Semiconductors insulator interface

To obtain a relationship between the voltage VK applied to the metal and the surface potential Vv, we assume a continuity of the electric field at the insulator-semiconductor interface that implies... 

In the case of negative bias, the Fermi level moves closer to the valence band edge. Consequently, the concentration of the majority of carriers (holes) at die insulator-semiconductor interface becomes laiger than in the bulk. This corresponds to the accumulation regime. When a positive bias is applied to die metal, the... 

A constant bias potential is applied across the sensor in order to form a depletion layer at the insulator-semiconductor interface. The depth and capacitance of the depletion layer changes with the surface potential, which is a function of the ion concentration in the electrolytic solution. The variation of the capacitance is read out when the semiconductor substrate is illuminated with a modulated light and the generated photocurrent is measured by means of an external circuit. 

Note that this is a very simplified case. A liquid junction, dual-layer insulator, trapped charges in the insulator, surface states at the insulator/semiconductor interface, channel doping profile, and multiple connecting metals have been omitted, for the sake of simplicity. They would be present in all real devices and situations, but would not affect the thought analysis in any significant way. 

O. Engstrom and A. Aim, Energy concepts of insulator-semiconductor interface traps, J. Appl. Phys., 54(9) (1983) 5240-5244. 

Let us now turn to the thickness of the conducting channel. The concept of thickness is not that obvious, because the actual distribution of charge-carriers decreases continuously from the insulator-semiconductor interface to the semiconductor bulk, so one can more sensibly speak of an effective thickness. The distribution can be estimated by resolving Poisson s equation (Eq. 3) ... 

Let d be the thickness of a monolayer and n the total number of layers (that is, the thickness of the film divided by d). The layers are numbered starting from the insulator-semiconductor interface. To estimate the density n (per unit area) of charge-carriers in the ith layer we apply Gauss s law to a cylinder of unit cross section limited by the boundaries between the ith layer and each of its neighboring layers. For a long channel device, the electric field F is perpendicular to the film, and we have ... 

Fig. 1.9. Variation of the potential drop at the insulator-semiconductor interface as a function of gate voltage for two values of the insulator capacitance.

Major improvements have been achieved by modification of the insulator-semiconductor interface. Most devices are grown by vapor deposition on silicon oxide. Because of the different physical and chemical nature of both materials, their association may lead to highly disordered interfaces, thus leading to poor performance. Heating the substrate [27, 78, 79] and depositing at a low rate [30, 78]... 

A possible way to solve this technologically is by introducing a monolayer of molecular dipoles at the gate insulator—semiconductor interface, thereby giving the option to control the interface states and hence switch-on voltage. See for instance Kobayashi et al, Nature Materials,... 

In Eq. (14.16), the sign of the right hand side equals that of the applied bias. The total charge in tlie semiconductor, Q, is related to the electric field at the insulator-semiconductor interface, F, according to Gauss s law ... 

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