2, Grupo de Desarrollo de Materiales y Estudios Ambientales, Departamento de Desarrollo Tecnológico, CURE, Universidad de la República, Rocha, Rocha, Uruguay
BiSI is a ternary semiconductor which can be employed in X and gamma ray detection at room temperature due to the following properties: band gap of 1.57eV, density of 6.4g/cm3, and absorption coefficient for 60keV radiation of 5.6cm2/g. This work deals with the synthesis mechanism of BiSI nanorods by the solvothermal method, followed by the study of the fabrication conditions to obtain BiSI pellets, and finally it determines the response to ionizing radiation of prototype detectors built with the pellets. The solvothermal synthesis uses Bi2S3 and I2 as precursors, 180°C temperature, and 20 h reaction time. The media used was either H2O or ethylene glycol (EG). The pellets were fabricated using the synthesized BiSI, varying the applied pressure and heat treatment (HT) conditions. Prototype detectors were built with the pellets by evaporating Au as contacts and attaching Pt wires with Aquadag and encapsulating them with acrylic. X-ray diffraction was used to identify the products phase and study the preferred orientation of the nanorods in the pellets. The morphology and size of the BiSI nanorods were studied under a transmission electron microscope, while the micro structural properties of the pellets were studied by scanning electron microscopy. For the detectors the dark current density (jo) and response to different doses of a 241Am source were studied with j-V curves with forward biasing. The electrical properties were related to the microstructure of the pellets. The solvothermal method yielded pure crystalline BiSI when EG was the medium, while with H2O remnant Bi2S3 was found. The decreasing of reaction times proved that Bi2S3 is not dissolved either in EG nor H2O, indicating that Bi2S3 works as a self-sacrificing template in the formation of BiSI. Furthermore, the Bi2S3 employed has a nanorod morphology, and in both cases BiSI grew in nanorod shape, although for BiSI with EG, amorphous carbon particles were also observed. The pressure seems to induce a preferred orientation of the nanorods within the pellet, but no difference was observed between the fabrication conditions. Alternatively, HT of pellets produced a change in morphology only for BiSI with EG. The jo measured for BiSI with H2O was in the order of mA, and no further characterizations were made, for these detectors were not suitable for room-temperature detection. For BiSI with EG, the jo of the HT pellet was one order of magnitude lower than for the pellets without it, and its response to the 241Am source, linear, with a signal to noise ratio of 7 for 20V. Finally, resistivities were calculated, and the best value obtained was in the order of 1011Ω-cm for HT sample. While carbon particles appeared to be a disadvantage for detector performance, they lowered jo, allowing for ionizing radiaton detection at room temperature. Further work is to be conducted to orient nanorods parallel to the electric field, which would improve charge carrier transport and hence detector performance.