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Components of a Photodiode Circuit

What if you are sitting in your workplace and suddenly you sense smoke around your premises? Now, a smoke detector can quickly notify you of this and can save you from potential risk as well. So what thing makes a smoke detector perform this job? A photodiode! Wait, so you don’t have a physics background to understand everything about a photodiode? 

Well, this is not a problem for us at all! We are going to explain all the important aspects of a photodiode right in this post for you! Let’s get started!

For starters, a photodiode is a little device that transforms light energy into current. These have mostly two corners called the P-side and N-side. You need to connect the P-side with a negative junction of the battery, and N-side goes with the positive one. 

So, if just a small amount of sunlight is put on a photodiode, it will change it into current in seconds. 

What is Photodiode Circuit?

A photodiode works similarly to a light detector that catches light and changes into current and voltage as per the use case. Now photodiodes are slow to respond in general cases when they are large.

It means the large surface area of a photodiode will not produce desired results

. You can also consider these similar to semiconductor diodes, but producing current and voltage from sunlight is the exception. 

Junctions of a Photodiode Circuit 


There are two types of junctions used by photodiodes, and these are:

  • PIN Junction
  • PN Junction


Components of a Photodiode Circuit 

There are different components of a photodiode. These include:

  • Lenses
  • Optical filters
  • Semiconductor

You must be thinking that a few types of photodiodes are the same as light-emitting diodes. Well, there are some similarities between the two that we need to discuss at this point. Both these diodes contain two junctions at the end. One is the cathode which is small, and the other is the anode which is large in size. 

  • Forward Bias: When the condition is forward bias, the current will be conventional, and its direction will be anode to cathode. 
  • Reverse Bias: Whereas when the condition is reverse bias, the current will go from cathode to anode. 

Types of Photodiode Circuit 

There is a large variety of photodiodes existing for the producers and users. These photodiodes vary in their features and purposes. Different types and different use cases. The functioning of these photodiodes is always the same; however, there are certain things that you must consider to get the appropriate photodiode for yourself. 

1. PN Photodiode Circuit 

  • It has been the first ever type of photodiode engineered and has vast applications in different domains.
  • Since it is an old type, you will not be stunned by its performance.
  • It performs its job mostly within its depletion area.
  • The size of the diode is really small compared to advanced diodes.
  • Also, it does not offer much sensitivity.

2. PIN Photodiode Circuit 

  • It is one of the typical photodiodes used nowadays.
  • Its role is to capture light and draw out photons from it. Also, this diode has no parallel for doing this job more efficiently.
  • The area between both the P and N terminals is large, which helps this diode trap more sunlight and get more photons out of it.
  • The capacitance of this diode is much smaller, which benefits its performance at the same time. 

3. Avalanche Photodiode Circuit 

  • Avalanche photodiodes are efficient for use when light is low.
  • The photon trapping ability of this photodiode is impressive, which is why it is exceptional in offering positive results.
  • However, one drawback of this photodiode is its noise which makes it less suitable for use in sensitive machines and other equipment.

4. Schottky Photodiode Circuit 

  • The junction of this diode is smaller in size, which reduces the capacitance at the same time.
  • Since the capacitance is less, it improves its performance at a fast speed.
  • Such a photodiode is crucial for improving the efficiency of optical communication, for example, fiber optics. 
  • It is beneficial when you need to work on higher bandwidth as well. 

How to choose the best Photodiode Circuit for yourself?

By far, it is clear that every photodiode has its own use cases and specifications. However, you don’t have to get confused between these since there are some factors that will help you for this purpose. Here’s how you can choose the best photodiode for your projects:

  • How much noise does the photodiode produce?
  • What is the wavelength of the photodiode?
  • Check about the reverse bias constraints of the photodiode you have your eyes on
  • What is the gain of the photodiode?
  • Is the photodiode responsive?
  • Does the photodiode support quantum efficiency?
  • What is the transit time of the photodiode?

Why do Photodiode circuits have extensive applications?

One reason can be their remarkable features. Due to this, several producers rely on different photodiodes to enhance the overall quality of their products. The devices that need to detect light mostly contain photodiodes. Let’s take a look at the following reasons for the wide acceptance of photodiodes in different domains:

  • These offer impressive linearity as compared to incident light
  • The noise is low, which reduces the chances of failure
  • Wide spectral response for better performance
  • Mechanically rugged that enhances the efficiency 
  • Featherweight structure and small size for easy adjustment
  • More longevity, unlike other variants

How to make a Photodiode Circuit?

The discussion remains inadequate if we don’t teach you to make a photodiode with simple tips. Don’t worry; you don’t have to go above and beyond to make your first photodiode or maybe revise your style to make better ones. There is a list of important materials that you need to collect to combine them for a stunning and highly efficient photodiode! The list looks like this:

  • Silicon: The suitable electromagnetic spectrum wavelength ranges between (190-1100) nm
  • Germanium: Go for the wavelength that is between (400-1700) nm
  • Indium, Gallium, Arsenide: The recommended wavelength is (400-1700) nm
  • Lead II Sulfide: Use wavelength of <1000-3500 nm
  • Mercury, Cadmium, Telluride: A perfect wavelength ranges between (400-14000) nm


Which Photodiode circuits are lower in noise?

If we compare the abovementioned wavelengths of photodiodes, it is clear that Silicon’s wavelength is suitable for producing less noise. 


Once you have all the important materials for the construction of a photodiode, it’s time to finally construct it. We are going to learn about the process in the following step-by-step guide:

  • You need two semiconductors (P-type and N-type) to produce a photodiode.
  • The P-type substrate is a little doped as compared to the N-type.
  • It enables seamless ion diffusion later.
  • The N-type substrate uses an epitaxial covering when constructing the photodiodes.
  • The purpose of this covering is to dope the N-type substrate more than the P-type.
  • Two contacts are important for developing the anode and cathode. 
  • You divide the diode among active and non-active regions for the sake of ease.
  • The non-active side is for Silicon Dioxide, while the active side is for trapping the sunlight.
  • The active side needs to be concealed with an anti-reflection substance that does not miss out on an iota of sunlight for transforming it into the current. 

Working on Photodiode Circuit 

Photodiodes follow a unique principle of working, and without discussing it, you will fail to understand the physics of photodiodes completely. So the function starts when the photodiode captures photons from sunlight. Now this will create electron holes on the photodiode because of the photoelectric effect. If absorption of these photons takes place in the depletion region, the electric field excludes the carriers present in this area. It will make the holes march toward the anode, and electrons will go toward the cathode. This movement will produce a photocurrent in the system. You need to keep the current as low as possible so that you can make the photodiode more sensitive for capturing sunlight. 

Modes of Operation of Photodiode Circuit 

There are three basic modes of operation among photodiodes. These include:

  • Photovoltaic Mode:  You can also call it zero-bias mode. There is a lightened photodiode that produces the voltage. It has a little dynamic range and does not need non-linear voltage at all. 
  • Photoconductive Mode: The type of photodiode required for this mode works on the reverse bias condition. The voltage is responsible for the improvement of the thickness of the depletion region. Due to this, the response time is less, along with the capacitance. Therefore, this is much faster than the photovoltaic mode. However, it makes a loud noise and might not be befitting for many applications. 
  • Avalanche Diode Mode: Avalanche diodes need high reverse bias conditions for work. The functioning of this mode looks like this. It amplifies the number of avalanches for all the electron holes. It results in more gain of the photodiode that gradually boosts the response. 

Advantages of Photodiode Circuit 

Wondering about the advantages of photodiodes? Well, these are not less! 

  • Photodiodes are efficient in offering less resistance when needed. 
  • These are reliable for fast speeds that are important for certain electronics.
  • These have more longevity.
  • The spectral response is also impressive of photodiodes.
  • Photodiodes do not consume much voltage.
  • These are durable, heavy-duty, and not heavy at all.
  • Photodiodes are highly sensitive to light which makes them efficient for several light-detecting devices.
  • Produce less dark current, which is important.
  • Offer impressive quantum frequency when needed.
  • Some types produce less mechanical noise, which is good.

Disadvantages of Photodiode Circuit 

It’s time to have an honest look at the drawbacks of photodiodes:

  • These are not reliable for temperature stabilization.
  • The current is not sufficient for operating the entire circuit at all.
  • The active area that traps sunlight is usually smaller in size.
  • Some types are poor, with light sensitivity.
  • An optimum temperature is important to make photodiodes work properly.
  • The photodiodes use offset voltage which can complicate different things.

Applications of Photodiode Circuit 

  • We are talking about some common applications of photodiodes first. These are photoconductors, photomultipliers, and photo-detecting devices.
  • Consumer electronics like CD players, TVs, smoke detectors, radios, clocks, camera light meters, and even streetlights use photodiodes.
  • Linear response photoconductors are crucial for the domain of science.
  • The medical field also relies on photodiodes, and medical equipment like monitors and tomography machines include photodiodes.
  • Optical communication also cannot breathe without such photodiodes for the sake of light regulation as well. 




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