Effect of nitrogen atmosphere and vacuum conditions on charge dynamics in mesoscale porous silicon

Optoelectronic properties of nano- and mesoscale porous silicon (PS) are strongly influenced by surface effects, owing to intrinsic and extrinsic electronic states within the bandgap. In addition, physisorption, chemisorption, and desorption of environmental species further alter the surface electronic structure, thereby modifying the surface potential barrier. However, the influence of gaseous environments and vacuum conditions on surface charge dynamics in PS is not fully understood. In this work, we systematically investigated environment-dependent surface charge dynamics in PS using transient surface photovoltage (SPV)—a non-destructive, highly surface-sensitive characterization technique. Our measurements revealed a multi-component photoresponse sensitive to ambient conditions, indicating physisorption/chemisorption-mediated charge exchange processes. Comparison of results obtained in gaseous environments and in high vacuum enabled separation of contributions to band bending from intrinsic surface states and from the adsorbate-induced ones. Furthermore, the study of the influence of illumination intensity on SPV transients showed that their onset slopes exhibit nonlinear scaling with illumination intensity, in contrast to the linear behavior typically observed in bulk semiconductors, suggesting a drift/diffusion-mediated charge redistribution in PS. By revealing environment-dependent transport behavior, this study provides insight into illumination-governed carrier dynamics as well as guidelines for the rational design of PS-based sensing devices.