We provide first observation of the effect of spatially uniform temperature change, causing non-affine thermal strain, on the optical properties of amorphous Si_xGe_1-x (x = 0.85, 0.60 and 0.15) thin films. The thermal strain was introduced by 7 cycles of cooling from room temperature to 77 K. It led to a decrease of the transmission, increase of absorption and red shift in the absorption edge (darkening). This effect of cycling is similar to the effect of increasing the Ge content. Analysis of the XPS spectra has shown that a certain fraction of homopolar Ge-Ge bonds were broken and Si-Ge heteropolar bonds were formed with cooling cycles. These changes, as creation of extra defects in the amorphous structure, can cause darkening, similarly to photo-darkening induced by laser irradiation. The darkening via thermal strain is a suitable technique to tune the optical and structural properties of thin films for different applications.

我们首先观察到空间均匀温度变化导致非仿射热应变对非晶Si _x Ge _1-x（x = 0.85、0.60和0.15）薄膜。通过从室温到77 K的7个冷却循环引入热应变。它导致透射率降低，吸收率增加和吸收边缘的红移（变暗）。循环的这种作用类似于增加Ge含量的作用。XPS光谱分析表明，在冷却循环中，一定比例的同质Ge-Ge键断裂，形成Si-Ge异质键。这些变化，由于在非晶结构中产生了额外的缺陷，可能导致变暗，类似于激光照射引起的光暗化。通过热应变变暗是一种适合用于不同应用的薄膜光学和结构特性调整技术。