Admittance studies of surface quantization in [100]-oriented Si metal-oxide-semiconductor field-effect transistors

The behavior of charge carriers in the inversion layer under surface-quantized conditions was observed by small-signal magnetoadmittance (Y) and manetoconductance (G) experiments on p-type (100) Si metal-oxide-semiconductor field-effect-transistor (MOSFET) structures. The two-dimensional character of the surface-quantized electron gas was further substantiated. The density of states was studied directly by the surface-capacitance technique. The dependence of Y on a number of variables was investigated, including (1) T≤4.22 ^∘{}K, (2) magnetic field (B≤12 T), (3) electric field excitation, (4) frequency, and (5) substrate doping (10¹⁹≤p≤2×10²⁰m³). Comparative studies of small-signal surface conductance and admittance were useful in establishing the advantages and limitations of each technique. It was observed that Y becomes frequency independent at frequencies below 500 Hz. Both the line shape and fine structure observed at Y at threshold are attributed to a bound-state band overlapping the conduction band resulting from surface-potential fluctuation. Circuit modeling of the MOSFET structures was found to be important in the interpretation of the admittance.