The resistivity measurements of semiconductors can not reveal whether one or two types of carriers are present; nor distinguish between them. However, this information can be obtained from Hall Coefficient measurements, which are also basic tools for the determination of carrier density and mobilities in conjuction with resistivity measurement.
As you are undoubtedly aware, a static magnetic field has no effect on charges unless they are in motion. When the charges flow, a magnetic field directed perpendicular to the direction of flow produces a mutually perpendicular force on the charges. When this happens, electrons and holes will be separated by opposite forces. They will in turn produce an electric field (h) which depends on the cross product of the magnetic intensity,, and the current density, J. h= Rx Where R is called the Hall coefficient. Now, let us consider a bar of semiconductor, having dimension, x, y and z. Letis directed along X andalong Z thenhwill be along Y, as in Fig. 2. Then we could write. Where Vh is the Hall voltage appearing between the two surfaces perpendicular to y and I =yz