How does photodiode work

Thus, this kind of photodiode is frequently utilized in high bandwidth BW optical communication systems like fiber-optic links. Please refer to this link to know more about the Schottky diode. Each type of photodiode has its own benefits and drawbacks. The selection of this diode can be done based on the application. The different parameters to be considered while selecting photodiode mainly include noise, wavelength, reverse bias constraints, gain, etc. The performance parameters of photodiode include responsivity, quantum efficiency, transit time, or response time.

These diodes are widely used in applications where the detection of the presence of light, color, position, the intensity is required. The main features of these diodes include the following. The required materials to make a photodiode and the range of electromagnetic spectrum wavelength range includes the following. Because of their better bandgap, Si-based photodiodes produce lower noise than Ge-based photodiodes.

In this design, the formation of P-type material can be done from the diffusion of the P-type substrate which is lightly doped. On the substrate of N-type, the N-type epitaxial layer can be grown. The contacts are designed with metals to make two terminals like anode and cathode.

The designing of the non-active surface can be done with silicon dioxide SiO2. On an active surface, the light rays can strike over it whereas, on a non-active surface, the light rays cannot strike. The working principle of a photodiode is, when a photon of ample energy strikes the diode, it makes a couple of an electron-hole.

This mechanism is also called the inner photoelectric effect. If the absorption arises in the depletion region junction, then the carriers are removed from the junction by the inbuilt electric field of the depletion region. Therefore, holes in the region move toward the anode, and electrons move toward the cathode, and a photocurrent will be generated. The entire current through the diode is the sum of the absence of light and the photocurrent. So the absent current must be reduced to maximize the sensitivity of the device.

The operating modes of the photodiode include three modes, namely Photovoltaic mode, Photoconductive mode, an avalanche diode mode. Photovoltaic Mode: This mode is also known as zero-bias mode, in which a voltage is produced by the lightened photodiode.

Photoconductive Mode: The photodiode used in this photoconductive mode is more usually reverse biased. This mode is too fast and displays electronic noise. Avalanche Diode Mode: Avalanche diodes operate in a high reverse bias condition, which permits the multiplication of an avalanche breakdown to each photo-produced electron-hole pair. Electronics For You. Home Technology Basics. Technology Basics Resources. Please enter your comment! Please enter your name here.

You have entered an incorrect email address! What's New Electronicsforu. Good News! Most Popular DIYs. Condensed Water Atomiser For Air-conditioners. Electronics Components. Testing Times. Photodiode current and laser diode output power are related by a transfer function given in the laser diode datasheet. Not only can photodiodes monitor the DC or CW output of a laser by providing current back to the laser system, they can also test a laser pulse shape and record peak powers of a laser pulse.

The information in datasheets for photodiodes include the four major components discussed earlier, the type of photodiode, peak sensitivity wavelengths, and most importantly size and cost.

Photodiodes that are already incorporated into the laser diode system can be limited in options and information. Laser datasheets usually give the maximum reverse voltage and sometimes the sensitivity of the photodiode.

If the specifications of the photodiode are extremely important to your laser design, custom builds or assemblies may be required to meet your needs. When deciding to reverse bias your photodiode, or not, it all comes down to balancing speed and noise and deciding what is most important. If your application depends on extremely low noise and low dark current, you should choose to not bias your photodiode. If speed is your main concern, you should choose to reverse bias your photodiode as the response time is improved.

In other words, if your application is precision based, photovoltaic mode will better fit your needs. If your application is speed high based, photoconductive mode or reversed biased mode will better fit this area. Reverse biasing the photodiode will be much more responsive than unbiased mode. If operating in photovoltaic mode, the response may need to be amplified. The type of photodiode may also affect your decision of bias. Certain types of photodiodes can only be reversed biased, and others may have amplification of the response internal to the system.

APDs will be effective in low light situations where sensitivity is critical but are expensive, P-N photodiodes are the most basic design and not widely used, and PIN photodiodes are the most common photodiode and the cheapest while having very low noise. As discussed earlier, the materials, size, and cost also affect the type of photodiode needed for the application.

Table 1 shows a simplified chart comparing three different photodiodes. Wavelength Electronics solves problems for researchers and OEMs that use high precision laser diodes, quantum cascade lasers, and thermoelectrics. We're always looking for individuals with analog electronics design experience that want to satisfy customers while continuing to learn. Please submit your resume if this sounds like you View Open Positions.

What is a Photodiode? P-N Photodiode Cross-section The depletion region creates a capacitance in the photodiode where the boundaries of the region act as the plates of a parallel plate capacitor. Key Performance Specifications There are four major parameters used in choosing the right photodiode and whether or not to reverse bias the photodiode.

It is the time needed for charge carriers to cross the P-N junction. This is directly affected by the width of the depletion region. Responsivity is the ratio of photocurrent generated from incident light, to that incident light power. This is called Quantum Efficiency. Dark current is the current in the photodiode when there is no incident light.

This can be one of the main sources of noise in the photodiode system. Photocurrent from background radiation can also be included in this measurement. Photodiodes are usually put into an enclosure that does not allow any light to hit the photodiode to measure the dark current.

Because the current generated by the photodiode can be very small, dark current levels can obscure the current produced by incident light at low light levels. Dark current increases with temperature. Without biasing, the dark current can be very low. The minority carriers generated at n-side or p-side will recombine in the same material before they cross the junction. As a result, no electric current flows due to these charge carriers. For example, the minority carriers generated in the p-type material experience a repulsive force from the external voltage and try to move towards n-side.

However, before crossing the junction, the free electrons recombine with the holes within the same material. As a result, no electric current flows. To overcome this problem, we need to apply external energy directly to the depletion region to generate more charge carriers. A special type of diode called photodiode is designed to generate more number of charge carriers in depletion region.

In photodiodes, we use light or photons as the external energy to generate charge carriers in depletion region. The working operation of all types of photodiodes is same. Different types of photodiodes are developed based on specific application.

For example, PIN photodiodes are developed to increase the response speed. PIN photodiodes are used where high response speed is needed. The different types of photodiodes are. PN junction photodiodes are the first form of photodiodes.

They are the most widely used photodiodes before the development of PIN photodiodes. PN junction photodiode is also simply referred as photodiode. Nowadays, PN junction photodiodes are not widely used. When external light energy is supplied to the p-n junction photodiode, the valence electrons in the depletion region gains energy. If the light energy applied to the photodiode is greater the band-gap of semiconductor material, the valence electrons gain enough energy and break bonding with the parent atom.

The valence electron which breaks bonding with the parent atom will become free electron. Free electrons moves freely from one place to another place by carrying the electric current. When the valence electron leave the valence shell an empty space is created in the valence shell at which valence electron left. This empty space in the valence shell is called a hole.

Thus, both free electrons and holes are generated as pairs. The mechanism of generating electron-hole pair by using light energy is known as the inner photoelectric effect. The minority carriers in the depletion region experience force due to the depletion region electric field and the external electric field. For example, free electrons in the depletion region experience repulsive and attractive force from the negative and positive ions present at the edge of depletion region at p-side and n-side.

As a result, free electrons move towards the n region. When the free electrons reaches n region, they are attracted towards the positive terminals of the battery. In the similar way, holes move in opposite direction. The strong depletion region electric field and the external electric field increase the drift velocity of the free electrons. Because of this high drift velocity, the minority carriers free electrons and holes generated in the depletion region will cross the p-n junction before they recombine with atoms.

As a result, the minority carrier current increases. When no light is applied to the reverse bias photodiode, it carries a small reverse current due to external voltage. This small electric current under the absence of light is called dark current. In a photodiode, reverse current is independent of reverse bias voltage.

Reverse current is mostly depends on the light intensity. In photodiodes, most of the electric current is carried by the charge carriers generated in the depletion region because the charge carriers in depletion region has high drift velocity and low recombination rate whereas the charge carriers in n-side or p-side has low drift velocity and high recombination rate.

The electric current generated in the photodiode due to the application of light is called photocurrent. The total current through the photodiode is the sum of the dark current and the photocurrent. The dark current must be reduced to increase the sensitivity of the device.

The electric current flowing through a photodiode is directly proportional to the incident number of photons.