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Gallium(III) Oxide

Ga2O3 oxide
Molar Mass
187.443 g/mol
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Properties

StateSolid
ColorWhite to transparent (single crystal)
SolubilityInsoluble in water; slowly soluble in hot strong acids
Melting Point1900 °C

About Gallium(III) Oxide

Gallium(III) oxide (Ga2O3, 187.443 g/mol) is the current darling of the wide-bandgap power-electronics community. It crystallizes in five known polymorphs (α, β, γ, δ, ε), with the monoclinic β-Ga2O3 phase stable at all conditions below the melting point — and it is the β phase that is interesting. β-Ga2O3 has a direct bandgap of 4.8 eV, which puts its absorption edge at 260 nm in the deep ultraviolet and gives a Baliga figure of merit (the standard yardstick for power-transistor materials) about four times higher than 4H-SiC and ten times higher than GaN. The estimated breakdown field is roughly 8 MV/cm, three times that of GaN — meaning a Ga2O3 power transistor with the same blocking voltage can be made an order of magnitude thinner with correspondingly lower on-resistance and switching loss. The killer feature, though, is melt growth: β-Ga2O3 can be pulled from the melt by edge-defined film-fed growth (EFG, the same method used for sapphire ribbon) at 1820 °C, producing 4- to 6-inch single-crystal wafers at a fraction of the cost of SiC or GaN substrates, both of which require sublimation or HVPE growth at much higher cost per area. The downside is that Ga2O3 has very poor thermal conductivity (~0.13 W/cm·K, an order of magnitude below SiC) and no shallow p-type dopant has been found — both of which are open research problems. Beyond power devices, Ga2O3 is the leading solar-blind UV photodetector material, a transparent conducting oxide when Sn- or Si-doped, and a phosphor host for Eu and Mn activators in the 280-380 nm range.

Where you'll encounter it

If you have ever sintered a piezoelectric ceramic or a YAG laser rod, the boule grower probably keeps a stash of Ga2O3 around as a sintering aid — it acts as a flux that lowers the densification temperature without ending up in the final phase. In an arc-emission spectrometer, gallium is one of the easier indium-group elements to standardize because Ga2O3 is non-hygroscopic and weighs out cleanly. The current commercial drive is Novel Crystal Technology in Japan and Flosfia, both of whom are sampling β-Ga2O3 SBDs and MOSFETs to electric-vehicle and solar-inverter customers.

Common Uses

  • β-Ga2O3 Schottky barrier diodes and MOSFETs for 1.2-10 kV power switches
  • Solar-blind UV photodetectors at <280 nm for missile-plume and corona detection
  • Sn- or Si-doped transparent conducting oxide for deep-UV optoelectronics
  • Sintering aid in piezoceramic and YAG-laser-host bulk densification
  • Phosphor host for Eu²⁺ activator emitting in the deep-UV and blue range
  • Catalyst support for Pt and Pd in propane dehydrogenation to propylene
  • ICP-OES calibration standard for trace gallium quantification in semiconductors
  • Gas sensor active layer for CH4 and ozone detection at 600 °C operating temperature

Safety Information

GHS: Eye irritation (Cat 2A, H319), Skin irritation (Cat 2, H315). Low acute toxicity — oral LD50 in rats > 10 g/kg. OSHA PEL 15 mg/m3 (total dust) under the nuisance-dust rule; ACGIH has not assigned a specific TLV for gallium oxide. Powder handling requires a NIOSH-approved dust mask and HEPA-filtered local exhaust; sintering and wafer-grinding operations should be wet-process or vented. No fire hazard. The clinical exposure concern is gallium itself: Ga3+ mimics Fe3+ in transferrin binding, displacing iron and accumulating in bone and tumor tissue — this is the basis for Ga-67 and Ga-68 nuclear-medicine imaging, but the same pharmacokinetics make chronic occupational exposure undesirable. Standard semiconductor-fab industrial hygiene applies.

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.

Constituent Elements

Ga — Gallium O — Oxygen

Frequently Asked Questions

What is the molar mass of gallium(III) oxide?
Ga2O3 has a molar mass of 187.443 g/mol. The breakdown: 2 × Ga (2 × 69.723 = 139.446) + 3 × O (3 × 15.999 = 47.997). Density of the β polymorph is 5.95 g/cm³ — a useful number when calculating wafer mass for handling-fixture design, since Ga2O3 wafers are noticeably heavier than silicon for the same diameter and thickness.
Why is Ga2O3 attractive as a power semiconductor?
Two reasons. First, the bandgap is 4.8 eV — wider than SiC (3.3 eV) or GaN (3.4 eV) — and the estimated breakdown field is around 8 MV/cm, three times GaN. The Baliga figure of merit, which scales as ε·µ·E_breakdown³, comes out four times higher than SiC, meaning a Ga2O3 device with the same voltage rating can be roughly an order of magnitude thinner with lower on-resistance and switching loss. Second, β-Ga2O3 grows from the melt by EFG at 1820 °C, producing 4- to 6-inch wafers at substantially lower cost than SiC (sublimation growth) or bulk GaN (HVPE), neither of which can be melt-grown at all. The open problems are poor thermal conductivity (~0.13 W/cm·K) and no shallow p-type dopant — both active research areas.
What is solar-blind UV detection?
Earth's atmosphere absorbs essentially all solar UV below 280 nm (the ozone Hartley band cuts it off), so a detector that responds only to photons shorter than 280 nm sees a black sky during daylight. Anything UV-bright in that band — a missile plume, a corona discharge on a high-voltage line, a hydrogen flame, a forest fire — stands out against zero background. Ga2O3 has its absorption edge at 260 nm (4.8 eV bandgap), placing the entire detector responsivity squarely inside the solar-blind window without needing the optical filters that silicon UV detectors require. That makes Ga2O3 the natural material for missile-warning receivers, gas-flame sensors, and astronomy instruments looking at hot stellar continua.