Mid-Wavelength Infrared Photo Response And Band Alignment For Sensitized Pbse Thin Films

PbSe thin films were deposited using the chemical bath deposition method and sensitized with iodine for enhanced IR photoconductivity. After sensitization, PbSe films showed a high photoresponse of 44.7% in terms of resistance change in the midinfrared wavelength range (3-5 mu m). To investigate the origin of high photoresponse in sensitized PbSe films, the bandgap, work function, and valence band maximum were measured by photoluminescence (PL) and X-ray photoelectron spectroscopy secondary cutoff and valence spectra. Infrared photoluminescence spectra showed a PbSe bandgap of 0.29 eV. Visible PL spectra showed a PbI2 bandgap of 2.41 eV. Work functions of as-grown PbSe and PbI2 in sensitized PbSe were determined to be 4.30 eV and 4.50 eV, respectively. An Ag/PbSe/Ag band diagram shows a measured barrier height of 0.25 eV at the PbSe/Ag interface due to Fermi level pinning. When the Ag/PbI2/PbSe/PbI2/Ag structure is biased and exposed to midwavelength infrared illumination, the electron flow is limited due to high barriers at the interfaces. Therefore, the only hole can flow after charge separation such that the electrical resistance of PbSe film is dramatically reduced. The measured bandgap, work function, and valence band maximum along with measured barrier height for metal contacts should help in providing the understanding of the charge transport mechanism in PbSe photoconductors.