Tuning of random rough surface statistics for optoelectronics

Abstract

Optical surface structuration is of primary interest for applications such as photovoltaics or photodetectors. Over last years, periodical patterns allowing antireflective effects with efficient properties have been designed and fabricated. Some specific issues such as diffraction of undesired high energy orders are a direct consequence of the periodical nature of this kind of pattern. Random rough surfaces allow the antireflective effect without these undesired diffraction effects. By tuning their statistics, random rough surfaces offer new degrees of freedom for antireflection but also for controlling the scattering (polarization, spatial distribution). The two main parameters of such surfaces are the height probability density function and the autocorrelation function. The height probability density function carries information about height of the structures. The autocorrelation function is a representation of the lateral distribution of the surface. Our photofabrication method uses a speckle pattern recorded on a photoresist. By controlling the exposure parameters, such as the number of exposure and the beam intensity distribution, one is able to control the statistics of the speckle, and so of the photofabricated surfaces. Using a chromatic confocal sensor, height mapping of these surfaces are performed. From these mappings, the height probability density and the correlation function are calculated. The experimental statistics are compared with the predicted theoretical ones showing a good agreement. Results are presented showing a significant modification of the statistics of the photofabricated surfaces.