Hydrogen Selenide
Properties
| State | Gas at room temperature |
| Color | Colorless |
| Solubility | Moderately soluble in water (weak acid, H2Se); very soluble in ethanol |
| Melting Point | -65.7 °C |
| Boiling Point | -41.3 °C |
About Hydrogen Selenide
Hydrogen selenide is the heavier, nastier cousin of H2S — a colorless gas that bends with a tiny H–Se–H angle of about 91°, almost a right angle, because the bonding orbitals on selenium have very little s-character. It's a slightly stronger acid than H2S (pKa1 = 3.89) and oxidizes in moist air to deposit red elemental selenium on whatever surface the leak happened to touch, which is sometimes the first hint that a cylinder isn't tight. The chemistry that matters in practice is selenization: in CIGS thin-film photovoltaics, you deposit a Cu-In-Ga metal precursor stack on a back-contact-coated substrate and then anneal it at 500–600 °C under H2Se, which diffuses in, reacts with the metals, and converts the stack into the chalcopyrite Cu(In,Ga)Se2 absorber layer in a single step. H2Se is also the standard Se source for MOCVD doping of GaAs and InP wafers, and it's the gas-phase precursor behind colloidal CdSe and ZnSe quantum-dot syntheses when an anhydrous selenide source is required. None of this happens at the bench scale — the gas demands gas-cabinet infrastructure with continuous monitoring.
Where you'll encounter it
If you've ever worked in a III-V or thin-film PV fab, the H2Se line is the one with the loudest interlocks and the most paranoid scrubber — a 0.05 ppm PEL means the gas-cabinet leak detector trips before you'd ever smell the garlic. CIGS PV plants running selenization furnaces at 550 °C maintain continuous PH3-style electrochemical sensors at the cabinet exhaust, with auto-shutoff valves wired to trip if the line drifts above 30 ppb. MOCVD operators doping GaAs n-type with H2Se thread the cylinder through a vented enclosure with mass-flow controllers calibrated to deliver sub-sccm flows because a single SLM leak would IDLH the entire fab in minutes. Quantum-dot synthesis labs that prefer the anhydrous H2Se route over selenourea or TOPSe handle it inside a glovebox-coupled bubbler line, never on an open hood.
Common Uses
- Selenization gas for CIGS thin-film photovoltaic absorber layer formation
- n-type dopant source in MOCVD growth of GaAs and InP epitaxial wafers
- Anhydrous selenide source for colloidal CdSe and ZnSe quantum-dot synthesis
- Calibration standard for selenium-specific gas chromatography detectors
- Specialty reagent for delivering Se(-II) in moisture-sensitive organic synthesis
Safety Information
GHS: Flammable gas Cat 1, Acute Tox. inhalation Cat 1 (fatal), STOT-RE Cat 1 (blood, liver). Occupational exposure and immediately-dangerous-to-life limits are among the lowest assigned to any industrial gas. The garlic odor is detectable below those limits but olfactory fatigue sets in within minutes, so smell is useless as a leak indicator. Cylinder use requires a ventilated gas cabinet, continuous electrochemical monitoring with auto-shutoff, an emergency scrubber on the exhaust, and SCBA available within reach. Chronic exposure causes hemolytic anemia and liver injury; acute exposure is rapidly fatal via cytochrome-c oxidase inhibition.
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. We deliberately do not publish occupational exposure limits or other regulatory thresholds: those values are revised over time and differ between jurisdictions, so the only correct source is the current SDS and the regulations that apply where you work.