The effect of substrate on the

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The effect of substrate on the

Metal-oxide-semiconductor structure[ edit ] The traditional metal-oxide-semiconductor MOS structure is obtained by growing a layer of silicon dioxide SiO 2 on top of a silicon substrate and depositing a layer of metal or polycrystalline silicon the latter is commonly used. As the silicon dioxide is a dielectric material, its structure is equivalent to a planar capacitorwith one of the electrodes replaced by a semiconductor.

When a voltage is applied across a MOS structure, it modifies the distribution of charges in the semiconductor. Conventionally, the gate voltage at which the volume density of electrons in the inversion layer is the same as the volume density of holes in the body is called the threshold voltage.

When the voltage between transistor gate and source VGS exceeds the threshold voltage Vththe difference is known as overdrive voltage. This structure with p-type body is the basis of the n-type MOSFET, which requires the addition of n-type source and drain regions.

Let's consider a MOS capacitor where the silicon base is of p-type. If a positive voltage is applied at the gate, holes which are at the surface of the p-type substrate will be repelled by the electric field generated by the voltage applied.

The effect of substrate on the

At first, the holes will simply be repelled and what will remain on the surface will be immobile neutral atoms of the donor type, which creates a depletion region on the surface. Remember that a hole is simply an acceptor atom, i.

Boron, which has one less electron than Silicon and therefore contributes an overall positive charge. What actually happens is that because Boron has one less electron in its outer shell than Silicon, it will in fact attract one electron from a nearby Silicon atom, leaving that Silicon atom with a positive charge, and that is actually how the hole generation happens in this case.

When the voltage is applied then, these holes will be repelled by the electric field, leaving immobile and neutral donor atoms on its places, i.

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One might ask how can holes be repelled if they are actually non entities in themselves? The answer is that what really happens is not that a hole is repelled, but electrons are attracted by the positive field, and fill these holes, neutralizing the atom and creating a depletion region, where no charge carriers exist.

As the voltage at the gate increases, there will be a point when the depletion region disappears, and the surface will be converted from p-type into n-type, as electrons from the bulk area will start to get attracted by the larger electric field. This converts the surface from p-type into n-type, and this is known as inversion.

The voltage at which this conversion happens is known as the threshold voltage and is one of the key and most important parameters in a MOSFET. In the case of a p-type bulk, Inversion happens when the intrinsic energy level at the surface becomes smaller than the Fermi level at the surface.

One can see this from a band diagram. Remember that the Fermi level defines the type of semiconductor in discussion. If the Fermi level is equal to the Intrinsic level, the semiconductor is of intrinsic, or pure type. If the Fermi level lies closer to the conduction band valence band then the semiconductor type will be of n-type p-type.

Therefore, when the gate voltage is increased in a positive sense for the given examplethis will "bend" the intrinsic energy level band so that it will curve downwards towards the valence band. If the Fermi level lies closer to the valence band for p-typethere will be a point when the Intrinsic level will start to cross the Fermi level and when the voltage reaches the threshold voltage, the intrinsic level does cross the Fermi level, and that is what is known as inversion.

At that point, the surface of the semiconductor is inverted from p-type into n-type. Remember that as said above, if the Fermi level lies above the Intrinsic level, the semiconductor is of n-type, therefore at Inversion, when the Intrinsic level reaches and crosses the Fermi level which lies closer to the valence bandthe semiconductor type changes at the surface as dictated by the relative positions of the Fermi and Intrinsic energy levels.

Structure and channel formation[ edit ] See also: An applied gate voltage bends bands, depleting holes from surface left.

The charge inducing the bending is balanced by a layer of negative acceptor-ion charge right. A larger applied voltage further depletes holes but conduction band lowers enough in energy to populate a conducting channel C—V profile for a bulk MOSFET with different oxide thickness.

The leftmost part of the curve corresponds to accumulation.Enzymes Function and structure. Enzymes are very efficient catalysts for biochemical reactions.

They speed up reactions by providing an alternative reaction pathway of lower activation energy. The metal-oxide-semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is a type of field-effect transistor (FET), most commonly fabricated by the controlled oxidation of has an insulated gate, whose voltage determines the conductivity of the device.

This ability to change conductivity with the amount of applied voltage can be used for amplifying or switching electronic. Ariostea High-tech Collections of porcelain stoneware tiles marble,stone, wood and granite effect for floors and wall coverings. An organic field-effect transistor (OFET) is a field-effect transistor using an organic semiconductor in its channel.

OFETs can be prepared either by vacuum evaporation of small molecules, by solution-casting of polymers or small molecules, or by mechanical transfer of a peeled single-crystalline organic layer onto a substrate. These devices .

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The effect of electroplating parameters and substrate material on tin whisker formation.

Substrate | Gallery of Computation