Carrier recombination velocities at the SiO2/Si interface investigated by a photo-thermal reflection microscopy

Photo-thermal reflection microscopy has been used for investigating semiconductor materials to evaluate carrier diffusivity, lifetime and surface recombination velocity. We developed this technique to obtain carrier recombination velocities at the interface between SiO2 oxide film and Si substrate. Two samples with different oxide film thickness of 92 and 45 nm were prepared. Since the oxide film layer does not absorb the pump and probe laser light, carrier recombination velocity at the SiO2/Si interface can be estimated. Curve fitting procedures with the theoretical prediction results in an estimation of the interface recombination velocity of 100 cm/s for thick oxide sample. When the sample was chemically etched, the recombination velocity increases to 2500 cm/s. The chemical etching results in the drastic increase of the recombination velocity. The etching solution may soak through the SiO2 oxide film layer and attack the Si surface during the chemical etching. Increase of the number of the interface traps induces the increase of the carrier recombination velocity at the interface. We, therefore, found that the present photo-thermal reflection (PTR) microscopy is a useful technique for investigating the carrier dynamics at SiO2/Si interface.