| Ⅳ-Ⅵsemiconductors PbX(X=S, Se, and Te) exhibit unique intrinsic characteristics, such as narrow and direct band gap (-0.3 eV at room temperature), symmetric band structure, and low Auger recombination rates resulting from the absence of a degenerate heavy hole band, etc. which make them as potential candidates for applications in mid-infrared (3-30μm) sensors and diode lasers. Moreover, these materials are characterized by high carrier mobilities, high dielectric constants, a positive temperature coefficient of the band gaps, as well as a negative pressure dependence of the band gap and the band extrema at the L point of the Brillouin zone (BZ) in contrast to conventionalⅢ-ⅤandⅡ-Ⅵsemiconductors, which will justify further experimental and theoretical investigation for the optical transition and optoelectronic devices application ofⅣ-Ⅵsemiconductors.AsⅣ-Ⅵsemiconductors devices are based on film structure, fabrication ofⅣ-Ⅵmaterials based devices with better performance will strongly depend on the knowledge of the film surface and the metal/semiconductor interface. Therefore, deep understanding of the nature of the interfaces involved in these devices, especially the behavior of metal overlayers onⅣ-Ⅵsemiconductor substrates will make further promotion to the field ofⅣ-Ⅵmaterials based devices. Based on the fundamental issues addressed onⅣ-Ⅵsemiconductors, in this thesis, we concentrated on the growth behavior ofⅣ-Ⅵsemiconductors on the BaF2(111) surfaces, and the interface behavior betweenⅣ-Ⅵsemiconductors and metals.First, the epitaxial growth of PbSe thin film on BaF2(111) is studied by means of scanning tunneling microscopy (STM). The results showed that PbSe thin films grow under the step-flow mode, the structures and morphologies of which depend crucially on Pb-to-Se atomic ratio in the growth process. For the PbSe film grown with an atomic ratio of Pb/Se≈1, the morphologies are dominated by smooth spirals. For the PbSe film grown with a higher Pb-to-Se atomic ratio (Pb/Se=1.01), besides some spirals structures, the V-defects appear in the film, which can be attributed to excessive Pb atoms congregating in the dislocation core area and relatively slow growth rate of (100) facets.The nature of metal/semiconductor interface has strong effect on the carrier-injection efficiency and the performance of IV-VI semiconductor based devices. We further performed investigations on the formation of Ag/PbTe(111) interface by using photoemission spectroscopy. The results showed that the Fermi level of the clean PbTe(111) surface is almost pinned at the conduction band minimum (CBM), i.e., at 0.02 eV below CBM. Upon initial Ag deposition, downward band bending (0.13 eV) at the Ag/PbTe(111) interface is detected. The photoemission spectroscopy results, together with ab-initio calculation, indicate that both Te and Pb outdiffuse to the outmost surface, and a single Te-terminated Pb-Te bilayer is formed over Ag film on PbTe(111). This phenomenon of the substrate atoms out-diffusion makes the metal/Ⅳ-Ⅵsemiconductor system highly unusual and very interesting. And also the present results will surely give us a deep understanding of the formation mechanism of the metal/Ⅳ-Ⅵsemiconductor interface.Recently the properties of magnetic thin films on semiconductor substrates have attracted much attention due to their potentialities for spintronic applications as spin injectors and spin analyzers for polarized currents into semiconductors. Using in situ scanning tunneling microscopy (STM) and X-ray photoemission spectroscopy, we carried out investigations of Mn growth on PbTe(111). The results showed that, the growth of Mn on PbTe(111) can be summarized as two steps:The first step is related to the substitutional interaction between deposited Mn and the substrate Pb atoms, i.e., at the initial deppsition of Mn, part of Mn adatoms substitute Pb atoms on the PbTe(111) surface, forming a (√3×√3)R30°MnTe islands, and part of Mn adatoms, together with the replaced Pb atoms, nucleate at the boundaries of the MnTe islands, forming the bright islands (loops) around the MnTe islands, and finally form regular 3D Pb capped Mn islands(10-27 nm) upon further Mn deposition. The second step is further Mn growth on the surface Pb atoms completely substituted surface. At this stage, the deposited Mn either cooperates into the 3D Pb capped Mn islands, and promotes the upright growth of the 3D Pb capped Mn islands, or nucleates and growths on the MnTe superstructure area. These results will promote a better understanding of formation of magnetic metal/Ⅳ-Ⅵ semiconductor interface and the related properties.
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