What is depletion approximation?

Depletion approximation: An idealization of the actual charge distribution in the depletion region that originates from the fact that the majority carriers have been removed. We say this region is “depleted” of majority carriers. It facilitates the use of Poisson’s equation because we can obtain a closed-form solution.

What is pn junction theory?

A PN-junction is formed when an N-type material is fused together with a P-type material creating a semiconductor diode.

Why does band bending occurs?

Band bending occurs when an electric field is applied to a semiconductor. When there isn’t an electric field being applied, the energy bands are not a function of position. Therefore, when an electric field is applied, energy is being supplied to the carriers in the material.

What are the assumptions of the depletion approximation?

Assumptions are: Depletion approximation: the electric field is confined to the junction region and there is no electric field in the quasi-neutral regions. No free carriers (n(x), p(x) = 0 ) in depletion region. 1 q d J n d x = ( U − G ) = 0 . This means that Jn is constant across the depletion region.

Is the abrupt depletion approximation more accurate under zero bias forward bias or reverse bias?

It is shown that the depletion approximation is accurate when reverse bias is applied and not accurate at forward or at zero bias condition. Besides, at larger doping concentration the accuracy is increased.

How do you calculate depletion region?

No free carriers (n(x), p(x) = 0 ) in depletion region. 1 q d J n d x = ( U − G ) = 0 . This means that Jn is constant across the depletion region. Similarly, Jp is also constant across the depletion region.

How depletion layer is formed?

The depletion region is caused by the diffusion of charges. Because of the concentration gradient holes diffuse from p-side to the n-side across the junction while electrons diffuse from the n-side to the p-side. The holes and the electrons diffusing towards each other combine near the junction.

What is an abrupt pn junction?

An abrupt junction is by definition a junction in which the doping type changes over a very small distance compared to the spatial extent of the depletion region (see below.) Figure EC1 : Donor and acceptor density profiles in an abrupt PN junction.

What is the diode theory?

• A diode is a device that acts like a conductor since. it allows current to pass in one direction (known as FORWARD BIASING) and it acts as an insulator since it blocks current passing in the opposite direction (known as REVERSE BIASING).

Why does energy band bend under an applied electric field?

An electric field develops from the metal to the semiconductor which drives the electrons towards the metal. By moving closer to the metal the electron could thus lower its potential energy. The result is that the semiconductor energy band bends downwards towards the metal surface.

What is the energy band diagram?

The energy band diagram of semiconductor is shown where the conduction band is empty and the valence band is completely filled but the forbidden gap between the two bands is very small that is about 1eV. For Germanium, the forbidden gap is 0.72eV and for Silicon, it is 1.1eV.