Indium Phosphide
Properties
| State | Solid (crystalline) |
| Color | Dark gray to black with metallic luster |
| Solubility | Insoluble in water and most acids; slowly soluble in concentrated HCl and HNO3 |
| Melting Point | 1062 °C |
About Indium Phosphide
Indium phosphide is the III-V semiconductor that quietly runs the fiber-optic internet. It crystallizes in the zinc-blende structure with In and P alternating on tetrahedrally coordinated sites, has a direct bandgap of 1.344 eV at 300 K (absorption edge at 925 nm), and — more importantly — its lattice parameter (5.869 Å) lets you grow ternary and quaternary alloys like InGaAs and InGaAsP that emit anywhere from 1100 to 1700 nm. That happens to span the two telecom transparency windows: 1310 nm (zero-dispersion in standard single-mode fiber) and 1550 nm (minimum attenuation in silica fiber, ~0.2 dB/km, where you also place EDFA amplifiers). Every long-haul optical fiber link, every datacenter top-of-rack 100/400G transceiver, every cellular fronthaul/backhaul radio, and every undersea cable repeater runs on InP-substrate distributed-feedback lasers and InGaAs/InP avalanche or PIN photodetectors. Beyond telecom, InP is the substrate of choice for the highest-speed heterojunction bipolar transistors — fT/fmax above 500 GHz — used in mm-wave radar, automotive 77 GHz sensing, and 6G research. The cost has stayed stubbornly high (4-inch InP wafers are roughly $1000 vs. $200 for GaAs and $50 for Si of the same size) because the InP melt has high P vapor pressure and the crystal is brittle, which limits boule diameter and yield.
Where you'll encounter it
If you've ever sent an email across the Atlantic, joined a video call, or pulled a Netflix stream — every photon along the way was generated by an InP-substrate DFB laser and detected by an InGaAs/InP photodiode somewhere in the network. In a transceiver fab the 4-inch InP wafers come out of MOCVD reactors with InGaAsP quaternary layers tuned to either 1310 nm (zero-dispersion) or 1550 nm (minimum attenuation), and the dicing yield drives the per-port cost of every 100G or 400G optic shipped to a hyperscaler. Researchers prototyping mm-wave 6G front-ends pick InP HBTs over SiGe specifically because the fT/fmax above 500 GHz is the only thing that gets you past 200 GHz carrier frequencies. Wet-etch any InP wafer in HCl/HNO3 and the PH3 monitor will trip — this is gas-cabinet chemistry.
Common Uses
- Substrate and active layer for 1310 nm and 1550 nm DFB telecom lasers
- InGaAs/InP PIN and avalanche photodetectors in optical-network receivers
- InP HBTs and HEMTs for mm-wave RF, automotive radar, and 6G research
- Mid-IR LEDs for non-dispersive infrared (NDIR) gas sensing of CO2 and methane
- Cd-free InP/ZnS quantum-dot emitters in QLED displays and biological imaging
Safety Information
GHS: Carc. 1B, STOT-RE 1 (respiratory tract), Aquatic Chronic 1. IARC Group 2A (probably carcinogenic to humans, based on rat inhalation studies showing lung tumors). OSHA PEL 0.1 mg/m³ as In; the carcinogen classification adds additional ALARA pressure on workplace exposure. Bulk wafers are not significantly hazardous to handle, but dicing, lapping, polishing, or chemical-mechanical planarization generates fine InP dust and PHx vapor that requires HEPA-filtered local exhaust and full respiratory PPE. Wet etching in HCl/HNO3 mixtures liberates phosphine traces — work in a fume hood with PH3 monitoring.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.