Lavalansefotodiodit

Lavalansefotodiodit, often abbreviated as APDs, are semiconductor devices that can detect very faint light signals. They operate by converting incident photons into electrical current. When a photon strikes the depletion region of the APD, it generates an electron-hole pair. An electric field within the device then accelerates these charge carriers.

The key characteristic of an APD is its avalanche multiplication effect. As the accelerated charge carriers gain enough energy, they collide with atoms in the semiconductor lattice, creating more electron-hole pairs. This process cascades, leading to a significant amplification of the initial signal. This internal gain makes APDs much more sensitive than standard photodiodes.

The multiplication factor, or gain, of an APD is dependent on the applied reverse bias voltage. As the voltage increases, the electric field strengthens, leading to a higher probability of impact ionization and thus greater gain. However, operating an APD too close to its breakdown voltage can lead to uncontrolled current flow.

APDs are employed in various applications where high sensitivity is crucial. These include optical communication systems for detecting weak signals, medical imaging technologies like PET scanners, distance measurement (LiDAR), and scientific instruments for low-light detection. Their ability to provide internal gain without external amplification makes them advantageous in compact and power-sensitive systems.