Piezoresistance in n-type silicon inversion layers at low temperatures

The magnitude of the subband splitting in inversion layers was investigated with piezoresistance measurements of n-type inversion channels on (100) and (110) silicon surfaces. Below 70 K the piezoresistance effect is no longer linear with stress and surface field. At high tensile and compressive stress two saturation regions occur corresponding to the magnitude of the subband splitting. The experimental results were compared with several models describing surface quantization. A self-consistent calculation shows the best agreement, whereas the triangular potential well model deviates more than 100%. For a (100) transverse configuration an anomalous behaviour was observed which is explained in terms of different relaxation times in the various subbands.