Final answer:
Increased gate-to-source voltage in a MOSFET causes a higher electric field which leads to increased scattering and interaction with the lattice structure, thereby reducing the mobility of carriers within the channel.
Step-by-step explanation:
The increase of gate-to-source voltage in a MOSFET device leads to a higher electric field across the oxide layer between the gate and the channel. This increased electric field can cause a scattering effect on the carriers within the channel, resulting in a decrease in carrier mobility. The electric field produced by the gate attracts carriers to the surface of the channel, which is more prone to scattering from the surface roughness and impurities. As a consequence, as the gate-to-source voltage increases, the carriers' ability to move freely is reduced, leading to a decrease in mobility and thus affecting the overall conductance of the MOSFET. Additionally, high electric fields can lead to increased interaction with the lattice structure, which can also detract from the mobility.