Three-dimensional defect characterization : focused ion beam tomography applied to tin sulfide thin films

Abstract

Porosity is postulated to be one of the reasons for the low efficiency of tin sulfide-based devices. This work is a preliminary investigation of the effects of two film growth parameters deposition rate and substrate temperature - on porosity. We employ the focused ion beam tomography technique to characterize and quantify porosity in tin sulfide thin films. We then generate 3D reconstructions of pores inside milled volumes from the films and quantify pore volumes. To explain the results, we employ nucleation theory and develop two different models: (a) a thermodynamic model that assumes pores form primarily from an effect known as "self-shadowing," whereby growth-rate anisotropy results in some grains that grow faster than their neighbors, and (b) a kinetic model that assumes a diffusion-driven process of void formation. We show that both models qualitatively support the experimental results, providing insight into process-structure relations that may improve film quality during growth.