  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.
