The n-Bi2S3/p-PbS heterojunction for room temperature LPG sensors

Heterojunction between bi-layer structured nanocrystalline films has been developed towards the liquefied petroleum gas (LPG) sensor at room temperature (27 °C) without post annealing treatment. These films consists of n-type Bi2S3 layer on fluorine doped tin oxide (FTO) coated glass substrate followed by deposition of p-type PbS layer to form heterojunction. However, simple and versatile successive ionic layer adsorption and reaction (SILAR) technique have been employed at room temperature (27 °C) to deposit the films. This technique involves ions as basic building blocks instead of atoms and hence growth rate can be controlled at ionic level. The completion of device was made by use of ohmic contacts using small drop of silver paste over p-PbS layer as a front contact and FTO coated glass substrate as a back contact. The device was kept overnight in order to dry the paste to ensure good contact. The formed heterojunction is porous with high surface area which enables enough space to adsorb and de-adsorb gas molecules easily and shows the gas response of 71% under the exposure of 1000 ppm concentration of LPG with 170 s and 300 s response and recovery time, respectively along with long term stability.