Optical modeling of Geon-Si focal plane arrays with diffractive light coupling

Coupling light via stochastic needle-like nanostructures (black silicon) on the back side of a Ge-on-Si photodiode provides an increase of light absorption (and thus of the quantum efficiency) while preserving the f3dB-bandwidth of the diode [1, 2]. When transferring this technique from a single photodiode to array-like devices such as focal plane arrays (FPAs), it comes to optical crosstalk in adjacent pixels. A simulation model based on the ray tracing program Zemax can determine the absorption in Ge-onSi FPAs under arbitrary illumination. It simulates the absorption in every individual pixel and thus enables the calculation of optical crosstalk, as well as the total absorption, as functions of different design parameters. It gives the opportunity to compile parameter surveys or to perform a design optimization of the array device. The simulation model can be easily adapted to similar applications, thus providing a wide range of usage.