Space Charge Limited Current Revisited: the Effect of Surface Traps
  We analyze the effect of surface traps on unipolar space charge limited current and find that they have a profound influence on the $I-V$ curves. By performing calculations that account for the presence of these traps, we can reproduce experimental observations not captured by the conventional theory that only considers the presence of traps in the bulk of the material. Through the use of realistic material parameters, we show that the effects discussed have clear experimental relevance. 
R. W. I. de Boer and A. F. Morpurgo