Gallium phosphide (GaP) is a III-V compound semiconductor with an indirect bandgap of approximately 2.26 eV (direct gap ~2.78 eV), making it optically transparent across much of the near-infrared and visible spectrum. Its lattice constant (0.545 nm) is close enough to silicon that GaP-on-silicon epitaxy is feasible, a property that distinguishes it from most III-V materials and underpins a photonic integration route.
The material’s investment relevance comes primarily from nonlinear photonics. GaP has one of the largest second-order nonlinear coefficients (χ(2) ≈ 70 pm/V) among semiconductors compatible with silicon-wafer processing. In thin-film waveguide form (GaP-on-insulator, GaPoI) it enables efficient second-harmonic generation, optical parametric amplification, and entangled-photon-pair generation at telecom wavelengths — capabilities that silicon nitride (no χ(2)) and lithium niobate (high cost, foundry-immature) struggle to match simultaneously. This positions GaP as a substrate for on-chip nonlinear light sources and quantum photonic circuits.
Frontier
- Can GaP-on-insulator be integrated with standard CMOS at foundry scale without process contamination?
- Does the χ(2) advantage over silicon nitride translate to competitive link budgets in co-packaged optics at 1550 nm?
- At what device volume does wafer-bonded GaP/Si become cost-competitive with native InP platforms?