Reverse Biasing and Breakdown Behavior of PureB Diodes

In PureB technology, a layer of pure boron is deposited on Si using a commercial single-wafer Si/SiGe epitaxial CVD reactor, forming ideal nm-deep ultrashallow junctions with low saturation currents [1]. As another attractive feature, the PureB layer itself has proven to be a robust front-entrance window for photodiode detectors for low penetration-depth beams such as DUV [2], VUV [2] and EUV [3] light, and low-energy electrons [4]. For all these applications, PureB detectors have been commercialized, mainly in the form of small clusters of millimeter-large photodiodes operated at moderate reverse biasing. Under these conditions the performance of these photodiodes surpasses that of other existing technologies on points such as internal/external quantum efficiency, dark current and degradation of responsivity. Both the optical and electrical degradation is related to the properties of the oxide interface at the perimeter of the diodes [3]. The depleted region at the interface should be kept as small as possible. This is commonly achieved by implementing implanted p-type guard rings and n-type channel stops [5]. The p-guard is also used to reduce the surface curvature in the doping near the device edge that otherwise can cause premature edge breakdown.