Light enters the photodiode region which is not folded and causes the formation of electron-hole pairs. Under the action of the electric field, electrons migrate to the avalanche region. Here, the electric field causes an increase in their speed as far as the collision with the crystal lattice creates another electron hole pair. In turn, these electrons can collide with the crystal lattice to create more electron hole pairs. In this way, a single electron created by light in an area that cannot create more.
Lets Learn Why photodiode is heavily doped?
The avalanche photodiode has a number of differences from ordinary PIN diodes. The avalanche process means that an electron produced by light in an undoped area is multiplied several times by an avalanche process. As a result, photodiodes for landslides are much more sensitive. But it turned out that it was almost nonlinear and, because of the avalanche process, the generated signal was much louder than one of the p-i-n diodes.
The doping level in the semiconductors influences the resistance, the most doped layers having the lowest resistance. For some current values passing through the diode layer, it is actually a series of different resistors, generating different voltage values depending on the layers.
Cause of photodiode heavily doped
P-i-N photodiodes are usually used in various applications. It consists of a transparent transparent contact layer at the top of the non-applied absorbent layer and a highly treated n-layer contact layer at the bottom. A discrete photodiode is made on a conductive substrate, as shown in the figure, which facilitates the formation of n-type contacts and reduces the number of steps in the process. The upper contact is usually a metal ring contact which has low contact resistance and also allows light to be absorbed into the semiconductor. An alternative approach uses transparent conductors, such as indium tin oxide (ITO). The area of the active device is formed by carving the mesa or by implanting protons in the adjacent area, which makes it isolated. Add a dielectric layer around the active area to reduce the drainage flow and ensure low contact chip capacity.
Reason of photodiode heavily doped
This photodiode uses an intrinsic semiconductor layer (N-doped or sometimes slightly doped) between the P and N layers, which has the effect of reducing the PN junction capacitance and thereby increasing the maximum switching speed, especially for fiber optic communication. The relatively deep intrinsic layer also offers a greater volume of photon-electron / hole conversion. The photodiode PIN is used in photoconductive mode with reverse bias applications; the relationship between the amount of light received and the electric current produced is basically linear and also relatively stable in the normal temperature range.
PIN photodiode operation
The PIN photodiode consists of a region p and a region n separated by a very strong intrinsic layer. The intrinsic layer is placed between the p region and the n region to increase the width of the thinning zone. Semiconductors P and n are highly processed. Therefore, the p region and the n region of the PIN photodiode have a large number of charge carriers for carrying electrical energy.
However, this charge carrier will not carry electric current under reverse bias conditions. On the other hand, intrinsic semiconductors are uncontrolled semiconductor materials. As a result, the intrinsic region does not have a charge carrier to produce electricity. Under reverse bias conditions, the major freight carriers in region n and region p are excluded from the intersection.
As a result, the width of the depletion zone becomes very large. As a result, the majority carriers will not carry electric current under reverse bias conditions. However, the minority carriers will carry electricity because they have a repulsive force from the external electric field. In a PIN photodiode, the charge carrier produced in the depletion region carries most of the electricity. The charge carriers produced in the p or n region produce only a small electric current.
When light energy or photons are applied to the PIN diodes, most of the energy is observed by the intrinsic or exhausting regions due to the width of the hatch. As a result, a large number of electron pairs are produced. The free electrons produced in the intrinsic region move toward the n-part, while the holes produced in the intrinsic region move towards the p-section.
In Simple Word Why photodiode is heavily doped?
Electrons and holes are free to move from one area to another carrying electrical current. When electrons and free holes reach region n and region p, they are attracted to the positive and negative terminals of the battery.