P-type one-sided hexagonal spiral drift detectors

A new P-type drift detector (PDD) with one-sided hexagonal spiral shaped cathodes around the center anode has been designed, simulated, constructed and tested. The signal in PDD is generated by the transport of holes (instead of electrons as in an n-type drift detector) in the bulk of the detector and their arrival to the anode. Large arrays of drift cells are required for the extended X-ray absorption fine structure experiments (EXAFS). The large number of cells forces the design of the drift cell with a minimal number of bonds per cell. The presented design creates the drift field by the spiral-based voltage divider. Moreover, the leakage current created at the depleted part of the detector surface is also collected without an external connection to the cell. The leakage current is collected directly on the inner terminal of the divider. The lithographic processes of the wafer are done only on one side resulting in a much faster fabrication. The lithography-less side of the detector was uniformly implanted with phosphorus creating a shallow, rectifying p/sup -/n/sup +/ junction. This side is exposed to the radiation. Positive charges in the native oxide help to keep the thickness of the dead entrance layer at the minimum. Moreover, this layer is not sensitive to the radiation damage caused by very low energy X-rays that do not damage the silicon structure and produce only additional positive charge in the oxide. For the first time, the design makes an active usage of the positive charge in the oxide as a rectifying junction on p-type silicon.