蒸发方法对Pb1-xGexTe薄膜微结构与光学性质的影响

Difference Between Microstructures and Optical Properties of Pb1-xGexTe Thin Films Evaporated Using Different Deposition Methods

碲锗铅（Pb1-xGexTe）是IV-VI族窄禁带半导体材料PbTe与GeTe的赝二元合金固溶体，是一种具有优势且机械强度高的高折射率光学薄膜材料。采用电子束蒸发和电阻蒸发两种方法在硅基片沉积了Pb1-xGexTe薄膜，使用扫描电镜和能量散射x射线分析仪表征薄膜表面形貌和化学组分，测量了薄膜在2．5～12μm的透射谱。相对于电阻蒸发，分析表明电子束蒸发的膜层中Ge含量更接近于源材料中的Ge含量，薄膜具有较大的晶粒尺寸，同时也具有较高的折射率和消光系数。因此，电子束蒸发具有保持复杂半导体材料化学配比一致性的优势。这种化学配比一致性和大晶粒尺寸使电子束蒸发的薄膜具有较高的折射率，而大晶粒造成的散射影响了薄膜的光学透明度。

Lead germanium telluride （Pb1-xGexTe）, a pseudo-binary alloy of IV-VI narrow gap semiconductors PbTe and GeTe, is considered as a potential mechanically robust high-index coating material.Pb1-xGexTe thin films are 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 are characterized using scanning electron microscopy （SEM） and energy dispersive X-ray analysis （EDX）, and the transmission spectra in a spectral range from 2. 5 μm to 12 μm are also examined. Thin films demonstrates columnar microstructure. Moreover, those evaporated using electron beam heating have Ce content closer to one in source material, much larger granular dimensions, and higher refractive index and extinction coefficient in comparison with those using resistance heating. Accordingly, the electron beam evaporation has the advantage of keeping the complex semiconductor material stoichiometric. It can be concluded that the stoichiometric consistency and large granular size of the electron beam evaporation films have higher refractive index. It can be deduced the scattering from the larger grains may impair the optical transparency of the films.