Methanol Pyrolysis-Mediated Reduction of GeO2 and Chemical Vapor Deposition of Polycrystalline Ge Films.

Methanol is a renewable, low-carbon chemical that can be obtained from biomass. GeO₂ is the main source for producing Ge, which is an important semiconductor. The current study aimed to investigate the reduction of GeO₂ and chemical vapor deposition of Ge using gaseous species generated by methanol pyrolysis. Mass measurement, X-ray diffraction and scanning electron microscopy techniques were used to determine the extent of the oxide reduction, and to characterize the products. CO and H₂ were predicted as the major reducing agents derived from the methanol pyrolysis at 1000 K to 1200 K, in agreement with the experimental measurement. It was found that the mass loss in GeO₂ increased to 85.5 pct as the reaction time and temperature were raised to 10 minutes and to 1200 K. The GeO₂ reduction was insignificant at 900 K, in contrast to the thermodynamic prediction, essentially owing to the sluggish reaction kinetics. At 1000 K, the significant reduction of GeO₂ to Ge, close to the thermodynamic equilibrium, was attained. At 1100 K to 1200 K, the experimental mass loss was more than the thermodynamics prediction. The discrepancy was explained by a mass-transport theory involving boundary layer in the gas phase over the powder bed. Ge films were deposited from the gaseous species generated upstream at 1200 K for 10 minutes on a Si (400) substrate held downstream in the reaction tube at 723 K to 923 K. Polycrystalline rough Ge thin films with pillar-like crystals were obtained when the substrate temperatures were 723 K and 823 K. At 923 K, a denser polycrystalline Ge film was grown probably owing to the enhanced Ge diffusion on the substrate surface. [ABSTRACT FROM AUTHOR]