The addition of trivalent impurities?such as boron, aluminium or gallium to an intrinsic semiconductor?creates deficiencies of valence electrons,called holes. It is typical to use B2H6?diborane gas to diffuse boron into the silicon material.

The electron and hole concentration in a semiconductor in thermal equilibrium is given by 2n_en_h=n²_i

Diffusion in a p-n junction is due to concentration gradient

In semiconductor physics, the depletion region, also called depletion layer, depletion zone, junction region, space charge region or space charge layer, is an insulating region within a conductive, doped semiconductor material where the mobile?charge carriers?have been diffused away