Photoluminescence Characteristics of Size-controlled Germanium Nanoparticles-Film

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Germanium nanoparticles were produced by the Flowing Gas Evaporation Method, where Ge was evaporated from the tungsten hot filament in a low He or Ar gas pressure with a high gas velocity. From the X-ray diffraction analysis of the systematically produced Ge-nanoparticles, the following results on crystal structure and the mean particle size were obtained. (1) Three kinds of structure of amorphous, diamond and tetragonal were formed depending on conditions of the gas pressure and the gas velocity. The amorphous Ge-nanoparticles were formed under the He gas conditions, that is, the pressure was below 0.3Torr and the velocity was over 20m/s. The most frequent formation of tetragonal Ge-nanoparticles was under the He conditions, where the gas pressure is from 1,0 to 2.0Torr and the gas velocity is from 0.3 to 20m/s, though the tetragonal structure was always found in the mixture with the diamond structure. Out of the He gas conditions mentioned above, Ge-nanoparticles with the ordinary diamond structure was formed. (2) The lattice parameters of the tetragonal structure was determined to be a = 0.538nm and c = 0.879nm from the X-ray diffraction measurement. These values are different from those of already observed in the high-pressure form. And also the c-parameter in the present case is smaller by about 3% than that of Ge-nanoparticles formed by the ordinary Gas Evaporation Technique. It is considered that the tetragonal structure formed in the present study is a new structure of germanium. (3) Photoluminescence measurements of both specimens of Ge-nanoparticles with diamond structure and with mixed structure of diamond and tetragonal showed the similar broad spectra in infrared region with the peak near 1550nm. The real peak may be in much longer wavelength, where it cannot be measured in the present setup because of the weakness of the detector.