Simulations of 3D silicon radiation detector structures in 2D and 3D

Three dimensional (3D) detector structures yield faster charge collection times compared to the ones realized by using the planar (2D) technology. The charge collection time is greatly dependent on the location of the incident ionising radiation. In this paper, the charge collection performance of a rectangular 3D detector structure is simulated by using the finite-element simulation software ISE-TCAD. The surface effects, surface charge and surface recombination, are shown to slow down the charge collection by 50% to 70%. The charge sharing between the neighboring pixel is studied by using 2D simulations at 20 V bias and the charge collected by the pixel of the MIP entrance is shown to be more than 95% in a major part of the pixel volume. In addition, it was shown that great care should exercised when analyzing 3D detector structures using 2D simulation tools. When the simulated structure is thinned down, the internal detector characteristics are altered and, since the RC-constant is proportional to square of the detector thickness, the charge collection time may decrease unexpectedly