Germane is the chemical compound with the formula GeH₄. It is the simplest germanium hydride and one of the most useful compounds of germanium. Like the related compounds silane and methane, germane is tetrahedral. It burns in air to produce GeO₂ and water.

Synthesis

Many methods are known for the industrial manufacture of germane. These processes can be categorized as (a) chemical reduction method, (b) an electrochemical reduction method, and (c) a plasma based method.

The chemical reduction method involves reacting a germanium-containing compound such as elemental germanium, germanium tetrachloride, or germanium dioxide with a reducing agent such as sodium borohydride, potassium borohydride, lithium borohydride, lithium aluminium hydride, sodium aluminium hydride, lithium hydride, sodium hydride, or magnesium hydride. The reaction can be carried out in either aqueous or in an organic solvent. On laboratory scale, germane can be prepared by the reaction of Ge(IV) compounds with hydride reagents. A typical synthesis involved the reaction of Na₂GeO₃ with sodium borohydride.

Na₂GeO₃ + NaBH₄ + H₂O → GeH₄ + 2 NaOH + NaBO₂

The electrochemical reduction method involves applying voltage to a germanium metal cathode immersed in an aqueous electrolyte solution and an anode counter-electrode composed of a metal such as molybdenum or cadmium. In this method, germane and hydrogen gases evolve from the cathode while the anode reacts to form solid molybdenum or cadmium oxides.

Lastly, the plasma synthesis method involves bombarding germanium metal with hydrogen atoms (H) that are generated using a high frequency plasma source to produce germane and digermane.

Reactions

In liquid ammonia GeH₄ is ionised forming NH₄⁺ and GeH₃⁻. With alkali metals in liquid ammonia GeH₄ reacts to give white crystalline MGeH₃ compounds. The potassium and rubidium compounds have the sodium chloride structure implying a free rotation of the GeH₃⁻ anion, the caesium compound, CsGeH₃ in contrast has the distorted sodium chloride structure of TlI.

Occurrence

Germane has been detected in the atmosphere of Jupiter.

Use in semiconductor industry

The gas decomposes near 600K to germanium and hydrogen. Because of its thermal lability, germane is used in the semiconductor industry for the epitaxial growth of germanium by MOVPE or chemical beam epitaxy. Organogermanium precursors (e.g. isobutylgermane, alkylgermanium trichlorides, and dimethylaminogermanium trichloride) have been examined as less hazardous liquid alternatives to germane for deposition of Ge-containing films by MOVPE.

Safety

Germane is flammable, potentially pyrophoric, and toxic.

References

External links

• PRAXAIR
• Airliquide
• pdf MSDS at MIT