Study On The Fabrication Of Germanium Materials By Wet Chemical Method

The fabrication of germanium materials including Ge nanocrystals and Ge thin films has attracted much more attention recently. In this work, stable germanate ion aqueous solution with high solid content was synthesized through interaction between hexagonal GeO2 powders and aqueous ammonia. A reducing agent NaBH4 was used to reduce GeO2 solute into nano crystalline Ge. Ge thin films were obtained by evaporating the hydrogenated Ge nano products. The morphologies, structures and growth mechanisms of these materials were investigated.The molar ratio of NaBrVGeO2 under which crystalline Ge products can be obtained is from 4 to 6. The reaction time and drying temperature are no less than 12 hours and 120°C, respectively. The best reaction conditions for synthesis of crystalline Ge products are as follows: The GeCh content of the germanate ion precursor is 3%, NaBH4/GeO2 molar ratio is 5, reaction time 24 hours and drying temperature 120°C. When the reaction time is 12 hours, the Ge nano samples consist of sphere-shape Ge nano particles (20-50nm). Worm-like crystallined Ge product was obtained as the reaction time remains 24 hours. The growth mechanism of the products follows Ostwald Ripening mechanism.Ge films could be prepared by evaporating hydrogenated Ge sol that was synthesized by interaction between NaBH4 and germanate ion aqueous solution. The films are composed of Ge nanoparticles with size of about 100 nm. The degree of crystallinity and thickness of the films increases with rising temperature. There is a sharp peak corresponding to crystalline Ge at about 300 cm-1 and an amorphous shoulder at 265-270 cm'1 in the Raman spectrum of the Ge film. The amorphous peak disappears gradually with increasing temperature, which is consistent with the XRD results. Photoluminescence (PL) peaks centralize at 693-835 nm. The strongest PL peak appears at 753 nm under excitation with 325 nm light. The observed Raman and PL are different from that of a single crystal Ge, which likely originates from the compressive strain in the crystal lattices. The Ge films are p-type and their hole densities are in the order of magnitude of 1023 cm-3 The average mobility of carrier is about 60 cm2.V...