LIMITATIONS OF RAY-TRACING TECHNIQUES IN OPTICAL MODELING OF SILICON SOLAR-CELLS AND PHOTODIODES

The physical optical effects which take place when the size of the sur face textures of a solar cell or a photodiode is in the micron range a re studied. Both the antireflective and the light trapping properties of linear periodic grooves of triangular cross sections are treated in the framework of an exact, coupled-wave, electromagnetic analysis. Th e most important physical optics effects are the diffraction of light at the groove edges, the interference of light reflected by the differ ent surfaces of the grooves, and the tunneling across the grooved surf ace of light incident from the silicon side at an angle greater than t he critical angle. There is also the effect of the interference of the light reflected by the front and back surfaces of the silicon layer w hich is important only for very thin layers. As the groove period incr eases above the wavelength, the exact results approach the geometrical optics predictions rather slowly in an oscillatory way. Simple physic al optics arguments are presented for obtaining a criterion for the ac curacy of ray tracing methods in optical modeling of surface textures. (C) 1998 American Institute of Physics. [S0021-8979(98)04822-1].