Accumulation region in MOSFET
MOSFET means Metal oxide semiconductor Field-effect Transistor.For this explanation Consider NMOS Transitore to understand accumulation, This means it has a p-type substrate, which means the substrate has holes as the majority of carriers throughout the substrate.
Now apply a negative voltage to the Gate, this voltage causes holes in the substrate to come near to the interface. Before applying voltage there were already holes present in the p substrate and after applying the negative voltage few more holes are moved toward the interface, in simple words same carriers are accumulating. This is called Accumulation.
Why a MOSFET in accumulation mode is not conducting?
When a negative voltage is applied to the gate, holes are attracted to the semiconductor-insulator interface, creating a conducting surface that extends from the bulk to the interface. However, because both the source and drain are n-type, in accumulation mode, the transistor behaves like an npn transistor, where the source and drain are insulated by two reverse-biased pn junctions. As a result, electrons in the source cannot flow to the drain, and no conduction channel is formed.
