragg gratings in a single step, AFM nano-oxidation lithography to place dots to within tens of nanometres, antimony-mediated facet engineering to suppress rotational twins in nanowires, and alternative dielectric masks for selective-area MBE.
GaAs is also the material against which theory and simulation are calibrated. It is described explicitly as a prototypical bulk semiconductor for coherent phonon experiments and used as the benchmark case for digital quantum simulation of optical absorption and gain spectra. That role, as the known-good reference, is itself evidence of maturity.
Evidence base
- 5 May 2026: a transportable ultraviolet clock laser using an ultra-stable cavity with crystalline AlGaAs/GaAs mirror coatings reached fractional frequency instability of about 2 x 10^-16, with acceleration sensitivity no greater than 4(2) x 10^-12 per ms^-2.
- 6 May 2026: AFM nano-oxidation lithography positioned GaAs quantum dots to 51(28) nm radial displacement inside free-standing asymmetric circular Bragg gratings, giving 245-fold photoluminescence enhancement and polarisation imbalance below 5 per cent.
- 5 May 2026: a single-step aspect-ratio-dependent etching process produced monolithic free-standing circular Bragg gratings without bottom reflectors, with FDTD predicting up to 68 per cent free-space extraction and 40 per cent lensed single-mode fibre coupling.
- 14 May 2026: a photon deterministically generated from an InAs/GaAs quantum emitter, mapped into Gottesman-Kitaev-Preskill code space, violated a Bell-like noncontextual hidden-variable inequality by 380 standard deviations.
- 24 June 2026: because AlGaAs/GaAs coatings planned for the A# gravitational-wave detector upgrade absorb the frequency-doubled 532 nm beam, a multi-wavelength stabilisation scheme using a 1596 nm auxiliary beam was proposed and demonstrated on a tabletop.
- 2 June 2026: in a survey of alternative selective-area MBE mask materials, Al2O3 showed promising selectivity within typical GaAs growth temperatures while HfO2 was highly non-selective up to 650 degrees C due to Ga adsorption.
- 16 June 2026: a DFT survey of zincblende III-V and II-VI semiconductors found AlSb, not GaAs, gave the largest visible-light shift-current response.
Open questions
- Do the free-standing circular Bragg grating designs actually deliver the simulated 68 per cent extraction and 40 per cent lensed-fibre coupling when measured, or does aspect-ratio-dependent etching introduce losses the FDTD model omits?
- Can AFM nano-oxidation positioning at 51(28) nm accuracy be parallelised to wafer-scale throughput, or does deterministic placement remain a one-device-at-a-time technique?
- Will AlGaAs/GaAs coatings survive into a deployed gravitational-wave detector upgrade, given that they force a redesign of arm-length stabilisation to avoid 532 nm absorption?
- Does the proposed epitaxial design for III-V-on-220 nm-silicon coupling work in fabricated devices, or does the (Al)GaAs refractive index keep quantum dot lasers off standard CMOS photonics lines?
Assessment drafted 2026-08-31 from up to 18 KB sources using the technology-scorecard framework; scores are a draft read pending review.