  Recently developed model allows for simulations of electric field influence on the surface states. The results of slab simulations show considerable change of the energy of quantum states in the electric field, i.e. Stark Effect associated with the surface (SSSE - Surface States Stark Effect). Detailed studies of the GaN slabs demonstrate spatial variation of the conduction and valence band energy revealing real nature of SSSE phenomenon. It is shown that long range variation of the electric potential is in accordance with the change of the energy of the conduction and valence bands. However, at short distances from GaN(0001) surface, the valence band follows the potential change while the conduction states energy is increased due to quantum overlap repulsion by surface states. It is also shown that at clean GaN(0001) surface Fermi level is pinned at about 0.34 eV below the long range projection of the conduction band bottom and varies with the field by about 0.31 eV due to electron filling of the surface states. 
On the nature of Surface States Stark Effect at clean GaN(0001) surface