Hall probe question...?

Magnetic field deflect the electrons and ions provided they have a velocity. In the Hall effect, you take a flat slab of semiconductor. Let x and y be the length and breadth and z is the height. Now what you do is to apply a magnetic field in the y direction and apply electric field in the x direction. Ions are held tight. Electrons move say in the negative x direction perpendicular to magnetic field. Due to the magnetic field they move in z direction. They up to edge of the semiconductor and stop. Electrons start collecting on xy plane. These electrons produce the Hall potential. Since electrons move with a constant velocity, there is equivalent resistivity. This define th Hall conductivity. If you know the electric and magnetic field then knowing the specific resity, you can estimate the eectron number density by the Hall potential, This is the trick.