No abstract

Atomic layer deposited (ALD) Al2O3 coatings were applied on black silicon (b-Si) structures. The coated nanostructures were investigated regarding their reflective and transmissive behaviour. For a systematic study of the influence of the Al2O3 coating, ALD coatings with a varying layer thickness were deposited on three b-Si structures with different morphologies. With a scanning electron microscope (SEM) the morphological evolution of the coating process on the structures was examined. The optical characteristics of the different structures were investigated by spectral transmission and reflection measurements. The usability of the structures for highly efficient absorbers and antireflection (AR) functionalities in the different spectral regions is discussed.

No abstract

Antireflective (AR) nanostructures offer an effective, broadband alternative to conventional AR coatings that could be used even under extreme conditions. In this publication, a possible fabrication process based on colloidal polystyrene (PS) nanosphere lithography for the fabrication of such AR structures on arbitrarily shaped fused silica substrates is presented and evaluated. Special emphasis is placed on the involved manufacturing steps in order to be able to produce tailored and effective structures. An improved Langmuir-Blodgett self-assembly lithography technique enabled the deposition of 200 nm PS spheres on curved surfaces, independent of shape or material-specific characteristics such as hydrophobicity. The AR structures were fabricated on planar fused silica wafers and aspherical planoconvex lenses. Broadband AR structures with losses (reflection + transmissive scattering) of <1% per surface in the spectral range of 750–2000 nm were produced. At the best performance level, losses were less than 0.5%, which corresponds to an improvement factor of 6.7 compared to unstructured reference substrates.

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 f 3dB -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-on-Si 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.