Of Pbs Thin Films And The Infrared Photosensitive Performance

Lead sulphide (PbS) is an important direct narrow gap semiconductor material with an approximate energy band gap of 0.4eV at 300K and a relatively large excitation Bohr radius of 18nm. These properties make Pbs very sensitive to infrared (IR) ray, so it's very suitable for infrared detection application. This material has also been used in many fields such as photoresistance, diode lasers, humidity and temperature sensor. IR detectors, made of polycrystalline lead sulfide (PbS) thin films are responsive in the near infrared region of 1-3 micron, is suitable for indoor fire alarm.The properties of PbS have been correlated with the growth conditions and the nature of substrates. The deposition processes include electrodeposition, microwave-heating and chemical bath deposition.(CBD). CBD method is presently attracting considerable attention, as it does not require sophisticated instrumentation, relatively inexpensive, easy to handle and convenient for large area deposition.In this paper, PbS films were prepared by chemical bath deposition method on ceramics, glass and silicon substrates with thiourea(SC(NH₂)₂), lead nitrate(Pb(NO₃)₂) and sodium hydroxide(NaOH). Through controlling the processing conditions such as the composition of deposition solution, deposition time and annealing temperature. X-ray diffraction studies show that the films are well crystallized according to the centered cubic structure, and new phase containing oxygen appears after heat treatment in a high temperature. The surface morphology is determined by scanning electron microscope measurements (SEM), which show that the films are accumulated by cubic grains approximately. The microstructure and optical properties of PbS thin film prepared by different thiourea concentration were measured, the results showed that with the rising of the thiourea concentration, the crystallite sizes of PbS thin films decreased, and the variety rate of the resistance increased. The electrical and optical properties of PbS films were measured in order to determine the optimal process for preparing PbS films. The results showed that the high-performance PbS films could be obtained on Si substrate under the conditions of lead nitrate concentration 0.175M, sodium hydroxide concentration 0.55M, thiourea concentration 0.175M, deposition time 60min, deposition temperature 30°C and annealing temperature 500°C.The Au film electrodes were deposited on PbS by vacuum evaporation, the PbS film was encapsulated into a transistor shell as infrared photosensitive resistance, the signal processing circuit was designed. The sample of infrared fire detector was prepared; the detector can make effective response to the candle fire with a distance of 3 meters.