This paper discusses the impacts of electric field and physical confinement around the pn-junction on the diffusion constant and carrier lifetime of various pn-junction devices fabricated on silicon-on-insulator (SOI) substrates. The discussion will introduce the key points leading to a fuller understanding of the physics ruling the steep transfer characteristics of ‘zero subthreshold swing and zero impact ionization field-effect transistor (Z2-FET)’ fabricated on SOI substrates. First, many past experimental results of silicon-on-insulator lateral, unidirectional, bipolar-type insulated-gate transistors (SOI Lubistor) are introduced to elucidate the current-voltage characteristics of recent insulated-gate silicon-on-insulator (SOI) pn-junction devices. Advanced physics-based models are introduced to understand the physical mechanisms that should be targeted to understand the transfer characteristics of self-aligned gate SOI Luibistor, offset-gate SOI Lubistor, and Z2-FET. By combining theoretical considerations and experimental results, the physics that may determine the operating characteristics of those devices are identified from the impact of electric field and physical confinement around the pn-junction on the carrier diffusion process.