 In the classical Poole-Frenkel theory a Coulombic trap potential is assumed, but steeper potentials belonging to multipolar defects or screened hydrogenic potentials are considered as well.Regarding the typology of traps, the Poole-Frenkel effect is described to occur for positively charged trap sites, i.e.for traps that are positive when empty and neutral when filled, in order for the electron to experience a Coulombic potential barrier due to the interaction with the positively charged trap.