Lambertian light trapping in thin crystalline macroporous Si layers

Lambertian light trapping is a benchmark for efficient light trapping. In this Letter we experimentally quantify the degree of Lambertian light trapping in a macroporous silicon layer. The optical absorption of the effective (26.7 ± 5.5) μm thick sample with randomly arranged pores yields a photogeneration corresponding to a maximum current density of (40.8 ± 0.4) mA cm^-2 and thus achieves a fraction of 0.985 ± 0.012 of the current density expected from a Lambertian light trapping scheme. The measured spectrum of the escape reflectance is well described with an analytic model assuming a complete randomization of the directions of light propagation.