Germane

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.

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Synthesis

Many methods are known for the industrial manufacture of germane.^[1] 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 contacting a germanium-containing compound such as elemental germanium, germanium tetrachloride, germanium oxide, germanide with a reducing agent such as sodium borohydride, potassium borohydride, lithium borohydride, lithium aluminum hydride, sodium aluminum 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.^[2]

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.

Occurrence

Germane has been detected in the atmosphere of Jupiter.^[3]

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.^[4] 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.^[5]

Safety

Germane is flammable, potentially pyrophoric, and toxic.

References

1. ^ US Patent 7,087,102 (2006)
2. ^ Girolami, G. S.; Rauchfuss, T. B. and Angelici, R. J., Synthesis and Technique in Inorganic Chemistry, University Science Books: Mill Valley, CA, 1999.
3. ^ Kunde, V.; Hanel, R.; Maguire, W.; Gautier, D.; Baluteau, J. P.; Marten, A.; Chedin, A.; Husson, N.; Scott, N. (1982). "The tropospheric gas composition of Jupiter's north equatorial belt /NH₃, PH₃, CH₃D, GeH₄, H₂O/ and the Jovian D/H isotopic ratio". Astrophysical J. 263: 443-467. doi:10.1086/160516.
4. ^ Venkatasubramanian, R.; Pickett, R. T.; Timmons, M. L. (1989). "Epitaxy of germanium using germane in the presence of tetramethylgermanium". Journal of Applied Physics 66: 5662-5664. doi:10.1063/1.343633.
5. ^ E. Woelk, D. V. Shenai-Khatkhate, R. L. DiCarlo, Jr., A. Amamchyan, M. B. Power, B. Lamare, G. Beaudoin, I. Sagnes (2006). "Designing Novel Organogermanium MOVPE Precursors for High-purity Germanium Films". Journal of Crystal Growth 287 (2): 684-687. doi:10.1016/j.jcrysgro.2005.10.094.