Fabrication of low dark-count PureB single-photon avalanche diodes

Single-photon avalanche diodes (SPADs) have been fabricated in Si by using PureB (Pure Boron) chemical-vapor deposition (CVD) to create both a nanometer-thin anode junction and robust light-entrance window. The device is sensitive to low-penetration-depth radiation such as UV light and low-energy electrons. Ideal I-V characteristics are obtained for operation in Geiger mode, whereas biasing is well above the breakdown voltage. The dark count rate (DCR) can be as low as 5 Hz at room temperature for an active area of 7 μm
²
. An implicit guard ring as small as 0.5 μm wide is implemented using an n-enhancement implantation in the central region of the diode, thus achieving a high fill-factor.