| Lead sulfide(PbS) thin films, suitable for the application of NIR photoconductive detection, have good photosensitive properties in the NIR region (1～3μm) for their direct narrow gap. PbS detectors are widely used in infrared guidance, infrared detection, fire detection and other military and civilian areas for their high photosensitivity and ability to work at room temperature without refrigeration. In this paper, the main performance parameters of PbS detectors made of PbS thin films are discussed, and a practical prototype of PbS fire alarm is produced successfully.PbS thin films were deposited on glass substrates by chemical bath deposition (CBD) and sensitized at different temperatures in air. The best sensitization temperature has been found out by comparing the microstructure and photoconductive sensitivity of PbS thin films before and after sensitization. In the meantime, the reasons why the photoelectric properties were greatly improved after sensitization have been discussed by analyzing the composition of films. When photosensitive surface is 3mm×3mm, the films have the resistance R□of about 1M?, photoconductive sensitivity S of 100%, which means they are applicable for IR detectors.Photoconductivity spectrum tests of PbS detectors showed relative sensitivity had a peak of about 2200nm. Ageing treatment can be taken to improve their responsibilities, but relative sensitivities are almost unchanged. R～T characteristics showed that the best operating temperature was below 40℃for PbS detectors. The detectors can be operated properly even under strong impact of ambient temperature. In additional, blackbody responsibility R of PbS detectors is up to 7.69×102 V/W, and D* is up to 0.23×108 cm·Hz1/2·W-1(500K,400,10).A prototype of PbS fire alarm was produced by designing a signal processing circuit. It is responsive to flickering flame with a 3 cm height, and the detection range is up to 7m with an angle more than 160°. |
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