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As you know, the physics of MOS capacitor is not simple. This applet is a 'good' effort given to provide a dynamic learning tool for this important MOS structure.
This applet is to illustrate the physics of MOS capacitor under an applied gate-bulk bias. Three important conditions are illustrated also: equilibrium condition, flat band condition, and the threshold condition. If the screen looks too busy, you could hide either the 'charge' profile or the energy 'band' diagram.
By using the bias arrows, the bias voltage can be set or varied. The 'charge' profile or the energy 'band' diagram can be studied.
If the bias is increased beyond the 'threshold' value, the increase of inversion charge under the gate oxide is illustrated by the 'thickening' of channel charge in the top diagram.
You can try various gate metals, oxide thickness, and Si doping type and level.
The bias control is most useful in observing what happens beyond threshold. Three additional points are: