3D simulations of irradiated one-sided dual-column 3D silicon detector

We undertook, at Brookhaven National Laboratory (BNL), full 3D simulations of one-sided dual-type column 3D Si detectors (p-type substrate) after irradiation levels up to 1×1016 neq/cm2. Etching does not extend all the way through the substrate, so that all electrodes are on the front side; the backside was neither supported nor processed, covered only with a layer of silicon dioxide. Hence, BNL's one-sided dual-type column 3D detectors are true one-sided detectors. Our simulations of the electric fields at various fluences will add to our knowledge about the practicable applicability of these detectors in the high-radiation environment of future colliders.Simulations show that the full depletion voltage, Vfd, for a dual-column 3D detector is about 1.4 times higher than that of a 2D (planar) pad detector with a thickness d, the same as the column spacing, Lp, in the 3D detector. Moreover, the highest E-field is near the n+ column, while the high E-field mainly is distributed between the n+ and p+ columns. The low E-field is between the two p+ columns, with its lowest point in the center of the unit cell with two p+ columns and two n+ columns.To fully deplete a dual-column 3D detector at 1×1016 neq/cm2 with a reasonable bias (≤200 V) necessitates reducing the column spacing, Lp, to 30 μm. The volume under the columns (10% of the total volume) can be depleted with a modest bias (≤200 V); this underlying volume is not a dead volume. In addition, this depletion volume can support detection sensitivity directly under the columns, thereby lowering the effective dead volume in a 3D Si detector.