How Does a Transistor Work?

Transistor miniaturization faces a fundamental limit because when terminals get extremely close quantum tunneling lets electrons pass through barriers that should block them, preventing a reliable off-state at tiny scales.

A positive gate voltage switches a transistor on because it attracts electrons toward the gate, reducing the depletion layer and creating a continuous conducting channel between source and drain that allows current to flow.

The depletion layer blocks current because recombination near the junction leaves behind fixed ion charges that create an electric field which repels incoming carriers and forms an energy barrier to conduction.

A depletion layer forms at an n–p junction because electrons diffuse from the electron-rich n-region into the p-region and recombine with holes, leaving a zone depleted of mobile charge near the boundary.

N-type and p-type regions stay electrically neutral overall because dopant atoms and the silicon lattice balance charges, so the 'n' or 'p' label denotes the dominant sign of mobile carriers, not net charge.

A hole behaves like a positive charge carrier because it is the absence of an electron, and when neighboring electrons move to fill that absence the net effect is a flow of positive charge across the lattice.

P-type doping increases conductivity because introducing a trivalent impurity (like boron) creates missing-electron sites called holes, and electrons moving into those holes produce effective charge flow.

N-type doping raises silicon's conductivity because adding a pentavalent impurity (like phosphorus) donates an extra electron into the lattice, increasing the number of free electrons that can carry current.