Avalanche photodiode

An avalanche photodiode having a semiconductor substrate provided with a lower electrode underneath said substrate, an amplification layer for producing pairs of electron-holes through an ionized collision of carriers injected by an internal electrical field, and an absorption layer for producing said carriers in accordance with splitting of the pairs of electron-holes by the internal electrical field, wherein the pairs of electron-holes are excited by an incident light ray, comprising:

• a contact layer formed on said absorption layer, said contact layer having a core section in the center thereof and at least a guard section spaced apart from each and forming a gap so as to electrically isolate the core section and reduce leakage current, which is not filled by said absorption layer, between said core section and said guard section;
• and,
• at least one upper electrode comprising at least one core electrode formed on said core section and at least one guard electrode formed on said guard section, said upper electrode generating the internal electrical field in cooperation with said lower electrode;
• and
• an adjustable activation region underneath the at least one upper electrode for the internal electrical field and an adjustable guard region underneath the at least one guard electrode, wherein a contour line defining a size of the adjustable activation region and the adjustable guard region is determined by an amount of electric potential applied to both the at least one upper electrode and the at least one guard electrode.