Thermal cycle impact on polycrystalline silicon: Direct observation of electrical properties degradation and interfacial nanocrystalline grain defects

Tracing interfacical nanocrystalline grain defects (NCGD) formation inducing electrical characteristic degradation in thermal remains a challenging issue for polycrystalline silicon (poly-Si) stable and reliable application in engineering. Here, we present a microelectromechanical systems (MEMS) unit, which is composed of tunnel oxide passivating contact poly-Si tandem layer. It is a pioneering work to explore poly-Si NCGD performance in the thermal cycle, which includes three case periods and lasts 2 years. We obtain the thermal expansion deformation of poly-Si and demonstrate it with the thermal cycle finite element model (TC-FEM). Then, we reveal the key factor to be carrier mobility decay, in which the nanocrystal finite element model (NC-FEM) predicts grain displacement (GD) increasing, otherwise electronic mobility data is measured and determined by the Hall method. Specifically, dislocation defection accumulation is induced by grain refinement (GR), grain size (GS), and grain boundary (GB) increasing. Moreover, multiple twinning phenomena are displayed with three-dimensional (3D) structural reconstruction, which provides the basis for the formation of new grains and substantiates the GR phenomena. The periodic lattice strain induces deep trap accumulation and chemical degradation during operation, which restricts the carrier mobility. Ultimately, the electron-hole’s scattering probability is enhanced, promoting the decrease in conductivity. These findings differ from the conventional poly-Si electrical properties changing mechanisms, which enrich our understanding of NCGD in poly-Si materials. Additionally, we obtain insights into the resistance drift and carrier transport mechanisms and unravel the structural and mechanistic hierarchical twinning processes governed by defects. The findings of this work can have significant implications for the stability and reliability of poly-Si field-effect transistors or the pursuit of high-efficiency tandem solar cells.