  A superconducting layer exposed to a perpendicular electric field and a
parallel magnetic field is considered within the Ginzburg-Landau (GL) approach.
The GL equation is solved near the surface and the surface energy is
calculated. The nucleation critical field of superconducting state at the
surface depends on the magnetic and electric fields. Special consideration is
paid to the induced magnetic-field effect cause d by diamagnetic surface
currents. The latter effect is strongly dependent on the thickness of the
sample. The effective inverse capacitance determines the effective penetration
depth. It is found that the capacitance exhibits a jump at the surface critical
field. An experiment is suggested for determining the change in the effective
capacitance of the layer.
