Table of Contents
Introduction:
It is a type of light sensor that transforms light into electrical energy (voltage or current). A photodiode is a type of PN junction semi-conducting device. An intrinsic layer exists between the p (positive) and n (negative) layers. To generate an electric current, the photodiode accepts light energy as an input.
The photodetector, Photo Sensor, and Light Detector are all terms for the same thing. The p – side of the photodiode is linked to the negative terminal of the battery (or the power supply), while the n – side is connected to the positive terminal of the battery.
Silicon, germanium, indium gallium arsenide phosphide, and indium gallium arsenide are common photodiode materials.
A photodiode has optical filters, a built-in lens, and a surface area on the inside. When the surface area of a photodiode rises, the response time decreases. Few photodiodes will have the appearance of a Light Emitting Diode (LED). It has two terminals, as indicated in the diagram below. The cathode is the smaller terminal, and the anode is the longer term.
The photodiode sign is similar to that of an LED, except the arrows in the photodiode point internally rather than outwards as in the LED.
Types of Photodiode
Despite the fact that there are many different varieties of photodiodes on the market, they all work on the same basic principles, some are enhanced by additional effects. Different varieties of photodiodes operate in somewhat different ways, but the fundamental operation of these diodes is the same. The following are the several varieties of photodiodes and how they are categorized depending on their construction and functionality.
- PIN Photodiode
- Avalanche Photodiode
- Schottky Photodiode
- PN Photodiode
PIN Photodiode: A PIN photodiode is currently the most widely used photodiode. This diode collects light photons more efficiently than a normal PN photodiode because the intrinsic area between the P and N sections is larger, allowing for more light to be gathered, and it also has a lower capacitance.
Avalanche Photodiode
Avalanche photodiode is a type of diode that uses the avalanche mechanism to achieve better performance than other types of diodes.
Optical signals are converted to electrical signals using these diodes. These diodes can be used in high-reverse-bias applications. The symbol for an avalanche photodiode is similar to that of a Zener diode.
Schottky Photodiode: The Schottky photodiode is made up of a Schottky diode with a tiny diode junction, which means it has a low junction capacitance and can function at high speeds. As a result, high bandwidth (BW) optical communication systems such as fiber-optic lines typically use this type of photodiode. For additional information on the Schottky diode, click here.
Each type of photodiode has its own set of advantages and disadvantages. This diode’s selection can be made dependent on the application. Noise, wavelength, reverse bias limitations, gain, and other parameters must all be considered while choosing a photodiode. Responsivity, quantum efficiency, transit time, and response time are some of the photodiode’s performance metrics.
These diodes are commonly employed in applications that require the sensing of light, color, position, and intensity.
PN Photodiode: The PN photodiode was the first to be created. Although its performance is not superior to that of other varieties, it is currently used in a variety of applications. The photodetection occurs mostly in the diode’s depletion zone. Although this diode is compact, it has low sensitivity when compared to others. For additional information on the PN diode, please see this page.
Working of a Photodiode
Covalent bonds are ionized when a light is used to illuminate the PN junction. This produces electron and hole pairs. The creation of electron-hole pairs produces photocurrents. When photons with energies more than 1.1eV collide with the diode, electron-hole pairs emerge. When a photon penetrates the depletion zone of a diode, it has a strong energy impact on the atom. As a result, an electron is released from the atom structure. Free electrons and holes are formed as a result of the electron release.
A negative charge is assigned to an electron, while a positive charge is assigned to a hole. There will be an electric field integrated into the depletion energy. Electron-hole pairs travel away from the junction as a result of the electric field. To produce photocurrent, holes migrate to the anode and electrons to the cathode.
The intensity of photon absorption and the energy of photons are directly related. When the energy of the pictures is lower, the absorption is higher. Inner Photoelectric Effect is the name given to this entire process.
Photodetector
Photodetectors are electronic devices that detect light in the form of optical power. Photodetectors are sometimes referred to as photon detectors since they make use of the photo-excitation of electric carriers in some way. Photodetectors typically produce an electrical output signal that is proportional to the incident optical power, such as a voltage or electric current. As a result, they fall under the category of optoelectronics.
Properties of Photodetector
- It needs to be responsive in a specific spectral range (range of optical wavelengths). The responsivity should be steady or clearly defined within a certain wavelength range in particular instances. Solar-blind photodetectors, for example, are sensitive only to short-wavelength UV light but not too visible sunlight, so having zero response in another wavelength range is critical.
- The responsivity indicates the amount of electrical signal obtained per unit of optical power. The optical wavelength determines this.
- In some circumstances, it’s vital to have both a high responsivity and a high quantum efficiency, because otherwise, more quantum noise is introduced. This affects the photon detection probability of photon-counting detectors, as well as the detection of compressed states of light.
- The detector should be able to handle a wide variety of optical powers. Damage issues or a nonlinear response can limit the maximum detected power, but noise often determines the minimum power. The dynamic range’s magnitude (usually expressed as the ratio of highest to least detectable power, e.g. in dB) is frequently the most essential factor. Over a dynamic range of more than 70 dB, some detectors (e.g. photodiodes) can exhibit good linearity.
Also read: Important Topic of Physics: Instantaneous Velocity
FAQs
When a photodiode is forward-biased, what happens?
The resistance of a diode is reduced when it is biased forward and increased when it is biased backward. When the diode is in forwarding bias, the current flows freely. Still, when the diode is in reverse bias, the current cannot flow.
Why does a photodiode have a reverse bias connection?
Since it permits current to flow, the forward bias depletion region between one junction is relatively thin. Because the current in the depletion region in reverse bias is substantially larger than in forwarding bias, the amount of current produced in reverse bias is greater. As a result, the photodiode is connected in reverse bias.
What are the requirements of a photodetector?
A photodetector must meet a variety of requirements depending on the application: It needs to be responsive in a specific spectral range (range of optical wavelengths). The responsivity should be steady or clearly defined within a certain wavelength range in particular instances.
How much current does a photodiode generate?
The output current increases linearly as the optical input power increases and then begins to become nonlinear, regardless of the wavelength of the input light. Different manufacturers' photodiodes will have varying degrees of saturation current, which is commonly between 1 to 10 mA.
