A two-dimensional, pixellated, monolithic semiconductor radiation
detector, in which each detector pixel is essentially a perpendicular
mode detector. This is achieved by an arrangement of anode spots, one for
each pixel located on the flux-exposed front surface of the detector
substrate, surrounding by a cathode array preferably in the form of a
network of lines, such that the field between the anodes and cathodes on
this front surface has a major component in the direction parallel to the
surface, and hence perpendicular to the incident photon flux. The
conductivity of the substrate is high near this front surface, since this
is where the highest level of absorption of photons takes place, and a
significant photoconductive current is thus generated between cathodes
and anodes. The conductivity is proportional to the incoming photon flux,
and decays exponentially with depth into the detector. Since all of the
conduction paths are in parallel to each other, the resultant conductance
between each anode and its surrounding cathode is the summation of all
those conductances.