Delaware Patent of the Month – September 2021

An avalanche photodiode (APD) is a highly sensitive semiconductor photodiode detector that exploits the photoelectric effect to convert light into electricity. These devices allow precise and fast measurements in nearly any condition but if not designed properly, they can be unreliable and difficult to use. Luxtera, LLC. has designed a more reliable focused field ADP.

The operation of a traditional ADP is based on the generation of hot carriers by a large applied field. Hot carriers produce new electron-hole pairs during a process called impact ionization. As the hot carriers produce new electron-hole pairs, they are in turn accelerated by the field, triggering more impact ionization and creating an avalanche of carrier generation. If in the presence of a semiconductor-dielectric surface, they may enter the dielectric, build up and become a fixed charge in a process called Hot Carrier Injection (HCI). Over time, this charge build up modifies the electric field profile and degrades the performance. 

Luxtera has designed their device with minimal HCI, creating a longer lasting and more reliable avalanche photodiode. Their device is designed with a special configuration of the cathode and charge layers. Thes positive and negative charge layers are systematically doped, with oxide interfaces on their top and bottom. The ADP absorbs optical signals in its absorbing layer, generating carriers and directs them to the cathode. This controlled direction is formed by the specific doping of the charge layers to form a pathway. This reduces the potential for HCI and improves performance and lifespan of the photodiode.

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