PbSe mid-IR photoconductive thin films (part I): Phase analysis of the functional layer

We could show that after annealing the following layer structure had formed: a bottom layer of PbSe (1 μm) and a top layer of Pb-Se-O-I (400 nm), containing (i) a poly-crystalline and (ii) a nano-crystalline phase. The poly-crystalline phase was found to be a solid solution of Se and I and yielded an average Pb/I mole fraction ratio of 3.1 and Pb/Se of 3.9, respectively. It contained the largest iodine mole fraction of ∼20 at.% while the nano-crystalline phase yielded less iodine (<10 at.%). This proves the great efficiency of the reactive annealing for functionalizing the polycrystalline PbSe films. The d-spacings, the chemical composition and the plasmon energies of the phases were measured and bar code these phases. The quaternary Pb-Se-O-I phases in the top layer have large unit cells and d spacings exceeding 0.8 nm. The poly-crystalline phase yielded two sharp plasmon peaks at 17.2 eV and 23.8 eV, respectively. Therefore, it can be clearly distinguished from PbSe, which yields a plasmon energy of 15 eV and d spacings smaller than 0.353 nm.