Influence of thermal oxidation on the interfacial properties of ultrathin strained silicon layers

In this work we examine the influence of thermal oxidation on the electrical characteristics of ultra-thin strained silicon layers grown on relaxed Si0.78Ge0.22 substrates under moderate to high thermal budget conditions in N2O ambient at 800 °C. The results reveal the presence of a large density of interfacial traps which depends on the oxidation process. As long as the strained silicon layer remains between the growing oxide and the underlying Si0.78Ge0.22 layer, the density of interface traps increases with increasing oxidation time. When the oxidation process consumes the s-Si layer the interface state density undergoes a significant reduction of the order of 40%. This experimental evidence signifies that the strained silicon-Si0.78Ge0.22 interface is a major source of the measured interfacial defects. This situation can be detected only when the front SiO2-strained silicon interface and the rear strained silicon-Si0.78Ge0.22 interface are in close proximity, i.e. within a distance of 5 nm or less. Finally, the influence of the material quality deterioration-as a result of the thermal treatment-to the interfacial properties of the structure is discussed.