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A new position sensitive detector for charged particles and X-rays is proposed based on pixels containing MOS transistors as preamplifiers. The output of the preamplifiers is shorted to strip buses to obtain two-dimensional information with readout requirements similar to a strip detector. The total pixel capacitance is low enough (20-40 fF) to allow a large potential increase at the pixel that collected the charge. The nonlinearity introduced by the large voltage rise effectively switches on the transistors of this pixel and leaves all the other pixels of the same line at a low transconductance state, resulting in an excellent noise performance.

The planar diode current is determined by the geometry revealed by three-dimensional simulations. Lower dimensional analysis is the basis of simplified one and two-dimensional models. Analytical computations yield approximations of the current of rectangular and square junctions. The proportionality of the current to the junction site is demonstrated when the diffusion length, thickness of the substrate and velocity of recombination cease to determine the current.