Rigorous electromagnetic simulation of CCD cell structures

The efficiency of light sensitive semiconductor elements is influenced by the flux and distribution of light intensity within the detector structure. This intensity distribution will depend on the geometric and optical features of the structure. It will also depend on the properties of the incident radiation (i.e., spectral distribution, polarization, coherence, angle of incidence etc.). For "large" structures, an approximation of the intensity distribution can be obtained by means of simple geometrical optics models. If the detector has feature sizes in the order of several wavelengths, however, this method fails to produce reliable results due to the fact that diffraction effects, which are completely ignored in geometrical optics, become more and more important. In the following analysis, light propagation in a 2-dimensional charge coupled device (CCD) cell structure is modelled by means of rigorous electromagnetic theory, both for the basic structure and a more complicated design with a microlens to increase incoupling efficiency. Parameters of the incoming radiation as well as the geometry of the structure are varied and the effects are demonstrated.