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Uncovering the history of APD: How did Japanese engineers change photoelectric detection technology?
In the development of modern science and technology, the progress of photoelectric detection technology has provided innovative solutions for countless application fields. Especially in high-sensitivity detection devices, avalanche photodiode (APD) is undoubtedly a prominent representative. The birth and evolution of this technology not only demonstrates the wisdom of engineers, but also ignites the spark of science, allowing more photons to enter our world. However, how did this revolutionary technology come about? What unknown stories are hidden behind its history?
The birth and early development of APD
The founder of avalanche photodiode is Japanese engineer Jun-ichi Nishizawa, who first proposed the concept of APD in 1952. However, research into avalanche collapse and photoelectric detection using p-n structures had already begun long before this patent. The foundation of these studies paved the way for the birth of APD, showing that scientific progress is often the accumulation of predecessors' wisdom and chemical reactions.
"It's a small step for photoelectric detection, but a big step for technological progress."
Analysis of the working principle of APD
The operating principle of APD is based on the phenomenon of impact ionization. In this process, photons provide energy to separate charge carriers in the semiconductor material, forming positive and negative pairs, allowing electric current to flow. By applying a high negative bias, the charge in the photoelectric effect can be multiplied through the avalanche effect. Therefore, the APD can be considered as a device that exerts a high gain effect on the induced photocurrent. It is worth mentioning that the higher the applied reverse bias voltage, the higher the gain degree. Standard silicon APDs can typically withstand 100–200 volts of reverse bias before breaking down, yielding a gain of about 100 times.
Exploration of new materials
With the advancement of technology, various material tests are applied in APD design. Silicon can be used to detect visible light and near-infrared light while maintaining low multiplication noise (excess noise), while germanium can detect infrared light up to 1.7 microns in wavelength, but has higher multiplication noise. In high-speed fiber optic communication applications, InGaAs materials can demonstrate their excellent performance, with the characteristics of low noise and high absorption efficiency, enabling us to develop rapidly in the field of optical communications.
"Challenging the limits of materials and advancing the future of optoelectronics."
Structure and performance limitations of APD
Structurally, APDs usually adopt more complex designs, like p+-i-p-n+, rather than a simple p-n structure. These complex structures make the performance of APDs more diverse, but also bring many challenges, such as improving quantum efficiency and controlling leakage current. Management of electronic black noise and dark current is critical as they affect the accuracy and sensitivity of the current.
Gain Noise Challenges and Solutions
When the gain requirement of the APD is extremely high (for example, reaching the level of 105 to 106), it is called a single-photon avalanche diode (SPAD). These detectors are often operated above the destruction voltage and therefore require immediate signal current limiting. Therefore, active and passive current extinguishing technologies are proposed to solve this problem. The application of these technologies not only improves the detection sensitivity, but also enables APD and its related technologies to be widely used.
"Great technology is born out of challenges."
Future Outlook
As an important milestone in photoelectric detection, the evolution of APD technology will undoubtedly play a key role in human exploration of the unknown and in information transmission. With a deeper understanding of the avalanche effect, materials science, and electronic engineering, how APDs will further improve their performance and break through existing application barriers in the future has become a hot topic that scientists continue to explore. As technology advances, can we witness another technological breakthrough that will allow APD to shine in a wider range of fields?
