S. Aloni et al., Photovoltage imaging of a single As-vacancy at a GaAs(110) surface: Evidence for electron trapping by a charged defect?, J CHEM PHYS, 115(4), 2001, pp. 1875-1881
We employed atomically-resolved surface photovoltage (SPV) imaging with a s
canning tunneling microscope, using super- and sub-band gap energy photons,
to map the potential distribution around a single As vacancy at a p-GaAs(1
10) surface. While the super-band gap (532 nm) SPV reflects the band bendin
g (including the tip-induced effect) in the dark, the sub-band gap (1064 nm
) SPV shows the change in band bending due to charge injection into the def
ect. We conclude that in the dark, the As vacancy introduces a surface stat
e, similar to0.63 eV above the valence band maximum, that has to be filled
with two electrons to maintain surface neutrality. However, under 1064 nm (
sub-band gap) illumination at room temperature, we observed a large negativ
e SPV feature (radius of 70-100 Angstrom), and a zero or low positive SPV z
one in its center, with a six-pointed star shape of similar to 15 Angstrom
radius. We interpret our findings as either negative photo-charging of the
defect, or positive charging that leads to a trapped electron state around
the defect. (C) 2001 American Institute of Physics.