No, a p-type semi-conductor slab cannot be physically joined with a n-type semi-conductor slab to produce a p-n junction.
If we physically join the two semi-conductor blocks, there will always be little microscopic gap or between the slabs due to roughness of the surfaces.
OR
In a forward biased p−n junction, potential barrier is lowered and hence the electrons and holes can easily cross the junction. In reversed biased p−n junction, the potential barrier is raised and hence the electrons and holes cannot easily cross the junction. For this reason, forward bias resistance is low compared to reverse biased resistance of p−n junction.