Chemical sensing properties of electrolyte/SiGe/SiO₂/Si structure

To investigate the surface properties of silicon germanium (SiGe) as a chemically sensitive membrane, SiGe layers deposited at Si₂H ₆ and GeH₄ ambience by low-pressure chemical-vapor-deposition (LPCVD) at 475 °C were prepared. First, the effect of ac measuring frequency on capacitance-voltage (C-V) curves obtained from a SiGe electrolyte-insulator-semiconductor (EIS) structure was studied. The pH sensitivity of SiGe-EIS structure was 59.8mV/pH, calculated from reference voltages in the pH range from 10 to 2. A voltage shift was observed in the same pH buffer solution for different measurement loops. To analyze the depth profile of a SiGe membrane, Auger electron spectroscopy (AES) was used. The formation of a native oxidation layer on the surface of SiGe was observed, and the layer had a thickness of 20 Å.