Editorial Feature

What is a Photodiode Array?

In optoelectronics, photodiode arrays play a vital role in various applications ranging from imaging to sensing and are crucial in converting light energy into electrical signals. This article explores the history, working principle, manufacturing process, applications, and commercial landscape of photodiode arrays.

What is a Photodiode Array?

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History of Photodiode Arrays

In the mid-20th century, researchers started to explore semiconductor materials for light detection. Initially, single photodiodes were used, but the need for larger and more efficient devices led to the advent of photodiode arrays. In the 1970s, introducing charge-coupled devices (CCDs) photodiode arrays revolutionized imaging technology by integrating multiple photodiodes into a single chip and enabling high-resolution imaging.

Working Principle of Photodiode Arrays

A critical component of how a photodiode array works is the photodiode that makes up the array. A photodiode works by converting light signal to electrical based on the principle of the photoelectric effect. Photons strike the semiconductor material within the photodiode, transferring energy to the electrons in the material, causing them to move and create an electrical current. A photodiode's sensitivity and response depend on the material's properties, like the bandgap energy and doping levels.

A photodiode array consists of multiple individual photodiodes arranged in a row or a two-dimensional matrix. Each photodiode operates as a separate light detector in the photodiode array and generates an electrical signal proportional to the incident light intensity.

Fabricating a Photodiode Array

A photodiode array is manufactured using a silicon wafer with conductive vias. The process involves depositing a doped epitaxial layer on one surface of the wafer, forming diode junctions with the substrate.

A patterned etching step defines an array of diode junctions. The photodiode array is connected to readout electronics on the opposite surface of the wafer through the conductive vias. The fabrication method includes pre-processing the wafer, depositing the doped epitaxial layer, and etching a pattern to define the diode junction array.

The resulting photodiode array can be used in imaging systems for various applications, such as medical, security, and industrial inspections. The fabrication process enables high-temperature subsequent steps and compatibility with complementary metal-oxide-semiconductor (CMOS) processes. The photodiode array and readout electronics are formed separately on the wafer, avoiding the need for coordinated double-sided photolithography.

Applications of Photodiode Arrays

Photodiode arrays find applications across various fields due to their ability to detect and convert light into electrical signals. For instance, photodiode arrays are extensively used in digital cameras, scanners, medical imaging devices, spectroscopic analysis, and optical communication. Most importantly, photodiode arrays are employed in various sensing applications such as proximity sensing, ambient light sensing, and gesture recognition.

Some research use cases of photodiode arrays are discussed below:

Analyzing Plant Extract-Mediated Synthesis of Silver Nanoparticles (Ag NPs) using Photodiode Array

A study published in 2021 discusses the application of a photodiode array in the analysis of plant extract-mediated synthesis of silver nanoparticles (Ag NPs). Photodiode arrays are utilized in conjunction with ultra-performance liquid chromatography (UPLC) and high-resolution mass spectrometry (HRMS) to analyze the phytochemical basis and mechanism of the green synthesis process.

The photodiode array helped identify and quantify various secondary metabolites present in the plant extract, providing insights into their roles as reducing and capping agents in the synthesis of Ag NPs.

By analyzing the postreaction residues and eluates from Ag NPs, the photodiode array assists in determining the compounds involved in the reduction process and their concentration changes. This application of a photodiode array contributes to a better understanding of the green synthesis of nanoparticles using plant extracts.

Analyzing Brassica Juncea L. Using Photodiode Array

Another 2021 study presents the application of a photodiode array (PDA) in the analysis of Brassica juncea L., a vegetable from the Brassicaceae family. The photodiode array is used in conjunction with high-performance liquid chromatography (HPLC) and mass spectrometry (MS) to profile bioactive compounds in the vegetable. The aim is to overcome the limitations of conventional one-dimensional LC by employing a comprehensive two-dimensional LC (LC×LC) system.

The LC×LC system provides higher resolving power and better separation of complex samples, leading to improved quantification data. A newly developed RP-LC×RP-LC system coupled with a photodiode array and MS detection is used for the untargeted metabolite content analysis of three different cultivars of Brassica juncea. The RP-LC×RP-LC system, coupled with a photodiode array, allows for the thorough characterization and quantification of bioactive compounds, including polyphenols, in Brassica juncea cultivars.

Commercial Landscape of Photodiode Arrays

The market for photodiode arrays has advanced rapidly in recent years with higher pixel densities, enhanced spectral sensitivity, and faster response times. Several companies specialize in the commercial manufacturing of photodiode arrays for different applications, including Hamamatsu Photonics, Onsemi, Excelitas Technologies, and Texas Instruments. Advancements in fabrication techniques and materials have led to improved performance and miniaturization of photodiode arrays and have opened up new possibilities in fields such as autonomous vehicles, virtual reality, and advanced robotics.

Photodiode Arrays: Conclusion

In conclusion, photodiode arrays have revolutionized the field of optoelectronics and continue to find widespread use in diverse applications. With ongoing research and development, we can expect further advancements in photodiode array technology, leading to even more sophisticated and powerful devices in the future.

Continue Reading: What are Light Emitting Diodes?

References and Further Reading

Arena, K., Cacciola, F., Dugo, L., Dugo, P., & Mondello, L. (2020). Determination of the metabolite content of Brassica juncea cultivars using comprehensive two-dimensional liquid chromatography coupled with a photodiode array and mass spectrometry detection. Molecules. https://www.mdpi.com/1420-3049/25/5/1235

Choi, H. (2003). Advantages of photodiode array. SCINCO. Co., Ltd., 74-27 Nonhyun-dong. https://citeseerx.ist.psu.edu/document?repid=rep1&type=pdf&doi=9e6b717ed9fe5ddf80b737dc73e3d48904a1e401

Kim, M., Lee, G. J., Choi, C., Kim, M. S., Lee, M., Liu, S., ... & Kim, D. H. (2020). An aquatic-vision-inspired camera based on a monocentric lens and a silicon nanorod photodiode array. Nature Electronics. https://www.nature.com/articles/s41928-020-0429-5

Pradeep, M., Kruszka, D., Kachlicki, P., Mondal, D., & Franklin, G. (2021). Uncovering the phytochemical basis and the mechanism of plant extract-mediated eco-friendly synthesis of silver nanoparticles using ultra-performance liquid chromatography coupled with a photodiode array and high-resolution mass spectrometry. ACS Sustainable Chemistry & Engineering. https://pubs.acs.org/doi/full/10.1021/acssuschemeng.1c06960

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Taha Khan

Written by

Taha Khan

Taha graduated from HITEC University Taxila with a Bachelors in Mechanical Engineering. During his studies, he worked on several research projects related to Mechanics of Materials, Machine Design, Heat and Mass Transfer, and Robotics. After graduating, Taha worked as a Research Executive for 2 years at an IT company (Immentia). He has also worked as a freelance content creator at Lancerhop. In the meantime, Taha did his NEBOSH IGC certification and expanded his career opportunities.  

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