Electrochemical capacitance voltage measurements in highly doped silicon and silicon-germanium alloys

Abstract

The electrochemical capacitance voltage technique has been used on highly boron doped SiGe and Si layers. Although the boron concentration is constant over the space charge depth, the 1/C2 versus voltage curves are not linear. They indeed present a negative curvature. This can be explained by the existence of deep acceptors which ionise under a high electric field (large inverse voltage) and not at a low inverse voltage. The measured doping concentration in the electrochemical capacitance voltage increases strongly as the inverse voltage increases. Thanks to a comparison with the boron concentration measured by secondary ions mass spectrometry, we show that the relevant doping concentrations in device layers are obtained for small inverse voltage in agreement with the existence of deep acceptors. At the large inverse voltage, the measured doping can be more than twice larger than the boron concentration measured with a secondary ion mass spectroscopy.