Structural and compositional properties of the PbS-Si heterojunction

The physical and chemical structure of thin-film PbS deposited from chemical solution on monocrystalline Si substrate was studied by electron microscopy, x-ray diffraction, and Auger electron spectroscopy. The as-grown PbS has been found to consist of a uniform polycrystalline film. The crystallite size and orientation were found to depend on the orientation of the substrate and were observed to vary between 0.25 and 0.4 μm. Low-temperature treatment of the PbS film was found to be an effective method for revealing the film structure, without altering the grain size. A secondary PbS macrostructure consisting of isolated chainlike clusters was found to coexist with the thin film. The dimensions of the clusters were generally up to an order of magnitude larger (∼3–5 μm) than the thickness of the film (0.5 μm). The microstructure of the cluster was found to be similar to that of the film, consisting of crystallites of the same size. The chemical structure of the PbS film and of the PbS-Si interface was investigated by Auger electron spectroscopy in conjunction with argon ion sputtering. Chemical depth profiles indicate a PbS film of uniform composition. No major contaminants were observed in the bulk of the film. A peak in oxygen content was found to exist at the PbS-Si interface and at the surface of the PbS film. Heat treatment in air increased the oxygen peaks substantially and reduced the sulfur concentration at the film surface.