Phototropic Growth of Semiconductor Mesostructures Exhibits Auto-Optimizing Interfacial Light Absorption

Abstract

Inorganic phototropic growth of chalcogen semiconductors wherein a uniform, incoherent, uncorrelated beam of light enables control over the morphology and growth direction of an evolving deposit in three-dimensional space at the nanoscale is explored. Such evolution is similar to natural phototropism exhibited by many photosynthetic plants wherein the physical extension of the biological system proceeds preferentially towards the time-averaged position of the sun. In analogy, during inorganic phototropic growth, a semiconductor material is electrodeposited under illumination and mass is addition is correlated with the spatial distribution of the light absorption. Highly periodic nanostructured films can be generated over macroscopic square centimeter areas in this manner. No laser source, photomask nor structure light field is necessary nor utilized. Additionally, no chemical templating agents (ligands, surfactants) are used. Isotropic morphologies consisting of ordered arrays of nanopores were generated using unpolarized illumination whereas linearly polarized light resulted in highly-anisotropic nanoridge/trough morphologies with the in-plane orientation of the patterns controlled by the direction of the light polarization. The pattern periodicity was encoded by the illumination spectral profile. A single periodicity in single spatial direction was only generated even with the use of broadband and multimodal spectral profiles and multiple polarization inputs and the periodicity was found to be sensitive to all investigated tuning of such profiles. Structures with nonequal periodicities in the two orthogonal in-plane directions could also be generated and both periodicities could be independently controlled. Structural complexity correlated with the complexity of optical inputs. Modeling of the growth using a combination of full-wave electromagnetic simulations of light absorption and scattering coupled with Monte Carlo simulations of mass addition successfully reproduced the experimentally observed morphologies and indicated that morphology development was in fact directed by evolution of the growth interface to maximize anisotropic light collection. This work may be useful for the high-throughput generation of light-trapping absorbers films, photonic elements, and platforms for (photo)electrocatalysts.