Abstract
The confinement of the electron gas in MOS structures fabricated on thin silicon on insulator (SOI) layers is studied with emphasis on the principle of volume inversion. Analytical solutions are proposed for the potential distribution across the film and energy quantization. It is found that the triangular potential well approximation, which holds in bulk Si MOS systems, is no longer valid in SOI. Instead, the potential becomes parabolic, and even rather flat for SOI films which are very thin (30 – 100 nm) and not intentionally doped (10 15 cm −3). The energy separation of the lowest subbands is extremely small so that the quantum effects can be ignored. This confirms that the minority carriers are absolutely free in the volume of the film, their distribution being totally governed by the Poisson equation and current conservation equation. The presence of the natural back gate in SOI-MOS structures makes possible not only the volume inversion or accumulation but also the transition from 3-D to 2-D systems.
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