Double Gate Bias Dependency of Low Temperature Conductivity of SiO2-Si-SiO2 Quantum Wells

The gate bias dependency of conductivity is examined in two Si quantum wells with well thickness tw = 7 nm and tw = 14 nm. The conductivity of the thinner device behaves smoothly whereas the thicker device shows strong non-monotonic features as a function of gate voltages. We show that a strong minimum in conductivity occurs close to the threshold of second sub-band. Another minimum is seen at high electron density at symmetric well potential. This feature is addressed to sub-band wave function delocalization in the quantization direction.