The difference between microstructures and optical properties of Pb_(1-x)Ge_xTe thin films evaporated using electron beam and resistance heating respectively

摘要

Lead germanium telluride (Pb_(1-x)Ge_xTe), a pseudo-binary alloy of IV-VI narrow gap semiconductors PbTe and GeTe, is considered a potential mechanically robust high-index coating material. Pb_(1-x)Ge_xTe thin films were evaporated on silicon substrates from the ingots of single crystals using electron beam and resistance heating, respectively. The surface topographies and compositions of thin-films were characterized by using scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX); the transmission spectra in a spectral range of 2.5～12 μm were also examined. Thin films demonstrated columnar microstructure; moreover, those evaporated using e-beam heating have much larger granular dimensions, in comparison with those using resistance heating. The measurement of transmittance reveals the advantage of perfect stoichiometry in e-beam evaporated thin films fails to improve optical properties. It can be deduced the scattering from the larger grains may impair the optical transparency. It can be concluded that electron beam evaporation is an optimum deposition choice.