Measurement of Surface Fermi Level in Phosphidized GaAs

The location of the surface Fermi level in phosphidized GaAs has been investigated using the Kelvin probe method. The surface Fermi level changes from an energy around 0.47 eV below the conduction band edge for the as-etched surface covered with a natural oxide layer to an energy of 0.25 eV after sufficient phosphidization by phosphine (PH3)-plasma treatment. On the other hand, isothermal capacitance transient spectroscopy measurement reveals that a new electron trap with an activation energy of 0.24 eV is introduced at or near the phosphidized surface. This provides experimental evidence that the location of the surface Fermi level is closely associated with that of the electron trap induced by PH3-plasma treatment.