HREELS analysis of band bending on sulfur-covered GaAs(100) surfaces

On clean and sulfur covered GaAs(100) surfaces the depletion layer thickness and the band bending are studied with high resolution electron energy loss spectroscopy (HREELS). The intensity and the frequency of the plasmon loss is analyzed within the framework of a two layer model. The sulfur is deposited from an electrochemical cell on the arsenic rich (2 X 4) and the gallium rich (4 X 2) surface of highly doped GaAs(100). After the deposition of sulfur at room temperature the LEED pattern changes to a (1 X 1) on both surfaces. After annealing to 550 degrees C a diffuse (2 X 1) reconstruction appears with a dramatic decrease in band bending. A second annealing step at slightly higher temperature resulted in a clear (2 x 1) LEED pattern and a slight increase in band bending. This is correlated with a decrease in sulfur content of the surface as observed with AES. After annealing to 650 degrees C the sulfur desorbed and the band bending on the resulting (4 X 1) surface was the same as on the clean surface. We could not detect a difference in band bending between the sulfur covered arsenic rich and the gallium rich GaAs(100) surface.