Influence of a silicon cap on SiGe passivation by anodic oxidation

We applied electrochemical oxidation as a low thermal budget process for the passivation of thin SiGe epilayers on Si substrate and compared the results with those obtained on thermally oxidized layers. The use of a thin silicon cap on the SiGe layer reduces the electrochemical corrosion with dissolution of Ge during oxidation and leads to a higher amount of GeO2 in the oxidized SiGe layer than anodic oxidation without a Si cap. The protected SiGe layer shows a slight Ge enrichment at the interface which is different from the behavior of the non-protected SiGe layer. The highest Ge pile-up is achieved by the thermally oxidized samples where the oxide layer is formed by nearly pure SiO2. Using photoluminescence spectroscopy we showed that the passivation and quality of the interface is best if no Ge enrichment occurs. The results suggest that electrochemical oxidation of SiGe layers is preferable to high temperature processing.