Material Considerations for Avalanche Photodiodes

Avalanche photodiodes (APDs) are widely used to detect and amplify weak optical signals by utilizing the impact ionization process. The choice of material is critical for the detection of a particular wavelength, and it is often expedient to use a combination of different materials to optimize the overall device performance. The APDs are now capable of covering a wide spectrum from the infrared down to the ultraviolet wavelengths. This paper will review the material requirements to achieve high gain with low excess noise at the different wavelength regions.